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United States Government Accountability Office: 
GAO: 

Report to the Ranking Member, Committee on Environment and Public 
Works, U.S. Senate: 

August 2011: 

Climate Monitoring: 

NOAA Can Improve Management of the U.S. Historical Climatology Network: 

GAO-11-800: 

GAO Highlights: 

Highlights of GAO-11-800, a report to the Ranking Member, Committee on 
Environment and Public Works, U.S. Senate. 

Why GAO Did This Study: 

The National Oceanic and Atmospheric Administration (NOAA) maintains a 
network of weather-monitoring stations known as the U.S. Historical 
Climatology Network (USHCN), which monitors the nation’s climate and 
analyzes long-term surface temperature trends. Recent reports have 
shown that some stations in the USHCN are not sited in accordance with 
NOAA’s standards, which state that temperature instruments should be 
located away from extensive paved surfaces or obstructions such as 
buildings and trees. GAO was asked to examine (1) how NOAA chose 
stations for the USHCN, (2) the extent to which these stations meet 
siting standards and other requirements, and (3) the extent to which 
NOAA tracks USHCN stations’ adherence to siting standards and other 
requirements and has established a policy for addressing nonadherence 
to siting standards. GAO reviewed data and documents, interviewed key 
NOAA officials, surveyed the 116 NOAA weather forecast offices 
responsible for managing stations in the USHCN, and visited 8 forecast 
offices. 

What GAO Found: 

In choosing USHCN stations from a larger set of existing weather-
monitoring stations, NOAA placed a high priority on achieving a 
relatively uniform geographic distribution of stations across the 
contiguous 48 states. NOAA balanced geographic distribution with other 
factors, including a desire for a long history of temperature records, 
limited periods of missing data, and stability of a station’s location 
and other measurement conditions, since changes in such conditions can 
cause temperature shifts unrelated to climate trends. NOAA had to make 
certain exceptions, such as including many stations that had 
incomplete temperature records. In general, the extent to which the 
stations met NOAA's siting standards played a limited role in the 
designation process, in part because NOAA officials considered other 
factors, such as geographic distribution and a long history of 
records, to be more important. 

USHCN stations meet NOAA’s siting standards and management 
requirements to varying degrees. According to GAO’s survey of weather 
forecast offices, about 42 percent of the active stations in 2010 did 
not meet one or more of the siting standards. With regard to 
management requirements, GAO found that the weather forecast offices 
had generally but not always met the requirements to conduct annual 
station inspections and to update station records. NOAA officials told 
GAO that it is important to annually visit stations and keep records 
up to date, including siting conditions, so that NOAA and other users 
of the data know the conditions under which they were recorded. NOAA 
officials identified a variety of challenges that contribute to some 
stations not adhering to siting standards and management requirements, 
including the use of temperature-measuring equipment that is connected 
by a cable to an indoor readout device-—which can require installing 
equipment closer to buildings than specified in the siting standards. 

NOAA does not centrally track whether USHCN stations adhere to siting 
standards and the requirement to update station records, and it does 
not have an agencywide policy regarding stations that do not meet its 
siting standards. Performance management guidelines call for using 
performance information to assess program results. NOAA’s information 
systems, however, are not designed to centrally track whether stations 
in the USHCN meet its siting standards or the requirement to update 
station records. Without centrally available information, NOAA cannot 
easily measure the performance of the USHCN in meeting siting 
standards and management requirements. Furthermore, federal internal 
control standards call for agencies to document their policies and 
procedures to help managers achieve desired results. NOAA has not 
developed an agencywide policy, however, that clarifies for agency 
staff whether stations that do not adhere to siting standards should 
remain open because the continuity of the data is important, or should 
be moved or closed. As a result, weather forecast offices do not have 
a basis for making consistent decisions to address stations that do 
not meet the siting standards. 

What GAO Recommends: 

GAO recommends that NOAA enhance its information systems to centrally 
capture information useful in managing the USHCN and develop a policy 
on how to address stations that do not meet its siting standards. NOAA 
agreed with GAO’s recommendations. 

View [hyperlink, http://www.gao.gov/products/GAO-11-800] or key 
components. For more information, contact Anu K. Mittal at (202) 512-
3841 or mittala@gao.gov. 

[End of section] 

Contents: 

Letter: 

Background: 

USHCN Stations Were Selected on the Basis of Several Factors, but 
Siting Conditions Played a Limited Role: 

USHCN Stations Meet Siting Standards and Management Requirements to 
Varying Degrees: 

NWS Does Not Centrally Track Whether USHCN Stations Meet Siting 
Standards or Have a Policy for Addressing Stations That Do Not Meet 
the Standards: 

Conclusions: 

Recommendations for Executive Action: 

Agency Comments and Our Evaluation: 

Appendix I: Scope and Methodology: 

Appendix II: Other National Climate Networks: 

Appendix III: Comments from the Department of Commerce: 

Appendix IV: GAO Contact and Staff Acknowledgments: 

Table: 

Table 1: Differences in Selected Siting Standards of National Climate 
Networks: 

Figures: 

Figure 1: NOAA's Organizational Structure for Managing the USHCN: 

Figure 2: Percentage of Climate Divisions, and Number of Active USHCN 
Stations, as of April 2011: 

Figure 3: Active USHCN Stations in 2010 That Did Not Adhere to One or 
More NWS Siting Standards: 

Figure 4: Comparison of Conditions at Two USHCN Stations That Do Not 
Meet NWS Siting Standards: 

Figure 5: Primary Factors Contributing to USHCN Stations Not Adhering 
to NWS Siting Standards: 

Figure 6: A USHCN Station with Obstructions to Temperature-Measuring 
Equipment but No Obstructions Shown on the Station Record: 

Figure 7: U.S. Climate Reference Network Station: 

Abbreviations: 

NCDC: National Climatic Data Center: 

NOAA: National Oceanic and Atmospheric Administration: 

NWS: National Weather Service: 

USHCN: U.S. Historical Climatology Network: 

[End of section] 

United States Government Accountability Office: 
Washington, DC 20548: 

August 31, 2011: 

The Honorable James M. Inhofe: 
Ranking Member: 
Committee on Environment and Public Works: 
United States Senate: 

Dear Senator Inhofe: 

The National Oceanic and Atmospheric Administration's (NOAA) weather 
forecast offices maintain a network of thousands of weather-monitoring 
stations throughout the United States, some with temperature records 
stretching back well over a century. These weather-monitoring stations 
are equipped to measure meteorological conditions at ground level-- 
usually the daily maximum and minimum temperatures and 24-hour 
precipitation totals--to support weather forecasts and for the study 
of climate. In 1987 NOAA designated a subset of these weather-
monitoring stations as the U.S. Historical Climatology Network 
(USHCN). The purpose of the USHCN is to monitor the nation's climate 
and, in particular, to analyze long-term surface temperature trends. 
On the basis of their analysis of data from a variety of sources, 
including temperature records from the USHCN, NOAA scientists have 
concluded that the average surface temperatures across the nation have 
warmed over the past century. 

The temperature measurements used in NOAA's analysis have been taken 
largely by trained volunteer observers at the weather-monitoring 
stations that are part of the USHCN. The stations are located at 
private residences, farms, and parks, as well as on the properties of 
universities, water treatment plants, airports, and other 
institutions. The volunteer observers generally record temperature 
measurements on a daily basis using equipment that NOAA has placed on 
their properties. NOAA has established standards for air temperature 
measurement, which state, among other things, that temperature 
instruments should be located away from extensive paved surfaces or 
obstructions such as buildings and trees. Siting conditions at 
stations can change over time, however, particularly for stations with 
many years of data, as volunteer observers make changes to their 
properties, urbanization occurs, or local land uses change. Recent 
reports have shown that some USHCN stations are not sited in 
accordance with NOAA's standards. 

According to NOAA officials, for many years the agency has recognized 
the need to improve confidence in its data on changes to the national 
climate and, as part of this effort, in 2001 took the initiative to 
establish a new national climate observation network, the U.S. Climate 
Reference Network. NOAA is also developing another new observation 
network designed to monitor regional climate trends. Unlike many of 
the stations in the USHCN, the monitoring stations for these new 
networks are generally located on government rather than private 
property and do not require a human observer to record temperature 
measurements. According to NOAA officials, however, the agency plans 
to continue relying on data from the USHCN to help characterize 
national and regional temperature trends. 

You asked us to examine issues related to the siting of USHCN 
stations. Specifically, we examined (1) how NOAA selected weather-
monitoring stations for inclusion in the USHCN, (2) the extent to 
which such stations meet siting standards and management requirements 
for weather-monitoring stations, and (3) the extent to which NOAA 
tracks USHCN stations' adherence to siting standards and management 
requirements and has established a policy for addressing stations that 
do not adhere to siting standards. As we discussed with your office, 
we focused our examination of these issues on NOAA's management of the 
USHCN and did not assess the effect of stations not meeting siting 
standards on the reliability of NOAA's analysis of temperature trends. 

