Sensitivity of Snow-Vegetation Interactions and Streamflow Regimes to Climate Change in Mountain Basins

English Abstract:

Understanding the interactions amongst snow processes, vegetation and runoff in mountains is crucial for climate change impact studies. In this research, a sensitivity analysis is carried out based on regional climate model scenarios, field measurements, and factors that control vegetation growth. The objectives are to investigate the interaction of concomitant vegetation and snow changes and to simulate transient changes in hydrological processes under climate change. Land cover changes alter the evapotranspiration, sublimation, snow redistribution, infiltration and runoff mechanisms which are responsible for the variability of subsurface storage, soil moisture, active layer thickness, and vegetation growth. The Cold Regions Hydrological Modelling platform (CRHM) is applied for modelling these mechanisms based on transient changes in vegetation. The model is tested in two well instrumented mountain headwater basins: Wolf Creek Research Basin, WCRB, with a very cold climate and discontinuous permafrost in the Canadian subarctic and Reynold Mountain East catchment, RME, in the Reynolds Creek Experimental Watershed with a moderate climate in Idaho, USA. The results showed that the hydrological impacts of warming decreased snowmelt runoff substantially in both basins. In WCRB warming increased the active layer depth, leading to conditions suitable for the growth of shrub tundra and conversion of some shrub tundra to forest and short vegetation to shrubs. In contrast, the hydrological response to warming in RME led to smaller snow drifts, which led to conversion of forests that were dependent on meltwater from snowdrifts to sagebrush and grass. The increase in forest area and expansion of shrubs in WCRB further decreased runoff generation at lower and middle elevations and moderated decreased runoff at higher elevations; the suppression of snow redistribution by wind shortened the melt season. The loss of forests from RME accelerated melt rates of the remaining snowpack and reduced evapotranspiration losses, slightly dampening the reduction in streamflow from the reduced snowmelt due to warming.