Abstract: This paper highlights the temporal and spatial variability of human bio-meteorological conditions based on temperature and relative humidity related index called Heat Index (HI) in India. Monthly mean maximum temperature and relative humidity records from 283 surface meteorological stations in India were used to analyze HI during summer (March to May) and monsoon (June to September) seasons for the last 60 years (1951 to 2010). The long-period climatology of HI suggests that all the regions of the country except the hilly regions are affected by human discomfort of varying levels during summer and monsoon seasons. The results showed increasing trend of HI in almost all the regions of India during the study period. Averaged over the country, HI is increasing during summer and monsoon seasons at the rate of +0.56 °C/decade and +0.32 °C/decade respectively which is statistically significant at 95% level. The increasing HI indicates high level of discomfort in both the seasons which is primarily due to increase in humidity in summer season and maximum temperature in monsoon season. Spatial distribution of HI indicates greater chances of heat related illness in India, more prominently in the southeast coastal regions (Andhra Pradesh, Orissa and Tamil Nadu) in summer and over northwest India (Rajasthan and Indo-Gangetic plains) in monsoon.
Keywords: Heat index, Maximum temperature, Relative humidity, Heat stress, Human health