| Mountain snowmelt-sourced watersheds across the western United States, such as the Colorado River Basin (CRB), commonly experience high interannual streamflow variability. In recent years, the CRB has experienced unprecedented drought conditions, further complicating water supply prediction and management during a period of rapid population growth and economic expansion in the region. Consequently, the need for increasingly accurate and timely water supply forecasts is critical for sustainable water management decision making. In an effort to explore forecasting improvements by quantifying the relationships between hydroclimatic variables and streamflow, a basin-wide synoptic climatology of the "early 21st century drought" reveals that warm and dry atmospheric circulation patterns have become increasingly common during the spring months each year, resulting in diminished annual reservoir inflow and net declines in storage. Among the basin headwaters, large precipitation events (LPEs) are shown to be significant predictors of basin streamflow and are linked to midtropospheric trough patterns, which advect moisture into the CRB, primarily from the tropical Pacific. These atmospheric conditions have become less common during the drought; therefore, LPEs have become rarer and drier, resulting in decreased total annual streamflow and earlier snowmelt observed throughout the basin. As reliable forecast skill continues to extend in lead time, efforts to improve water supply forecasting resources should emphasize the roles of prevailing synoptic patterns, LPEs, and storm event moisture sources, as predictors of total annual streamflow. |
