Human-impacted water resources: Domain stratification and mapping to determine hydrologically similar units

Geographic Information Systems (GIS) and multivariate statistical analyses were used to partition the United States into Human Influenced Water Environmental Classes (HIWECs) for the purpose of determining hydrologically similar units within the conterminous United States. Such a framework could be used to investigate various categories of watersheds throughout the country or to establish observatory sites in variant hydrologies. These HIWECs represent areas that are relatively homogeneous with respect to the human influence variables of land cover, population density, and water use; the climate variables of temperature and precipitation; and the physical variables of slope, bedrock permeability, and soil permeability. These variables combine to characterize hydrologic condition and collectively represent the major hydrologic variability that exists across the U.S. GIS was first used to break each of the variables into low to high ranges. Multivariate statistics were then used to identify and cluster areas that share similar characteristics in multivariate data space. HIWECS can serve as a framework for development of water research and management; observatory sites can be selected to capture variant hydrologies that incorporate the human influence element with the criteria that each type of human-influenced hydrologic condition, or class, be represented.