To examine NOAA's selection of USHCN stations, we reviewed NOAA 
documents describing the selection process, interviewed NOAA 
scientists, and analyzed NOAA data on all stations that constitute the 
USHCN. We analyzed the data to determine the extent to which USHCN 
stations meet the criteria NOAA scientists considered important for 
the purpose of monitoring long-term temperature trends, such as 
geographic distribution of stations. To assess the extent to which 
USHCN stations meet siting standards and management requirements for 
weather-monitoring stations, we surveyed all 116 NOAA weather forecast 
offices in the contiguous 48 states, which are responsible for 
managing these stations, and received a response rate of 100 
percent.[Footnote 1] Our questionnaire included questions regarding 
adherence to siting standards, reasons for stations not adhering to 
the standards, and general management challenges. We visited a 
nonprobability sample of 8 weather forecast offices across the country 
to discuss these issues in greater depth, observe siting conditions at 
a total of 19 USHCN stations managed by the offices, and review 
weather forecast office files for network stations to examine 
adherence to general management requirements for weather-monitoring 
stations. The set of 19 USHCN stations we visited was also a 
nonprobability sample we selected to ensure that we observed a variety 
of siting conditions. To ensure geographic distribution in the weather 
forecast offices we visited, we selected 2 offices in each of the four 
NOAA regions in the contiguous United States, and we selected the 
specific offices we visited to ensure a range of sizes in terms of the 
offices' forecast areas. Because we used a nonprobability sample of 
weather forecast offices and USHCN stations to visit, the information 
we obtained from these visits cannot be generalized to other weather 
forecast offices or USHCN stations. The visits instead provided us 
with more in-depth information on the perspectives of various 
participants in the weather forecast offices about managing weather-
monitoring stations and examples of station siting conditions. To 
evaluate the extent to which NOAA tracks USHCN stations' adherence to 
siting standards and management requirements and has established a 
policy for addressing stations that do not adhere to siting standards, 
we reviewed NOAA documents and interviewed NOAA officials responsible 
for managing weather-monitoring stations. Appendix I presents a more 
detailed description of our scope and methodology. 

We conducted this performance audit from August 2010 through August 
2011, in accordance with generally accepted government auditing 
standards. Those standards require that we plan and perform the audit 
to obtain sufficient, appropriate evidence to provide a reasonable 
basis for our findings and conclusions based on our audit objectives. 
We believe that the evidence obtained provides a reasonable basis for 
our findings and conclusions based on our audit objectives. 

Background: 

NOAA's National Weather Service (NWS) manages the approximately 11,000 
weather-monitoring stations across the country that are part of the 
Cooperative Observer Program.[Footnote 2] Volunteer observers at the 
stations generally record daily maximum and minimum temperatures and 
24-hour precipitation totals and submit the data to NWS over the 
telephone, by Internet, or by mail. The records for stations in the 
Cooperative Observer Program can stretch back well over a century, 
with some records predating the establishment of NWS in 1890.[Footnote 
3] NWS uses data from these Cooperative Observer Program stations to 
support weather forecasts and warnings and other public service 
programs. The data are also used by others, including state 
climatologists, farmers, and resource planners such as energy 
providers that use weather information to anticipate and plan for 
varying levels of energy consumption. 

NOAA's National Climatic Data Center (NCDC)[Footnote 4] established 
the USHCN in 1987 by selecting a subset of weather-monitoring stations 
from the existing Cooperative Observer Program network of stations. 
The USHCN currently consists of 1,218 stations. NCDC has twice revised 
the makeup of stations that compose the USHCN--in 1996 and 2009--
primarily to extend the weather records of stations that have closed 
over time as volunteer observers have discontinued their service. To 
address this issue, NCDC added data from nearby stations with similar 
temperature trends that are continuing to gather and report data. In 
all, NCDC has added over 100 stations as of the latest revision in 
2009. NCDC does not have a direct role in managing USHCN stations but 
relies on NWS's weather forecast offices throughout the contiguous 
United States to continue to manage the stations as part of the larger 
group of weather-monitoring stations in the Cooperative Observer 
Program. For example, NCDC relies on weather forecast offices to 
maintain records on the location of the stations and other conditions 
that can affect weather observations, including the types of equipment 
used to measure temperature and precipitation and the time of 
observation. 

NCDC uses USHCN data to assess and monitor climate variation and 
change, including to quantify national-and regional-scale temperature 
trends within the contiguous 48 states. On the basis of its analysis 
of USHCN data, NCDC estimates that the average surface temperature 
across the contiguous states has warmed by about 1.4 degrees 
Fahrenheit since 1895.[Footnote 5] NCDC's analysis has also identified 
areas of the country where temperatures have cooled or remained 
relatively stable. NCDC combines temperature records from the USHCN 
with temperature records from weather-monitoring stations around the 
world to analyze global temperature trends. This analysis has in turn 
been summarized in the assessment reports of the Intergovernmental 
Panel on Climate Change, an international body that reviews and 
assesses the most recent scientific and technical information produced 
worldwide relevant to the understanding of climate change. 

NWS headquarters establishes the policies, standards, and requirements 
for managing the Cooperative Observer Program, and weather forecast 
offices in six NWS regions (central, eastern, southern, western, 
Alaska, and Pacific) have responsibility for recruiting and training 
observers and installing and maintaining temperature-measuring 
equipment and rain gauges on observers' properties. NWS applies the 
same standards and requirements to all stations in its Cooperative 
Observer Program, including those in the USHCN. In particular, NWS has 
established siting standards for measuring air temperature to ensure 
uniformity in meeting national and international requirements for 
climate observation.[Footnote 6] The standards, which cover conditions 
in the immediate vicinity of the stations, specify that temperature- 
measuring instruments should: 

* not be sited on rooftops; 

* be installed over level terrain; 

* be installed at least 100 feet from any extensive concrete or paved 
surface; 

* be mounted 4 to 6 feet above the surface; and: 

* be no closer than four times the height of any nearby building, 
tree, fence, or similar obstruction. 

NWS guidelines state that implementation of these standards should be 
flexible and balanced with other factors, such as the availability of 
space. According to NWS, these siting standards are based in part on 
recommendations of the World Meteorological Organization, an agency of 
the United Nations that, among other things, coordinates the 
activities of member states to generate data and information on 
weather and climate in accordance with international standards. For 
example, according to World Meteorological Organization guidelines, 
the best sites for measuring air temperature are over level ground; 
freely exposed to sunshine and wind; and not shielded by or close to 
trees, buildings, and other obstructions.[Footnote 7] 

NWS has also established management requirements for weather-
monitoring stations that call for inspections of stations and updates 
of station records to reflect any changes. The requirements for 
inspections call for a minimum of one inspection by weather forecast 
office officials per year and specify that during these inspections, 
the officials are to review observers' practices for taking weather 
measurements, check equipment and perform any needed repairs, and 
assess the conditions surrounding the station, among other things. The 
management requirements state that, even if there are no changes at a 
station, officials from weather forecast offices should update each 
station record at least once every 5 years. To provide a complete and 
permanent record of a station, NWS has designed an information system 
that weather forecast offices are to use to record the dates of 
inspections and update station records.[Footnote 8] Such records are 
used by NCDC and other researchers to help interpret weather records 
from a station and determine how factors such as station location and 
measurement instruments affect the weather records. Figure 1 depicts 
the roles of NWS and NCDC in managing the USHCN. 

Figure 1: NOAA's Organizational Structure for Managing the USHCN: 

[Refer to PDF for image: illustration] 

National Oceanic and Atmospheric Administration: 

* National Weather Service headquarters: Establishes policies, 
standards, and requirements for managing the Cooperative Observer 
Program: 
- Regional offices: Implement and ensure compliance with national 
policy; 
- Weather forecast offices: Manage weather-monitoring stations: 

National Weather Service headquarters: Manages: Cooperative Observer 
Program: Comprises about 11,000 weather stations located across the 
country. 

* National Environmental Satellite, Data, and Information Service: 
- National Climatic Data Center: Selects USHCN stations, analyzes 
national- and regional-scale temperature trends, and archives all 
station documentation. 

National Environmental Satellite, Data, and Information Service: 
Manages: USHCN: Includes a subset of 1,218 stations in the contiguous 
48 states (within the Cooperative Observer Program). 

Source: GAO. 

[End of figure] 

USHCN Stations Were Selected on the Basis of Several Factors, but 
Siting Conditions Played a Limited Role: 

According to NCDC officials, achieving a relatively uniform geographic 
distribution across the contiguous 48 states was a high priority when 
selecting USHCN stations and was balanced with other factors, 
including how long stations had collected temperature records, limited 
periods of missing temperature data, and the stability of measurement 
conditions. According to NCDC officials, consideration of siting 
conditions in the immediate vicinity of stations played a limited role 
in both the initial selections in 1987 and when stations were added in 
1996 and 2009 because they considered other factors, such as 
geographic distribution, to be more important to the analysis of long-
term temperature trends. 

NCDC Selected USHCN Stations by Balancing Geographic Distribution with 
Other Factors: 

NCDC officials told us that in selecting stations for the USHCN, the 
agency placed a high priority on achieving geographic distribution 
across the contiguous 48 states, so that the network could help 
identify both national and regional warming and cooling trends. To 
achieve the geographic distribution needed to identify regional 
trends, according to agency officials, NCDC aimed to select a minimum 
of two stations from each of the 344 climate divisions across the 
country.[Footnote 9] NCDC officials acknowledged that they encountered 
difficulties achieving the desired geographic distribution in certain 
areas of western states--such as Nevada--that have a relatively low 
population density and thus fewer stations to choose from because of a 
lack of volunteers to serve as observers. As a result, according to 
NCDC officials, station density is slightly higher across the eastern 
states than in the western states. Our analysis of all 1,218 USHCN 
stations (including active stations and those that were inactive or 
closed) found that while NCDC generally met its aim of two stations 
per climate division, 14 percent of climate divisions had fewer than 
two stations.[Footnote 10] As of April 2011, 20 percent of climate 
divisions had fewer than two active stations (see figure 2). According 
to NCDC officials, the existing climate divisions are only one way to 
partition the nation's climate, and if divisions were being developed 
today, the climate divisions would differ in number and in the areas 
they cover. 

Figure 2: Percentage of Climate Divisions, and Number of Active USHCN 
Stations, as of April 2011: 

[Refer to PDF for image: pie-chart] 

More than two stations: 58%; 
Two stations: 22%; 
One station: 15%; 
No stations: 5%. 

Source: GAO analysis of USHCN data. 

[End of figure] 

According to NCDC officials and documents describing the process used 
to select USHCN stations in 1987 and to amend the list of stations in 
1996 and 2009, the agency also sought stations that had temperature 
records dating back to the early 20th century, had limited periods of 
missing data, and had a limited number of station changes, but 
sometimes made exceptions to these factors. 

