Proper characterization and understanding of droughts and their potential links to climate and hydrologic factors is essential for water resources planning and management in drought sensitive-watershed like Yakima basin. Particularly, given the ongoing multi-agencies efforts to adopt a complex and ultra-expensive water management plan in the basin in order to ensure water security during severe droughts, detail study of historical and future droughts is critical and timely.

In this study, we propose a comprehensive and probabilistic assessment of drought characteristics and their trends in the Yakima basin based on historical (1912-2016) and projected (2018-2090) climate and hydrology data, and taking into consideration the proposed water management plan and impact of future climate and uncertainty. For improved characterization of the different drought conditions, a new drought indicator will be developed by combining drought indices from total water supply, precipitation, snowpack, temperature, streamflow, and reservoir storage. Bivariate frequency analysis, taking into account the potential correlation between severity and duration, will be applied to characterize and predict drought frequency, severity and duration. Bayesian statistics along with ensembles of future climate and hydrologic projections will be used to quantify the uncertainty in the estimated return period, severity and duration of droughts. The effectiveness of the proposed water management plan in reducing frequency and severity of droughts will be evaluated under various plausible climate projections.

Besides providing a much needed insight about characteristics of droughts and their contributing factors, the outcome from the project is expected to have a direct contribution to the ongoing discussion of the effectiveness of the water management plan and its benefit and cost analysis. The research will be extended further in the future to improve understanding of drought risks posed by future climate on water scared but agriculturally fertile regions throughout U.S. and other parts of the world, with the overall goal of enhancing regions ability to deal with expected future severe and frequent droughts and increased water demands through comprehensive and forward looking water management strategies and drought forecasting and monitoring.