Brown, T.C., P. Froemke, W. Mahat, and J.A. Ramirez. 2016. Mean Annual Renewable Water Supply of the Contiguous United States. Briefing paper. Rocky Mountain Research Station, Fort Collins, CO. 55 pp.
Our fresh water supply begins as precipitation falling on land and fresh waters. From there the water naturally evaporates from the land or vegetation, percolates down to groundwater aquifers, or flows toward sea via rivers and streams. Water that evaporates is unavailable for use until it falls again elsewhere as precipitation. What remains is available for use by humans and other species (until it reaches the sea), and in a broad sense is our fresh water supply.
We estimated water supply across the contiguous 48 states for the period 1981-2010. Political, administrative, and land cover boundaries were mapped over the gridded water supply estimates to indicate the amount of water that becomes available in respective land areas. These water supply estimates are an update of those provided by Brown et al. (2008). Compared with Brown et al., these new estimates incorporate more recent precipitation and temperature data, apply a different water yield model, and utilize more and newer land cover data.