An Experimental and Modeling Investigation of the Impact of Silvicultural Manipulation on Snow Hydrology in the Cedar River Watershed, WA

Over the past 80 years, forest harvesting throughout the western U.S. has resulted in a shift in the dominant forest structure to young, dense forests. Meanwhile, declining trends in mountain snow water equivalent (SWE), summer river flow, and earlier snowmelt have largely been attributed to climate with little consideration of the impact of the concurrent changes in vegetation from forestry practices. Silvicultural manipulation has the potential to increase snow water storage, change snowmelt timing and restore ecological processes that might normally be adversely affected by climate change. This study is primarily concerned with snowmelt timing, since it is crucial to watershed management in basins with limited reservoir storage. Any delay in snowmelt from silvicultural manipulation could reduce winter flood hazards and increase summer runoff when water demand for cities and agriculture is the highest. This study commenced in the 2009 water year and takes place in the Cedar River Watershed, WA, located in the climate-sensitive intermittent snow zone. Using a combination of distributed field measurements and point and distributed hydrologic models, we are investigating i) the heterogeneity of snow accumulation and melt in different forest structures, and ii) which forest changes are of comparable magnitude to climate change in their effects on snow hydrology.