Efficiency of the Summer Monsoon in Generating Streamflow within a
Seasonally Snow-Dominated Headwater Basin of the Colorado River
Abstract
The North American Monsoon occurs July-September bringing significant
rainfall to Colorado River headwater basins. This rain may buffer
streamflow deficiencies caused by reductions in snow accumulation. Using
a data-modeling framework, we explore the importance of monsoon rain in
streamflow generation over historic conditions in an alpine basin.
Annually, monsoon rain contributes 18{plus minus}7% water inputs,
generates 10{plus minus}6% streamflow and increases water yield
3{plus minus}2% the following year. The bulk of rain supports
evapotranspiration in lower subalpine forests. However, rains have the
potential to produce appreciable streamflow at higher elevations where
soil storage, forest cover and aridity are low; and rebounds late season
streamflow 64{plus minus}13% from simulated reductions in snowpack as
a function of monsoon strength. Interannual variability in monsoon
efficiency to generate streamflow declines with low snowpack and high
aridity, implying the ability of monsoons to replenish streamflow in a
warmer future with less snow accumulation will diminish.