Simulating Interactive Effects of Frozen Soil Hydrological Dynamics in the Caribou-Poker Creek Research Watershed, Alaska

Abstract:

Degradation of permafrost due to increased global warming has the potential to dramatically affect soil thermal, hydrological, and vegetation regimes. To explicitly simulate the soil moisture effects of soil thermal conductivity and heat capacity and its effects on hydrological response, we included the capability to simulate the soil thermal regime, frozen soil and permafrost in the Geophysical Institute Permafrost Laboratory (GIPL) model in the physically based, distributed watershed model Gridded Surface Subsurface Hydrologic Analysis (GSSHA). The GIPL model simulates soil temperature dynamics, the depth of seasonal freezing and thawing, and the permafrost location by numerically solving a one-dimensional nonlinear heat equation with phase change. The GSSHA model is a spatially explicit hydrological model that simulates two dimensional groundwater flow and one-dimensional vadose zone flow. The GIPL model is used to compute a soil temperature profile in every two-dimensional GSSHA grid. GSSHA uses this information to adjust hydraulic conductivities for both the vertical unsaturated soil flow and lateral saturated groundwater flow. The newly coupled system was applied in the Caribou-Poker Creek Research Watershed (CPCRW), a 104 km² basin north of Fairbanks, Alaska. The watershed lies in the zone of discontinuous permafrost and is reserved for ecological, hydrological, and climatic research with no current human influence (other than scientific research). In the application we calibrate the hydrologic model to sub-watersheds and then apply the model to the larger ungaged watershed to assess the impacts of frozen soil and permafrost on the watershed response. Initial simulation result indicates that freezing temperatures reduces soil storage capacity thereby producing higher peak discharges and lower base flow.