* Number of years of temperature records. In order to detect long-term 
temperature trends, NCDC aimed to select stations that had a long 
history of temperature records, ideally dating back to the early 20th 
century. In some cases, however, NCDC selected stations with a shorter 
history of temperature records than was ideal to ensure geographic 
distribution of stations across the contiguous 48 states, according to 
officials. NCDC officials also told us that they created composite 
stations to achieve a minimum record length when no stations in a 
particular geographic area had been collecting temperature records as 
long as they sought. According to NCDC officials, they create a 
composite station by combining data from one or two stations that have 
closed with data from an active station in the same area whose 
temperature records overlap in time with records from the closed 
station or stations and continue to the present. NCDC officials told 
us that they compare the stations' overlapping temperature trends 
before creating a composite to help ensure that the climates at the 
stations are similar. According to NCDC documents, the initial 
selection of USHCN stations in 1987 included 84 composite stations, 
and, as of the latest revision to the network in 2009, the number of 
composite stations had increased to 208, largely in response to 
station closures. Our analysis of the 1,218 stations that make up the 
USHCN as of the latest revision in 2009, including composite stations, 
found that NCDC has largely achieved its desired record length. 
Specifically, as of 2010, over 85 percent of the stations had a record 
length dating back more than 100 years, and another 14 percent had 
temperature record lengths of 76 to 100 years. Less than 1 percent of 
stations had record lengths of 75 or fewer years. 

* Extent of missing data. NCDC officials told us that they also 
attempted to select USHCN stations with limited periods of missing 
data but that they often had to select stations with incomplete 
temperature records, including stations that were missing data for 
multiple years, because few stations have complete records. For 
example, about half the data from the Little Falls Mill Street 
station, located in upstate New York, are missing. The station's 
record has data for a few years in the 19th century, but data in the 
intervening years are sparse, with frequent gaps in the middle of the 
20th century, according to a 1990 NCDC report on the USHCN.[Footnote 
11] According to NCDC, various factors result in missing data, such as 
periods when a volunteer observer is not available or when instruments 
malfunction and need to be repaired. Our analysis of temperature 
records shows that only 24 of the 1,218 USHCN stations (about 2 
percent) have complete temperature data from the time they were 
established through 2010; the remaining 98 percent of stations are 
missing an average of 5 percent of temperature data. To generate 
uninterrupted temperature records, NCDC uses estimates for the missing 
data based on records from nearby stations in the larger set of 
Cooperative Observer Program weather-monitoring stations. For example, 
according to agency officials, NCDC used this process to fill in 
missing data for the Little Falls Mill Street station. According to 
NCDC officials, filling in missing data ensures that temperature 
records from all areas of the contiguous 48 states are represented 
when the agency uses the USHCN to identify national temperature trends. 

* Stability of measurement conditions. A final consideration in 
selecting USHCN stations was NCDC's desire to maximize the stability 
of measurement conditions--such as station location, type of 
temperature-measuring instrument, and time of day when observations 
were recorded--because such stability makes it easier to discern 
actual temperature trends at a station. NCDC officials told us that, 
like stability in other measurement conditions at USHCN stations, 
stability in siting conditions facilitates officials' ability to use 
temperature data to accurately identify long-term warming and cooling 
trends, even if those conditions do not meet NWS siting standards. 
Most stations with long temperature records, however, are likely to 
have undergone multiple changes in measurement conditions.[Footnote 
12] For example, according to NCDC's records, the Reno, Nevada, USHCN 
station was originally located at an NWS weather forecast office 
before being moved in the mid-1930s to an airport and then again in 
the 1990s to another location at the same airport. According to NCDC, 
such changes in measurement conditions may cause a rise or drop in the 
temperatures recorded at stations, which could affect the temperature 
trends identified using the USHCN. For example, NCDC has studied the 
impact of a gradual change in the time that observers record 
temperature measurements from afternoon to morning observation times 
and concluded that the change has obscured the warming trend across 
the contiguous 48 states, which would otherwise have appeared more 
pronounced. NCDC officials told us that they use statistical methods 
to identify significant shifts in temperature data unrelated to actual 
trends in temperature and to adjust the data to remove such shifts. 
[Footnote 13] According to NCDC officials, all 1,218 USHCN stations 
have undergone at least one change in measurement conditions requiring 
such an adjustment, with an average per station of four to five 
changes. 

NCDC officials acknowledged that a greater degree of stability of 
measurement conditions than typically found at USHCN stations would be 
preferable. As a result, NCDC has established a new network of surface 
weather-monitoring stations specifically to monitor the nation's 
climate--the U.S Climate Reference Network--and is establishing a 
second one--the U.S. Regional Climate Reference Network (see appendix 
II). According to agency officials, they have developed criteria for 
selecting locations for stations in the new networks to help ensure a 
greater degree of station stability in comparison with the USHCN and 
reduce the need to identify and remove shifts in temperature records 
that are unrelated to actual warming or cooling. NCDC officials told 
us these new networks can be used to construct a continuous 
temperature record with the USHCN once the new networks have a 
sufficient period of overlap with the USHCN to allow for a comparison 
of temperature trends. 

Siting Conditions at Weather-Monitoring Stations Played a Limited Role 
in Selections for the USHCN: 

The extent to which stations met specific NWS siting standards played 
only a limited role in the initial selection of stations for the USHCN 
in 1987 and when the makeup of the USHCN was revised in 1996 and 2009, 
according to NCDC officials. NCDC officials told us they considered 
other factors, such as geographic distribution and a long history of 
temperature records, to be more important to their ability to analyze 
long-term temperature trends than strict adherence to NWS's siting 
standards. For example, NCDC has included in the USHCN the Central 
Park station in New York City, which has a temperature record dating 
to 1876 and has had limited moves, even though current information on 
the station shows it is encircled by trees. NCDC officials said that, 
in an effort to consider some information on siting as part of the 
process of selecting stations, they obtained recommendations from 
state climatologists and others with detailed knowledge of the siting 
conditions at stations in their states. 

NCDC officials told us that another reason siting conditions played a 
limited role in their initial selection of USHCN stations in 1987 was 
that NCDC had limited information about siting conditions at the time. 
NCDC officials said they generally did not visit stations to examine 
siting conditions, except for a few stations near their headquarters 
in Asheville, North Carolina, because it was not feasible to do so 
with so many stations distributed nationwide. In addition, according 
to NCDC officials, when they first considered stations for inclusion 
in the USHCN, they had more limited electronic access to station 
histories and information about siting conditions than they do today. 
NCDC officials also said that the station histories they did have may 
not have included all relevant siting information, such as proximity 
to obstructions. 

According to NCDC officials, they may have kept some weather-
monitoring stations that do not meet specific NWS siting standards out 
of the USHCN by generally excluding many sites in large urban areas. 
For example, weather-monitoring stations located in large urban areas 
may be too close to extensive paved surfaces or obstructions to meet 
specific NWS siting standards. Nevertheless, individual stations were 
excluded because they were located in a large urban area, not because 
they did or did not meet a specific NWS siting standard. Similarly, 
NCDC officials told us that many stations with the longest records 
were not selected because NCDC considered the temperature records for 
these stations to have been affected by the stations' location in or 
adjacent to large urban areas. Nevertheless, the officials told us, 
NCDC made exceptions and selected some stations in or near large urban 
areas. According to NCDC's 1987 report on its initial designation of 
the USHCN, 70 percent of the selected stations were located in areas 
with populations of less than 10,000 in the 1980 census, and 90 
percent were located in areas with populations of less than 50,000. 
[Footnote 14] 

USHCN Stations Meet Siting Standards and Management Requirements to 
Varying Degrees: 

According to our survey of NWS weather forecast offices, close to half 
of USHCN stations do not adhere to one or more siting standards. 
Weather forecast offices cited a variety of factors that contributed 
to stations not adhering to siting standards, such as the use of 
temperature-measuring equipment that limits NWS's ability to locate 
stations so that they adhere to the standards. With regard to 
management requirements for USHCN stations, we found that the weather 
forecast offices generally but not always met requirements to conduct 
annual inspections and update station records. 

Close to Half of USHCN Stations Do Not Meet NWS Siting Standards: 

The survey responses we received from weather forecast offices that 
manage stations included in the USHCN indicate that about 42 percent 
of the active stations in 2010 did not adhere to one or more of the 
NWS siting standards for air temperature measurement.[Footnote 15] 
This percentage is slightly higher than the percentage not meeting the 
standards in the larger set of Cooperative Observer Program stations 
in the contiguous 48 states, of which the USHCN is a part. 
Specifically, according to our survey responses, about 37 percent of 
the active Cooperative Observer Program stations in 2010 did not 
adhere to one or more of the standards.[Footnote 16] 

The two standards most commonly cited by weather forecast offices as 
unmet by USHCN stations were distance to obstructions, such as 
buildings and trees, and distance to extensive concrete or paved 
surfaces (see figure 3). According to weather forecast offices' survey 
responses, only a small fraction of the stations did not adhere to the 
other siting standards, including that temperature-measuring 
instruments be mounted 4 to 6 feet off the ground. In particular, 
according to our survey responses, only five active USHCN stations 
(less than 1 percent) were located on a rooftop. 

Figure 3: Active USHCN Stations in 2010 That Did Not Adhere to One or 
More NWS Siting Standards: 

[Refer to PDF for image: vertical bar graph] 

Standard not met: Distance to obstructions; 
Percentage of active USHCN stations: 33%. 

Standard not met: Distance to concrete/paved surfaces; 
Percentage of active USHCN stations: 20%. 

Standard not met: Height above surface; 
Percentage of active USHCN stations: 3%. 

Standard not met: Not over level terrain; 
Percentage of active USHCN stations: 2%. 

Standard not met: Other; 
Percentage of active USHCN stations: 1%. 

Source: GAO analysis of survey results. 

