Modeling streamflow sensitivity to climate warming and surface water inputs in a montane catchment

Study region: Gordon Gulch, an upper-montane forest watershed in the Colorado Front Range. Study focus: As the climate warms, the fraction of precipitation falling as snow is expected to decrease and the timing of snowmelt is expected to shift earlier in spring. In snow-dominated regions, these changes in snow accumulation and melt prompt us to examine downstream changes in streamflow. The objective of this study is to understand how changes in precipitation phase and snowmelt timing alter the timing of surface water inputs (i.e. rainfall and snowmelt) and the partitioning of these inputs between evapotranspiration and streamflow. We used the Distributed Hydrology Soil Vegetation Model and Weather Research and Forecasting Model-based projections of future climatic conditions to simulate streamflow. New hydrological insights for the region: Modeled annual streamflow decreased by 22% for the period 2071–2100. Surface water inputs increased during winter when atmospheric water demand was relatively low. Subsequently, the winter-period partitioning of water (as rain or snowmelt) to streamflow (as opposed to evapotranspiration) increased, by 15%, while partitioning to evapotranspiration decreased, effectively buffering what would have otherwise been a larger net streamflow decline associated with warming. Seasonal streamflow buffering is unique to snow-influenced systems, as the magnitude and timing of water released from snowpacks is sensitive to warming. This effect may diminish as warming drives snow-influenced systems toward rain-dominance, with implications for hydrological and ecological processes and water-resource management.