Byย Sarah Perkins-Kirkpatrick, UNSW AustraliaAndrew King, University of Melbourne, and Geert Jan vanย Oldenborgh
On May 19, Indiaโs all-time temperature record was smashed in the northern city of Phalodi in the state of Rajasthan. Temperatures soared to 51โ, beating the previous record set in 1956 byย 0.4โ.
India is known for its unbearable conditions at this time of year, just before the monsoon takes hold. Temperatures in the high 30s are routine, with local authorities declaring heatwave conditions only once thermometers reach a stifling 45โ. But the record comes on the back of an exceptionally hot season, with several heatwaves earlier in the year. So whatโs to blame for these scorchingย conditions?
Much of India is in the grip of a massive drought. Water resources are scarce across the country. Dry conditions exacerbate extreme temperatures because the heat energy usually taken up by evaporation heats the airย instead.
The complex relationship between droughts and heatwaves is an area of active scientific research, although we know a preceding drought can significantly amplify the intensity and duration ofย heatwaves.
Indiaโs drought was a possible factor in the earlier heatwaves in April over central and southern India. However, Rajasthan, where 51โ was recorded, is always bone-dry in May. So the drought made no difference to the recordย temperature.
The El Niรฑoย effect
We have also experienced one of the strongest El Niรฑo events on record. While the current event has recently ceased, its sting is certainly still beingย felt.
El Niรฑo episodes are associated with higher-than-average global temperatures and have also been a factor in some of Indiaโs past heatwaves. However, there is no direct connection to El Niรฑo in Rajasthan, because its climate at this time of year is so dryย anyway.
India also has an extreme air pollution problem. Caused largely by domestic fuel and wood burning, it kills up to 400,000 people every year. This pollution, made up of fine particles called aerosols, also has the effect of cooling the local climate by reflecting or absorbing sunlight before it reaches the ground, thus reducing the likelihood of the most extreme highย temperatures.
So although India is no stranger to extreme heat at this time of year, the smog has kept record-breaking high temperatures at bay โ until now. This is what makes the record in Phalodiย remarkable.
Longer-term heatย extremes
A study published in 2013 analysed annual trends in extremes and found no significant change in the intensity of extreme Indian temperatures between 1951 and 2010. The high levels of local air pollution were probably behind the lack ofย change.
However, the study found a significant increase in the frequency of extreme temperatures and a remarkable trend in the duration of warm spells in India, as the map below shows. Warm spells, defined as at least six days of extreme temperatures relative to the location and time of year, increased by at least three days per decade over 1951-2010 โ the largest trend recordedย globally.
It is worth keeping in mind that these trends are annual and are influenced by extremes all year round. However, monthly trends in the frequency of Indian temperature extremes for May, which can be found on the CLIMDEX climate database, show an increase over the past 60ย years.
Based on local station data, the Indian Meteorological Department reported that many northern states experienced an average of eight heatwave days each March-July between 1961-2010. Trends in โnormalโ and โsevereโ heatwaves increased over this time, and in particular over the last decade of theย analysis.
Some Indian regions also tended towards longer and more intense heatwaves after an El Niรฑo, and northwestern states of India, where Phalodi is located, tend to experience more intense events anyway. Trends in the intensity of extreme temperatures are less clear and vary across theย country.
Different spatial and temporal scales and methods of quantifying extreme temperature hamper a direct comparison of the two studies described above. However, they both document an increase in the frequency of extreme temperatures over India, which is consistent with many other regions worldwide. Heatwave indices and the hottest yearly temperature have only increased significantly in a relatively small region of westernย India.
What will the futureย bring?
Most climate models do not do a great job of capturing observed trends in heatwaves over India, because large-scale models struggle to accurately represent the localised effect ofย aerosols.
It is therefore difficult to use them in great detail for future projections, particularly if pollution levels continue or even increase. However, if air pollution is reduced, temperatures will rise with a vengeance. We know this from experience over Europe, where summer temperature trends were virtually zero up to the 1980s and very strong afterwards, once air pollution wasย controlled.
Even though this is the hottest time of the year for the region, the recent weather should not be dismissed as regular. It is feasible that Indiaโs pollution problem has been โhidingโ extreme heatย spikes.
While any clean-up activities will have many positive local health impacts, these are likely to cause more intense heatwaves in future. This will be amplified by background warming due to climate change, which is also likely to drive increases in the frequency of temperatureย extremes.
Last year India and neighbouring Pakistan suffered similarly atrocious conditions, killing thousands of people. This yearโs death toll is already in the hundreds, with numbers sure to riseย further.
India is already highly vulnerable to the health impacts of oppressive heatwaves and, as climate change continues, this vulnerability will grow. It is therefore imperative that heat plans are put in place to protect the population. Thatโs a difficult prospect in places that lack communications infrastructure or widespread access to airย conditioning.
In the longer term, this episode shows that the global warming targets agreed in Paris have to be taken seriously, so that unprecedented heatwaves and their deadly impacts donโt become unmanageable in this part of the world.
Sarah Perkins-Kirkpatrick, Research Fellow, UNSW AustraliaAndrew King, Climate Extremes Research Fellow, University of Melbourne, and Geert Jan van Oldenborgh, Climate researcher, Royal Dutch Meteorological Institute.ย This article was originally published on The Conversation. Read the original article.
Main image: A man refreshes on a Calcutta Street in 2005. Creditย Jorge Ryan, Creativeย Commons.
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