Why was Pakistan extreme precipitation stronger in 2022 than in 2010?

Abstract

In Pakistan, five continuous extreme precipitation events in the summer (July‒August) of 2022 caused disastrous floods, depriving thousands of people's lives and ruining millions of hometowns. This tremendous disaster in Pakistan also happened in 2010 but with three concentrated extreme precipitation events in the middle of summer. The amount of Pakistan heavy daily precipitation in 2022 surpasses that in 2010 record, making it the strongest precipitation event ever recorded. To comprehensively understand the causes of extreme precipitation in Pakistan, this study investigated the anomalies in atmospheric circulation and moisture contribution of 2010/2022 extreme precipitation and compared their differences. The results show that an atmospheric blocking over northern Europe in both 2022 and 2010 enhanced convection in Pakistan by transporting cold‒dry air from the high-latitude region and benefiting warm‒wet monsoonal air marching to Pakistan. By employing a moisture track model, the main moisture sources for summer precipitation in Pakistan were identified. It is found that moisture contributions except from Eurasia were enhanced, causing extreme precipitation. In particular, enhanced moisture contribution from the southern Indian Ocean and the northern Indian continent in 2022 are more prominent than that in 2010. The increased moisture contribution in 2010 was due to increased evaporation induced by warming sea surface in the Indian Ocean, while much richer moisture transport in 2022 was attributed to the enhanced cross‒equatorial flow induced by the anomalous subtropical high in the Southern Hemisphere. Therefore, attention should be paid to the role of subtropical high in the Southern Hemisphere in addition to those in Northern Hemisphere in understanding disastrous extreme precipitation events in Pakistan.