Climate Elasticity of Low Flows in the Maritime Western U.S. Mountains

Summer streamflow is an important water resource during the dry summers in the western United States, but the sensitivity of summer minimum streamflow (low flow) to antecedent winter precipitation as compared with summer evaporative demand has not been quantified for the region. We estimate climatic elasticity of low flow (percent change in low flow divided by percent change in climatic forcing variable) with respect to annual maximum snow water equivalent (ESWE), winter precipitation (EPPT), and summer potential evapotranspiration (EPET) for 110 unmanaged headwater catchments in the maritime western U.S. mountains. We find that |EPET| is larger than |EPPT| and |ESWE| in every catchment studied and is 4–5 times larger than both, on average. Spatial variations in E are dominated by three patterns. First, |EPPT|, |ESWE|, and |EPET| are largest and most variable among semiarid catchments and decrease nonlinearly with increasing values of the humidity index (the ratio of annual precipitation to annual evaporative demand). Second, |EPPT| and |EPET| are lower in snow-dominated catchments than in rain-dominated catchments, suggesting that snow cover reduces the proportional response of low flows to climatic variability. Third, |EPPT|, |ESWE|, and |EPET| are lower in slow-draining catchments than in fast-draining catchments, for which baseflow recession storage coefficients are used to represent the rate at which catchment water storage is translated into streamflow. Our results provide the first comparison of summer low-flow elasticity to PPT versus PET and its spatial variation in the maritime western U.S. mountains.

Duke Scholars

Author Sarah Cooley Earth and Climate Sciences