February 8, 2012 John Walsh, Expectations and uncertainties in projections of Arctic hydrologic change, University of Alaska Fairbanks

Expectations and Uncertainties in Trajectory of Arctic Hydrologic Change

John Walsh, University of Alaska Fairbanks

The trajectory of the Arctic hydrologic cycle is one of the grand challenges in the study of high-latitude environmental change, and it has significant implications for planning and adaptation.  We will survey the evidence for changes in the Arctic’s terrestrial water budget over the past half century, and will consider projections of future change and their uncertainties.  Evidence for recent change includes in major climate assessments includes increases of Arctic river discharge, precipitation and moisture atmospheric fluxes into the Arctic.  However, evidence of drying in the boreal forest regions points to a climate-driven increase of evapotranspiration.  Scenarios of future change in global climate models show additional drying, as increases of evapotranspiration over a longer summer season continue to outweigh increases of precipitation.  However, large uncertainties in the surface moisture state arise from changes in permafrost, vegetation, fire regime and moisture availability from ice-diminished seas of the Arctic.  The relative proportions of rain and snow may also change in ways that alter the seasonal cycle of surface runoff and soil moisture.