HR: 0800h
AN: U41C-0625    [Abstracts]
TI: Application of the VIC hydrologic model to explore the role of permafrost in observed Eurasian Arctic streamflow changes
AU: * Adam, J C
EM: jadam@u.washington.edu
AF: University of Washington, Box 352700, Seattle, WA 98195-2700, United States
AU: Lettenmaier, D P
EM: dennisl@u.washington.edu
AF: University of Washington, Box 352700, Seattle, WA 98195-2700, United States
AB: Eurasian river discharge into the Arctic Ocean has increased since the 1930s, potentially impacting deep water formation in the North Atlantic and consequently the strength of the thermohaline circulation. However, long-term streamflow and precipitation trends are inconsistent, particularly for river basins underlain with permafrost, which suggests another source of water. We apply the VIC model to explore the potential contribution of permafrost melt to observed streamflow trends. In so doing, we have made various improvements to the model to handle decadal-scale permafrost dynamics. The use of a zero-flux computational bottom boundary allows for long-term temperature changes in the model's deeper soil layers, while the placement of the model's bottom boundary at several times the thermal damping depth minimizes the build- up of heat storage along the boundary. To improve computational efficiency, we distribute the thermal nodes used to solve the sub-surface heat equation exponentially with depth, and perform a grid transformation to solve the system in linear space. We solve the system implicitly to ensure numerical stability at time-steps larger than one hour, which also improves computational efficiency. Finally, we incorporate an excess ground ice and surface subsidence algorithm, in which porosity and soil depth decrease as excess ground ice melts. To explore the degree to which permafrost melt may have contributed to observed streamflow increases, we adjust the concentration of ground ice at various depths in the soil column until simulated streamflow trends match observed. In this way, we can comment on the plausible contributions of precipitation, evapotranspiration, and sub-surface storage changes to observed streamflow increases in select permafrost basins. We show results for our test basin, the Aldan River basin, an unregulated tributary to the Lena River. The Aldan River basin, 89 percent of which is underlain by continuous permafrost, has had significant streamflow increases since the mid 1940s. We demonstrate that permafrost melt may have been an important contribution to streamflow increases beginning in the 1950s to 1960s.
DE: 0545 Modeling (4255)
DE: 0702 Permafrost (0475)
DE: 0744 Rivers (0483, 1856)
DE: 1621 Cryospheric change (0776)
DE: 1807 Climate impacts
SC: Union [U]
MN: 2007 Fall Meeting