Groundwater chemistry and quality of Lower Chalakudy River Basin, India during extreme climatic events: Lessons to understand for evolving future mitigation measures in Western Ghats, India

This study uses geochemical methods to analyze how extreme precipitation events impact groundwater hydrochemistry and geochemical processes in the shallow aquifer systems of the Lower Chalakudy River Basin (LCRB), southern Western Ghats, India, within the context of climate change. A total of 84 groundwater samples were collected during Pre-Extreme Precipitation Events (PEE), Extreme Precipitation Events (EPE), and Post-Extreme Precipitation Events (PoEE). The groundwater is dominated by mixed types rich in Ca 2+ -Mg 2+ -Cl. Geochemical modeling indicates saturation of carbonate minerals and undersaturation of evaporites, suggesting active silicate weathering. Strong positive correlations are observed between TDS with Ca, EC, Mg, K, HCO 3 , and Cl in almost all samples, regardless of the extreme events. Principal Component Analysis (PCA) extracted three significant principal components, explaining a total variance of 84.02%, 81.08%, and 80.66% for PEE, EPE, and PoEE, respectively. The hydrogeological signatures of the LCRB are influenced by reverse ion exchange and silicate weathering. The Pollution Index of Groundwater (PIG) shows insignificant pollution; however, spatial interpolation through Empirical Bayesian Kriging (EBK), combined with Semivariogram modeling, of heavy metals reveals human health risk assessment (HHRA), with Hazard Index (HI) values exceeding limits for Non-Carcinogenic Risks (NCR) in both adults and children. The relative abundance of the Carcinogenic Risk (CR) factor for trace elements in the study area follows the order of Cr> Cd> As, in PEE, Cd> Cr> As, in EPE, Cd> As in PoEE. A comprehensive understanding of these dynamics is crucial for efficient water resource management and adaptation strategies in response to climate change. • Reverse ion exchange and active silicate weathering shape the groundwater mineral compositions. • EBK with semivariogram modeling was used to interpolate heavy metal HHRA • NCR values for children are much higher during PEE and EPE periods. • Cr, Cd, and As concentrations are elevated in both adults and children, raising concerns about health aspects • Climate change-driven extreme rainfall events influence groundwater hydrochemistry