Emerging Dairy Heat-Stress Hotspots in India: A High-Resolution Temperature-Humidity Index Analysis Using AgERA5 and CMIP6 Climate Projections

Heat stress is emerging as a critical constraint to livestock productivity in tropical and subtropical regions under accelerating climate change. India, the world’s largest milk producer, is particularly vulnerable due to its predominantly open and climate-exposed dairy production systems. Despite increasing concern, long-term and spatially explicit assessments integrating both temperature and humidity drivers of livestock heat stress remain limited. This study presents a comprehensive evaluation of historical (1979-2024) and future (2025-2100) thermal stress dynamics across six major dairy-producing states of India: Uttar Pradesh, Rajasthan, Madhya Pradesh, Gujarat, Maharashtra, and Andhra Pradesh using high-resolution AgERA5 reanalysis data and downscaled CMIP6 projections from the ACCESS-CM2 model under SSP2-4.5 and SSP5-8.5 scenarios. Thermal stress was quantified using the Temperature-Humidity Index (THI) and classified into standard physiological stress categories. Historical analysis reveals persistent moderate-to-severe heat stress during the pre-monsoon and monsoon seasons, with peak THI values exceeding 82-84 in Gujarat, Rajasthan, and Andhra Pradesh. Annual moderate-to-severe stress exposure exceeds 130 days in Gujarat, 125 days in Andhra Pradesh, and 115 days in Uttar Pradesh, driven by maximum temperatures frequently reaching 38-44 °C and elevated nocturnal minima above 26 °C. Future projections indicate a marked intensification of thermal stress. Under SSP5-8.5, severe THI exposure is projected to exceed 180-200 days annually in arid and semi-arid regions by the late century, accompanied by warming of 2.5-3.8 °C in Tmax and 2.0-3.0 °C in Tmin. The results reveal a transition from seasonal to chronic heat stress regimes across major dairy landscapes, highlighting emerging livestock climate-risk corridors in western and central India. These findings provide high-resolution evidence to support climate-resilient dairy management and policy planning under future warming conditions.