REGIONAL MODELING OF GLACIERS IN THE OLYMPIC MOUNTAINS, WASHINGTON

Glaciers are important sources of water for their surrounding localities. Their dependence on temperature and precipitation make them a good indicator of climate and climate change. The glaciers of the Olympic Mountains are important to study because they exist at elevations below 2400 m in a temperate climate, making them especially sensitive to climate change. To evaluate the future of these glaciers we apply the Regional Glaciation Model, which is a distributed 2-dimensional plan-view model that incorporates a positive degree day melt model and calculates the thickness, area, and volume change of the glacier at time steps of one year. Inputs include elevation data, CMIP5 global climate model results for past and future climate projections over the domain, and PRISM climate data for downscaling the spatial variations in precipitation in air temperature. The model is tuned to fit glacier extents based on the US Geological Survey 1:24,000 maps, which date to about 1980. Sensitivity analyses show that 84% of observed ice area was successfully predicted, providing confidence in the model capabilities. However, a spatial bias exists that accumulates too much ice on northeastern-facing slopes, we suspect the cause is faulty distribution of precipitation. Model results indicate the glaciers will largely vanish by the year 2100 and that the retreat towards that end is currently underway.