and management has increased as a result of a more integrated approach to environmental and natural resource planning.
Existing climate databases are limited in terms of geographic coverage of climate data, data formats, data homogeneity, data quality, period of record, data record serial completeness, computerized availability, and/or timeliness. Many long term NWS data records in urban areas are largely unadjusted for the dramatic urban and industrial growth during this century. Of the 8,000 currently active U.S. weather stations, only 492 have been checked for instrument and location changes and adjusted for population (Hughes et al. 1991). Data from other stations are not representative of larger, more rural regions, complicating comprehensive spatial climate analysis. Urbanization has been most dramatic in affecting temperatures (particularly summer minimums) and to some extent precipitation, although urban effects on precipitation are more difficult to quantify.
Precipitation data have high spatial variability and are needed not just in daily increments but in hourly and 15 minute intervals to fully evaluate pollutant transport through the soil profile. Wintertime precipitation in cold regions of the country and particularly in the western U.S. in the form of ice or snow is very important in the evaluation of airborne dry or storm deposited pollutants. The mountain snowpack delays release of airborne pollutants accumulated in its layers until spring when the snowpack profiles become isothermal or otherwise have free water passing through. This situation creates significant short-term high concentrations of the pollutants (Sommerfeld et al. 1990). Since more than 70 percent of the water that flows in the West comes from melting mountain snows, this phenomenon is critical to subsequent water quality.
Solar radiation, relative humidity, and wind information are collected sparsely, mostly at aviation centers. For other areas this information requires considerable estimation and extrapolation for spatial analysis. Potential evaporation information also is collected sparsely, usually in areas where irrigation water management has required the data to guide water use and maximize crop production. Air quality data, except in populous areas, are scant, providing an inadequate database for spatial analysis.
Although not necessarily part of a climate database, soil moisture and soil temperature, important factors in chemical fate and transport, are sparsely observed nationwide. A 1991 SCS pilot project monitoring global climatic change identified more than 300 separate collection efforts for these two soil parameters. This information is in a variety of formats, specifications, and quality (USDA 1991b). However, much of this data collection is driven by irrigation water management needs, which do not necessarily match the data needs for ground water vulnerability assessments.
Several regional and national efforts are attempting to index climate information available from many sources for common use. A catalog of