December 9, 2009 Bob Bolton, Simulation of streamflow in a discontinuous permafrost environment using a modified first-order, non-linear rainfall-runoff model., International Arctic Research Center, University of Alaska Fairbanks

Simulation of streamflow in a discontinuous permafrost environment using a modified first-order, non-linear rainfall-runoff model.

Bob Bolton
International Arctic Research Center, University of Alaska Fairbanks

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 specific, it dominates the response of many of the hydrologic processes 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 an increased runoff generation generation during precipitation events, decreased baseflow between precipitation events, and relatively wetter soils compared to permafrost-free areas. Over the course of a summer season, the thawing of the active layer (the thin soil layer about the permafrost that seasonally freezes and thaws) increases the potential water holding capacity of the soil, resulting in a decreasing surface water contribution during precipitation events and a steadily increasing baseflow contribution between precipitation events.

Simulation of stream flow in this region is challenging due to the rapidly changing thermal (permafrost versus non-permafrost, active layer development) and hydraulic (hydraulic conductivity and soil storage capacity) conditions in both time and space (x, y, and z-dimensions). Many of the factors that have a control on both permafrost distribution and the thawing/freezing of active layer (such as soil material, soil moisture, and ice content) are not easily quantified at scales beyond the point measurement. In this study, these issues are addressed through streamflow analysis – the only hydrologic process that is easily measured at the basin scale.

Following the general procedure outlined in Kirchner (2008), a simple rainfall-runoff model was applied to three small head-water basins of varying permafrost coverage. A simple, first-order, non-linear differential equation that describes the storage-discharge relationship were derived from three years of stream flow data. The storage-discharge relationship is developed for each month of the summer thaw period (June-September). The monthly relationships are then combined to form a single storage-discharge relationship that changes smoothly throughout the summer period. By allowing the monthly storage-discharge equations to vary through time, the variation in runoff due to changes in the active layer thaw are represented. This simple, nonlinear equation describing the storage-discharge relationship is used to simulate streamflow from evapotranspiration and precipitation data. Simulation results from in the Caribou-Poker Creeks Research Basin, located about 50 km north-east of Fairbanks, Alaska will be presented.