Arctic Precipitation and Evaporation: Model Results and Observational Estimates

Abstract

Observational estimates of precipitation and evaporation over the Arctic Ocean and its terrestrial watersheds are compared with corresponding values from the climate model simulations of the Atmospheric Model Intercomparison Project (AMIP). Estimates of Arctic regional mean precipitation from several observational sources show considerable scatter, and the observational estimates based on gauge-adjusted station data are considerably larger than the other observational estimates. While the AMIP model simulations of precipitation also show scatter, the ensemble mean of the models? precipitation exceeds even the higher (gauge-adjusted) observational estimates over the Arctic Ocean and its major watersheds. The difference between simulated precipitation and evaporation (P ? E), representing the net freshwater gain (runoff) by the surface, also exceeds the observational estimates by 44%?83% over the Arctic Ocean and by generally smaller percentages over the terrestrial watersheds. The ensemble model mean of the annual P ? E exceeds the corresponding river discharges of the Ob and Mackenzie Rivers by 62% and 14%, respectively. The simulated P and E are highly correlated across the AMIP models, and the interannual (as well as the seasonal) variations of P and E are highly correlated in the output of most of the individual models, implying a coupling of the regional P and E in the models. The only formulational feature found to be common to the high-P (and high-E) models is the use of a specified rather than a computed soil moisture. A preliminary examination of the reanalyses of the National Centers for Environmental Prediction shows that the differences between the reanalysis-derived P and E are closer to the observational estimates than are the AMIP estimates. However, the magnitudes of the reanalysis-derived P and E, individually, are higher than the corresponding observational estimates.