Evaluation of surface water fluxes of the pan‐Arctic land region with a land surface model and ERA‐40 reanalysis

The seasonal, spatial, and latitudinal variability of precipitation (P), evapotranspiration (E), and runoff (R) are examined for large Arctic river basins and for the entire pan‐Arctic domain using a 21‐year off‐line simulation of the Variable Infiltration Capacity (VIC) macroscale hydrology model and the ERA‐40 reanalysis. Observed P used in the VIC model (corrected for gauge catch deficiency) is compared with that from the ERA‐40 reanalysis. Gridded values of evapotranspiration minus precipitation (E‐P) are calculated from the ERA‐40 atmospheric water budget, and estimates of implied E are obtained as the residual of observed P and ERA‐40 E‐P. The ERA‐40 P is surprisingly close to observations on an annual basis over the large river basins (especially accounting for known errors in the observations). Furthermore, ERA‐40 P is quite consistent with observations in terms of interannual, spatial, and latitudinal variations. ERA‐40 E is generally higher than both VIC E and implied E in spring and autumn. However, VIC estimates more E in June and July than either ERA‐40 or the atmospheric budget for the Yenisei, Ob, and Mackenzie River basins. The ERA‐40 bias toward early snowmelt and a double runoff peak (not present in VIC or observations) indicates the need for improvements in the ECMWF land surface scheme. The long‐term means of ERA‐40 vapor convergence P‐E for the Lena, Yenisei, Ob, and Mackenzie are not in balance with observed runoff, mainly due to the uncertainties in computed P‐E and observed streamflow.