Process-Informed Regional Climate Modeling for South Asia: The SARCI Framework

South Asia—home to more than a quarter of the global population—faces escalating climate risks that require scientifically credible and actionable climate information. Yet current global climate models exhibit persistent temperature and precipitation biases, reaching up to 25% and 100% of their mean values, respectively, which limits their utility for regional assessments and policy planning. To address these limitations, we develop the South Asia Regional Climate Information (SARCI) framework: a regionally optimized, process-informed system designed to improve simulations of the South Asian Summer Monsoon (SASM) and generate high-fidelity climate information.

SARCI features a customized atmospheric model based on NCAR CESM/CAM5, incorporating targeted enhancements to key physical parameterizations—stochastic entrainment for deep convection (STOCH), a dynamic convective adjustment timescale (DTAU), supplementary gravity-wave sources (GW), and region-specific similarity functions for land–air turbulent fluxes (LTF)—alongside structured parameter tuning and a statistical bias-correction and downscaling module. A systematic component-wise attribution quantifies the incremental influence of each enhancement. DTAU reduces precipitation biases and improves the annual cycle through better moisture convergence, cloud cover, and equatorial waves. STOCH and GW improve precipitation, circulation, and moisture distribution, with STOCH providing additional skill in equatorial waves. LTF primarily improves near-surface temperature with marginal precipitation benefits. Parameter tuning consolidates these gains and resolves residual inconsistencies, while the downscaling module corrects remaining magnitude errors and delivers quarter-degree, policy-relevant fields.

Together, these sequential improvements reduce longstanding SASM-related biases, yield more realistic regional circulation, and preserve acceptable global model performance. By clarifying the physical origins of model improvements and integrating co-production and regional optimization, the SARCI framework provides credible, actionable climate information for South Asia and offers a scalable pathway for other climate-vulnerable regions of the Global South.