Asked to comment on this, study co-author and chair of the Centre for Atmospheric Sciences at IIT Delhi Sagnik Dey told Dialogue Earth, “Heat is a risk factor, causing diseases which cause death. Therefore, in the death certificate, it’s not mentioned. Similar is the rationale for ’smoking’ or ‘air pollution’. Smoking cannot kill people – smoking can cause cancer or heart diseases or stroke, which kill people. So, you will never find ’smoking’ as the cause of death.
“In epidemiology studies, we link the risks to deaths or disease [morbidity] – the interpretation is the deaths from all possible causes attributable to that risk factor. This is standard practice.”
Policy implication
The authors say the heterogeneity they found in heat stress impact across diverse climate zones in India should lead to the development of an early warning system that keeps these regional variations in mind.
IMD heatwave warnings differ across climatic zones in the country. The researchers say the index they used will improve these warnings. Asked what the improvement will be, the components of the index used in the study and the relationship between this index and the wet bulb globe temperature (WBGT) used in some countries to add parameters important to human health, Dey said, “IMD does not use any specific index. They provide heatwave warning. The indices are to quantify the stress when someone is exposed to heat and should consider relative humidity, wind and direct radiation along with temperature.”
“All existing indicators were developed based on data from developed countries. We did earlier studies to find that none of the indices match with each other in terms of comfort classes. We tweaked WBGT to represent Indian climate conditions better, but as of now, it is done based on statistics. Epidemiological studies are required to fine tune the thresholds. There is a discussion going on how to integrate IHI into the learning system.”
Asked to explain why heat stress should be different in different areas, Dey told Dialogue Earth, “India has six climate zones, and there is no reason to believe that the comfort thresholds should be the same. We know that heat stress is not just temperature, but many other factors are relevant. So, logically, the risk should also vary. In our analysis, we showed evidence that this is indeed the case. Other studies also concur with the fact that the risk is very different in dry heat [what we found in our arid or semi-arid regions] vs humid heat [we found in subtropical humid or other climate zones].
“What we should do in the future is conduct epidemiological studies across the diverse climate zone and validate the statistical-based thresholds and fine tune it.”
K J Ramesh, the former head of IMD, said that because there is heterogeneity in heat stress across India, the IMD and National Disaster Management Authority have city-level heat action plans. “Those are being followed and are saving lives. We’re learning by doing. I wish this had been mentioned in the paper.”
He added, “Heterogeneity can be at various levels and can have major impacts. In one of the years between 2015 and 2017, it was found that infant deaths in certain hospitals in Telangana had gone up significantly in midsummer. Upon checking, it was found that all these hospitals had their maternity wards on the top floor. Now they have been asked to shift those wards. These micro-level differences are important.”
He also disagreed with the study drawing a relationship between PM2.5 pollution and heat stress. “PM2.5 and other pollutants rise in the atmosphere and get dispersed in the summer.”
Asked what construction workers and others who had to be outdoors should do to reduce heat stress, Ramesh said, “They should not work between 1 and 4 pm. They can start earlier, at 6 am.”
This article was originally published on Dialogue Earth under a Creative Commons licence.
