Simulating Long-term Landcover Change and Water Yield Dynamics in Forested, Snow-dominated Rocky Mountain Watersheds

Changes in the extent, composition, and configuration of forest cover over time due to succession or disturbance processes can result in measurable changes in streamflow and water yield. Removal of forest cover generally increases streamflow due to reduced canopy interception and evapotranspiration. In watersheds where snow is the dominant source of water, yield increases and advanced peak discharge are attributed to increased snow accumulation, and enhanced melt rates in forest openings. Because knowledge of long-term watershed-level streamflow responses to landcover dynamics is limited by relatively short-term gage data, we present a modeling approach that combines existing vegetation and hydrologic simulation systems to evaluate these interactions. Our findings suggest that both vegetation and hydrologic characteristics of the research watershed are at the limits of their estimated natural ranges. Although species composition remained fairly stable over time, the size and connectivity of current landcover patches are at the upper end of the estimated temporal distribution. The large proportion and continuous nature of forest cover associated with current conditions coincide with water yield, peak discharge rates, and flow variability that are at the low end of their modeled distributions.