This paper presents and evaluates a method for the construction of long-range and wide-area temporal spatial datasets of daily precipitation and temperature (maximum and minimum). This method combines the interpolation of daily ratios/fractions derived from ground-based meteorological station records and respective fields of monthly estimates. Data sources for the described implementation over the conterminous United States (CONUS) are two independent and quality-controlled inputs: 1) an enhanced compilation of daily observations derived from the National Climatic Data Center digital archives and 2) the Parameter-Elevation Regressions on Independent Slopes Model (PRISM) maps. The results of this study show that this nonconventional interpolation preserves the spatial and temporal distribution of both the PRISM maps (monthly, topography-sensitive patterns) and the original daily observations. Statistics of a preliminary point comparison with the observed values at high-quality and independent reference sites show a reasonable agreement and a noticeable improvement over the nearest station method in orographically sensitive areas. The implemented datasets provide daily precipitation and temperature values at 2.5-min (around 4 km) resolution for 1960-2001. Combining seamless spatial and temporal coverage and topographic sensitivity characteristics, the datasets offer the potential for supporting current and future regional and historical hydrologic assessments over the CONUS.

BASINS (Better Assessment Science Integrating Point and Nonpoint Sources) version 3.0, is the updated software system developed by the U.S. Environmental Protection Agency Office of Water in order to meet the requirements of developing Total Maximum Daily Load (TMDL) programs. BASINS provides an enhanced set of nation‐wide databases, several new and interchangeable tools and models integrated in a new modular architecture, operating within ArcView Geographical Information System (GIS) for desktop PCs. This paper describes the integration of three new key components: (1) a tool that optimizes the automatic definition and segmentation of the watershed and stream network based on topography (Digital Elevation Models), NHD (National Hydrography Dataset) or other ancillary stream data; (2) a tool to define the Hydrologic Response Units (HRUs) over the watershed and subwatersheds; and (3) SWAT (Soil and Water Assessment Tool) model and a respective integrated user‐friendly interface. The first two components, based on raster functionality, improve the previously adopted simplistic methods for the hydrologic definition, segmentation and basic geomorphic assessment of the watershed and open to the usage of external datasets besides those distributed with the whole BASINS package. In addition, these components share generating datasets, hereby promoting the usage by other tools and models as well as other models that in the future could be introduced in BASINS. The third component introduces the SWAT model into BASINS. SWAT is a hydrologic distributed model with proven success in watershed assessment of both agricultural and urban scenario management effects on water quality and is based on over 30 years of USDA modeling experience. The description of these integrated components is followed by a simple, yet promising, application to the Upper North Bosque River watershed in Texas, using the default data distributed with BASINS.

This paper introduces AVSWAT, a GIS based hydrological system linking the Soil and Water Assessment Tool (SWAT) water quality model and ArcView  Geographic Information System software. The main purpose of AVSWAT is the combined assessment of nonpoint and point pollution loading at the watershed scale. The GIS component of the system, in addition to the traditional functions of data acquisition, storage, organization and display, implements advanced analytical methods with enhanced flexibility to improve the hydrological characterization of a study watershed. Intuitive user friendly graphic interfaces, also part of the GIS component, have been developed to provide an efficient interaction with the model and the associated parameter databases, and ultimately to simplify water quality assessments, while maintaining and increasing their reliability. This is also supported by SWAT, the core of the system, a complex, conceptual, hydrologic, continuous model with spatially explicit parameterization, building upon the United State Department of Agriculture (USDA) modeling experience. A step-by-step example application for a watershed in Central Texas is also included to verify the capability and illustrate some of the characteristics of the system which has been adopted by many users around the world.