Moisture transport associated with large precipitation events in the Upper Colorado River Basin

Abstract

Interannual streamflow variability poses numerous water supply forecasting and management challenges for mountain snowpack‐sourced basins across the western United States. Previous studies have shown that substantial proportions of annual precipitation occur during relatively few large precipitation events (LPEs) and consequently, such events tend to be significant predictors of streamflow for many basins, including the Upper Colorado River Basin (UCRB). While some primary pathways of atmospheric moisture transport, particularly atmospheric rivers, have been linked with extreme precipitation events across the western United States, this study seeks to expand on this knowledge by quantifying the relationships between moisture transport regimes, LPEs, and streamflow observed in the UCRB. A climatological analysis of integrated vapour transport, via a self‐organizing maps synoptic classification procedure, is used to identify geographic regimes of moisture transport that lead to LPEs, as observed at snow telemetry sites across the UCRB headwaters. Trajectory analyses are also calculated to further characterize LPE‐inducing atmospheric river pathways by subbasin in the UCRB. Results indicate that LPEs throughout the basin most commonly coincide with amplified trough patterns, which advect Pacific moisture into the UCRB from the southwest, through Southern California and the Four Corners region; patterns that are positively correlated to streamflow. LPEs occurring in northern portions of the UCRB exhibit a secondary corridor, featuring west to east‐oriented moisture transport, in association with zonal to meridional flow regimes. Highly amplified ridges over the region rarely lead to LPEs, as such patterns deflect or suppress moisture from the UCRB. These results suggest that climate projections of future enhanced meridional flow aloft will lead to continued streamflow variability in the UCRB.