Using USDA statistics and MODIS satellite data, USGS scientists have developed a consistent methodology to rapidly assess irrigation change across the conterminous United States. MODIS Irrigated Agriculture Data for the U.S. maps were created for 2002 and 2007. The 2002 and 2007 maps have estimated accuracy of 86 percent and 91 percent, respectively, based on assessments completed for central California, Snake River basin, and Central Plains. The overall change in irrigated area from 2002 to 2007 was +3 percent, but changes showed definite regional patterns. Changes in irrigation extent and related water use may be associated with a number of factors including drought severity, access to water supply, and water costs.
The national geospatial irrigated area data improves wall-to-wall drought monitoring models. These models are used by researchers in the USGS, universities, agricultural seed companies, and private research labs to investigate biophysical carbon sequestration, predict agricultural productivity and crop-water use and investigate how land use practices affect biogeochemistry (for example, carbon and nitrogen exchange), and estimate the effects of irrigation within a mesoscale weather forecasting model. Future work will investigate relationships among cropping patterns (crop types) and climate.