Existing Climate Data Sources and Their Use in Heat Island Research

Historical analysis requires many years--perhaps decades--of continuous data to assess urban temperature trends. Such data is available generally from three sources: the cooperative network, observations at military installations, and first-order National Weather Service (NWS) stations.

The cooperative network

The cooperative network consists of stations from a variety of sources that voluntarily report their data to the National Climatic Data Center (NCDC) for compilation. Data reported include daily maximum temperature, daily minimum temperature, daily precipitation, and sometimes daily snowfall and daily pan evaporation. The climate record amassed through the cooperative network includes records with coverage ranging from a few years to over a century.

The cooperative network station index is available on-line both through the National Center for Atmospheric Research (NCAR) and through the NCDC. Station records include station names and numbers, latitude, longitude, elevation, and the starting and ending dates of operation. Table 1 illustrates the concentration of weather stations in certain cities in the southwestern U.S. This index can thus be searched to find climate records by location and by coverage period. However, every time a station is moved a new index entry is created. Longer climate records can be created by linking these different records as long as precautions are taken to guarantee historical homogeneity.

			# of Stations
Weather Station	Latitude	Longitude	Total	Active
Wichita Airport, KS	37°39'	97°26'	8	8
Omaha Eppley Airfield, NE	41°18'	95°54'	13	11
Tulsa WSO Airport, OK	36°12'	95°54'	9	9
Amarillo WB Airport, TX	35°14'	101°42'	3	3
Austin WSO Airport, TX	30°17'	97°42'	17	13
Dallas-Ft. Worth Meacham Field, TX	32°49'	97°21'	15	12
Houston WB City, TX	29°46'	95°22'	19	12
San Antonio Nursery, TX	29°18'	98°28'	8	8
Phoenix, AZ	33°27'	112°4'	12	10
Tucson - University of Arizona, AZ	32°15'	110°57'	4	4
Sacramento WSO City, CA	38°31'	121°30'	18	15
Los Angeles Int'l Airport, CA	33°56'	118°24'	57	48
Albuquerque, NM	35°6'	106°37'	9	9
Las Vegas, NV	36°10'	115°8'	12	7
Reno WSFO Airport, NV	39°30'	119°47'	8	8
Salt Lake City, UT	40°46'	111°53'	10	9

Table 1: Numbers of stations currently in the Cooperative Stations List in the NCDC inventories for U.S. surface data within 1° of cities in the southwestern United States.

Another larger collection of cooperative network data is provided as the "Summary of Day" data set from NCDC. Each weather station's Summary of the Day data set includes temperature, sky conditions, precipitation, and wind direction and speed. This data are available on-line as well as collected on a CD-ROM from EarthInfo, Inc. (EarthInfo 1997). The station changes in each record are summarized in station histories, which are available either in brief encoded format, or as longer descriptions provided by NCDC. Unlike the HCN, the sites included in this resource have not been screened to assure historical homogeneity. Thus, records should be subjected to quality control procedures to adjust for both documented and undocumented discontinuities using several standard techniques (Karl and Williams 1987, Karl et al. 1986).

First Order Stations and military installations

To fully capture the effect of urban areas on their climate, daily extrema of temperature are insufficient. For example, urban surfaces with high thermal capacities, reduced sky view factors, and diminished convective heat exchange due to reduced winds may cool or heat slower than rural areas. The resulting temperature difference in the late afternoon is especially important for energy use since utility demands peak during that time. However, a comparison of urban and rural temperature extrema will not detect this effect. Higher time-resolution data are available from first-order weather stations operated by the NWS, predominantly at civilian airports. Air temperatures are recorded hourly, as well as other weather conditions such as precipitation, insolation, and wind speed and direction. These stations are useful for obtaining data representative of a larger area due to the flat, uniform surroundings of the sites. However, the number of records is typically limited. Such weather data are available from the NCDC. Daily precipitation, snowfall, evaporation, and temperature maxima, minima, and averages from these stations are included in the cooperative network data sets.

Military installations, especially airports, also maintain weather towers and record climate information at hourly intervals. These data can be obtained through the NCDC and are typically quite expensive. However, given the sparse coverage of NWS first-order stations, these data can prove crucial to historical understanding of urban climates in some areas.

An extensive, global inventory of first-order and military stations is available on-line from the NCDC. Data entries include station number, call letter, name, country, latitude, longitude, and elevation. More information about the stations can be gathered by reaching NCDC or often through the journal Local Climatological Data. The number of first-order and military weather stations recording hourly climate data in each state, according to the NCDC's National Weather Service-U.S. Air Force-Navy Station List, is given in Table 2. The number of stations in each state is often roughly proportional to its area.

Other data sources

Many other collections of data that may be of use in urban heat island research have been compiled. A number of these data sources are accessible through the Carbon Dioxide Information Access Center (CDIAC), NCDC, NCAR, and others (see appendices). Continue to: Chapter IIC. Historical Analysis of the Urban Climate of Los Angeles