Seasonal predictability of the extreme Pakistani rainfall of 2022 possible contributions from the northern coastal Arabian Sea temperature

During the summer of 2022, Pakistan and northwestern India were hit by an unprecedented spell of heavy rainfall. Despite capturing major tropical climate anomalies, almost all seasonal prediction systems failed to predict the extreme event, far surpassing the 2010 event. While trying to find possible causes of such a failure through an analysis of inter-member anomalies and numerical experiments, we have discovered that the positive sea surface temperature anomalies in the northern coastal Arabian Sea were one of the key factors behind the event. Although the ensemble mean prediction by the original system captured only 7% of the observed precipitation anomalies over Pakistan, the sensitivity experiments, in which the model sea surface temperature in the northern Arabian Sea was nudged to observation, captured about 25% of the observed anomalies. Improving our ability to predict the conditions of the northern Arabian Sea will contribute to better forecasting of extreme rainfall events such as the one experienced in Pakistan in 2022. Further analysis and possible coordinated sensitivity experiments with multi-models are necessary for a better understanding and improving the prediction.

Takeshi Doi, Swadhin K. Behera, Toshio Yamagata