The Arabian Sea is like a giant battery that releases heat through rain. Usually it warms up gradually, but sometimes the water gets a few degrees hotter than normal, and the monsoon goes haywire. These events are called marine heatwaves, and they act like a conductor suddenly speeding up the whole orchestra.
Scientists looked at satellite images spanning forty years and found two causes of overheating. Short heatwaves, lasting about nine days, occur when winds die down over the sea and clouds clear away: the sun beats down as if on a pot without a lid, and evaporation nearly stops. Long heatwaves, lasting more than three weeks, come from afar, fueled by El Niño in the Pacific Ocean.
Such a vortex in the eastern part of the sea intensifies downpours in India, while in the north it affects Pakistan. Before the 2022 floods in Pakistan, the water had indeed overheated, and the heaviest rains came ten days after the peak. Now that we understand how this works, we can warn people about flood risks in advance.
The 2022 Pakistan flood affected about 33 million people and claimed nearly 1500 lives. The marine heatwave that preceded it peaked just ten days before the heaviest rains.
In Kim Stanley Robinson's novel The Ministry for the Future, extreme heat in India triggers a chain of climate catastrophes. In the book, the Arabian Sea also becomes a source of destructive monsoons, echoing the mechanism described in this paper.