Climate elasticity of streamflow in the United States

Precipitation elasticity of streamflow, epsilon (p), provides a measure of the sensitivity of streamflow to changes in rainfall. Watershed model-based estimates of epsilon (p) are shown to be highly sensitive to model structure and calibration error. A Monte Carlo experiment compares a nonparametric estimator of epsilon (p) with various watershed model-based approaches. The nonparametric estimator is found to have low bias and is as robust as or more robust than alternate model-based approaches. The nonparametric estimator is used to construct a map of epsilon (p) for the United States. Comparisons with 10 detailed climate change studies reveal that the contour map of epsilon (p) introduced here provides a validation metric for past and future climate change investigations in the United States. Further investigations reveal that epsilon (p) tends to be low for basins with significant snow accumulation and for basins whose moisture and energy inputs are seasonally in phase with one another. The Budyko hypothesis can only explain variations in epsilon (p) for very humid basins.