Evaluation of the RegCM4 high-resolution climate simulations for the upstream of major rivers over Tibetan Plateau

Abstract:

The evaluation of the RegCM4 regional climate model at a high-resolution simulation at 10 km, applied over Tibetan Plateau, is presented. This simulation covering the period from 1980 to 2010 is nested in a RegCM4 simulation at 30 km resolution, driven with boundary forcing data from the ERA-Interim reanalysis dataset. A new daily observational dataset is employed as reference data to evaluate the temperature and precipitation simulations for the inner model domain and five largest river basins originated in TP (i.e., the source region of Yangtze River, Yellow River, Mekong River, Salween River, and Brahmaputra River). In comparison with low-resolution model run (R30), the cold biases for area-averaged temperature were reduced from -2.5°C to -0.1°C and wet biases in summer mean precipitation were reduced from 58% to 25% in high-resolution model run (R10). The substantial warming trends and slight wetting trends were basically reproduced by both RegCM4 simulations. Annual mean precipitation trends from both simulations show a better agreement with the observations than the ERA-Interim which underestimates the annual mean precipitation trends in most regions, whereas both the RegCM4 and ERA-Interim consistently underestimate the annual mean temperature trends when compared with the observation. Besides, the overall improvement in the modelling trends for annual mean temperature and precipitation in R10 is limited when compared with R30. The spatial distributions of extreme precipitation were also captured reasonably in both RegCM4 simulations and the better performance is detected in the R10 simulation. The findings above show that RegCM4 with a high-resolution 10 km is capable of reproducing the major regional climate features over the TP, but a great deal of uncertainties still exist especially in the subregion Brahmaputra River basin. This is related to the situation that the 10 km resolution simulation in RegCM4 may still not fine enough to resolve the topoclimates over the complex Himalayan terrain in Brahmaputra River basin.