Climate change intensified rain that fueled Pakistan’s deadly floods
Climate change made peak rainfall last month in Pakistan’s Sindh and Balochistan provinces — which contributed to the devastating flooding that has affected 33 million people — 75% more intense than it would have been in a world without warming, according to an analysis by World Weather Attribution (WWA), a scientific group that studies the link between extreme weather events and climate change.
In addition to the rainfall, a heat wave in India and Pakistan earlier this year, also fueled by climate change, worsened the flooding that left a third of Pakistan under water, the scientists found.
The death toll from the floods has risen to nearly 1,500 and the physical damage to the country may surpass $30 billion. More than a million homes are damaged and thousands of schools and health facilities were destroyed.
“The levels of rainfall have been startling and this was an unprecedented disaster,” said Ayesha Siddiqi, an assistant professor of geography at the University of Cambridge. “At the same time, the disaster was a result of vulnerabilities constructed over many years.”
The built environment and social conditions in Pakistan exacerbated the monsoon’s impacts. Cities, towns, infrastructure and farms were built in flood plains. High levels of poverty and recent political instability left the nation less prepared for disaster.
The group conducted two different analyses on the rains in Pakistan as the disaster was still unfolding.
In one, it analyzed the annual five-day maximum rainfall data during the monsoon season in the worst-hit provinces of Sindh and Balochistan. It found that the rain concentrated in the southern provinces was 75% more intense than it would have been if the world hadn’t already warmed by about 1.2° Celsius since pre-industrial times. The models suggest that rainfall intensity over a similar five-day period will significantly increase in the future if the planet warms by 2ºC.
Researchers also looked at climate change’s influence on the whole monsoon season — a 60-day period between June and September — in the much larger area of the Indus River basin. For this second study, they found that climate change is making such rainfall across the whole region 50% more intense, although the high variability of rainfall in this part of the world makes the conclusion uncertain. Shortfalls in the ability of climate models to capture some features of regional weather made it difficult to estimate the increase in likelihood.
“The monsoon is notoriously difficult to predict,” said Fahad Saeed, a researcher at the Center for Climate Change and Sustainable Development in Islamabad. “Most of the models are developed in the global North and some of the processes crucial for this region of South Asia are not integrated in those particular models — so there’s a gap.”
In May, WWA determined that high heat in Pakistan and India was made 30 times more likely by greenhouse gas pollution. Heat studies like that one have become relatively simple for the scientists to carry out, because they rely mostly on basic facts about global warming: There’s more heat in the atmosphere, so temperatures are rising more often and to higher levels. Floods and droughts include hydrological factors as well, adding complexity to the task.
“The role of climate change is much larger in heat waves than it is in extreme rainfall events like this one,” said Friederike Otto, a senior lecturer in climate science at Imperial College London. “Naturally some years are very wet and some drier — we don’t have much data to really quantify what’s the return time of such an event.”
In the recent floods, the heaviest water came to the south and west of the country, an arid region where monsoon behavior varies a lot from year to year, leaving limited data patterns for researchers to work with. Rainfall in the area is particularly sensitive to the presence of La Niña — a cooling phase of the Pacific Ocean like this year’s — and also to hot springtime weather. Pakistan is home to 7,000 glaciers that also melted more than usual in the summer heat, although they probably caused much less flooding than the rain.
Even if they can’t say how much more likely it is, the group of scientists believes there is an increasing likelihood of a similar event taking place in a warmer world, Otto said.
Pakistani officials have warned of more floods in some areas over the weekend, and the government is trying to fend off a food crisis after floodwaters swamped crops and swept away livestock.
“No country deserves this fate, but particularly not countries like Pakistan that have done almost nothing to contribute to global warming,” United Nations Secretary-General António Guterres said on Sept. 9, urging the international community to give the nation “massive financial support.”
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