Notes: The percentages sum to more than the total of 42 percent of 
stations that did not meet siting standards because some stations did 
not meet more than one standard. Other reasons for not adhering to 
siting standards include location on a rooftop and temporary 
relocation because of construction. 

[End of figure] 

We also visited a nonprobability sample of 8 weather forecast offices 
and 19 stations in the USHCN that are managed by these offices. During 
these visits, we observed stations that were located closer to 
obstructions or to extensive concrete or paved surfaces than specified 
in the siting standards, although the degree to which the stations did 
not adhere to the standards varied. For example, figure 4 shows 2 
stations that did not meet the siting standards. One station was 
located too close to a building and trees at a wildlife preserve in an 
otherwise relatively undeveloped area, but the other station was 
located in a relatively urban area and surrounded by a parking lot, 
building, and street. 

Figure 4: Comparison of Conditions at Two USHCN Stations That Do Not 
Meet NWS Siting Standards: 

[Refer to PDF for image: 2 photographs] 

Photographs depict the following: 
1) Too close to a building; 
2) Surrounded by a parking lot, a building and a street. 

Source: GAO. 

Note: The temperature-measuring instruments in each photograph are the 
taller objects with slatted devices on top of thin poles. The shorter 
objects are rain gauges. 

[End of figure] 

Weather Forecast Offices Cited a Variety of Factors That Contribute to 
Stations Not Adhering to Siting Standards: 

The two factors most commonly cited by NWS weather forecast offices 
responding to our survey as contributing to USHCN stations not 
adhering to one or more of the siting standards were (1) NWS's 
preference for locating stations at sites that provide a high degree 
of station stability and data continuity, even if these sites do not 
adhere to standards, and (2) the use of temperature-measuring 
equipment that limits NWS's ability to locate stations so that they 
adhere to the standards (see figure 5). 

Figure 5: Primary Factors Contributing to USHCN Stations Not Adhering 
to NWS Siting Standards: 

[Refer to PDF for image: horizontal bar graph] 

Factor: A preference for station stability and data continuity; 
Percentage of active USHCN stations: 24%. 

Factor: The use of temperature equipment attached to a cable; 
Percentage of active USHCN stations: 20%. 

Factor: Other reasons; 
Percentage of active USHCN stations: 15%. 

Factor: Inability to relocate instruments without causing a 
discontinuity in temperature records; 
Percentage of active USHCN stations: 8%. 

Factor: Preference of observers for where temperature equipment is 
located on their properties; 
Percentage of active USHCN stations: 6%. 

Factor: Limited funding to relocate stations; 
Percentage of active USHCN stations: 4%. 

Source: GAO analysis of survey results. 

Note: Other factors contributing to USHCN stations not adhering to 
siting standards include the difficulty of recruiting volunteer 
observers at sites that meet the standards and observers' properties' 
being too small to locate temperature-measuring instruments as far 
from obstructions as specified in the standards. 

[End of figure] 

* Preference for station stability and data continuity. In our survey 
of weather forecast offices, the most commonly cited factor 
contributing to USHCN stations not meeting the siting standards was a 
preference for locating stations at sites that provide stability and 
continuity of data. For example, officials in the Tampa weather 
forecast office told us that one USHCN station that was located in a 
downtown area and did not meet siting standards has a temperature 
record that begins before 1895, the first year of data used in the 
USHCN. They said they could either keep this station open or close it, 
since there were no other options that met the standards either on the 
current observer's property or in the surrounding area. They chose to 
keep the station open because of its long temperature record. 

* Limitations due to temperature-measuring equipment. The use of 
temperature-measuring equipment that is connected by a cable to an 
indoor readout device can require installing equipment closer to 
buildings than specified in the standards, according to our survey. 
Weather forecast office staff must dig trenches for the cables, and 
paved surfaces such as sidewalks and driveways, as well as the cost of 
cable for trenching, can limit the length of trenches and consequently 
the ability to locate stations so that they adhere to the siting 
standards. According to data from NCDC, about three-quarters of 
stations in the USHCN use such equipment. 

NWS headquarters officials told us they hope to replace cabled 
temperature-measuring equipment with new wireless equipment that can 
more easily be located in accordance with siting standards. 
Specifically, the NWS headquarters office with overall responsibility 
for the Cooperative Observer Program has developed a draft plan for 
the program that envisions replacing current equipment with wireless 
equipment. The draft plan does not specify the number of stations 
where equipment will be replaced but rather calls for evaluating 
weather-monitoring stations to determine if they meet the siting 
standards, identifying candidate stations for installing wireless 
equipment or relocating them to meet siting standards, and identifying 
stations that are candidates for being closed. NWS officials said, 
however, that the agency has not yet approved the plan for 
implementation. We did not specifically ask about wireless equipment 
in our survey, but 35 weather forecast offices entered comments 
expressing support for replacing the temperature-measuring equipment 
currently used at weather-monitoring stations with wireless equipment. 
Twenty of the offices specifically cited the ability to improve 
station siting as the reason for making this change. Comments entered 
by weather forecast offices on our survey, as well as the draft plan, 
also cited greater ease of installation and maintenance as additional 
benefits of wireless equipment. For example, installing wireless 
equipment would not require digging a trench for a cable. 

Even if NWS approves the draft plan, the use of wireless equipment may 
not address all siting issues. First, according to NWS officials, 
commercially available wireless equipment has not yet been developed 
that meets NWS standards for temperature observations at a cost that 
is feasible for use at weather-monitoring stations nationwide. The NWS 
official in charge of monitoring the development of wireless equipment 
said, however, that such equipment would most likely be available 
within 5 years. Second, the use of wireless equipment, when available, 
would not allow NWS to improve siting at all stations that do not 
currently meet the standards. For example, the observers' properties 
at some of the stations we visited were too small to allow any 
temperature-measuring equipment to be placed far enough from buildings 
or other obstructions to meet the siting standards, regardless of 
whether the equipment was wireless or cabled. NWS officials 
acknowledged that the use of wireless equipment would improve station 
siting but not eliminate all stations that currently do not meeting 
siting standards. 

NWS officials also described a wide range of other factors 
contributing to stations not adhering to siting standards. These 
include: 

* the difficulty of recruiting new volunteer observers at sites that 
meet standards, particularly as the nation's population has become 
more mobile and thus less apt to serve as long-term observers; 

* properties that may be too small or have trees or other features 
that make it difficult to locate instruments as far from obstructions 
as the standards specify; 

* the reluctance of observers to allow equipment sited in a location 
on their property that would meet the standards; 

* changes to the observer's property (e.g., growth of trees) or 
urbanization of the surrounding area that can cause the stations to 
not meet standards; and: 

* natural geographic features in certain areas, such as heavily 
forested or mountainous terrain, that can hamper the ability to meet 
the standards. 

NWS Weather Forecast Offices Have Generally but Not Always Met the 
Requirement to Annually Inspect Stations and Periodically Update USHCN 
Station Records: 

Our review of files for USHCN stations at 8 weather forecast offices, 
as well as our survey results, show that the offices have generally 
but not always met the requirement to annually inspect stations to 
maintain temperature-measuring equipment and determine if changes have 
occurred requiring station records to be updated, such as changes to 
siting conditions. Our file reviews also show that the offices 
generally but not always met the requirement to periodically update 
station records, even if no changes had taken place at a station. 
According to NCDC and NWS officials, it is important to annually visit 
stations and keep station records up to date so that users of the 
stations' temperature records, such as NCDC, know the conditions under 
which the observations were recorded. Any information NCDC has about 
these conditions, according to agency officials, can be used in 
conjunction with its statistical methods to identify significant 
shifts in a station's temperature data that are unrelated to actual 
warming or cooling trends and to adjust the data to remove such shifts. 

* Annual inspections. The results of our survey indicate that in 2010, 
102 of 114 weather forecast offices met the annual inspection 
requirement for stations in the USHCN.[Footnote 17] According to our 
survey results, 12 offices did not meet the requirement at a total of 
35 stations. In reviewing files at the 8 weather forecast offices we 
visited, we also found instances where the annual inspection 
requirement was not met in 2008 and 2009. Specifically, the results of 
our file reviews show that 3 of the 8 offices did not meet the annual 
inspection requirement for five stations in 2008, and 1 office did not 
meet the requirement for one station in 2009.[Footnote 18] In 
contrast, for the stations where the requirement had been met, the 
weather forecast offices had frequently conducted multiple inspections 
during a year. For example, office staff may have visited a station 
multiple times to repair equipment, to temporarily relocate 
temperature-measuring instruments to allow for construction at the 
observer's property, or to meet the requirement for semiannual 
inspections of stations that also record precipitation. 

* Station record updates. Until 2005, NWS required that station 
records be updated at least once every 10 years. At that time, NWS 
changed the requirement to once every 5 years. In reviewing files at 
the 8 weather forecast offices we visited, we found that two of the 8 
offices had consistently met the requirement to update station records 
within 5 years.[Footnote 19] In contrast, at two of the other offices, 
the time between updates for four stations was over 10 years. At the 
remaining four offices, the time between updates for one or more 
stations was over 5 years but less than 10 years. For example, one 
office did not update a record dated February 2002 until January 2011--
almost 9 years after the previous update. When the weather forecast 
offices updated records, the types of changes they documented included 
those that can cause shifts in temperature data unrelated to any 
actual temperature change, including replacement or relocation of 
temperature-measuring equipment, changes in time of observation, and 
descriptions of obstructions. 

