Sensitivity of the Indian Summer monsoon rainfall to land surface schemes and model domain in a regional climate model ‘RegCM’

This study examines the sensitivity of regional climate model version 4.7 (RegCM4.7) to the choice of the land surface scheme (LSS) and model domain in simulating the Indian summer monsoon rainfall (ISMR). The RegCM4.7 shows improved performance in simulating the ISMR on using the Community Land Model version 4.5 (CLM) LSS as compared to the Biosphere–Atmosphere Transfer Scheme (BATS) over the most part of India. However, the (CLM) LSS as compared to the BATS over most parts of India. However, the value addition of using CLM over BATS varies spatially and also the choice of domain. For example, a more significant improvement in simulating mean precipitation is seen over the eastern (western) flank of central India on using the larger Coordinated Regional Climate Downscaling Experiment (CORDEX-SA) domain, while western and southern India shows a larger improvement in the Indian (IND) model domain. The model performance greatly improves on using the smaller Indian (IND) model domain as compared to the larger CORDEX-SA domain for the precipitation intensity greater than 15 mm/day. The best model performance in simulating the ISMR and its associated features is obtained when CLM LSS is used in combination with the IND domain (e.g., CLM IND model setup). It is found that the impact of the model domain is higher as compared to the LSS towards improved ISMR simulation. The smaller model domain size helps in the better simulation of the convective precipitation. The CORDEX-SA domain produces imperfect low-level jets (shifted westwards), which tend to reduce the moisture supply towards the Indian land region, thus leading to dry rainfall bias over the central Indian region. The BATS scheme also performs poorly in this regard as compared to the CLM scheme. The inclusion of CLM scheme in a model setup that uses the IND domain largely overcomes the problem of dry bias over the Indian region.