Why rising humidity is becoming a bigger threat than heatwaves in India

Intense heat is scorching India. The India Meteorological Department (IMD) has predicted that several parts of the country will witness above-normal heatwave days this year.

Temperatures are expected to surpass 40 degrees Celsius, even in regions that may not report heatwaves. However, this outlook does not include a silent threat that has been making India’s summer unbearable — humid heat.

Let’s take a closer look.

What is moist heat?

Moist heat is a combination of soaring temperatures and high humidity.

Humidity is a measure of the amount of water vapour in the air. It occurs when water vapour in the atmosphere enters the air through the evaporation of water at the surface.

As temperatures increase in the summer, the capacity of the air to hold water vapour rises more than in the winter months.

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How does humid heat impact the human body?

Humid heat is bad for the body. A hot and humid day makes people more uncomfortable than dry and hot weather.

As the body heats up, sweat is released to cool it down. When we sweat, the body evaporates water from our skin, absorbing energy and bringing down heat.

However, when the air is saturated with water vapour, the human body struggles to regulate its temperature through sweating.

In dry heat conditions, the body does not feel as hot because humidity is much lower and sweat can evaporate from the skin.

Thus, scientists rely on wet-bulb temperature (WBT) that combines heat and humidity. The “wet bulb effect” or “wet bulb temperature” defines how effectively the body can cool down in severe heat and humid conditions, as per National Geographic.

Amid high heat and humidity, the body fails to cool itself through sweating. This results in the body overheating, thus leading to heat stress, exhaustion and heat stroke.

How dangerous is humid heat in India?

Humid heat is becoming increasingly dangerous in India’s coastal areas. Since 1981, heat stress along the country’s coasts has significantly intensified, owing to the combined surge in temperature and humidity, according to a new long-term study led by scientists at IMD.

IMD Pune scientist P Rohini and colleagues, who examined data from 1981 to 2020, found that wet-bulb temperatures have risen across seasons. The study shows that extreme heat and humidity events have increased, especially since the early 2000s.

There has been a greater surge in humidity along India’s east coast with each degree of warming than on the west coast, as per the IMD analysis.

As heatwaves become more frequent and intense, high humidity is making temperatures feel even more punishing.

“WBT levels are critical determinants of heat exhaustion and heatstroke; these findings have significant implications for human health and safety,” P Vijaykumar, assistant professor in the Department of Environmental Science, University of Kerala, told Mongabay-India.

People take a bath in the river Ganges on a hot summer day in Varanasi on April 19, 2026. AFP

Heat stress has significantly contributed to weather-related deaths globally. The elderly, those with underlying illnesses, and workers in the informal sector are more vulnerable to the threat of humid heat.

A 73-year-old fisherman in Kerala told Mongabay-India that he begins fishing early in the morning but returns soon due to unbearable heat. “I go for fishing at 5 am, but come back by 8 am, whether I get enough fish or not,” Mariyani Miyelpillai said. “I cannot manage this heat.”

Studies show there has been a rapid spike in extreme humid heat worldwide, with some places nearing or even exceeding the limits of human survivability.

Another study of India’s coastal regions has found that wet-bulb temperatures have risen over the past four decades.

According to a recent assessment by the Council on Energy, Environment and Water, most Indian districts, which are home to a large number of people, are susceptible to high to very high heat risk.

“India is entering an era where heat risk is becoming more complex and more widespread,” a researcher with the organisation told Down to Earth magazine. “It is no longer just about extreme temperatures. Humidity, nighttime heat and duration of heat events are all becoming critical factors.”

A recent study published in the journal Climate Dynamics, which analysed more than 80 years of weather data, found that the southwest monsoon controls the timing and geography of moist heatwaves. Places like Kerala, which features a long coastline and monsoon-driven climate, are at a higher risk of thermal stress.

“Heat stress is not just about temperature. It is about how the body experiences heat,” a senior official associated with Kerala’s State Disaster Management Authority was quoted as saying by Down to Earth. “In a place like Kerala, humidity plays a major role. We are seeing more cases where people feel severe stress even when temperatures are below heatwave thresholds.”

What can India do?

The increase in heat stress could slash India's work performance by 30-40 per cent by the end of the century, as per a study. This should ring alarm bells and lead to plans to protect labour who work in the open under intense heat.

Experts say India needs to quickly update its heat response systems. “We need to move beyond temperature-based alerts. Heat index and wet-bulb temperature should be integrated into early warning systems, especially in humid regions,” a public health specialist working on heat action plans told Down to Earth. 

Awareness and advance warning can help reduce heat-related health issues. Akshay Deoras at the University of Reading in the UK, who led the research published in Climate Dynamics, said to the magazine: “We often find people being more aware of dry heatwaves in India, given the scorching summer season, but moist heat remains less known and is therefore more dangerous. Outdoor public gatherings are notorious for causing heat exhaustion. Advance warning of a moist heatwave could allow organisers to reschedule activities and strengthen medical preparedness.”

With inputs from agencies