The visible footprint of climate change on Pakistan’s floods

The analysis carried out by World Weather Attribution slips that global warming increased the severity of this meteorological phenomenon. However, there are doubts about its impact because the models applied do not reflect the variability of the territory.

The destruction of almost 2 million homes and 1,000 deaths is the toll left by the South Asian monsoon that flooded Pakistan in recent weeks. And there is a high probability that climate change will intensify this phenomenon.

The suspicions stem from the findings of a new analysis by the World Weather Attribution network of scientists, who use climate models, weather observations and other tools to determine whether global warming increased the likelihood or severity of recent extreme weather events.

However, in this case, it is not clear to what extent climate change played a role.

It is relatively simple to conduct an attribution study that assesses the influence of warming on heat waves, where higher average temperatures raise the baseline from which these suffocating phenomena start.

This group has calculated precisely how much climate change altered the odds of the scorching Pacific Northwest heatwave last year, saying such conditions would be “at least 150 times rarer without human-induced climate change.” It also analysed Britain’s recent heatwave and concluded that climate change made it “at least 10 times more likely”, while that of Pakistan and India earlier this year became “30 times more likely”.

But the researchers noted in a news release that using climate models to identify the role of global warming in amplifying the monsoon season proved more complicated. World Weather Attribution attributed the uncertainty to a combination of the large variability in heavy rainfall patterns over long periods, natural processes that models may not fully capture, as well as the climatic peculiarities of the territory. The Indus River basin is located on the western edge of the region’s monsoon area, where there are large differences in rainfall trends between dry west and humid east.

On the other hand, meteorological records clearly show that the heaviest rainfall periods in the region have intensified in recent decades, by approximately 75% in the two most affected provinces. Some models found that climate change may have increased rainfall by as much as 50% during the five wettest days of the two-month monsoon season in those areas.

“So while it is difficult to give a precise figure for the contribution of climate change, the footprints of global warming are evident,” Friederike Otto, a senior lecturer in climate science at Imperial College London and one of World Weather Attribution’s leaders, wrote in a statement.

In a scientific paper published Thursday, the team of researchers noted that a combination of weather forces caused the extreme rainfall. They included the phenomenon dubbed “La Niña,” which cools the upper ocean waters and carries more rainfall than usual in much of the world, along with unusually warm spring and summer weather in Pakistan. Those elevated temperatures also accelerated the melting of the thousands of glaciers that feed the Indus River, though it’s unknown how much this contributed to the flooding.

Climate scientists have long warned that global rainfall patterns will become more irregular as the planet warms, making very wet and dry periods more common. Among other factors, warmer air retains more moisture, absorbs water from soils and plants, and alters atmospheric pressure systems. The UN’s Intergovernmental Panel on Climate Change projects that in the coming decades South Asia’s monsoons will become more variable from year to year, but will increase in overall intensity throughout the twenty-first century.

In addition, Pakistan’s heaviest rainy days are likely to become even more extreme as temperatures rise, according to World Weather Attribution. That highlights the need for the country to shore up its riverbanks, homes and other infrastructure to protect citizens, and for wealthy nations, which have produced a grossly disproportionate share of climate pollution, to do all they can to help.

Source: MIT Technology Review