Navigating water stability and crop resilience in a changing climate: insights from SPEI, CWSI, and CMIP6 projections

Monsoon-dominated agricultural regions face increasing hydro-climatic stress driven by climate change, yet a critical methodological gap persists: no integrated, spatially explicit framework simultaneously links drought dynamics, crop water stress, and system-level stability under future climate projections. South Korea exemplifies this challenge, where seasonal water deficits, rising evaporative demand, and dependence on monsoon rainfall create compounding vulnerabilities for agricultural resilience. Here we develop a multi-index framework combining the Standardized Precipitation Evapotranspiration Index (SPEI), a modified Crop Water Stress Index (CWSI), and a Reliability-Resilience-Vulnerability (RRV) stability metric to quantify spatio-temporal patterns of water stress and resilience. Observations (1985-2014) were used to evaluate and bias-correct multiple CMIP6 models under SSP2-4.5 and SSP5-8.5. Continuous climate fields were interpolated, and Crop Water Zones (CWZs) were derived using a percentile-based 3 × 3 classification that combines interpolated RRV and CWSI. Results show increased precipitation variability and higher evaporative demand, intensifying seasonal water stress, particularly in summer and autumn. Differences between scenarios are modest in the near term, but both indicate expansion of high-risk CWZs. Bias correction improves agreement with observations; however, performance metrics are interpreted cautiously given methodological constraints. Spatial patterns indicate a shift from stable/resilient to more critical/high-risk conditions, revealing emerging vulnerabilities in agricultural systems. This framework provides a transferable approach for assessing climate-driven water stress and supports adaptive water management in monsoon-influenced regions.