Sep 15, 2022 - Energy & Environment

Climate change worsened Pakistan's flooding rains, study finds

Flooding survivors from monsoon rains in Pakistan leave their homes on Sept. 9, 2022.

Flooding survivors from monsoon rains leave their flooded homes in Sehwan, Pakistan on September 09, 2022. (Adeel Ahmed/Anadolu Agency via Getty Images)

Large swaths of Pakistan are underwater from unusually prolific monsoon rains, which have killed nearly 1,500 people. Now a new study shows the connections between the flooding and climate change.

The big picture: The study, released Thursday, shows human-caused global warming may have boosted 5-day rainfall amounts in the hardest-hit areas of Pakistan by up to 50%.

  • This means that without human-caused global warming, one-third of the rains that fell would not have occurred, researchers said in an online briefing.
  • The study notes the large uncertainty regarding how climate change affects monsoon rainfall in Pakistan due to the region's high natural variability from year-to-year, and the relative paucity of historical rainfall records.
  • Some climate models showed that nearly the entirety of the precipitation increase could be attributed to climate change.

Driving the news: The Pakistan floods are visible via Earth observing satellites, with lakes appearing where dry land had been, after the Indus River overflowed its banks, and broke through or overtopped dams and other flood control structures.

  • The floods have affected more than 33 million people.
  • U.N. Secretary-General António Guterres last week visited Pakistan and called the flooding the result of climate change, stating on Sept. 9, "We have waged war on nature, and nature is striking back, and striking back in a devastating way."
  • Pakistan's government has blamed the disaster on climate change, a claim the study's authors said has merit to it.

Zoom in: The new analysis comes from 26 members of the World Weather Attribution group, which is a loose-knit international team of climate researchers.

  • They looked at the rains that fell in Pakistan, and simulated the event both with and without current levels of greenhouse gases in the atmosphere.
  • The researchers focused specifically on two time periods, the 60-day stretch of heaviest rains across the Indus River basin between June and September, and a five-day stretch of torrential rains in the southern provinces of Sindh and Balochistan.
  • Sindh and Balochistan both had their wettest Augusts on record, with seven to eight times their typical monthly totals, the study notes.
  • Natural variability associated with the monsoon prevented clear results from the 60-day rainfall totals, but the conclusions were drawn regarding the five-day totals.

Yes, but: This disaster wasn't caused by heavy rains alone. The highly vulnerable population also played a major role, with high poverty rates, an unstable government and lack of an effective early warning weather system serving to worsen the disaster.

Of note: Interestingly, an extreme heat event, itself tied to climate change, may have helped set up the rains, in an example of a compound climate disaster.

  • The Asian Monsoon is triggered each summer by the differential heating between the land mass of South Asia, and the waters of the Bay of Bengal and Indian Ocean to the south.
  • This past spring, Pakistan and India experienced a record-breaking heat wave, which increased land surface temperatures.
  • The extreme heat, with temperatures exceeding 120°F, intensified an area of low pressure, known as a "heat low," over Pakistan, according to Fahad Saeed, a researcher at the Center for Climate Change and Sustainable Development in Islamabad and coauthor of the new study.
  • This may have helped to draw more moisture northward, toward India and Pakistan, he said.

What they're saying: "I think climate change is an important driver insofar as we do see quite a large increase in the intensity of this event," said Friederike Otto, of Imperial College in London, the lead author of the study.

  • "Up to 50 or 75% increase in intensity of rainfall is huge and especially in a region that is very vulnerable," she said.
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