Hyderabad’s scorching heat: How wet-bulb temperature, urban heat islands impact the city

Hyderabad's weather conditions are influenced by two key factors: wet-bulb temperatures and urban heat islands. Many residents may not be familiar with wet-bulb temperature, a phenomenon where both air temperature and humidity combine to significantly affect the human body.

Hyderabad: Compared to districts, maximum temperatures in Hyderabad are always lesser by a degree or two. And yet, people in Hyderabad feel as if they are in a pressure cooker whenever there is high humidity and sometimes we also experience desert like conditions due ‘loo’, the hot and very dry winds, even if maximum temperature is around 40 degree Celsius.

Such weather experiences in Hyderabad are due to twin phenomena of wet-bulb temperatures and urban heat islands. Many in Hyderabad might not be even aware of wet-bulb temperature, which is a unique condition in which both air temperature (heat) and humidity significantly impact the human body.

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When the wet bulb temperature reaches its critical limit of 35 degree Celsius along with high humidity, the human body can no longer effectively cool itself causing heat strokes and even death. Sometimes, the hot winds (Loo) further add to the overall heat, making it even more difficult for people to go about their normal lives.

Wet bulb temperatures reflect the human body’s ability to cool itself through sweating. In situations when humidity and temperatures both are high, then the sweating doesn’t take place and the body does not cool down adequately. On most occasions, this situation leads to heat strokes and fatalities.

Adding to all this is Urban Heat Island (UHI) effects, which further exacerbates these conditions by contributing to higher local temperatures. Urban health islands occur when urban areas experience significantly higher temperatures than their surrounding rural counterparts. The temperature difference is largely attributed to modification of land surfaces by human activities.

In Hyderabad, thanks to tall concrete buildings, narrow streets, cement surfaces, and dwindling green cover, there is always this perception of very hot temperatures, although, day time temperatures in districts are more by 2 to 3 degree Celsius.

To combat such diverse weather patterns, the Director of Public Health (DPH) had recently issued a health advisory, urging people to do their best not to venture out between 12 noon and 3 pm.

“If you feel dizzy, body temperature 104 F, you have a rapid heart rate, shallow breathing, totally disoriented, ataxia (lack of muscle coordination) then you are experiencing a heat stroke. You must quickly rush to a doctor for treatment. It is best not to venture out between 12 noon and 3 pm,” DPH, Dr B Ravinder Naik, in the advisory said.