Tropical cyclones followed quickly by deadly heatwaves will be a growing threat as global temperatures continue to rise to a dangerous level for human beings, according to climate scientists in Ireland and the UK.
The scientists say their research should act as a “stark warning”. They say it should raise awareness of what up to now was a hidden hazard so measures can be put in place to protect vulnerable communities, potentially adding up to millions of people.
Areas most at risk are the Gulf of Mexico, the Bay of Bengal (India), The Philippines and northwest Australia, which include some of the most densely populated coastal areas on the planet.
Until now, little was known about the possibility of dangerous heatwaves following major tropical cyclones, which are very intense storm systems that form over tropical oceans and have winds of hurricane force.
Dr Conor Murphy of Maynooth University, working with Dr Tom Matthews and Prof Rob Wilby at Loughborough University, examined what they described as “the tropical cyclone-deadly heat connection”. They conclude the hazard could rapidly increase in frequency coinciding with global heating.
Deadly heat refers to temperatures that feel like 40.6 degrees Celsius and above, taking into account humidity; a threshold identified as potentially dangerous to humans. This figure was exceeded in parts of mainland Europe this summer.
The scientists highlight an additional exacerbating factor; the inevitability of “mega-electricity blackouts” known to follow powerful tropical cyclones. These occurred with the 2013 Typhoon Haiyan (Philippines); 2017 Hurricane Maria (Puerto Rico); and 2012 Typhoon Bopha (Philippines) incurring 3.2-6.1 billion customer hours of lost supply over one or two months.
With some 1.6 billion units in operation globally, air conditioning reduces vulnerability to extreme heat so populations with a heavy reliance on the units may become exposed in the event of power failure brought about by tropical cyclones.
The threat may also extend beyond those with loss of air conditioning as cyclones can leave millions of people without a home, and relief housing may not provide safe refuge from extreme heat.
The team assessed how likely tropical cyclone-heat events are in the recent climate and how this likelihood may change as Earth continues to warm.
They used computer models to generate future possible climates, and predict extreme weather events occurring in worlds 1.5 degrees, 2 degrees and 4 degrees warmer than pre-industrial times – the time period used as a baseline as it is before fossil fuels were burnt on a large scale, seriously altering the climate.
They also used observational records from 1979 to 2017 to see how hot and humid temperatures have been in the wake of previous major tropical cyclones that hit land.
The team found the tropical cyclone-heat hazard has affected only a small number of people over the past 30 years and mainly in remote northwest Australia. This, they conclude, has been a matter of luck.
Dr Murphy, who is based at Icarus Climate Research Centre, said that while a tropical cyclone heat event had not yet impacted a heavily populated coastline, the likelihood was growing.
“This is because relatively small changes in global mean temperature lead to relatively large increases in the frequency of dangerous humid heat in the low-latitude locations impacted by tropical cyclones.”
The team’s results were published on Monday in Nature Climate Change.
Dr Matthews added: “Tropical cyclones occur most frequently towards the end of the summertime (when the sea surface is warmest), after humid heat over land areas has peaked. This time lag helps explains why, to date, we haven’t often seen deadly heat following tropical cyclones.”
However, as the climate warms further, “the rapid rise in humid heat means late summers are more likely to generate potentially deadly heatwaves – during the window when tropical cyclones are more common”.
If the world warms by just 2 degrees the number of people directly affected by this hazard would rise to more than 2 million people over a 30-year period, they predict.
The researchers say what is even more concerning is the fact the number of people affected will almost certainly be much bigger than their predictions as they do not factor in population growth or potential changes to the cyclones themselves.
“Our results present a simple but stark warning: with no change in tropical cyclones but plausible rises in global temperatures, potentially deadly heatwaves are more likely to follow tropical cyclones and eventually strike vulnerable populations,” Prof Wilby said.