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<p>This study evaluates the performance of the RegCM4.7 regional climate model in reproducing two major drought years (2009 and 2015) over India’s Core Monsoon Region (CMR). Simulations were carried out at two spatial resolutions: 25&#xa0;km (non-nested) and 9&#xa0;km (nested) to examine the added value of high-resolution modeling. The nested experiment was performed offline, using the 25&#xa0;km outputs as lateral boundary conditions for the finer CMR domain. Model evaluation employed multiple quantitative metrics, including the Rainfall Anomaly Index (RAI), Probability of Detection (POD), False Alarm Ratio (FAR), and Critical Success Index (CSI). Additional verification through Taylor diagram statistics was used to assess correlation, variability, and overall model skill against IMD observations. Diagnostic analyses of wind, specific humidity, and outgoing longwave radiation (OLR) confirm that RegCM4.7 captures the principal drought characteristics such as weakened monsoonal circulation, reduced moisture transport, and suppressed convection. The nested 9&#xa0;km simulation demonstrates notable improvements in spatial rainfall variability, bias reduction, and mesoscale representation, emphasizing the role of increased spatial resolution and land-atmosphere coupling in enhancing drought diagnostics over monsoon-dominated regions.</p>

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Fidelity of nested RegCM in representing Indian monsoon droughts through resolution-dependent simulations

  • 期刊论文

  • 发表日期：

    2026年3月31日

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  • R. Bhatla,
  • Aashna Verma,
  • R. K. Mall,
  • Hari Shankar Patel

摘要

This study evaluates the performance of the RegCM4.7 regional climate model in reproducing two major drought years (2009 and 2015) over India’s Core Monsoon Region (CMR). Simulations were carried out at two spatial resolutions: 25 km (non-nested) and 9 km (nested) to examine the added value of high-resolution modeling. The nested experiment was performed offline, using the 25 km outputs as lateral boundary conditions for the finer CMR domain. Model evaluation employed multiple quantitative metrics, including the Rainfall Anomaly Index (RAI), Probability of Detection (POD), False Alarm Ratio (FAR), and Critical Success Index (CSI). Additional verification through Taylor diagram statistics was used to assess correlation, variability, and overall model skill against IMD observations. Diagnostic analyses of wind, specific humidity, and outgoing longwave radiation (OLR) confirm that RegCM4.7 captures the principal drought characteristics such as weakened monsoonal circulation, reduced moisture transport, and suppressed convection. The nested 9 km simulation demonstrates notable improvements in spatial rainfall variability, bias reduction, and mesoscale representation, emphasizing the role of increased spatial resolution and land-atmosphere coupling in enhancing drought diagnostics over monsoon-dominated regions.