Freshwater influx to the Gulf of Alaska (GOA) is strongly influenced by glacier runoff as roughly one fifth of its drainage basin is covered by glacier ice. During the last decades GOA glaciers have generally thinned and retreated and hence precipitation stored in the glaciers as snow and ice has been released augmenting streamflow and freshwater influx to the Gulf of Alaska. Glaciers draining to the GOA are highly sensitive to climate warming and mass loss rates are expected to increase. It is hypothesized that runoff from glaciers will initially increase by more than 50% as wastage accelerates, but then will reach a turning point upon which runoff will decrease as the glaciers shrink and partly disappear. Hence, the changes in the hydrological cycles due to glacier wastage are substantially larger than expected changes in any other component of the water budget in this region.
The research will quantify these changes in runoff. A glacier runoff model is used to simulate the current magnitude and timing of runoff from glaciers that drain to the Gulf of Alaska and project how glacial runoff along the Gulf of Alaska will change by 2100 in response to future climate scenarios in Alaska downscaled by a high resolution regional climate model. Further, potential changes to the biogeochemical fluxes into freshwater and marine ecosystems associated with the projected changes in glacier runoff are assessed. Results provide regional scale estimates of glacier runoff changes and associated impacts on biogeochemical fluxes for the GOA. A modeling strategy is developed that can be used to evaluate glacier runoff changes and hydrologic ?tipping points? in other heavily glacierized regions. Moreover, the downscaled climate scenarios we develop will be available for other impact studies. Visualization products of the results are made available to the Mendenhall Glacier visitor center, which is visited by approximately 350,000 people each year.
This project contributed to a new glacier inventory that reveals that there are more than 25,000 glaciers in Alaska covering almost 90,000 km2, but the ice masses are shrinking in response to climate warming. Climate scenarios specifically adjusted to Alaska show substantial climate warming over the coming decades. Using a suite of climate scenarios we find that Alaskan glaciers may lose 18 - 45% of their current volume due to warming by the end of the century, and there will be a substantial reduction in runoff from the glaciers. A substantial part of recent mass loss comes from iceberg calving of roughly 50 glaciers that flow into the Gulf of Alaska, in total approximately 16 Gigatonnes/year between 1985 and 2012. Columbia Glacier, one of the largest tidewater glaciers in Alaska halved its volume over the period 1957-2007, and has rapidly retreated over the last decades, however, its rapid retreat may be nearing its end as the glacier will recede onto land. We also find a very complex pattern of front variations of Alaska's tidewater glaciers over the last 5 decades. While some glaciers have retreated dramatically (for example Columbia), others have advanced, and many have shown both periods of advance and retreat indicating that the link between climate changes and glacier behaviour is complicated for tidewater glaciers. The changes in glaciers that we have documented have direct implications for the freshwater influx into the Gulf of Alaska and sea-level rise. Glacier changes will also impact downstream ecosystems by changing the timing and magnitude of streamflow and altering the water quality of freshwater and near-shore marine ecosystems. In particular, changes in glacier runoff will alter the quantity of organic matter and nutrients in streams that receive glacier runoff. We also find that the glaciers have a cooling effect on summer stream temperatures which becomes stronger as glacier coverage increases. This project also generated a set of high-resolution (20km) regional climate change data over Alaska and its surroundings for the period 1970-2100. The downscaled 20th-century regional climate (as represented by surface temperature and precipitation) exhibits clear seasonal variability. Except for summer, seasonal surface temperatures over Alaska are generally colder than over the North Pacific Ocean and warmer than over the Arctic Ocean. Summer surface temperatures, on the other hand, particularly over the lowlands of Alaska, are much warmer over land. The annual amplitudes of seasonal mean surface temperature variation in Alaska are around 30 K along the north coast, 10–20 K along the west coast, 20–40 K in the Interior, and less than 10 K over the Gulf of Alaska. Mountain impacts on surface temperatures are readily apparent, with colder surface temperatures over mountains seen throughout the year. Most precipitation occurs in the southern part of downscaling domain, with strong precipitation centers along the southeast coast of Alaska and west coast of Canada. Mountain lifting effects result in strong coastal precipitation, with many detailed features captured by the high-resolution model. Over Alaska, precipitation primarily occurs along the south and southwest coasts and southeast panhandle. Over the southwest coastal areas, precipitation primarily occurs during summer and fall. Influenced by the storm track over the North Pacific Ocean, strong precipitation occurs during fall and winter. Under greenhouse gas forced climate change scenario, Alaska will experience the following major changes: 1) a significant warming trend, with strongest temperature increases over the Arctic Ocean due to a reduction in Arctic sea ice coverage; 2) enhanced precipitation along the north and southeast coasts of Alaska, the west coast of Canada, and over the Arctic Ocean; and 3) Drier conditions over most land areas in Alaska.
