Drought Characterization: Indicators and Decision-Making

Droughts can cause significant economic losses throughout society. To mitigate impacts, key questions arise: How do we predict the onset of a drought? How severe is it? When do we take action? How do we know it's over? To provide a framework for addressing these questions, we characterize the onset, severity, spatial extent, and recovery of droughts using several drought indicators, and apply this approach to the analysis of drought in the state of Washington. We reconstruct four historical drought events (1976-77, 1987-1988, 2000-2001, and 2004-2005), using the Standardized Precipitation Index (SPI)-3, 6, 12, 24, 36, the Standardized Runoff Index (SRI)-3, 6, 12, 24, 36, and Soil Moisture Percentile (SMP) as indicators, with monthly updates, in each of the state's 62 Water Resource Inventory Areas (WRIAs). We also compare drought triggers based on the evolution of drought conditions and management decisions during the four droughts. Our results suggest the indicators detected the onset and recovery of drought conditions, in many cases, up to four months before state declarations. More generally, this approach can provide a scientific foundation to characterize and predict drought events, and support drought management decisions.