Rising heat and humidity are becoming life-threatening, especially in vulnerable regions. The wet-bulb temperature—a key health metric—shows the point where the body can no longer cool itself through sweat
Published Apr 17, 2025 | 7:00 AM ⚊ Updated Apr 17, 2025 | 7:00 AM
Synopsis: Telangana has declared heatwaves and sunstrokes as “State-Specific Disasters” amid alarming 2024 data: 28 of 33 districts faced over 15 heatwave days, with Nalgonda and Mancherial crossing 30. Urban regions now battle a double threat—intensified ‘Urban Heat Island’ effect and the deadlier ‘Wet Bulb Impact,’ a lethal combination of soaring temperatures and high humidity levels
Everyone knows what a bulb is—from curious school kids to busy adults. But ever heard of the ‘Wet Bulb Impact’? Unless you’re a science geek or a health expert, probably not. Yet this little-known phenomenon is becoming a major threat—especially now, as Telangana reels under an unforgiving heatwave.
In a recent announcement declaring heatwaves and sunstrokes as “State-Specific Disasters,” Telangana’s Special Chief Secretary Arvind Kumar revealed shocking statistics: in 2024, 28 out of the state’s 33 districts endured at least 15 days of heatwaves, with some districts like Nalgonda and Mancherial facing over 30 scorching days.
Urban areas, already battling the ‘Urban Heat Island’ effect, are now facing a double whammy thanks to the lesser-known but deadlier ‘Wet Bulb Impact’—a dangerous mix of extreme heat and humidity.
Construction workers, daily labourers, and residents of cities like Hyderabad and Warangal are among the most vulnerable. But what exactly is the Wet Bulb Impact—and why should you care?
At first glance, it might sound like a weird science experiment—but it’s actually a life-or-death measurement when it comes to extreme heat.
You’re outside on a super hot day, running around, sweating like crazy. Normally, your sweat helps you cool down—kind of like when water evaporates off your skin, it takes some heat with it, and you feel a bit better. That’s your body’s built-in AC system. Cool, right?
Now picture this: it’s not just hot, but it’s also super humid—like the air is so full of water that it feels like you’re breathing soup. That’s when things get scary. When the air is already stuffed with moisture, your sweat can’t evaporate anymore. It just sits there, making you feel sticky and gross—and worse, your body can’t cool down.
The wet-bulb temperature represents the lowest temperature air can reach through the process of evaporation—think of it like the natural air-conditioning our bodies rely on through sweat. But here’s the catch: when humidity is high, that cooling system breaks down.
That’s what scientists call the Wet Bulb Effect. It’s measured by taking a regular thermometer, wrapping it in a wet cloth, and blowing air on it. If it’s dry out, the water in the cloth evaporates fast and cools down the thermometer. But if it’s humid, evaporation slows or stops, and the temperature stays high.
Now imagine your body is that thermometer. When it’s too hot and too humid, and the wet-bulb temperature gets close to your body’s own temperature (around 35°C), your body’s “cooling system” just gives up. That can lead to heatstroke, or worse, especially for people who work outside like construction workers or farmers.
So, think of the Wet Bulb Impact like trying to dry off with a wet towel in a steamy bathroom—it’s just not gonna work. And if your body can’t cool down, it’s like your internal engine starts to overheat. Not good.
As climate change increases both temperatures and humidity in many regions, the risk of reaching dangerous wet-bulb temperatures is rising, making this phenomenon a growing concern for public health and safety
The wet-bulb temperature sets a physiological limit for human survival. A wet-bulb temperature of 31°C is extremely dangerous, and 35°C is considered unsurvivable for more than a few hours, even for healthy people at rest, because the body can no longer shed excess heat
As the climate continues to warm, the combination of high heat and humidity poses an increasingly critical threat to human survival, especially in regions already vulnerable due to socioeconomic and environmental conditions.
Wet-bulb temperature—representing the lowest temperature at which the body can cool itself through evaporation—serves as a key indicator of how dangerous heat conditions are for human health.
When wet-bulb temperatures rise, the body’s ability to cool itself through sweating becomes compromised. Under normal circumstances, sweat evaporates from the skin, carrying away heat and helping to regulate core body temperature.
However, when the air is already saturated with moisture, this evaporation slows down or stops altogether. As a result, the body retains heat, and internal temperatures can rise to dangerously high levels within a short span of time.
The immediate health effects of high wet-bulb temperatures can manifest as a range of heat-related illnesses. At wet-bulb temperatures between 28°C and 30°C, individuals often experience heat exhaustion, characterised by symptoms such as heavy sweating, dizziness, nausea, fatigue, and muscle cramps.
As conditions worsen and temperatures climb to between 30°C and 32°C, the body may enter a state of severe heat stress, marked by a rapid heart rate, confusion, shortness of breath, and general weakness.
Beyond this range, when wet-bulb temperatures approach 32°C to 35°C, the risk of heat stroke becomes significant. At this stage, sweating may cease entirely, the skin becomes dry, and core body temperature can exceed 40°C, leading to fainting and potentially life-threatening complications.
Once the wet-bulb temperature reaches or exceeds 35°C, the body’s thermoregulatory mechanisms can no longer function, and without immediate medical intervention, death can occur within hours due to organ failure, seizures, or systemic collapse.
Though 35°C has traditionally been regarded as the physiological threshold beyond which human survival is impossible, recent research indicates that serious health risks can emerge even at lower thresholds.
Some studies suggest that wet-bulb temperatures as low as 31.5°C may be hazardous to healthy adults engaged in moderate physical activity. Reflecting this, the United States National Weather Service has designated 31°C as a point of “extreme danger,” reinforcing the need for earlier and more aggressive intervention during heat events.
The physiological effects of high wet-bulb temperatures extend beyond heat stroke. As the body attempts to shed heat by redirecting blood flow to the skin, internal organs may receive reduced circulation.
Certain populations face heightened risks during extreme wet-bulb conditions. Older adults are particularly susceptible due to their reduced ability to regulate body temperature and the presence of underlying health conditions.
Outdoor labourers, such as construction workers and agricultural workers, are also highly vulnerable, as they often endure prolonged exposure to high temperatures while engaging in physically demanding tasks.
Individuals with chronic medical conditions—including cardiovascular, respiratory, and renal diseases—are at increased risk of complications, as thermal stress can exacerbate their underlying health issues.
Additionally, people living in dense urban environments often suffer from the Urban Heat Island effect, where built-up areas retain heat more than surrounding regions. In cities with limited green space and inadequate ventilation, residents may be subjected to elevated temperatures both during the day and at night, leaving them with little opportunity for relief.
(Edited by Ananya Rao)
