Gravel Parameterization Schemes and its Regional Assessment on Tibetan Plateau Using RegCM4

Abstract

Abstract In this study, the impact of gravel was taken into account in the regional climate model version 4.7, which was driven by the ERA‐Interim with a resolution of 1.5 km in this numerical experiment. The gravel parameterization schemes and the original soil hydrothermal parameterization schemes were used in the regional soil hydrothermal simulations on the Tibetan Plateau (TP), respectively. The performance of the two schemes in simulating the soil moisture (SM) was assessed. Moreover, three areas were selected in terms of the distribution of gravel content on the TP to investigate the differences in the internal mechanism of the model between the two schemes. The performance of the gravel schemes in simulating SM is generally improved compared with that of the original schemes. The simulation effect is superior in the southeastern TP. Except for the southeastern TP, the performance in simulating the temporal variations of SM below the soil depth of 1.0 m still needs to be improved. The fractional saturated area (fsat) and the fraction of the inundated area (fh2osfc) are two pivotal variables that control the important component of the hydrologic process. There may be a threshold for the increase of fh2osfc, when the increase of fh2osfc is lower than this value, the main effect of increasing fh2osfc is to reduce the surface moisture that is, divided into the input of soil. However, when the increase of fh2osfc is higher than this value, the main effect of increasing fh2osfc is to increase the bottom drainage from the surface water store. The increasing gravel content will induce the decreasing mineral soil saturated hydraulic conductivity, which leads to SM increases, the opposite is true.

Keywords

• the Tibetan Plateau
• the gravel schemes
• regional assessment
• RegCM4.7