An international team of climate scientists reports that, even considering the large natural variability of the South Asian monsoon and gaps in climate data for the region, the most extreme rainfall that drove deadly flooding in Pakistan during August and September was intensified by human-caused global warming.
The World Weather Attribution analysis released Sept. 15 looked at the total rainfall for a 60-day period spanning much of the monsoon season, as well as at the most intense five-day periods, when the rains overwhelmed many flooding defenses, killing about 1,500 people, destroying 1.7 million homes and leaving about one third of Pakistan under water, according to a Sept. 9 update from Pakistan’s National Disaster Management Authority. Two southern provinces, Sindh and Balochistan, each experienced their wettest August ever recorded, receiving 7 and 8 times their normal August rainfall respectively.
The team used several climate models to analyze the influence of warming, and reported that “The majority of models and observations … show that intense rainfall has become heavier as Pakistan has warmed. Some of these models suggest climate change could have increased the rainfall intensity up to 50 percent during the wettest five-day periods.”
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“We have very large uncertainties,” said Sjoukje Philip, a climate scientist at the Royal Netherlands Meteorological Institute and co-author of the attribution study. “But based on observations and models together, and combining that with our theoretical knowledge, we now find that it’s likely that climate change played a role, although it’s difficult to quantify these changes.”
When they used the models to assess future risks, they found that if the climate warms 2 degrees Celsius above the pre-industrial level, “rainfall intensity will significantly increase further for the five-day event,” she added.
Co-author Fahad Saeed said it’s important to consider climate conditions leading up to the extreme rainfall. Before the monsoon started, Pakistan experienced a long, extreme heatwave that was made 30 times more likely by human-caused warming, according to a previous analysis by World Weather Attribution. That heat wave set up a weather pattern that also made the extreme rains more likely, bringing the monsoon closer to the hardest-hit regions of Pakistan.
“Instead of following the normal pathway towards the northern part of the country,” he said, “they ran toward two southern provinces, which are basically arid and semi-arid” areas with hard, dry soils that don’t typically get much rain, and can’t absorb it well when it does fall.
The result was an “unprecedented disaster” that nevertheless was similar to previous flooding, particularly in 2010, said co-author Ayesha Siddiqi, a geography lecturer and environmental justice expert at the University of Cambridge who examined why Pakistan was so vulnerable to the flooding.
A Destructive Colonial Legacy
“Since colonial times state planning in this part of South Asia has historically been focused on a very modernist engineering paradigm which relies on mega projects for water management, and also for flood management,” she said. “This has resulted in a number of documented challenges, such as breaching of banks, and creating sudden changes in river flows and feeding flood waves.”
The legacy of colonialism has played a role in the flooding of the lower part of the Indus River Basin, she added. Drainage systems designed to create arable land during British rule amplified the flooding, she said. Those systems have been problematic even in non-flood years, with “an ideological belief in these types of solutions since colonial times,” making people more vulnerable, she said.
There is also the potential to make changes that could reduce vulnerabilities, with “discussions in the social science community about how to work with the natural ecology of the river that could be looked at for future planning,” she said.
Siddiqi said flaws in Pakistan’s disaster management systems also left people more vulnerable, particularly a “disconnect between policies at the top and the voices at the bottom” and unclear emergency management communications. Construction projects that block natural water courses continue to contribute to the problem, she added, because they leave the water with no place to go, slowing recovery.
“Taking all of these factors together, it is important to remember that the disaster was a result of vulnerability constructed over a number of years, and it shouldn’t be seen ahistorically as the outcome of just one kind of sudden or sporadic weather event,” she said.
And there is more trouble ahead, said lead author Friederike Otto, a climate scientist at Grantham Imperial College. Predicting specific extreme flood events far in advance is not possible, but “because of climate change,” she said, “and because of the fact that emissions are still rising … the chance of record-breaking heat waves is higher every year than the year before.”
Saeed said there are other aspects of colonialism that worsened Pakistans’ vulnerability to the flooding, including the data bias in global climate models, most of which have been developed in the Global North.
“Some of the processes which are very crucial for South Asia are not included in the models,” he said. “Since they are not integrated into those particular models, there is a data gap. There’s also a dearth of research. Scientists from South Asia should come together to determine the right data and make sure they’re included in the models,” he added.
Reducing vulnerability will require a “much more local understanding and management of water,” Siddiqi added. “Do we need to rethink where we’re putting up a bunch of levies, which had a different purpose when British colonial rulers wanted to irrigate certain areas for political purposes?”
Post-colonial scholars are already discussing how to talk to more indigenous holders of knowledge “to understand how these very small water forces used to work before the large mega projects just swallowed them whole.”
There is no neat answer, she continued.
“It’s more about needing to shift the way we think about some of these things, and I don’t think Pakistan can do that in a silo,” she said. “I think it requires a much more overarching understanding and shift in the way we see knowledge and science and the way we see things like water and river ecologies and Indigenous knowledge systems.”