India's metropolitan cities usually register higher temperatures in May, June and July.
We are not even into June yet, and a large part of North and Central India is already grappling with severe heatwave. On Wednesday, several areas in Delhi and Rajasthan recorded a temperature of over 50 degrees Celsius.
On Thursday, after last evening's shower, the weather improved in the national capital, and the temperature dropped to 41.8 degrees Celsius. Among other cities, Mumbai was at 33 degrees Celsius, Bangalore 30.4 degrees Celsius and Chennai registered a temperature of 39 degrees Celsius.
India's metropolitan cities usually register higher temperatures in May, June and July. This phenomenon is attributed to the urban heat-island effect, making the cities significantly warmer than their surroundings.
What is the Urban Heat Island Effect?
In simple words, the urban heat island effect takes place when urban regions record higher temperatures than their rural surroundings. This mostly occurs due to human activities, buildings, and infrastructure in urban areas that absorb and retain heat more effectively than natural landscapes.
It is worth noting that rising temperatures are not limited to India, and the conditions are getting worse all over the world. According to scientists, one reason for this excessive heat in India is the El Nino effect, which is responsible for the change in the global weather pattern.
What is the El Nino Effect?
El Niño is characterised by unusually warm ocean temperatures in parts of the Pacific Ocean. It also results in the rise of sea surface temperatures. The El Nino cycle started in 2023 and its effect is expected to last until June this year.
The phenomenon is responsible for the extreme summer this year. However, soon El Nino will start to weaken and La Nina will come into effect.
What is the La Nina Effect?
La Nina is the cooling of the water in the Pacific Ocean. While it occurs at irregular intervals, La Ninna is associated with widespread changes in the weather patterns. India is likely to witness a good monsoon this year once the La Nina comes into effect.
Why does heatwave occur?
Many changes taking place in our atmosphere and oceans give rise to heatwave in the North Central and Eastern parts of the country. It's highly dangerous because it triggers heat stress in our bodies.
Dry Heat Stress: Dry heat stress occurs when the temperatures rise but if the humidity remains low. In this intense heat, it becomes difficult for the body to cool down its temperature through sweating. This can lead to dehydration and other health-related concerns. There is less possibility of humidity in summer in Central and North Western India, therefore, the region faces a greater number of dry heat stress cases.
Moist Heat Stress: This is humid heat stress. This occurs when the humidity gets mixed with rising temperature. In this condition, too, the body fails to cool down itself through sweating and heat stress rises. People in eastern coastal areas like Odisha, Andhra Pradesh, Tamil Nadu and Maharashtra face such conditions. These regions record a high number of moist heat stress cases when the temperature is high in the monsoon season.
A recent study by IMD revealed that in the last 40 years, in India (between 1980 to 2020), there has been a 30% rise in heat stress cases due to humidity being involved with rising temperatures.
During this period, the average heat index in Central India, North West India and Eastern coastal areas witnessed their temperature rising 4 to 5 degrees Celsius above their normal summer temperature.