Arctic GIS Workshop Poster Abstract
GIS Assessment of Glaciers, Equilibrium Line Altitudes, and Climate Sensitivity: A Case Study from Southwestern Alaska
Recent advances in GIS make it possible to assemble large, empirical, multiparameter datasets that bear on environmental variation, process, and change. For example, GIS permits analysis of the extent, area-altitude relations, microclimatic, and major climatic relationships of all glaciers within a region. Complementary to laser-altimetry and field measurements of mass balance, this approach takes advantage of spatial, rather than temporal, variation to better understand glacier-climate relationships.
A case study for the Ahklun Mountains, southwestern Alaska, demonstrates the feasibility, resolution, and glacier-climate significance of the new approach. Data sources include high-resolution DEM's (grid-cell spacing of 62 m), gridded PRISM climate estimates, and digitized glacier outlines from 1:63,360 topographic maps (based on aerial photography from 1972-1973). Using raster GIS, 32 parameters were calculated for each of the 106 cirque and small valley glaciers in the Ahklun Mountains, including area, elevation, slope angle, aspect, curvature, potential insolation, backwall height, hypsometric Equilibrium Line Altitude (ELA; based on an Accumulation Area Ratio of 0.6), summer temperature, winter precipitation, and sensitivity to climate induced changes in ELA. The 106 cirque and small valley glaciers have a median size of 0.26 km2, a total area of 59.6 km2, and a statistically preferred aspect of 334°. Hypsometric ELA averages 929 m ± 127 m. Ten percent of the ELA variation is explained by a trend surface dipping 5 m/km southwestward toward the Bering Sea as a moisture source. Inclusion of aspect, a basin coefficient, backwall height, distance from lakes, and upslope area in stepwise multiple regression brings explanation to a level of 52%, and highlights the importance of microclimatic/topographic controls on ELA and mass balance. Furthermore, 73% of ELA variation is explained by winter precipitation, summer temperature, aspect, and other microclimatic variables.
Sensitivity to a rise in ELA is estimated from area-altitude relationships. With an increase in steady-state ELA of only 50 m, accumulation areas would shift from ca. 60% of each glacier surface to only 28% on average, and total glacier area would decrease 40% to about 36 km2.
Errors for the parameters are insignificant in comparison with high local variability. Results include not only datasets, but the ability to draw meaningful relationships from spatial trends. The Ahklun glaciers will be strongly affected by climate-induced changes in accumulation or ablation.
An NSF-funded project was recently initiated to ascertain glacier-climate relationships across Alaska using GIS. This project will measure numerous parameters for all Alaskan glaciers across strong climatic and glaciodynamic gradients, will clarify climatic controls on mass balance, and will identify which glaciers are most sensitive to 21rst century climate change.