April 2025 brought extreme heat to Pune, with daily highs between 40°C and 43°C, posing severe health risks especially for the elderly. A study by IISER Pune found that “critical environmental thresholds” were breached multiple times, making it difficult for older adults to regulate their core body temperatures and raising serious concerns about increasing heat stress in Indian cities.
Researchers noted that core body temperature is tightly controlled and even slight rises can signal stress or illness. The body mainly cools through sweat evaporation, but this mechanism struggles during high heat and humidity. When the body can no longer keep core temperature stable, it enters a danger zone. In Pune, such conditions occurred several times throughout April especially affecting people aged 65 and above.
Critical Hours Lasted From Morning to Evening
Using a heat budget model and real-time environmental data, scientists discovered that critical conditions were most frequent between 12 pm and 4 pm. However, for elderly individuals, dangerous sweat rate exceedances were observed between 9:30 am and 6:00 pm. This suggests that the standard public health advisory to avoid the noon to 4 pm window may no longer be enough.
Quantifying Heat Risk for the First Time
According to IISER’s Assistant Professor Joy Monteiro, this is the first time researchers have quantified how environmental heat translates to real health risks for vulnerable populations. “We’ve seen that even in the green IISER Pune campus, elderly individuals faced long durations of heat stress,” Monteiro explained. “In hotter regions like Vidarbha, which already reported several heat stroke cases, the danger is even greater.”
The team calculated “sweat rate exceedances” on many April days. These occur when the body produces more sweat than can evaporate, making it ineffective at cooling. Some days saw this exceedance lasting up to 8 hours, especially when maximum temperatures crossed 40°C. Prolonged exposure to such conditions increases the risk of core temperatures rising above 40°C, a threshold where heat stroke is likely.
Elderly & Vulnerable Groups at Greater Risk
Besides age, health conditions like diabetes and dehydration also limit the body’s cooling ability. “Women often avoid drinking water to skip using public toilets, which can be unsanitary. This makes even younger people more susceptible,” Monteiro said. The study emphasizes the need to rethink public heat safety guidelines and raise awareness on hydration, shade access, and cooling facilities.
As Heatwaves Get Worse, Prevention is Key
With rising global temperatures and increasing urban heat island effects, scientists warn that such extreme heat events may become more common. The IISER Pune study offers critical insights into the hidden dangers of high temperatures and calls for urgent public health and infrastructure responses to protect vulnerable groups.