Through our survey and visits to 8 weather forecast offices, weather 
forecast office officials identified a number of challenges to their 
ability to ensure that station records are updated and to carrying out 
other responsibilities for managing stations in the Cooperative 
Observer Program, including those in the USHCN. In our survey, the 
most frequently cited challenge was that weather forecast offices rely 
on staff assigned to manage the stations to also assist with other 
office responsibilities. Competing mission requirements at the offices 
was a closely related and often-cited challenge. For example, weather 
forecast offices operate 24 hours a day, and office officials 
explained that staff assigned to manage the stations may also be 
expected to work shifts, which limits the time they can visit the 
stations. Some weather forecast offices we visited told us that 
turnover and reductions in the number of staff assigned to the 
Cooperative Observer Program results in the loss of institutional 
knowledge needed to manage weather-monitoring stations. Weather 
forecast offices, particularly those with large areas to cover, also 
identified long driving distances to stations as a challenge. For 
example, officials at one office we visited told us that completing 
the required annual station visits requires driving 17,000 miles per 
year; that the round-trip drive to some stations takes longer than 10 
hours, leaving limited time to maintain equipment or install equipment 
at new stations; and that during the winter, some stations are 
inaccessible. 

NWS Does Not Centrally Track Whether USHCN Stations Meet Siting 
Standards or Have a Policy for Addressing Stations That Do Not Meet 
the Standards: 

NWS does not use its information systems to centrally track whether 
USHCN stations adhere to siting standards or if weather forecast 
offices are meeting the requirement to update station records at least 
once every 5 years. NWS also does not have an agencywide policy on 
what actions to take at stations that do not adhere to siting 
standards, which creates the potential for inconsistency in how 
weather forecast offices address such stations. The lack of 
centralized electronic tracking of performance information for the 
USHCN and the lack of an agencywide policy on the actions to take at 
stations that do not meet siting standards limit NWS's ability to 
manage the USHCN in accordance with performance management guidelines 
and federal internal control standards. 

NWS Does Not Have Centrally Available Information to Assess USHCN 
Performance: 

NWS's siting standards for weather-monitoring stations and the 
requirement that station records be updated at least once every 5 
years in effect establish goals for each weather forecast office to 
meet. NWS does not, however, centrally capture data on the extent to 
which stations in the Cooperative Observer Program and the USHCN meet 
its siting standards and station record update requirement. NWS has an 
information system it uses to help manage weather-monitoring stations, 
but the system has several limitations. The information system allows 
the agency to record basic identifying information about the stations 
and the conditions under which volunteer observers record weather 
observations, including some information about siting conditions and 
the dates of station record updates. According to NWS officials, 
however, the agency did not design the system to centrally track 
adherence to siting standards or the requirement to update station 
records at least once every 5 years. As a result, NWS is limited in 
its ability to use its information system to track USHCN performance 
information. 

The information system NWS uses to track information related to 
Cooperative Observer Program stations, including those selected for 
the USHCN, has the following specific limitations: 

* Limited information on adherence to station siting standards. 
According to NWS headquarters officials, they cannot query their 
information system to identify the specific weather-monitoring 
stations that do not meet siting standards or the total number of 
stations that do not meet standards. For example, in 2009, NCDC 
requested that NWS verify siting conditions at USHCN stations for a 
study evaluating the effects of siting conditions on temperature 
trends.[Footnote 20] NWS headquarters did not have a way to easily 
gather this information and instead had to direct its regional offices 
to have weather forecast office staff verify siting conditions at the 
stations. According to NWS officials, weather forecast office staff 
did not make special visits to the stations to gather the information 
requested by NCDC, as these stations might not have been on their 
immediate visit schedule, but reviewed files instead. 

* Incomplete information on siting conditions. NWS guidance for using 
the information system directs weather forecast offices to enter 
descriptions of obstructions at weather-monitoring stations. We found 
that in some cases, however, such descriptions may not accurately 
reflect whether temperature-measuring equipment meets the siting 
standard related to obstructions. This discrepancy can arise because 
NWS guidance directs weather forecast offices to describe obstructions 
in relation to a station's rain gauge. We found that obstructions to 
temperature measuring-equipment can differ from those to the rain 
gauge, depending where the two instruments are located. For example, 
the record for one USHCN station we visited did not include any 
obstructions because the rain gauge was on a rooftop where there were 
no obstructions. The station's temperature-measuring equipment, 
however, was at ground level and surrounded by buildings on three 
sides and, as a result, did not meet NWS's standards for siting 
temperature sensors. (The station's temperature-measuring equipment 
can be seen in figure 6.) In addition, NWS guidance for using the 
information system does not direct weather forecast offices to enter 
descriptions of other conditions that might indicate whether specific 
siting standards are being met, such as proximity to extensive 
concrete or paved surfaces. 

Figure 6: A USHCN Station with Obstructions to Temperature-Measuring 
Equipment but No Obstructions Shown on the Station Record: 

[Refer to PDF for image: photograph with inset enlargement of 
measuring equipment] 

Source: GAO. 

[End of figure] 

* Limited ability to track whether the requirement to update station 
records is being met. The NWS information system is designed to allow 
weather forecast office staff to enter the date each station record is 
updated and to store previous versions of station records. NWS 
officials stated, however, that the information system is not set up 
to centrally track the performance of weather forecast offices in 
updating station records within the required 5-year time frame. In 
addition, the system is not set up to allow NWS to notify weather 
forecast offices when station records are nearing the 5-year mark and 
need to be updated. NWS regional offices and weather forecast offices 
are instead responsible for tracking the status of updates. For 
example, an official at one office we visited told us that he 
sometimes forgets to update station records within the 5-year time 
frame but that the NWS regional headquarters keeps track of the 
requirement. 

* Inconsistent identification of stations included in the USHCN. The 
NWS information system includes information about all stations in the 
Cooperative Observer Program, including those designated by NCDC as 
part of USHCN, but NWS does not consistently use the system to 
identify USHCN stations. Specifically, station records allow weather 
forecast offices to indicate whether stations are part of the USHCN, 
but offices had done so in only some of the station records we 
reviewed. As a result, NWS headquarters officials cannot use their 
information system to determine which stations NCDC has designated as 
part of the USHCN. Officials at some of the weather forecast offices 
we visited were also unsure which of the stations they manage had been 
designated as part of the USHCN. According to NCDC officials, it is 
important that weather forecast offices have the ability to determine 
which stations belong to the USHCN so that they can set appropriate 
priorities for the maintenance, repair, and replacement of temperature-
measuring equipment at these stations. 

Our work related to the Government Performance and Results Act of 1993 
[Footnote 21] and the experience of leading organizations have shown 
the importance of developing program performance goals that identify 
desired results of program activities and reliable information that 
can be used to assess results.[Footnote 22] NWS headquarters officials 
we spoke with acknowledged the need to centrally track performance 
information related to the management of Cooperative Observer Program 
stations, which includes those selected for the USHCN. The officials 
said they only recently began tracking the requirement that weather 
forecast offices inspect stations at least once annually. According to 
these officials, they selected annual station inspections as a 
performance indicator because the inspection requirement is easy to 
track using the current information system for managing the stations. 
NWS provided us with summary data on inspections for all stations in 
the Cooperative Observer Program, including USHCN stations. The data 
show that the percentage of stations for which weather forecast 
offices met the annual inspection requirement increased from 70 
percent in 2005 to 80 percent in 2010.[Footnote 23] 

NWS headquarters officials also told us that the agency has begun 
upgrading its current information system and that they are considering 
options to notify weather forecast offices when updates of station 
records are overdue and to better track adherence to siting 
conditions. The officials said they hope to complete the upgrade by 
the end of fiscal year 2013, depending on the availability of funding. 
Options being considered for tracking siting conditions include 
photographs of stations and the use of a rating scale to summarize the 
extent to which stations adhere to siting standards, similar to the 
rating scale created for the newer networks developed specifically for 
climate monitoring (see appendix II for further details). According to 
our survey results, 63 percent of weather forecast offices believe 
that the use of photographs in the NWS information system would be 
either very helpful or extremely helpful in evaluating stations' 
adherence to siting standards. In addition, 52 percent of the offices 
responded that the option to check a box in a station's electronic 
record to indicate that it does not adhere to the standards would be 
either very helpful or extremely helpful. Some offices also suggested 
other tools they would consider helpful in evaluating siting 
conditions at stations, such as the use of commercially available 
satellite imagery and maps. 

NWS Does Not Have an Agencywide Policy to Address Stations That Do Not 
Adhere to Siting Standards: 

NWS does not have an agencywide policy for stations not adhering to 
siting standards that clarifies for staff in weather forecast offices 
whether the stations should be closed, relocated, or maintained in 
their present condition to preserve the continuity of their 
temperature records. Standards for internal control in the federal 
government call for federal agencies to document their policies and 
procedures to help managers achieve desired results.[Footnote 24] 
Without an agencywide policy, weather forecast offices do not have a 
basis for making consistent decisions about what actions to take at 
USHCN stations that do not adhere to siting standards. 

NWS headquarters officials we spoke with acknowledged that they had 
not developed an agencywide policy on the actions, if any, that 
weather forecast offices should take to address stations that do not 
adhere to siting standards. They said they recognized the need to 
develop an agencywide policy and that, in the absence of such a 
policy, decisions on how to address stations that do not meet siting 
standards are up to individual weather forecast offices. For example, 
they said weather forecast offices might consult with NCDC or state 
climatologists when deciding whether to close stations that do not 
meet siting standards, but that such outreach is not required. 

In the absence of an agencywide policy, the NWS western regional 
office directed weather forecast offices in the region to stop 
submitting data to NCDC from stations with "egregious" siting 
conditions in a format that would allow NCDC to use these data when 
analyzing long-term temperature trends. The meaning of "egregious" was 
not defined and was left to each weather forecast office to interpret. 
According to NWS officials, none of the other three regional offices 
in the contiguous United States have developed a similar policy. 
According to the western regional manager responsible for the 
Cooperative Observer Program, the region's policy affected about a 
dozen stations, which had not been designated as part of the USHCN. 
Through our visits to weather forecast offices, however, we found 
that, even in the western region, the offices did not consistently 
implement the region's policy. In particular, an official at one of 
the two offices we visited in the region told us he did not follow the 
policy because doing so would have affected the majority of stations 
in his state. 

