Monsoon-dependent rivers, such as the Thamirabarani and Cauvery play critical roles in South India’s water and livelihoods. This review compares the hydroenvironmental and socio-economic characteristics of two important peninsular India river basins—the Thamirabarani and the Cauvery—over 2014–2023. The Thamirabarani River, a short perennial river originating in the Western Ghats, flows through Tamil Nadu. The Cauvery River spans Karnataka, Tamil Nadu, and Puducherry, with complex hydrology. Both basins are influenced by the southwest and northeast monsoons (NEM). The Thamirabarani Basin receives over 55% of its annual rainfall during the NEM, averaging around 1,050 mm/year. The Cauvery Basin shows wide spatial variability, from 600 mm to 2,000 mm/year, depending on elevation and location. Groundwater dynamics show contrasting patterns. The Thamirabarani Basin maintains shallow water tables (2–3 m pre-monsoon), relatively stable due to consistent recharge and lower abstraction. In contrast, several heavily agricultural blocks in the Cauvery Basin exhibit seasonal fluctuations of 5–7 m, with pre-monsoon depths exceeding 12 m. Spatial and statistical analyses indicate strong correlations between rainfall variability and groundwater responses, especially in agriculturally intensive regions. Rainfall trend and groundwater fluctuation analyses highlight the influence of shifting monsoons on aquifer recharge and water security. The socio-economic assessment—highlighting the implications for agriculture, urban demand, and inter-state conflicts—emphasizes the need for integrated water resource management. These strategies include rainwater harvesting, regulated groundwater extraction, and crop planning based on climatic trends. These insights are relevant to other monsoon-dependent basins facing similar hydrological and socio-economic pressures under changing climate conditions.