Placing Potomac River Droughts in Context Using Synthetic and Paleoclimatic Data

Water supply planning for the Washington, D.C. metro area has historically been geared toward the worst drought conditions within the hydrologic record. Recent work expanded the planning context through use of a synthetic hydrology dataset developed using autoregressive models. Analysis using synthetic data and a forecast of 2025 demands showed only a slight chance of water supply shortages under drought conditions more extreme than the 1930–31 event—a 0.2% chance in any year, with only 6 days of shortages over the entire 540 year simulation. ICPRB is expanding the drought risk analysis in two ways. One is by performing statistical analyses on the outputs of water supply system simulations using the synthetic hydrology. These analyses will shed light on the severity and risk of the 1930–31 drought as well as the more severe droughts introduced by the synthetic dataset. ICPRB is also using reconstructions of climatic variables (e.g., Palmer Drought Index, precipitation) to expand the scope of drought risk analysis. Results using the synthetic data show drought risks to be slightly greater than would be estimated with the historical record. Quantitative results using the paleoclimatological data are highly uncertain but suggest the potential for extreme droughts if the basin were to shift into a dry hydrologic regime. Implications for planning and policy are discussed and directions for on-going work are described.