On the evaluation of snow water equivalent estimates over the terrestrial Arctic drainage basin

Comparisons between snow water equivalent (SWE) and river discharge estimates are important in evaluating the SWE fields and to our understanding of linkages in the freshwater cycle. In this study, we compared SWE drawn from land surface models and remote sensing observations with measured river discharge (Q) across 179 Arctic river basins. Over the period 19882000, basin-averaged SWE prior to snowmelt explains a relatively small (yet statistically significant) fraction of interannual variability in spring (April-June) Q, as assessed using the coefficient of determination (R 2). Averaged across all basins, mean (RS)-S-2 vary from 0.20 to 0.28, with the best agreement noted for SWE drawn from a simulation with the Pan-Arctic Water Balance Model (PWBM) forced with data from the European Centre for Medium-Range Weather-Forecasts (ECMWF) Re-analysis (ERA-40). Variability and magnitude in SWE derived from Special Sensor Microwave Imager (SSM/I) data are considerably lower than the variability and magnitude in SWE,drawn from the land surface models, and generally poor agreement is noted between SSM/I SWE and spring Q. We find that the SWE versus Q comparisons are no better when alternate temporal integrations-using an estimate of the timing in basin thaw-are used to define pre-melt SWE and spring Q. Thus, a majority of the variability in spring discharge must arise from factors other than basin snowpack water storage. This study demonstrates how SWE estimated from remote sensing observations, or general circulation models (GCMs), can be evaluated effectively using monthly discharge data or SWE from a hydrological model. Copyright (C) 2007 John Wiley & Sons, Ltd.