Spatial and Temporal Distribution of Hydraulic Properties to Represent Discontinuous Permafrost in a Spatially-distributed, Process-based Hydrologic Model

Bob Bolton, UAF-WERC

The sub-arctic environment can be characterized by being located in the zone of discontinuous permafrost. Although the distribution of permafrost in this region is site specific, it dominates the response to many of the hydrologic processes in this region, including stream flow, soil moisture dynamics, and water storage processes. In areas underlain by permafrost, ice-rich conditions at the permafrost table inhibit surface water percolation to the deep subsurface soils, resulting in increased runoff generation during precipitation events, decreased baseflow between precipitation events, and relatively wetter soils.

The objective of our research is to use a spatially-distributed, process-based hydrologic model, TopoFlow, to simulate and predict soil moisture dynamics and all other hydrologic processes throughout a sub-arctic watershed. Simulation of the hydrologic processes is challenging due to rapidly changing thermal (permafrost versus non-permafrost, active layer development) and hydrologic (hydraulic conductivity and storage capacity) conditions in both time and space (x, y, and z-dimensions). Our approach to this problem is to spatially and temporally vary hydraulic conductivity (proxy for permafrost distribution) and porosity (proxy for storage capacity) with active layer development. Simulation results (17, 50, and 80% permafrost distribution throughout the model domain) display higher peak discharges, longer recession, and lower baseflows for higher permafrost simulations compared to lower permafrost simulations. As the active layer increases throughout the simulation period, baseflow increases for all representations of the permafrost condition.

This model will be applied to the three small sub-basins of the Caribou-Poker Creeks Research Watershed, located 48 km north of Fairbanks, Alaska. These sub-basins, which are underlain with approximately 3, 19, and 53% permafrost, are being simulated to explore the effects of vegetation, soil type, presence or absence of permafrost, and the amount and timing of precipitation on hydrologic processes in this region.