Patterns of Hydrologic Sensitivity to Climate in the Western US: Implications for Future Predictions

Abstract:

A key challenge for resource and land managers is predicting the consequences of climate warming on streamflow and water resources. During the last century in the western United States, significant reductions in snowpack and earlier snowmelt have led to an increase in the fraction of annual streamflow during winter and a decline in the summer. However, this increase and decrease in streamflow is mediated by the climate and landscape. Here we explore key landscape and climate metrics for interpreting hydrologic sensitivity to climate using observed flow from a range of watersheds across the western United States. Our results indicate that the recession constant and fraction of precipitation falling as snow are the two primary controls on hydrologic sensitivity to climate in this region. Dry season flows in watersheds that drain slowly from deep groundwater and receive precipitation as snow are most sensitive to climate warming. In terms of peak flow, watersheds are most sensitivity to the consistency (i.e. signal-to-noise ratio) in fraction of precipitation falling as snow. Our results also indicate that not all trends in western United States are associated with changes in snowpack dynamics; we observe declining flow in late fall and winter in rain-dominated watersheds as well. These empirical findings support both theory and hydrologic modeling and have implications for how hydrologic sensitivity to climate change is evaluated and interpreted across broad regions.