ECO-HYDROLOGIC RESPONSES OF MOUNTAIN FORESTED WATERSHEDS TO CLIMATE WARMING: INTERACTIONS AMONG SNOWMELT, SOIL/GEOLOGY AND VEGETATION WATER USE

At regional scales, spatial variation in eco-hydrologic processes is a complex function of geology, soil, topography, climate and vegetation patterns. Understanding how these different controls vary and interact remains a key challenge for climate change impact assessment. In snow-dominated mountain environments, there is growing evidence that reduced snow accumulation and earlier melt is already occurring and is an important driver of summer streamflow and ecosystem responses. Modelling these responses requires estimation not only of the spatial pattern of melt response to warming, but also of vegetation water use. For both vegetation water use and streamflow responses, soil and subsurface storage mediates system sensitivity to changes in water inputs relative to available energy. We use a coupled process-based model of ecosystem hydrologic and carbon cycling, RHESSys, to demonstrate that soil moisture drainage and storage characteristics exert a significant control on how forest water use, carbon cycling and mortaility respond to earlier snowmelt. We focus our modeling scenarios on sites with measurements of streamflow, and vegetation growth that can be used to evaluate model performance. We then use the model to show how projected changes in terrestrial ecosystem responses alter streamflow regimes and may have important implications for aquatic and human communities. These modeling studies provide an expanded perspective on landscape-level sensitivities to climate warming, and can provide guidance for the strategic design of data assimilation and monitoring strategies.