Changes to Glacier Runoff and Downstream Effects on the Susitna Basin, Alaska Over the Twenty-First Century

Abstract:

Runoff from glaciers in the upper Susitna Basin, Alaska will change as the climate changes over the next century. The quantity and seasonality of river flow in the 13,289 km^2 basin depends on glacier runoff to an extent that belies the small percentage of the basin's area that is covered by glaciers (4%). We run a physically-based hydrological model (WaSiM) to project 21st century river discharge for the basin, explicitly including the glacier component of runoff. Climate inputs come from a CCSM CMIP5 RCP6.0 scenario downscaled to a 20km-5km nested grid using the Weather Research and Forecasting (WRF) Model and are adjusted with a local bias correction. From 2010-2029 to 2080-2099 the basin-wide mean-annual temperature will rise 2.5 degrees and total precipitation will rise 2%, with a 13% decrease in snowfall and a 20% increase in rainfall. WaSiM runs indicate that glaciers will lose about 40% of their area, evapotranspiration will increase, and permafrost will thaw. Annual runoff will remain relatively steady, but the timing of the peak spring runoff will shift to an earlier date (by about 1 month) and late summer runoff will be reduced (by about 50%) compared to present.