Impact of spring Tibetan Plateau snow cover on extreme precipitation in Pakistan in July and August 2022

Abstract

Record-breaking extreme precipitation occurred in July and August 2022 in Pakistan, causing flooding and landslides. In this study, the characteristics and mechanisms of these extreme precipitation events are investigated. The consecutive extreme precipitation events emerged in July and mid to late August. Precipitation above 500 mm occurred in the northern and southern regions of Pakistan, and the maximum precipitation was concentrated in the same regions. The diagnosis indicated that the precipitation extremes were closely tied to anomalous late spring snow cover in the western Tibetan Plateau. In July, owing to the reduction of late spring snow cover, the strengthened diabatic heating promoted the South Asian High (SAH) and its pumping effect, which contributed to abundant water vapor and strong southeasterly jet along the southwest Tibetan Plateau. Cooperating with the cyclone over Arabian Sea, extreme precipitation with a return period of 50 years occurred in Pakistan. In August, the SAH was an anomalously strong and eastward extension at 200 hPa. In the middle troposphere, the blocking high-pressure over western Russia was extremely active, and the West Pacific Subtropical High shifted anomalously westward, extending to the Tibetan Plateau. Cyclone anomalies occurred over the Arabian Sea and Bay of Bengal. With the atmospheric circulation anomaly, the southeasterly jet shifted southward, and water vapor was transported from the Arabian Sea and Bay of Bengal to south Pakistan, causing extreme precipitation with a return period of 30 years in August.