NCDC officials told us that, as NWS develops a policy regarding how to 
address stations in the Cooperative Observer Program (including those 
designated as part of the USHCN) that do not meet siting standards, it 
should consider how NCDC uses the temperature data from the stations. 
Because the data from USHCN stations are used to identify long-term 
climate trends and the stations were thus selected in part on the 
basis of the stations' stability of measurement conditions and 
continuity of data, NCDC officials said they would caution NWS against 
relocating or closing stations that do not meet siting standards. NCDC 
officials said they would consider closing a station only in certain 
situations, such as an observer not following NWS guidelines when 
recording weather observations. 

Conclusions: 

Given the importance of data from the USHCN in monitoring and in 
formulating public policy related to climate change, it is important 
that the public and policymakers have confidence that the network is 
being managed effectively. NWS has developed station siting standards 
and management requirements for the USHCN, and performance management 
guidelines dictate that NWS should gather data on the extent to which 
these standards are being met. But NWS's information system does not 
centrally capture such information. As a result, the agency cannot 
easily measure the USHCN's performance against its siting standards 
and management requirements. Without more complete data on siting 
conditions, including when siting conditions change, it is difficult 
for agency management to assess the extent to which the stations meet 
its siting standards. Similarly, NWS does not have easily accessible 
data on when station records were last updated for monitoring whether 
the records are being updated at least once every 5 years as the 
agency requires. In addition, although federal internal control 
standards call for agencies to develop policies to maintain control 
over program activities, NWS has not established agencywide policy for 
what to do when, over years and decades, stations no longer adhere to 
its siting standards because conditions have changed. In the absence 
of such policy, it is not clear to weather forecast office officials 
whether stations that do not adhere to siting standards should remain 
open because data continuity is important for analyzing long-term 
climate trends, or whether the stations should be moved or closed. As 
a result, without a policy with actions for all offices to follow, 
weather forecast offices may be taking different approaches to address 
stations that do not meet siting standards. 

Recommendations for Executive Action: 

To improve NWS's ability to manage the USHCN in accordance with 
performance management guidelines and federal internal control 
standards, as well as to strengthen congressional and public 
confidence in the data the network provides, we recommend that the 
Secretary of Commerce direct the Administrator of NOAA to take the 
following two actions: 

* Enhance NWS's information system to centrally capture information 
that would be useful in managing stations in the USHCN, including (1) 
more complete data on siting conditions (including when siting 
conditions change), which would allow the agency to assess the extent 
to which the stations meet its siting standards, and (2) existing data 
on when station records were last updated to monitor whether the 
records are being updated at least once every 5 years as NWS requires. 

* Develop an NWS agencywide policy, in consultation with NCDC, on the 
actions weather forecast offices should take to address stations that 
do not meet siting standards. 

Agency Comments and Our Evaluation: 

We provided a copy of our draft report to the Department of Commerce 
for review and comment. In written comments from the department, NOAA 
agreed that it can improve its ability to manage the USHCN in 
accordance with performance management guidelines and federal internal 
control standards. NOAA also agreed with our two recommendations. 
Regarding our first recommendation, NOAA stated that NWS has begun the 
planning process to upgrade the existing information system that 
captures data for managing Cooperative Observer Program stations, 
including those that are a part of the USHCN. According to NOAA, the 
upgrade will include the ability to capture more complete data on 
siting conditions and to determine if a station's record has been 
updated in the last 5 years. Regarding the second recommendation, NOAA 
said that NWS will work with NCDC to develop a policy to assist 
weather forecast offices in taking action on stations that do not meet 
siting standards. 

NOAA also stated that it understood that, given the scope of our 
review, we did not assess the effect of stations not meeting siting 
standards on the reliability of the agency's analysis of temperature 
trends. Nevertheless, NOAA added that it was important for our 
findings to include a discussion of the published peer-reviewed 
studies that have explicitly examined the USHCN's data quality and its 
effects on the reliability of NOAA's temperature trend data. We did 
not include such a discussion in our report because this issue was 
outside the scope of our work. We did, however, reproduce NOAA's list 
of relevant studies on this topic together with its comments. NOAA 
also provided technical comments, which we incorporated into the 
report as appropriate. NOAA's comments are reproduced in appendix III. 

As agreed with your office, unless you publicly announce the contents 
of this report earlier, we plan no further distribution until 15 days 
from the report date. At that time, we will send copies to the 
appropriate congressional committees, the Secretary of Commerce, and 
other interested parties. In addition, this report will be available 
at no charge on the GAO Web site at [hyperlink, http://www.gao.gov]. 

If you or your staff members have any questions about this report, 
please contact me at (202) 512-3841 or mittala@gao.gov. Contact points 
for our Offices of Congressional Relations and Public Affairs may be 
found on the last page of this report. Key contributors to this report 
are listed in appendix IV. 

Sincerely yours, 

Signed by: 

Anu K. Mittal: 
Director, Natural Resources and Environment: 

[End of section] 

Appendix I: Scope and Methodology: 

To determine how the National Oceanic and Atmospheric Administration 
(NOAA) selected stations for the U.S. Historical Climatology Network 
(USHCN) from the larger set of existing stations in the Cooperative 
Observer Program network, we reviewed documents from NOAA's National 
Climatic Data Center (NCDC) describing the selection process, 
interviewed NCDC officials, and analyzed NCDC data on stations in the 
USHCN. Specifically, we reviewed documents written by NCDC officials 
to identify the factors the agency considered important for monitoring 
long-term temperature trends, and we interviewed NCDC officials 
regarding these factors, as well as how they applied them in the 
selection process. We also obtained data from NCDC on the geographic 
distribution of USHCN stations across the contiguous 48 states and the 
length and completeness of the stations' temperature records. The data 
we obtained and analyzed came from NCDC's version 2 of the USHCN. 
[Footnote 25] We assessed the reliability of the data by 
electronically testing them and comparing selected samples to data 
from other NOAA sources to check for obvious errors in accuracy and 
completeness. We also reviewed information about the data and the 
systems used by NCDC to produce the data, interviewed NCDC officials 
knowledgeable about the data, and worked with officials to clarify 
inconsistencies before using the data in our analyses. We determined 
that the data were sufficiently reliable for reporting on the extent 
to which USHCN stations met the factors NCDC considered important in 
selecting the stations. 

To examine the extent to which USHCN stations meet National Weather 
Service (NWS) siting standards and management requirements for weather-
monitoring stations, we developed and administered a survey of 
meteorologists-in-charge at the 116 NWS weather forecast offices 
responsible for managing stations in the network.[Footnote 26] Our 
questionnaire included questions about adherence to siting standards, 
reasons for stations not adhering to the standards, and general 
management challenges. The survey was Web based and accessible through 
a secure server. On February 7, 2011, we sent an e-mail notification 
to the 116 meteorologists-in-charge describing the survey and 
notifying them that it would be activated on the Internet shortly. On 
February 9, 2011, we formally activated the survey and sent another e-
mail containing a link to the survey along with each respondent's 
unique username and password. We sent follow-up e-mail messages on 
February 16, 2011, and February 24, 2011, to those who had not yet 
responded. Then, starting on March 11, 2011, we contacted the 
remaining nonrespondents by telephone or e-mail. The questionnaire was 
available online until March 23, 2011. By that date, the surveys were 
completed by all 116 weather forecast offices, for a response rate of 
100 percent. 

Because our survey covered all weather forecast offices in the 
contiguous 48 states, not a sample of them, it was not subject to 
sampling error. Surveys are, however, subject to nonsampling errors. 
For example, how a particular question is interpreted, sources of 
information available to respondents, and how the data are entered in 
a database or are analyzed can introduce unwanted variability into 
survey results. We took steps in developing the survey, collecting the 
data, and analyzing them to minimize such nonsampling errors. For 
example, GAO survey specialists designed the questionnaire in 
collaboration with GAO staff who had subject-matter expertise. In 
addition, we conducted four pretests of the draft questionnaire to 
ensure that the questions were clear and unambiguous, terminology was 
used correctly, the questionnaire did not place an undue burden on 
agency officials, the information could feasibly be obtained, and the 
survey was comprehensive and unbiased. We conducted each of the four 
pretests over the telephone with one or more NWS officials from each 
of the four NWS regions in the contiguous United States. On the basis 
of the feedback we received, we made changes to the content and format 
of the survey after each of the four pretests. When we analyzed the 
data, an independent GAO analyst checked all computer programs. Since 
this was a Web-based survey, respondents entered their answers 
directly into the electronic survey, eliminating the need to key data 
into a database, thus minimizing data entry errors. 

Our survey results are also subject to errors made by weather forecast 
office staff regarding the number of stations they reported as not 
adhering to siting standards. For example, one weather forecast office 
indicated in its survey response that one USHCN station in its area 
was on a rooftop, but office staff later told us that the survey 
response was wrong and that none of its USHCN stations is located on a 
rooftop. In addition, the number of stations reported by weather 
forecast offices as not adhering to siting standards is subject to the 
staff's interpretation of NWS's siting standards. For example, it is a 
matter of interpretation and judgment by NWS staff whether objects 
surrounding a station, such as trees or structures, are considered to 
be obstructions and thus whether a station is considered to meet or 
not meet the siting standards. The response to our survey from one 
weather forecast office we visited indicated that the temperature-
measuring equipment at only one of its USHCN stations was closer to an 
obstruction than specified in the siting standards. We observed 
obstructions at all three stations we visited, however, and the 
records for these stations also listed obstructions. 

In calculating the percentages of the total number of active stations 
that met the specific criteria we asked about in our survey questions, 
we did not use responses from weather forecast offices that provided 
incomplete or inconsistent information. Depending on the percentage 
being calculated, we did not use responses from at most 6 of the 116 
offices. For example, we did not use responses from 3 offices when 
calculating the percentage of active USHCN stations that did not 
adhere to one or more of the siting standards, and we did not use 
responses from 5 offices when calculating the percentage of active 
Cooperative Observer Program stations not adhering to one or more of 
the standards. 

