India is possibly moving away from just using temperature to declare a heatwave in its official communications with the Indian Meteorological Department, preparing a new warning system, factoring in humidity, which could better depict the alarming conditions that prevailed in the coastal areas, experts believe.
The new guidelines proposed will include a percentile-based warning system whereby an alert can be declared if the temperature goes above the 95th percentile for a specific region. Put simply, it implies that if the temperature goes above the recorded 95 per cent of the time at the location, then an alert should be declared.
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The proposed move comes at a time when the weathermen are admitting that the current system does not quite depict the impact of hot and humid weather on conditions, especially in coastal states where the temperatures may not hit the normal limits but still make living impossible.
Speaking about why the change is necessary, M Mohapatra said it is often seen in the coastal areas that, despite not hitting the desired mark, it becomes very difficult for one to live there.
“For example, in coastal parts of South India, we may not see temperatures reaching 44 or 45 degree C, but it is very hot because the humidity index is very high. If the models are showing that in the next couple of days, the temperature will be higher than the 95th percentile, we will give a heat wave alert. So, we will not wait for the maximum temperature to exceed 5 degrees above normal,” HT quoted Mojapatra.
“We have started giving percentile-based alerts already,” he added.
Currently, the IMD terms a heatwave in the plains if temperatures reach 45 deg Celsius, or rise to a level of 4.5 to 6.4 degrees Celsius above the normal. In coastal areas, there needs to be a minimum temperature of 37 degrees Celsius and a deviation of 4.5 degrees Celsius from the normal, criteria which experts feel have failed to adequately assess the contribution of humidity.
The scientific community has largely welcomed the changes as being more local and relevant.
“It is a good decision. Using percentiles is much more meaningful than absolute values. That is what we proposed in our research papers and monograph. Percentiles help specify extremes at a given location irrespective of the background mean. There is no universal rule for heatwave definition. It should reflect the meaning and purpose of a heatwave alert,” said M Rajeevan.
Discussion of revised heat wave warnings comes amid forecasts of a brutal summer in India. Earlier, the IMD stated that minimum temperatures in parts of coastal Karnataka, along with a few other regions, would exceed 95th as well as 98th percentiles.
There have also been growing concerns about the likelihood of an El Nino occurring later this year. Predictions from the World Meteorological Organisation and the U.S. National Oceanic and Atmospheric Administration indicate an almost 80 per cent chance of El Nino occurring between June and August.
Meteorological organisations have already warned that there is likely to be dominance of above normal land temperatures in most parts of the world in the coming few months, while even rainfall in India might be below normal till July.
Researchers have been increasingly interested in "wet-bulb temperature," which measures humidity and heat to see the ease with which human beings are able to cool their bodies by sweating.
When wet-bulb temperature approaches skin temperature, perspiration becomes useless, resulting in the risk of heat stroke and even death. While 35 degrees Celsius was long thought to be the upper survival limit of wet-bulb temperature, it was recently suggested by a group of Harvard University scientists that it might be closer to 31 degrees Celsius, suggesting that heat risk might be greater than previously anticipated.