Groundwater constitutes the primary source of freshwater for irrigated agriculture across South Asia, yet accelerating climate variability, unregulated abstraction, and demographic pressures are precipitating severe aquifer depletion in many regions. Tamil Nadu, a water-stressed state in peninsular India, epitomises these intersecting challenges: its agricultural sector depends critically on monsoon-fed groundwater recharge across the Cauvery, Thamirabarani, and coastal river basins, while simultaneously facing an increasing frequency of droughts, erratic northeast monsoon rainfall distribution, and saltwater intrusion in coastal aquifers.

This systematic review synthesises peer-reviewed literature published between 2018 and 2026 to critically examine how climate variability is altering groundwater recharge, storage, and quality, and how these hydrological shifts cascade into measurable losses in agricultural productivity. The review evaluates the role of geospatial technologies — including GRACE-FO-based terrestrial water storage monitoring, optical and synthetic aperture radar (SAR) remote sensing, GIS-based hydrological modelling (SWAT, MODFLOW), climate and drought indices (SPI, PDSI, NDVI, VCI), and machine learning algorithms — in quantifying and predicting these coupled dynamics at regional and basin scales.

Special attention is given to the Cauvery and Thamirabarani river systems as contrasting analogues for semi-arid and humid agricultural contexts, respectively. The review identifies critical gaps in integrated modelling, data infrastructure, and policy uptake. It proposes concrete directions for climate-resilient water management, managed aquifer recharge, precision irrigation, and evidence-based agricultural adaptation. This synthesis is intended as a comprehensive scholarly reference for researchers and postgraduate students in agronomy, hydrology, environmental science, and geospatial disciplines.