To examine in greater depth the extent to which USHCN stations meet 
siting standards and management requirements for weather-monitoring 
stations, we visited a nonprobability sample of 8 NWS weather forecast 
offices. To ensure geographic distribution in the weather forecast 
offices we visited, we selected two offices in each of the four NWS 
regions in the contiguous United States, and we selected the specific 
offices we visited to ensure a range of sizes in terms of the offices' 
forecast areas. We also selected offices with differing structures for 
supervising staff assigned to manage the Cooperative Observer Program 
and with a range of other programs the offices are responsible for, 
such as marine forecasts. To examine adherence to siting standards for 
weather-monitoring stations, we observed siting conditions at a 
nonprobability sample of 19 USHCN stations. We selected stations to 
visit to ensure variety in the type of temperature-measuring equipment 
used at the stations and other factors that could affect siting 
conditions. During the station visits, we developed and used a 
checklist that tracked how well the conditions of the site met what 
was recorded in the stations' records. In addition, we reviewed files 
on USHCN stations at each of the weather forecast offices we visited. 
We reviewed records and annual inspection reports from a total of 81 
USHCN stations. We entered information from the records and inspection 
reports into a database to capture information on the extent to which 
weather forecast offices adhered to the requirements to update station 
records and conduct annual inspections, among other things. Because we 
used a nonprobability sample to select weather forecast offices and 
USHCN stations to visit, the information we obtained from these visits 
cannot be generalized to other weather forecast offices or USHCN 
stations. The visits instead provided us with information on the 
perspectives of various participants in the weather forecast offices 
about managing weather-monitoring stations and examples of station 
siting conditions. 

To gather additional information on the extent to which USHCN stations 
meet NWS siting standards for weather-monitoring stations, we also 
reviewed academic literature that addressed issues and concerns 
related to siting of weather-monitoring stations, including those in 
the USHCN. We also reviewed NWS's policy directives related to station 
siting and interviewed officials in NWS headquarters, regional 
offices, and weather forecast offices who were responsible for 
managing the Cooperative Observer Program. In addition, we interviewed 
the person at the NWS training center responsible for training NWS 
staff on management and operation of the Cooperative Observer Program 
and individuals who have raised concerns about the extent to which 
stations in the USHCN are meeting siting standards. 

To evaluate the extent to which NWS tracks USHCN stations' adherence 
to siting standards and management requirements and has established a 
policy for addressing stations that do not adhere to siting standards, 
we took several actions. In particular, we evaluated the types of data 
that are captured in NWS's information system for managing weather- 
monitoring stations--the Cooperative Station Service Accountability 
system. We also interviewed NWS officials responsible for managing the 
USHCN, as well as NCDC officials; reviewed NWS policy directives, 
briefings, and memorandums related to managing the network; and 
examined data on the extent to which NWS conducted the required annual 
inspections of weather-monitoring stations. To determine the extent to 
which NWS has established a policy to address stations that do not 
adhere to siting standards, we reviewed NWS documents, such as agency 
directives, memos, briefings on the future of the Cooperative Observer 
Program, and an executive summary for a draft strategic plan for the 
program. In addition, we interviewed NCDC officials and NWS officials 
from regional, headquarters, and weather forecast offices and from the 
Cooperative Observer Program training center. 

[End of section] 

Appendix II: Other National Climate Networks: 

Since 2001, NOAA has supported establishment of two new networks of 
climate monitoring stations. The first to be established, the U.S. 
Climate Reference Network, is intended to detect indications of 
climate change at a national scale. This network consists of 114 
stations in the contiguous 48 states, and NOAA has plans to expand the 
network to include stations in Alaska. The purpose of the second new 
network, the U.S. Regional Climate Reference Network, is to detect 
indications of climate change at a regional rather than national 
scale. As of July 2011, this network consisted of 63 stations in the 
southwestern United States, and NOAA hopes to complete the 
installation of stations for the network across the contiguous 48 
states by about 2020, depending on the availability of funding. 
According to NOAA, once both networks are fully established, about 538 
locations in the contiguous United States will have either a U.S. 
Climate Reference Network station or a U.S. Regional Climate Reference 
Network station. 

The station-siting standards for the two new networks have 
similarities to the siting standards established for the Cooperative 
Observer Program and that also apply to the USHCN, such as 
installation over level terrain and not on rooftops. The new networks 
also have differences, including instances where the siting standards 
for the new networks are more stringent. For example, the standards 
for the U.S. Climate Reference Network call for stations to be located 
farther from concrete or paved surfaces than specified in the 
standards for stations in the USHCN. The differences reflect the fact 
that, whereas NCDC designated stations for the USHCN from an existing 
network of NWS weather-monitoring stations, NOAA has specifically 
located and designed stations in the newer networks for monitoring the 
nation's climate. For example, the use of automated equipment, as well 
as solar power at many stations, allows for greater flexibility in 
locating stations in comparison with NWS weather-monitoring stations 
that rely on volunteer observers and equipment connected by a cable to 
an indoor readout device. Similarly, to the extent possible, NOAA has 
placed a priority on locating stations for the new networks on public 
lands, such as national and state parks. According to NOAA, in 
comparison with the properties of volunteer observers, such locations 
have a higher probability of continuing in their present condition 
without major changes for long periods of time (50 to 100 years). 
Figure 7 depicts a station in the U.S. Climate Reference Network. 

Figure 7: U.S. Climate Reference Network Station: 

[Refer to PDF for image: photograph] 

Source: NCDC. 

[End of figure] 

NOAA has also established a process to evaluate and select potential 
sites for stations in the new networks. For example, selecting 
stations for the U.S. Regional Climate Reference Network includes 
field and desk surveys, which involve collecting information about the 
site's condition from photographs and other sources; evaluation of the 
surveys by a site selection panel; a vote among panel members to 
decide among candidate locations; and final approval or disapproval of 
panel recommendations by a site selection lead. See table 1 for 
differences in the siting standards applied to the USHCN and the new 
climate networks. 

Table 1: Differences in Selected Siting Standards of National Climate 
Networks: 

Siting standard: Site-ranking system; 
Cooperative Observer Program, including stations in the USHCN: No 
ranking system; 
New networks: Five classes, with 1 being the best sited and 5 the 
worst; the extent to which stations meet the standard for distance 
from artificial heating sources is one of the primary criteria for 
temperature measurement. NCDC aims to select class 1 station locations. 

Siting standard: Distance from artificial heating sources; 
Cooperative Observer Program, including stations in the USHCN: 100 
feet from any extensive concrete or paved surfaces; 
New networks: For class 1, more than 300 meters (or almost 1,000 feet) 
from artificial heating or reflecting surfaces, such as buildings, 
concrete surfaces, and parking lots. 

Siting standard: Distance from obstructions; 
Cooperative Observer Program, including stations in the USHCN: No 
closer than 4 times the estimated height of any nearby building, tree, 
fence, or similar obstruction; 
New networks: For class 1, no closer than about 10 times the height of 
surrounding vegetation. 

Source: GAO analysis of NOAA's siting standards. 

[End of table] 

[End of section] 

Appendix III: Comments from the Department of Commerce: 

United States Department of Commerce: 
The Secretary of Commerce: 
Washington, D.C. 20230: 

August 22, 2011: 

Ms. Anu K, Mittal: 
Director: 
Natural Resources and Environment: 
U.S. Government Accountability Office: 
441 G Street, NW: 
Washington, DC 20548:  

Dear Ms. Mittal:  

Thank you for the opportunity to review and comment on the Government 
Accountability Office's draft report entitled "Climate Monitoring: 
NOAA Can Improve Management of the U.S. Historical Climatology 
Network" (GAO-11-800). On behalf of the Department of Commerce, I have 
enclosed the National Oceanic and Atmospheric Administration's 
programmatic comments to the draft report.  

Sincerely,  

Signed by: 

Rebecca M. Blank: 
Acting Secretary of Commerce: 

Enclosure:  

[End of letter] 

Department of Commerce: 
National Oceanic and Atmospheric Administration: 

Comments to the Draft GAO Report Entitled "Climate Monitoring: NOAA 
Can Improve Management of U.S. Historical Climatology Network" (GAO-11-
800, August 2011): 

General Comments: 

The Department of Commerce's National Oceanic and Atmospheric 
Administration (NOAA) appreciates the opportunity to review the 
Government Accountability Office's (GAO) draft report on the U.S. 
Historical Climatology Network (USHCN) and agrees that NOAA can 
improve its ability to manage the USHCN in accordance with performance 
management guidelines and federal internal control standards. 

NOAA notes the statement in this report that the GAO "did not include 
an assessment into the effect of stations' not meeting siting 
standards on the reliability of NOAA's analysis of temperature 
trends." NOAA understands that these scientific findings were not the 
subject of this GAO review. Nevertheless, it is important context for 
GAO's findings to include a discussion of the published peer-reviewed 
studies that have explicitly examined the network's data quality and 
its effects on the reliability of NOAA's temperature trend findings 
Such studies have confirmed that corrections applied to USHCN data 
based on peer-reviewed algorithms can largely account for the impact 
of instrument and siting changes. In fact, adjusted USHCN temperatures 
are well aligned with recent measurements from instruments whose 
exposure characteristics meet the highest standards for climate 
monitoring. 

For GAO's reference, a list of relevant studies is included as an 
appendix to this response. 

NOAA Response to GAO Recommendations: 

The draft GAO report states, "To improve NWS's ability to manage the 
USHCN in accordance with performance management guidelines and federal 
internal control standards, as well as strengthen congressional and 
public confidence in the data the network provides, we recommend that 
the Secretary of Commerce direct the Administrator of NOAA to take the 
following two actions:" 

Recommendation is "Enhance NWS's information system to centrally 
capture information that would be useful in managing stations in the 
USHCN, including: 

* more complete data on siting conditions, including when siting 
conditions change, which would allow the agency to assess the extent 
to which the stations meet its siting standards, and; 

* existing data on when station records were last updated to monitor 
whether the records are being updated at least once every 5 years as 
NWS requires." 

