3 months of the summer of 2023 have passed so far. Compared to last year, this summer has been less scorching. The temperatures in Mumbai Metropolitan Region (MMR) were around 40℃ in March and April 2022. This year, it was only in April, temperatures rose to that uncomfortable level. March 2023 was surprisingly pleasant this time, more so because we anticipated something harsher. After the 23rd April 2023, temperature have dropped by few degrees and most importantly it has become somewhat tolerable again.
But this
summer has left an indelible mark on our memory due to several deaths caused by
heatstroke on 16th April 2023. Deaths of heatstroke is not the
possibility one typically associates with MMR. We have train track deaths and
reckless driving for such association. (Perhaps we add ‘mauled by stray dogs’
as well, if not now then in near future!)
Those
deaths reminded me of climate fiction ‘The Ministry for the Future’ by Kim
Stanley Robinson. This novel opens with a climate catastrophe in the form of
heatstroke and author has referred to wet-bulb temperatures to make sense of
this tragedy. As I read about Kharghar heatstroke deaths, I kept wondering
about the wet-bulb temperature. Wet-bulb temperature is the temperature of a
thermometer wrapped inside the wet cloth. Such temperature is typically lesser
than the temperature of the surroundings. Some energy from the wet cloth is
utilized for evaporation of the water and that leads to drop in the
temperature. (Following part is based on my understanding of the phenomenon. I
declare that I am not expert in Physics and hence there is some chance that I
might be inaccurate in some implications.)
This is
precisely what our body does to cool itself. The evaporation of sweat leads to
fall in our body temperature and allows body to maintain temperature in the
region where body functions are not affected. There are certain thresholds for
our body temperatures. Wet-bulb temperature more than 30℃ can be discomforting
while more than 35℃ can be deadly.
Humidity
plays a key role in determining the wet-bulb temperature. In case of high
humidity, there is little scope for wet body (human body for example) to put
additional water vapor in the surroundings. So high levels of humidity mean
lesser scope of wet body temperature to fall from surroundings. That’s why
sweat lingers on the body in humid places while in dry places one feels as if
one is not sweating.
A thumb
rule for wet-bulb temperature in humid place like Mumbai, assuming relative
humidity of 65%, is that it will be around 5℃ less than the surrounding
temperature. That’s why temperatures around 35℃ in Mumbai are something we can
manage since it means wet-bulb temperature below 30℃, something our body can
tolerate well. But as mercury starts rising above 35℃, heat becomes bothersome.
In case, we encounter close to 40℃ with high humidity, it can be lethal, at
least to those of us who are more vulnerable.
This is
what makes high temperatures in humid places more threatening than similar
temperatures in dry places. In dry places, like Vidarbha, if one has adequate
water intake and other safety measures, body can regulate its temperature
through perspiration. But in humid places, even with adequate water intake,
perspiration can turn ineffective in maintaining low enough body temperature
when one is exposed to sun for long. More importantly, many dry and hot places,
summer heat is part of common psyche so that heuristics has been developed to
minimize the heat effect. But in Mumbai, deadly heat is a recent phenomenon,
which means individual decision making about it is likely to be sub-optimal. Till
the deadly heat becomes part of common understanding of Mumbaikars, there will
be misjudgements and there will be fatal consequences.
The fact
that summer temperatures cannot be predicted well due to unpredictability
introduced by climate change makes it more of a problem. Not many of us will
choose to have pessimistic estimate (that this summer will be a high
temperature one). We are by design creatures who think things are in our
favour. So may be next year, there will be election rallies during daytime, and
we will end up exposing many to possibility of heatstroke if summer temperatures
in 2024 turn out to be more like 2022 than 2023. The festivities and gathering
during summer can expose many vulnerable individuals if temperatures turn out
to be unpredictably higher than what we choose to believe.
In short,
climate change has resulted in a haunting spectre for MMR. MMR is a humid
region due to its proximity to the sea. If summers are going to be increasingly
hotter, then heatstroke will be the new threat that one might have to account
for. This is especially true considering ever crowded nature of the MMR. And
the threat will creep inside our homes soon. If temperatures are to increase up
to 45℃, many of us might be vulnerable even within confines of our homes or
offices.
The
differentiating line, between heat being deadly or not in such humid places, is
that of access to air-conditioning. Obviously, it will coincide with our
existing fault-lines of income and wealth inequalities. But as more of us
choose to buy our way to safety through ACs, more we will push ourselves or
some of us to a precipice with no return possible.