Tibetan Plateau warming-induced abnormal distribution of south Asian monsoon precipitation contributes to Pakistan's fatal flood in 2022

Devastating floods in July-August 2022 led to one-third of Pakistan being under water. The rainfall over Pakistan in these months was extreme—four to six times the 30-year average. We investigate the cause of this historically unprecedented flooding and extreme rainfall using station measurements and reanalysis datasets. In July-August 2022 there was an abnormal distribution of south Asian summer monsoon (SASM) precipitation characterized by more precipitation in Southern Pakistan and Central India but less precipitation in the south of the western Tibetan Plateau. The abnormal distribution of monsoon rainfall was dominated by the weakening of the 200-hPa northern westerly winds and SASM, and associated with anomalous westward moisture transport in the south of the Tibetan Plateau. Moreover, the temperature of the western Tibetan Plateau reaches its peak in 2022. The “heat pump effect” of the Tibetan Plateau led to positive geopotential height anomalies over Pakistan and the western Tibetan Plateau in the mid-to-upper troposphere. This blocked the 200-hPa northern westerly winds and shifted them northward. At the lower troposphere, the easterly winds are enhanced, and the SASM is suppressed. Furthermore, the Tibetan Plateau warming caused increased glaciers melt and large amounts of meltwater that feed the upper Indus River and worsened the floods. In the context of global warming, summers temperatures and melting will increase in the Tibetan Plateau. Our results indicate that this will cause massive flooding over Pakistan, such as in 2022, to become a common occurrence.