Dynamical downscaling generally performs poorly on the Tibetan Plateau (TP), due to the region’s complex topography and several aspects of model physics, especially convection and land surface processes. This study investigated the effects of the cumulus parameterization scheme (CPS) and land-surface hydrology scheme (LSHS) on TP climate simulation during the wet season using the RegCM4 regional climate model. To address these issues and seek an optimal simulation, we conducted four experiments at a 20 km resolution using various combinations of two CPSs (Grell and MIT-Emanuel), two LSHSs (the default TOPMODEL [TOP], and Variable Infiltration Capacity [VIC]). The simulations in terms of 2-m air temperature, precipitation (including large-scale precipitation [LSP] and convective precipitation [CP]), surface energy-water balance, as well as atmospheric moisture flux transport and vertical motion were compared with surface and satellite-based observations as well as the ERA5 reanalysis dataset for the period 2006–2016. The results revealed that the model using the Grell and TOP schemes better reproduced air temperature but with a warm bias, part of which could be significantly decreased by the MIT scheme. All schemes simulated a reasonable spatial distribution of precipitation, with the best performance in the experiment using the MIT and VIC schemes. Excessive precipitation was produced by the Grell scheme, mainly due to overestimated LSP, while the MIT scheme largely reduced the overestimation, and the simulated contribution of CP to total precipitation was in close agreement with the ERA5 data. The RegCM4 model satisfactorily captured diurnal cycles of precipitation amount and frequency, although there remained some differences in phase and magnitude, which were mainly caused by the CPSs. Relative to the Grell scheme, the MIT scheme yielded a weaker surface heating by reducing net radiation fluxes and the Bowen ratio. Consequently, anomalous moisture flux transport was substantially reduced over the southeastern TP, leading to a decrease in precipitation. The VIC scheme could also help decrease the wet bias by reducing surface heating. Further analysis indicated that the high CP in the MIT simulations could be attributed to destabilization in the low and mid-troposphere, while the VIC scheme tended to inhibit shallow convection, thereby decreasing CP. This study’s results also suggest that CPS interacts with LSHS to affect the simulated climate over the TP.

由于该地区复杂的地形和模型物理的多个方面，特别是对流和地面过程，动态降尺度通常在青藏高原（TP）上表现不佳。本研究使用RegCM4区域气候模型研究了积云参数化方案（CPS）和陆面水文学方案（LSHS）对雨季TP气候模拟的影响。为了解决这些问题并寻求最佳模拟，我们使用两种CPS（Grell和MIT-Emanuel），两种LSHS（默认TOPMODEL [TOP]和可变渗透能力[VIC]）的各种组合在20 km分辨率下进行了四个实验）。根据2米气温，降水量（包括大尺度降水[LSP]和对流降水[CP]），表面能-水平衡，并将大气水分通量和垂直运动与地面和卫星观测以及ERA5重新分析数据集（2006-2016年）进行了比较。结果表明，使用Grell和TOP方案的模型可更好地再现空气温度，但具有温暖的偏差，而MIT方案可以部分降低该偏差。所有方案都使用MIT和VIC方案模拟了降水的合理空间分布，并在实验中具有最佳性能。Grell方案产生了过多的降水，这主要是由于LSP被高估了，而MIT方案大大减少了高估，并且CP对总降水的模拟贡献与ERA5数据非常吻合。RegCM4模型令人满意地捕获了降水量和频率的昼夜周期，尽管相位和幅值仍然存在一些差异，这主要是由CPS引起的。相对于Grell方案，MIT方案通过降低净辐射通量和Bowen比，产生了较弱的表面加热。因此，东南部TP的异常水汽通量传输大大减少，导致降水减少。VIC方案还可以通过减少表面加热来帮助降低湿偏压。进一步的分析表明，MIT模拟中的高CP可能归因于对流层中低层的不稳定，而VIC方案倾向于抑制浅对流，从而降低CP。