Alkalinity-salinity-sustainability: Decadal groundwater trends and its impact on agricultural water quality in the Indian Peninsula

Groundwater degradation due to alkalinity and salinity threatens irrigation-dependent agriculture, particularly in the Indian Peninsula. Over-extraction, erratic monsoons, and intensive farming have worsened groundwater quality, impacting soil health and crop productivity. The study examines long-term (2002−2022) spatio-temporal variations in pH, electrical conductivity (EC), and bicarbonate (HCO₃⁻) datasets, integrating them with Gravity Recovery and Climate Experiment (GRACE)-derived groundwater anomalies and rainfall variability through the Standardized Precipitation-Evapotranspiration Index (SPEI) employing hierarchical clustering. It further compares these variations with irrigation indices assessing sodium (Na) hazards and water suitability to identify critical hotspots for water sustainability. From 2002 to 2022, groundwater in the Indian Peninsula has shifted towards neutral to slightly alkaline conditions, with declining alkalinity in previously high-alkaline regions (mid-Gangetic plains) and increasing salinity in arid zones. Rising EC, driven by irrigation return flows and groundwater over-extraction, alongside fluctuating HCO₃⁻ levels, highlights the growing impact of agricultural and climatic stressors on water quality. From 2012 to 2022, groundwater levels (GWLs) declined sharply in mid-Gangetic plains due to over-extraction. The issue was further exacerbated by worsening drought conditions as revealed by SPEI. Increasing mineral undersaturation has led to rising fluoride (F⁻) and hardness issues, and deteriorating irrigation indices indicate worsening salinity and Na hazards. Expanding clusters of high-risk states underscore the need for targeted groundwater management strategies. Future research should explore adaptive irrigation practices and policy measures to mitigate groundwater quality decline and sustain agricultural productivity.