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

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 (f(sat)) and the fraction of the inundated area (f(h2osfc)) are two pivotal variables that control the important component of the hydrologic process. There may be a threshold for the increase of f(h2osfc), when the increase of f(h2osfc) is lower than this value, the main effect of increasing f(h2osfc) is to reduce the surface moisture that is, divided into the input of soil. However, when the increase of f(h2osfc) is higher than this value, the main effect of increasing f(h2osfc) 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.

Automated summary

In this study, the impact of gravel in a regional climate model was considered and evaluated. The addition of gravel in the simulation generally improved the model performance in simulating soil moisture, especially in the southeastern Tibetan Plateau. However, there is still room for improvement in simulating temporal variations of soil moisture at depths below 1.0 meters. The study also found that increasing gravel content may affect soil saturation conductivity and soil moisture content.