Southern India’s agricultural workforce — numbering over forty million in Tamil Nadu and Andhra Pradesh combined, the majority of whom are engaged in transplanting, weeding, and harvesting operations under direct solar radiation during the April-June peak thermal period — constitutes one of the world’s largest populations of outdoor workers exposed to extreme occupational heat stress. The Intergovernmental Panel on Climate Change’s Sixth Assessment Report (2021) projects that wet bulb globe temperature exceedances of 32°C, which correspond to the International Labour Organisation’s Danger threshold for strenuous outdoor work, will occur across South Indian agricultural districts with progressively greater frequency and duration through 2050, driven by the combination of rising mean temperatures and the Indian Ocean Dipole-modulated shifts in monsoon timing that are already producing longer pre-monsoon heat periods than historical baselines recorded.This study presents field-measured Wet Bulb Globe Temperature (WBGT) data from three Tamil Nadu districts (Vellore, Tirunelveli, Thanjavur) collected across a five-year observational period (2019–2024), linked to agricultural worker health outcome data from a cross-sectional survey of 2,184 field workers conducted in 2023, to quantify the dose-response relationship between WBGT exposure levels and heat illness incidence (heat exhaustion, dehydration, cardiovascular symptoms) and to evaluate the differential effectiveness of adaptation interventions including scheduled rest breaks, cooling vests, hydration stations, and shift time adjustment in reducing heat illness incidence in field-realistic conditions.