The surface energy balance at local and regional scales - a comparison of general circulation model results with observations

Abstract

Mostly, GCMs tend to overestimate the mean monthly levels of net radiation by about 15%-20% on an annual basis, for observed annual values in the range 50 to 100 Wm-2. This is probably the result of several deficiencies, including i) continental surface albedos being undervalued in a number of the models, resulting in overestimates of the net shortwave flux at the surface (though this deficiency is steadily being addressed by modelers); ii) incoming shortwave fluxes being overestimated due to uncertainties in cloud schemes and clear-sky absorption; iii) land-surface temperatures being under-estimated resulting in an underestimate of the outgoing longwave flux. In contrast, and even allowing for the poor observational base for evaporation, there is no obvious overall bias in mean monthly levels of evaporation determined in GCMs, with one or two exceptions. Rather, and far more so than with net radiaiton, there is a wide range in values of evaporation for all regions investigated. -from Authors