Lake and wetland variability in regions of seasonal and permanent soil frost

Northern Eurasian plays an important role in global climate partially due to the potential for positive carbon-cycle feedbacks associated with the interaction between frozen soil, temperature, and moisture. In particular, this region is characterized by numerous wetlands and lakes in areas of both seasonal and permanent soil frost. Soil ice content has a large influence on the temporal and spatial variation of soil moisture in these wetlands, which have the potential to produce large amounts of methane under saturated conditions. As soil temperatures increase, ice melt may result in more drainage and less soil saturation in areas of seasonal frost and discontinuous permafrost. In permafrost areas, the ice layer may provide a barrier to restrict drainage and subsequently increase surface inundation. Simulation of such changes in wetland extent is limited by understanding of the spatial heterogeneity of surface saturation. The Variable Infiltration Capacity (VIC) macroscale hydrologic model was modified to represent sub-grid variability in wetland distribution by integrating a modified topographic wetness index approach. In addition, simulation of changes in the extent of lake and wetland systems is improved by allowing the exchange of moisture content between lakes and adjacent wetlands. The modified VIC model is evaluated with respect to observations of water table depth and runoff obtained over a period of three decades from the Valdai research station located south of St. Petersburg, Russia. The variability in simulated wetland extent is then evaluated between 1930 and 2000 in the Upper Volga and Zapadnaya Dvina watersheds (seasonal soil frost) and the Yeloguy and Syum watersheds (discontinuous permafrost). The average wetland area determined from simulated hydrology is compared to landcover classifications derived from L-band satellite synthetic aperture radar imagery. This work was carried out at Purdue University, at the University of Washington, and at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.