Preface to special section on fifty years of research and data collection: US Department of Agriculture Walnut Gulch Experimental Watershed

This special section of Water Resources Research and the associated Web site (http://www.tucson.ars.ag.gov/dap/) describe 50 years of data collection and the most recent research results at the U.S. Department of Agriculture (USDA) Agricultural Research Service (ARS) Walnut Gulch Experimental Watershed (WGEW) in southeast Arizona. The goal of this compilation is to encourage cooperative, interdisciplinary studies of semiarid ecohydrology at WGEW based on continuing long-term measurements of soils, vegetation, hydrology, and climate.