Abstracts
SEARCH Open Science Meeting
October 27, 2003
Seattle, Washington, USA
Terrestrial Changes in Polar Regions, Evidence, Attribution and Implications
Larry D. Hinzman1
1Water and Environmental Research Center, University of Alaska Fairbanks, 437 Duckering, PO Box 755860, Fairbanks, AK, 99775-5860, USA, Phone 907-474-7331, Fax 907-474-7979, ffldh@uaf.edu
The effects of a warming climate on the terrestrial regions of the Arctic are already becoming apparent; some subsequent impacts are also becoming evident. It is expected that the effects and consequences of a warming climate will become even more evident within the next 10 to 50 years. These changes will affect the Arctic Basin through impacts on regional weather, oceanic circulation patterns, salinity and temperature gradients, sea ice formation, and water properties. It is difficult to quantify the long-term effects of a changing climate, but it is possible to envision many of the changes that we should expect.
The broadest impacts to the terrestrial arctic regions will result through consequent effects of changing permafrost structure and extent. As the climate differentially warms in summer and winter, the permafrost will become warmer, the active layer (the layer of soil above the permafrost that annually experiences freeze and thaw) will become thicker, the lower boundary of permafrost will become shallower and permafrost extent will decrease in area. These simple structural changes will affect every aspect of the surface water and energy balances. As the active layer thickens, there is greater storage capacity for soil moisture and greater lags and decays are introduced into the hydrologic response times to precipitation. When the frozen ground is very close to the surface, the stream and river discharge peaks are higher and the base flow is lower. As the active layer becomes thicker, the moisture storage capacity become greater and the lag time of runoff increases. As permafrost becomes thinner, there can be more connections between surface and subsurface water. As permafrost extent decreases, there is more infiltration to groundwater. This has significant impacts on large and small scales. The timing of stream runoff will change, reducing the percentage of continental runoff released during the summer and increasing the proportion of winter runoff. This is already becoming evident in Siberian Rivers. As permafrost becomes thinner and is reduced in spatial extent, the proportions of groundwater in stream runoff will increase as the proportion of surface runoff decreases, increasing river alkalinity and electrical conductivity. This could impact mixing of fresh and saline waters, formation of the halocline and seawater chemistry. Other important impacts will occur due to changing basin geomorphology. Currently the drainage networks in arctic watersheds are quite immature as compared to the more well-developed stream networks of temperate regions. These stream channels are essentially frozen in place as the major flood events (predominantly snowmelt) occur when the soils and streambeds are frozen solid. As the active layer becomes thicker, there will be significantly increased sediment loads delivered to the ocean. Presently, the winter ice cover on the smaller rivers and streams (<10,000 km2) are completely frozen from the bed to the surface when spring melt is initiated. However, in lower sections of the rivers there are places where the channel is deep enough to prevent complete winter freezing. Break-up of the rivers differs dramatically in these places where the ice is not frozen fast to the bottom. Huge ice chunks are lifted by the flowing water, chewing up channels bottoms and sides and introducing massive sediments to the spring runoff. As the air temperatures become higher and the active layer becomes thicker, we have reason to believe the surface soils will become drier. As the surface soils dry, the feedbacks to local and regional climate will change dramatically, with particular emphasis upon sensible and latent heat flux. This may impact recycling of precipitation, capabilities to predict weather and may indeed increase variability of many processes and variables, including convective storms.
Abstract Categories: Changes on Land
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