The Columbia University Water Center, Veolia Water and Growing Blue have issued a new report titled America's Water Risk: Water Stress and Climate Variability. The report examines water risk by evaluating both existing demand as well as variations in renewable water supply. The report offers a means to estimate water risk and map it for the U.S. at a county level. The report highlights on a U.S. map that severe water stress will occur over much of the agricultural belt of the Midwest as well as the arid regions of California and Arizona.

The measures of water risk are estimated using over sixty years of precipitation and the current water use pattern for each county. Two risk metrics are developed to capture the influence of within year dry periods (Normalized Deficit Index – NDI) and of drought across years (Normalized Deficit Cumulated – NDC). The NDI is computed as one number for each year using historical daily rainfall data for the area and current daily water needs. It measures the maximum cumulated water shortage each year during the dry period that needs to be provided for from groundwater or from surface water storage or transfers from other areas. The NDC is computed as one number over the historical climate record. It represents the largest cumulative deficit between renewable supply and water use over the entire period. Consequently, it reflects the stress associated with multi-year and within-year drought impacts at a location.

An infographic from Growing Blue summarizes the report findings and key data provided. It emphasizes the increased risk of water scarcity in cities and counties as climate change increases drought potential.

The report, America's Water Risk: Water Stress and Climate Variability, is available at http://growingblue.com/wp-content/uploads/2013/05/GB_CWC_whitepaper_climate-water-stress_final.pdf.