Role of tropical-extratropical interactions in the unprecedented 2022 extreme rainfall in Pakistan: A historical perspective

Abstract

Pakistan experienced widespread floods that associated with two intraseasonal rainfall events in July–August 2022, resulting in significant loss of life and property. The study investigates the impact of tropical-extratropical interactions on extreme intraseasonal rainfall events over Pakistan in boreal summer. The intraseasonal rainfall events are identified and classified into extreme and moderate types based on their amplitudes. Both types of rainfall events were associated with the northward propagating Boreal Summer Intraseasonal Oscillation (BSISO). However, extreme events were accompanied by less coherent northward propagation of BSISO than moderate events. The Silk Road Pattern (SRP) teleconnection plays a critical role in extreme rainfall events over Pakistan. During extreme events, positive geopotential height anomalies and anticyclonic circulation at 200 hPa are observed in association with the slowly eastward and southward evolutions of the SRP. Positive temperature anomalies associated with the positive geopotential height anomalies extend southwestward from the upper-level to the low-level, leading to low-level heating and negative surface pressure over the Iran plateau. They further induce low-level moisture flux convergence and upward vertical motions over Pakistan, resulting in extreme rainfall. These features are not apparent during moderate events. The extratropical signals associated with the July 2022 intraseasonal rainfall event are similar to those composited results of extreme rainfall events, while reversed signals were observed for the August 2022 event. The outcomes of this study suggest that the intraseasonal variations of the SRP are crucial precursors for extreme rainfall over Pakistan.