A half-degree increase in average summer temperatures or heat waves that are longer by just two days could lead to a significant rise in the number of deaths in India, a new research paper warns. The Indian summer has already been brutal in recent years with heat wave deaths occurring with greater regularity, especially in heat-prone regions of Andhra Pradesh, Telangana and Odisha. A new analysis of mortality during heat waves shows that the toll could rise by two and a half times over the next 50 years, given the projected average temperature increase of less than one degree Celsius.

In a paper published in the journal Sciences Advances last week, researchers described trends in temperature rise, number of heat wave days and mortality between the years 1960 and 2009. Based on these trends and temperature-increase forecasts as a result of climate change, they predict a substantial increases in heat-related mortality, especially mass heat-related mortality events in which more than 100 people die.

Data from the National Disaster Management Authority clearly shows the rising number of heat-wave deaths in recent years.

The National Disaster Management Authority’s own guidelines on heat waves say that it is likely that the actual death tolls have been higher than these reported numbers because heat-related illnesses are often recorded inaccurately and figures from rural areas are difficult to obtain. Scroll.in reported on the undercounting of heat wave deaths in Telangana in the summer of 2016.

The major finding of the new study is that while there is a 13% probability of mass heat-related mortality events with summer mean temperatures at 27°C, the probability jumps to 32% if summer mean temperatures rise by just 0.5°C to 27.5°C. Similarly, the probability of heat-related mass mortality events rises from 46% to 82% if the the average number of heat wave days across India rises from six days to eight days.

“In India, temperatures have been increasing and this year, in the early part of summer, there were very high temperatures and that had caused high mortality,” said Subimal Ghosh, one of the authors of the paper and associate professor at the department of civil engineering at the Indian Institute of Technology, Bombay. “This comes a surprise to most people because no one expects 45°C during March. The challenge is that when this happens people are not really prepared for it.”

The new study builds on previous research by Ghosh and his colleagues that showed how extreme heat waves are more likely to occur earlier in the year – possibly even striking in early April. The earlier research, which predicts trends in heat waves towards the later half of the century, showed that even large regions of southern India and the east and west coasts that are currently unaffected by severe heat waves, will be severely affected after 2070.

High mortality is not only a result of consistently high temperatures. Poverty is also a significant factor in mortality. The new study uses a metric called income-weighted heat wave days to show that during the heat waves of 1972, 1988, 1998, and 2003, there were more than 10 heat wave days on average across India and a correspondingly high death toll of between 650 and 1,500 people. However, during the heat waves of 1973, 1983, 1984 and 1995, there were between eight and 12 heat wave days but a low number of deaths. This is probably because the heat waves occurred in less populous and/or wealthier regions.

This is simply because the poor have less access to shelter, clean drinking water and air conditioning.

The only way to keep heat wave mortality low is to implement heat wave action plans. In 2013, Ahmedabad became the first Indian city to implement such a plan, which includes sending out warnings about spikes in temperatures, communicating heat management strategies to the public and providing shelters with water and other relief. Other cities that have followed suit are Surat, Nagpur and Bhubaneswar.

However, according to Ghosh, heat waves are still not taken as seriously as other disasters.

“The IMD has actually done a very good job in forecasting heat waves and the media has also done a good job in reporting these forecasts,” he said. “But you still find that, while people get scared and do not go out of their houses if there is a flood or extreme rainfall, they still go out even when there is a forecast of extreme heat.”

For millions in India, however, whose livelihoods depend on daily labour outdoors, staying away from the killer heat is still not a choice.