Simulating Pan-Arctic Runoff With a Macro-Scale Terrestrial Water Balance Model

Abstract

A terrestrial hydrological model, developed to simulate the high-latitude water cycle, is described along with comparisons to observed data across the pan-Arctic drainage basin for the period 1980--2001. Gridded fields of plant rooting depth, soil characteristics (texture, organic content), vegetation, and daily time series of precipitation and air temperature provide the primary inputs used to derive simulated runoff at a grid resolution of 25 km across the pan-Arctic. The Pan-Arctic Water Balance Model (P/WBM) includes a simple scheme for simulating daily changes in soil frozen and liquid water amounts, with the thaw/freeze model (TFM) driven by air temperature, modeled soil moisture content, and physiographic data. P/WBM-generated maximum summer active-layer thickness estimates differ from a set of observed data by an average of 12\,cm at 27 sites in Alaska, with many of the differences within the variability (1 $\sigma$) seen in field samples. Simulated long-term annual runoffs are in the range 100 to 400\,mm year$^{-1}$, with highest runoffs found across northeastern Canada, southern Alaska, and Norway. Lower simulated runoff is noted along the highest latitudes of the terrestrial Arctic in North America and Asia. Good agreement exists between simulated and observed long-term seasonal (winter, spring, summer/fall) runoff to the 10 Arctic sea basins ($r$ = 0.84). Model water budgets are most sensitive to changes in precipitation and air temperature, while less affect is noted when other model parameters are altered. Increasing daily precipitation by 25\,% amplifies annual runoff by 50 to 80\,% for the largest Arctic drainage basins. Ignoring soil ice by eliminating the TFM sub-model results in runoffs which are 7 to 27\,% lower than the control run. The spatial and temporal variability of freshwater export along continental margins is also explored. This flux represents a merging of simulated discharge and observed data. The results of model sensitivity experiments, along with other uncertainties in both observed validation data and model inputs, emphasize the need to develop improved spatial data sets of key geophysical quantities---particularly climate time series---to better estimate terrestrial Arctic hyrological budgets.

Department

Earth Sciences, Earth Systems Research Center

Publication Date

12-2002

Journal Title

EOS, Transactions American Geophysical Union, Fall Meeting, Supplement

Publisher

American Geophysical Union Publications

Document Type

Conference Proceeding

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