The effects of arctic vegetation changes on the hydrologic cycle

Over the last fifty years, Northern Hemisphere high latitude land areas have warmed at rates greater than that which can be explained by the atmospheric rise in greenhouse gases alone. Changes in the albedo of the ocean and land, whether from the loss of Arctic Ocean sea ice, changes in land cover, or changes in winter precipitation patterns account for much of the amplified warming. Although the loss of sea ice is directly related to greenhouse gas warming and changes in low-level winds, variability in the discharge of freshwater from Arctic river basins is also a contributor. While changes in river discharge can be related to precipitation, snow and ice melt, and human modification of the landscape, natural vegetation changes due to warming are also altering the land surface hydrologic cycle and changing the flux of freshwater to the Arctic Ocean. Satellite imagery has shown that the Arctic is becoming greener, which not only affects the surface and lower-tropospheric energy budget, but also modifies the hydrologic cycle through altering the partitioning of transpiration and plant-soil evaporation. This leads to changes in precipitation recycling and runoff, which can ultimately affect the discharge of freshwater. To illustrate this mechanism, results of a land cover change and precipitation-recycling analysis using North American Regional Reanalysis data will be presented for the Mackenzie Basin in North America. Additionally, results from a dynamic global vegetation model will be presented to evaluate the potential consequences of continued extreme warming on Arctic ecosystems and to variability in the hydrologic cycle in the Arctic.