Three climatic factors creating the unbearable conditions in many states

Moisture levels in many parts of India are much higher than normal. States like Odisha and West Bengal are even experiencing humid heatwaves, which have made living conditions unbearable for residents. 

This is happening because of moisture being pumped in by multiple weather systems over the country, which is being further fuelled by the general warming of the atmosphere and the oceans. 

Odisha and Gangetic West Bengal have been experiencing heatwave conditions since April 15 and April 17, respectively, according to the India Meteorological Department (IMD). Interior Karnataka has been hit by heatwaves since April 23. 

The sub-Himalayan parts of West Bengal also started suffering from heatwaves since April 24, along with the Rayalaseema region of Andhra Pradesh. Rare heatwaves started affecting Kerala on April 26, along with Bihar. The Konkan region of Maharashtra is suffering from its second bout of humid heatwaves since April 27. 

In many of these regions, it is not just the rising temperatures that are causing discomfort but also increased relative humidity levels that indicate the presence of heat-trapping moisture in the atmosphere. IMD has also indicated hot and humid weather and warm night conditions in several places across India in the past month or so, especially in the southern peninsular India. 

When the moisture levels in the atmosphere are high, the air becomes saturated and cannot hold more water vapour. This increases the felt ambient temperature of an area and also leads to less sweating in humans and animals. 

This increases the internal body temperatures as there is no way for heat to escape and increases discomfort. When such conditions prevail for a prlonged period of time, it impacts human health, especially the heart and brain, and can also be fatal. But why is there so much moisture in the atmosphere currently?

“There are two huge anticyclones over the Arabian Sea and the Bay of Bengal currently, which are bringing winds on shore to Odisha and West Bengal and to the Konkan region of Maharashtra,” KJ Ramesh, a climate scientist and former director-general of IMD, told Down To Earth (DTE). 

Anticyclones are regions of high atmospheric pressure where the winds blow in a downward sinking motion, compress and heat up. They cause heatwaves by making winds move in a downward direction and blocking other weather systems that may dissipate heatwaves. 

They are common over India during the pre-monsoon period, according to Ramesh. “These winds are pumping moisture from the sea onto land, increasing the relative humidity levels even in the interior regions,” he added.

The anticyclone over the Arabian Sea is still causing rainfall in West Asia, according to Ramesh. The region suffered unprecedented rainfall and flooding in mid-April fuelled by warming. 

In northern and western India, along with the anticyclone over the Arabian Sea, moisture is also being brought in by the continuous western disturbances. These extra tropical storm systems travel from the Mediterranean region through Iran, Afghanistan and Pakistan to bring most of northern, western and central India’s winter rainfall and cause thunderstorms during the spring and summer seasons. 

But global warming and consequent climate change have been changing the character of these western disturbances, increasing their frequency towards the spring and summers and causing them to move more towards the southern latitudes. 

“When the western disturbances are more towards the south, which is the case currently, they can push moisture into western India along with the anticyclone,” explained Ramesh. 

“Anticyclones are there and the west coast is getting humidity from warm northern Arabian Sea. Interior is getting a lot of humidity from the south of Sri Lanka and Bay of Bengal,” Raghu Murtugudde, professor of climate studies at the Indian Institute of Technology, Bombay and emeritus professor at the University of Maryland, told DTE. 

“We are in summer so land is heating like crazy and El Nino is adding its tadka (seasoning) with global warming on top. Warm temperatures means deadly humidity. Soil moisture and all waterbodies evaporate rapidly and of course we have circulation bringing humidity from the oceans around us. Each degree of warming brings 7 per cent more humidity so it’s an exponential rise,” explained Murtugudde. 

Good news may be on the way for some of these regions as thunderstorms and rainfall are likely from May 5 onwards, according to Ramesh.