Climate change contributes to the record-shattering 2022 Pakistan rainfall

From mid-June until the end of August 2022, a sequence of torrential rains and deluges pummeled Pakistan, displacing more than 30 million residents with a death toll of near 2000. The accumulated amount exceeds the centennial average of 126 mm by about 7 standard deviations (50 mm), reaching a value of 487 mm and breaking its record over a century. The extraordinary extremity underscores the urgency for understanding the physical drivers of the event and the relations with human-induced climate change.

Here, we find that distinctive from the historical floods which tend to occur over the relatively wet northern mountains, the 2022 rainfall took place over arid southern Pakistan. Unlike the floods over northern mountains which had closer associations with extratropical westerly troughs, the heavy downpours in 2022 were primarily initiated by the synoptic low-pressure systems (LPS). The longevity and intensity of LPS were sustained and enhanced by the cross-equatorial monsoon flow, which has trended upward since the 1970s and is at a historical high. In combination with the zonal inflow of moisture induced by La Niña, a corridor of heavy rainfall extending from the Bay of Bengal toward southern Pakistan formed.

The signal of greenhouse-gas-forced changes in the heavy rainfall over Pakistan and the cross-equatorial monsoon flow is detectable in climate models, confirming that the likelihood of such extreme events would increase under future warming.