Why in news?
Scientists from the University of Reading and the UK Met Office reported in February 2026 that “moist heatwaves” occurring during India’s southwest monsoon can be predicted several weeks in advance. The study drew attention because such heatwaves, driven by high humidity and high temperature, pose serious health risks and are less widely understood than dry heatwaves.
Background
Heatwaves are periods of unusually high temperatures, but when they coincide with very high humidity they become “moist heatwaves”. Humid air slows the evaporation of sweat from the skin, making it harder for the body to cool itself. Scientists measure the combined effect of heat and humidity using the wet‑bulb temperature — the lowest temperature a surface can reach by evaporating water. A wet‑bulb temperature of around 35 °C is widely considered the upper limit of human survivability, although recent research suggests this threshold may vary by age and physical fitness.
How moist heatwaves affect people
- Impaired cooling: When humidity is high, sweat remains on the skin instead of evaporating. The body’s core temperature rises, increasing the risk of heat exhaustion and heatstroke.
- Health risks: Prolonged exposure to moist heat can strain the heart and lungs, leading to cardiovascular and respiratory illnesses. Older adults, young children and outdoor workers are especially vulnerable.
- Hidden danger: Because moist heatwaves often occur during the monsoon, people may underestimate their severity compared with the scorching dry heat of pre‑monsoon summer. This lack of awareness can delay protective actions.
Predicting moist heatwaves
The new study analysed weather data from 1940 to 2023 and found that moist heatwaves are closely linked to the active and break phases of the southwest monsoon. When the monsoon trough is active over the northern plains and central India, these regions face the greatest risk. During breaks, the risk shifts to southern and eastern India. Researchers also identified a larger weather pattern called the Boreal Summer Intraseasonal Oscillation, a 30–90 day cycle of convection that can be forecast two to four weeks in advance. Monitoring this pattern could provide communities with early warnings.
Response and adaptation
Recognising moist heatwaves early allows authorities to issue timely advisories, schedule outdoor work for cooler hours and prepare cooling shelters. Long‑term strategies include improving urban design to reduce heat build‑up, planting more trees, promoting access to clean water and ensuring that public health systems can handle surges in heat‑related illnesses. Public education campaigns can also help people understand the dangers of humid heat and adopt protective measures.
Source: Down To Earth