Sensitivity study of RegCM4.7 model to land surface schemes (BATS and CLM4.5) forced by MPI-ESM1.2-HR in simulating temperature and precipitation over Iran

In order to evaluate the performance of the Regional Climate Model version 4.7 (RegCM4.7) and understand the impact of land surface schemes in simulating precipitation and temperature over Iran, two thirty-year simulations were conducted using the Biosphere-Atmosphere Transfer Scheme (BATS) and the Community Land Model version 4.5 (CLM4.5). The boundary and initial conditions data of the MPI-ESM1.2-HR Earth system model were downscaled from an initial resolution of 100 x 100 km to 30 x 30 km. Both schemes were assessed against ECMWF Reanalysis v5 (ERA5) data, with temperature prediction using the BATS scheme generally reducing bias, except in spring. The CLM4.5 model exhibited a high correlation with ERA5 data, particularly in winter. Evaluation using Root Mean Square Error (RMSE), Nash-Sutcliffe Efficiency, and Kling-Gupta efficiency indices favored the CLM4.5 model in spring and winter. However, the annual temperature correlation coefficient between the two schemes showed minimal difference. In order to enhance precipitation simulation, the common linear scaling bias correction method was modified. Precipitation simulation demonstrated improved accuracy with Modified Linear Scaling (MLS) bias correction method, with the BATS scheme showing reduced bias and lower error rates. While the Kling-Gupta and Nash-Sutcliffe indices slightly favored the BATS scheme, the difference was marginal. Conversely, the Normalized RMSE (NRMSE) index favored RegCM-CLM4.5 in spring and winter. The values of the correlation coefficient and the relative standard deviation resulting from the two land surface schemes (models) had negligible differences with each other. Overall, Taylor diagram analysis suggested similar performance of both schemes at these scales.