Human-caused climate change may have played a role in the deadly floods that submerged parts of Pakistan in recent weeks, according to an analysis looking at how much global warming was to blame for this extreme event.
Researchers from the World Weather Attribution group say climate change may have increased the intensity of rainfall. However there were many uncertainties in the results, so the team was unable to quantify the scale of the impact.
The team, including scientists from Pakistan, India, the Netherlands, France, Denmark, South Africa, New Zealand, the US and the UK, used published, peer-reviewed methods to perform an event attribution study.
The researchers focussed on two aspects of the event: The annual maximum of the mean 60-day precipitation during June-September over the Indus river basin, and the annual maximum of the mean 5-day precipitation in June-September over the worst hit provinces Sindh and Balochistan.
Pakistan received more than three times its usual rainfall in August, making it the wettest August since 1961. The resulting floods killed over 1,500 people, affected more than 33 million people and destroyed 1.7 million homes.
The two southern provinces, Sindh and Balochistan, each experienced their wettest August ever recorded, receiving 7 and 8 times their usual monthly totals, the report said.
"The flooding occurred as a direct consequence of the extreme monsoon rainfall throughout the summer 2022 season exacerbated by shorter spikes of very heavy rain particularly in August hitting the provinces Sindh and Balochistan," the authors of the study noted.
"The devastating impacts were also driven by the proximity of human settlements, infrastructure, and agricultural land to flood plains, inadequate infrastructure, limited reduction capacity, and an outdated river management system," they said.
The report also pointed out underlying vulnerabilities driven by high poverty rates and socioeconomic factors, and ongoing political and economic instability contributed to the impacts of the floods.
The researchers noted that the 5-day maximum rainfall over Sindh and Balochistan is now about 75 per cent more intense than it would have been had the climate not warmed by 1.2 degrees Celsius.
The 60-day rain across the basin is now about 50 per cent more intense, meaning rainfall this heavy is now more likely to happen, they said.
However, the report noted that there are large uncertainties in these estimates due to the high variability in rainfall in the region, and observed changes can have a variety of drivers, including, but not limited to, climate change.
To determine the role of human-induced climate change in these observed changes, the team looked at the trends in climate models with and without the human-induced increases in greenhouse gases.
The regions involved are at the western extreme end of the monsoon region, with large differences in rainfall characteristics between dry western and wet eastern areas.
However, for the 5-day rainfall extreme, the majority of models and observations the researchers analysed show that intense rainfall has become heavier as Pakistan has warmed, according to the researchers.
Some of these models suggest climate change could have increased the rainfall intensity up to 50 per cent for the 5-day event definition, they said.
"Looking at the future, for a climate 2 degrees Celsius warmer than in preindustrial times, models suggest that rainfall intensity will significantly increase further," the authors said.
"Our results are in alignment with recent Intergovernmental Panel on Climate Change (IPCC) reports," they added.