Long‐Term Experimental Evaluation of a High‐Resolution Atmospheric General Circulation Model From a Hydrological Perspective

Abstract

AbstractThe reproducibility of Atmospheric General Circulation Model (AGCM) results in the current climate was evaluated to assess annual and monthly mean climate values from a hydrological perspective and to elucidate factors affecting them. Reproducibility was confirmed for precipitation, air temperature, and runoff, which were compared with basin‐average values to describe deviations in reproduced AGCM data. AGCMs have been successively applied over 65 years in the current climate, and annual mean values of precipitation generally have a positive bias in most basins and those of air temperature have a negative bias. However, runoff shows no clear pattern of bias. For monthly means, precipitation has positive and negative biases in July in the Northern Hemisphere. In January in the Southern Hemisphere, precipitation has a positive bias. In both months, air temperature has a negative bias. Factors contributing to this bias are discussed. From a hydrologic perspective, the annual mean bias in air temperature performs better in explaining the apparent evapotranspiration (i.e., precipitation minus runoff) than the bias in precipitation. In the tropics, the air temperature bias has a correlation coefficient of −0.176 with the precipitation bias and −0.406 with apparent evapotranspiration (negative values indicate a better correlation). However, this was not the case for the monthly average air temperature bias, possibly because of climatological influences or the inadequate representativeness of runoff in land surface models. The results show that runoff bias may contribute to air temperature bias. Accordingly, we propose a new method for comparing runoff bias and climate bias.