Humid Heat Emerges as India’s Most Dangerous Climate Threat, With Kerala at the Frontline

A new study published in the journal Climate Dynamics has identified humid heat, driven by the monsoon and rising wet-bulb temperatures, as India’s most dangerous climate threat, with Kerala experiencing the most severe impacts. The research, led by Akshay Deoras at the University of Reading in the UK, analyzed over 80 years of weather data to demonstrate how the southwest monsoon governs the timing and geography of moist heatwaves across the country.

Unlike dry heat, humid heat combines high temperature and high humidity, which interferes with the body’s ability to cool itself through sweating. When sweat cannot evaporate efficiently, the body’s cooling system fails, leading to a rapid rise in core temperature, increased strain on the heart, and in extreme cases, heatstroke that can develop within hours.

Monsoon as Key Driver of Moist Heat Risk

The study reveals for the first time that the monsoon is the primary factor determining where and when deadly humid heat risk develops across India. As monsoon patterns can be forecast weeks in advance, this predictability creates real opportunities for preparation and protection of vulnerable populations.

For decades, heatwave warnings in India have been based solely on temperature thresholds. Although, the research shows that temperature alone does not capture the physiological stress experienced by the human body during humid conditions. The findings indicate that India’s heat response systems must evolve quickly to address this growing threat.

Regional Vulnerability and Increasing Frequency

Additional research confirms that even Indian states which historically have not experienced heatwaves, such as Himachal Pradesh and Kerala, are now exhibiting a higher frequency of extreme heat events. Analysis of Kerala specifically shows that in 2023, the state experienced its deadliest heatwave during one of the warmest years in the past century.

Nationwide surveys indicate that majorities of Indians have experienced severe heat waves (71%) in the past 12 months, and a significant portion believe global warming is affecting extreme weather events. When provided a short definition, 96% of Indians think global warming is happening, with no districts falling below 90% in this belief.

Understanding the Physiological Threat

The human body maintains a stable internal temperature primarily through the evaporation of sweat. In high humidity, the air is already saturated with moisture, which prevents sweat from evaporating effectively. The body cannot dissipate heat, causing core temperature to rise. This condition, known as heat stress, can progress rapidly to heat exhaustion and heatstroke if not addressed.

Wet-bulb temperature, which combines air temperature and humidity, is a critical metric for assessing this risk. When wet-bulb temperatures exceed 35°C, even healthy individuals resting in the shade cannot survive for more than a few hours, as the body can no longer cool itself.

Implications for Public Health and Policy

The study’s authors emphasize that early warning systems based on monsoon forecasts could significantly improve preparedness for humid heat events. Given that the monsoon’s timing and intensity can be predicted with reasonable accuracy weeks ahead, authorities have a window to implement protective measures such as opening cooling centers, adjusting work schedules, and issuing targeted health advisories.

Experts urge that India’s current heat action plans, which primarily focus on temperature thresholds, must be updated to incorporate humidity and wet-bulb temperature metrics. This shift would allow for more accurate risk assessment and timely interventions, particularly in highly vulnerable regions like Kerala.

Conclusion

As climate change continues to intensify both temperature and humidity levels across the Indian subcontinent, humid heat is emerging as a paramount threat to public health. The research underscores that addressing this danger requires moving beyond traditional temperature-based warnings to embrace a more comprehensive understanding of heat stress that includes humidity. With reliable monsoon forecasts offering a predictive advantage, India has the opportunity to strengthen its resilience and protect its population from the increasingly lethal impacts of moist heatwaves.