The number sounds alarming but is most likely an underestimate. Research shows that India is underreporting heat mortality, which in turn is inhibiting adaptive policies like early warning systems and better public health preparedness.
For one, the government counts only death by heat stroke and heat exhaustion as heat wave deaths. The narrow definition does not account for the way “heat exposure stresses underlying physiological systems”, a study on heat mortality in Ahmedabad said. Heat exposure exacerbates respiratory diseases and renal failure that might not result in same-day deaths but could show up with a time lag of a few days.
The study found that mortality rates in the city of Ahmedabad were 43% higher in May 2010 when the city experienced a heat wave as compared to the same days in 2009 and 2011. An excess of 1,344 deaths occurred in May 2010, relative to the average for the years before and after.
The researchers accessed the day-wise death counts from Ahmedabad Municipal Corporation. Since the cause of the deaths was not documented by officials, it could be argued that the excess deaths in May 2010 may not necessarily be related to the heat. However, the researchers checked the government's epidemic surveillance system to rule out any outbreaks that could have contributed to an increase in mortality rates in 2010 – which implies that, all things the same, more people die in conditions of extreme heat.
The bad news is that heat waves are likely to intensify in the future, according to climate change researchers. Like the rest of the world, over the last century, India has turned hotter, with temperatures rising in the range of 0.8 to 1°C, with an increasing number of hot days.
"The heat waves are projected to be more intense, have longer durations and occur at a higher frequency and earlier in the year," said a research paper published in April 2015. The paper projects future heat waves in India based on multiple climate models. It finds that large parts of southern India and the East and West coasts, which are presently unaffected by severe heat waves, could be severely affected after 2070. This could lead to increased mortality.
The researchers draw attention to the fact that the Indian government does not consider heat waves as a serious risk to human health and heat hazards are not counted among the priorities of its disaster management plan.
"Our results suggest the necessity of adaptation policies to address the adverse effects of heat wave hazards," the paper states. "Although there are limitations in the present approach, our results are the first step in alerting policy makers to plan responses to more intense and persistent heat waves."