NOAA Response: NOAA concurs with this recommendation. The National 
Weather Service (NWS) is currently in the planning stages to upgrade 
the existing information system that is used for Cooperative Observer 
Program (COOP), and therefore USHCN, metadata. This upgraded system 
will include the ability to capture more complete data on siting 
conditions and will record whether a station has been updated in the 
last 5 years. This system is planned to be operational by the end of 
fiscal year 2013, depending on the availability of funding. 

In order to better identify a COOP station as belonging to the USHCN 
dataset, the National Climatic Data Center (NCDC) will coordinate this 
designation with the NWS. In turn, the NWS will mark this designation 
in the COOP network database. 

Recommendation 2: "Develop an NWS agencywide policy, in consultation 
with NCDC, on actions weather forecast offices should take to address 
stations that do not meet siting standards." 

NOAA Response: NOAA concurs with this recommendation. The NWS, working 
with NCDC, will develop a policy to assist Weather Forecast Offices to 
take action regarding COOP stations that do not meet siting standards. 
Without a strong partnership between the nowcasting; forecasting, and 
climate monitoring communities, where all parties agree to the policy, 
the long-term reliability of the USHCN data set and COOP networks for 
climate purposes may not be fully realized. 

Appendix A: Peer-reviewed Studies Regarding Artificial Changes in 
Temperature Associated with Changes in Station Environment and 
Observing Practices: 

Hubbard, K. G., and X. Lin, 2006: Reexamination of Instrument Change 
Effects in the U.S. Historical Climatology Network. Geophysical 
Research Letters, 33, L15710, doi:10.1029/2006GL027069. 

Karl, T.R., C.N. Williams, Jr., P.J. Young, and W.M. Wendland, 1986: A 
Model to Estimate the Time of Observation Bias Associated with Monthly 
Mean Maximum, Minimum and Mean Temperatures for the United States. 
Journal of Climate And Applied Meteorology, 25 (2), 145-160. 

Menne, M. J., C. N. Williams Jr., and M. A. Palecki (2010), On the 
Reliability of the U.S. Surface Temperature Record, Journal of 
Geophysical Research, 115,1311108, doi:10.1029/2009.1D013094. 

Menne, KJ., C.N. Williams, and R.S. Vose, 2009: The United States 
Historical Climatology Network Monthly Temperature Data - Version 2. 
Bulletin of the American Meteorological Society, 90(7), 993-1107. 

Peterson, Thomas C., 2006: Examination of Potential Biases in Air 
TeMperature Caused by Poor Station Locations. Bulletin of the American 
Meteorological Society, 87, 1073-1089. 

Pielke, R. A., Sr., and Coauthors, 2007a: Documentation of 
Uncertainties and Biases Associated with Surface Temperature 
Measurement Sites for Climate Chance Assessment. Bulletin of the
American Meteorological Society, 88, 913-928. 

Vose, R.S., C.N. Williams, T.C. Peterson, T.R. Karl, and D.R. 
Easterling, 2003: An Evaluation of the Time of Observation Bias 
Adjustment in the US Historical Climatology Network. Geophysical 
Research Letters, 30 (20), 2046, clim3-l--3-4 
doi:10.1029/2003GL018111, 2003 (15 October 2003). 

[End of section] 

Appendix IV: GAO Contact and Staff Acknowledgments: 

GAO Contact: 

Anu K. Mittal, (202) 512-3841 or mittala@gao.gov: 

Staff Acknowledgments: 

In addition to the contact named above, Stephen D. Secrist (Assistant 
Director), Richard Bulman, William Carrigg, Joanna Chan, Ellen W. Chu, 
Joseph Cook, Alysia Davis, N'Kenge Gibson, Stuart Kaufman, Cheryl 
Peterson, Anne Rhodes-Kline, and Jerome Sandau made key contributions 
to this report. 

[End of section] 

Footnotes: 

[1] NOAA has 122 weather forecast offices, including 116 offices in 
the contiguous 48 states. Because NOAA established the USHCN to 
analyze trends in the contiguous 48 states, no USHCN stations are 
located in the 6 weather forecast offices in the Alaska and Pacific 
regions and in San Juan, Puerto Rico, although there are weather-
monitoring stations in these areas. 

[2] Throughout this report, we refer to stations in the Cooperative 
Observer Program as weather-monitoring stations. 

[3] Before 1890, weather-monitoring stations were managed by the Army 
Signal Corps. 

[4] NCDC, which is part of NOAA's National Environmental Satellite, 
Data, and Information Service, is the nation's archive of weather data 
and uses these data to assess and monitor climate variation and change. 

[5] C. Fenimore et al., "United States," Bulletin of the American 
Meteorological Society, vol. 92, S175-S179 (2011). 

[6] NOAA has also developed siting standards for its new networks 
specifically designed for climate monitoring--the U.S. Climate 
Reference Network and the U.S. Regional Climate Reference Network. The 
standards for the new networks have similarities to those for the 
Cooperative Observer Program but also differences, including instances 
where the standards for the new networks are more stringent. Appendix 
II summarizes these similarities and differences. 

[7] World Meteorological Organization, Guide to Meteorological 
Instruments and Methods of Observation, 7th ed., WMO-No. 8 (Geneva, 
Switzerland: 2008). 

[8] Called the Cooperative Station Service Accountability system, 
NWS's information system is a national database containing information 
on all Cooperative Observer Program and USHCN stations. 

[9] Each of the 48 contiguous states is divided into as many as 10 
climate divisions (areas that have a similar climate). For example, 
Nevada is divided into four climate divisions, and New York has the 
maximum of 10 climate divisions. 

[10] Active stations exclude stations that have closed, often due to 
the lack of an observer to record weather observations, as well as 
inactive stations that weather forecast offices may expect to return 
to active status or ultimately decide to close if no observer is 
available. NCDC does not exclude data from inactive and closed USHCN 
stations when analyzing temperature trends; instead, it uses the data 
available from when the stations were active. 

[11] T. R. Karl et al., United States Historical Climatology Network 
(HCN) Serial Temperature and Precipitation Data, ORNL/CDIAC-30, NDP- 
019/R1 (Oak Ridge, Tenn.: Carbon Dioxide Information Analysis Center, 
Oak Ridge National Laboratory, U.S. Department of Energy, 1990). 

[12] NWS guidelines state that weather forecast offices should seek 
out weather station observers who are likely to record data over a 
long period and at around the same time each day and that the offices 
should avoid moving instruments at stations with a long record of 
temperature measurements. The guidelines also establish procedures for 
managing changes in measurement conditions when such changes occur. 

[13] We did not evaluate the methods used by NCDC to identify and 
remove shifts in temperature data caused by changes in measurement 
conditions, as this was outside the scope of our review. 

[14] F. T. Quinlan et al., United States Historical Climatology 
Network (HCN) Serial Temperature and Precipitation Data, NDP-019 (Oak 
Ridge, Tenn.: Carbon Dioxide Information Analysis Center, Oak Ridge 
National Laboratory, U.S. Department of Energy, 1987). 

[15] This percentage is based on survey responses we received from 113 
of the 116 weather forecast offices. We did not use responses from the 
3 offices that provided incomplete or inconsistent information needed 
to calculate this percentage. See appendix I for further information 
on the steps we took to verify the accuracy of survey responses. 

[16] This percentage is based on survey responses from 111 of the 116 
weather forecast offices and does not include stations that do not 
measure air temperature. We did not use responses from the 5 offices 
that provided incomplete or inconsistent information needed to 
calculate this percentage. 

[17] We did not include survey responses from two weather forecast 
offices that provided inconsistent information. 

[18] The results of our file review are based on a nonprobability 
sample of weather forecast offices and cannot be generalized to other 
offices. 

[19] The results of our file review are based on a nonprobability 
sample of weather forecast offices and cannot be generalized to other 
offices. 

[20] M. Menne et al., "On the Reliability of the U.S. Surface 
Temperature Record," Journal of Geophysical Research, vol. 115, D11108 
(2010). 

[21] Pub. L No. 103-62, § 3, 107 Stat. 285 (1993), codified at 5 
U.S.C. § 306. The act was recently amended by the GPRA Modernization 
Act of 2010, Pub. L. No. 111-352, 124 Stat. 3866 (2011). 

[22] For example, see GAO, The Results Act: An Evaluator's Guide to 
Assessing Agency Annual Performance Plans, [hyperlink, 
http://www.gao.gov/products/GAO/GGD-10.1.20] (Washington, D.C.: April 
1998). 

[23] NWS officials cautioned that there is potential for differing 
interpretations among weather forecast offices regarding the 
requirement for annual inspections. In particular, the requirement can 
be strictly interpreted as 365 days from the date of the last visit or 
more generally interpreted as at least one time during the course of a 
year. 

[24] GAO, Standards for Internal Control in the Federal Government, 
[hyperlink, http://www.gao.gov/products/GAO/AIMD-00-21.3.1] 
(Washington, D.C.: November 1999). 

[25] NCDC released version 2 of USHCN in 2009 to account for station 
closures and update the list of stations selected for inclusion in the 
network. NCDC also revised its statistical methods for use in version 
2. According to NCDC officials, version 2.5 of USHCN replaced version 
2 as of June 2011. The officials told us that version 2.5 is the U.S. 
component of NCDC's global network of weather stations. 

[26] NWS has 122 weather forecast offices, including 116 offices in 
the contiguous 48 states. Because NCDC established the USHCN for 
analysis of trends in the contiguous 48 states, no USHCN stations are 
located in the 6 weather forecast offices in NWS's Alaska and Pacific 
regions and in San Juan, Puerto Rico, although there are Cooperative 
Observer Program stations in these areas. 

[End of section] 

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