Development of a Demand Sensitive Drought Index and Its Forecasting for Climate Adaptation and Water Management over the Continental United States

Drought has cascading effects on the environment, economy and society. Seasonal water deficits resulting from natural variability in rainfall coupled with increased demands have severe implications for the adequacy of water storage in both surface and groundwater stores. Managers need better estimates of potential shortfalls in supply due to droughts of varying severity and duration. While global and national drought indicators exist, none directly connect existing or projected water demand to the potential deficit during the drought. They are essentially supply based. However, the temporal patterns of both demand and supply ultimately determine the stress or impact. Consequently, assessment of risk for various sectorial operations could be much better informed if appropriate stress indices were developed for drought conditions relative to current and projected demands, and their likelihood assessed for future climate scenarios. The present research addresses this methodological gap by (1) developing new drought indices that consider both water supply and current or projected sectorial demands, and (2) developing insights into the large-scale climatic drivers for forecasting drought onset, duration and severity up to one season ahead for climate informed adaptive risk assessment and long-term planning. We present an application at a county level for the conterminous United States considering more than 60 years of rainfall data as the renewable supply, and water demand patterns for 3 sectors (agricultural, industrial, and domestic use). The demand data are available at the county level. Consequently, we use the county rather than river basins as the unit of analysis. The county is also a spatial resolution consistent with political decision making. The index is useful for indicating whether small or large surface storage will suffice, or whether the extent of groundwater storage or external transfers, or changes in demand are needed to achieve a sustainable solution.