Future Water Availability in a Warming World

As climate warms during the 21st century, resultant changes in water availability are an extremely important issue for society, perhaps even more important than the magnitude of warming itself. Yet our climate models disagree in their forecasts, limiting our ability to plan accordingly. This disagreement must be examined more closely to determine its causes. A comparison between two drought measures, the Supply Demand Drought Index (SDDI) and soil moisture was conducted to determine the relative abilities of the two measures to estimate future shortages or abundances of water globally. Five General Circulation Models (GCMs) showed dry areas becoming drier and wet areas becoming wetter in the 21st century according to both SDDI and soil moisture trends. Each measure has its own strengths and weaknesses, which are evaluated. However, since SDDI and soil moisture define drought using somewhat independent methods, both are useful in understanding regional differences. A regional evaluation of future water availability in seven regions displaying significant disagreement or agreement between the five GCMs or drought measures is a subject of current research to complement previous research on global-scale evaluation of future water availability. These water-sensitive regions, the Southwestern United States, Southern Europe, Eastern China, Australia, Siberia, Colombia and Uruguay, highlight areas in which the land surface scheme and atmospheric supply and demand show opposing trends, which will assist in further understanding model differences.