Anatomy of the 2022 Scorching Summer in the Yangtze River Basin Using the SINTEX-F2 Seasonal Prediction System

In July and August 2022, the Yangtze River basin (YRB) experienced its hottest summer since 1961. The SINTEX-F2 seasonal prediction system initialized in early May predicted the hotter-than-normal summer due to its successful prediction of central Pacific La Ni & ntilde;a, negative Indian Ocean Dipole and the resultant warming in the tropical West Pacific-East Indian Ocean (TWP_EIO). The common SST forcing explains only about 26% to the heatwave strength, while the internal variations in the anomalous warming in the TWP_EIO and Europe, surplus precipitation in Pakistan, and local land-air interaction account for approximately 65%, based on the analysis of 108 ensemble members. These factors have collectively increased the maximum temperature over the YRB through the enhancement and westward expansion of western North Pacific subtropical high. Our findings quantify the relative contributions of external forcing and internal variations to the unprecedented hot event, offering insights into its forming mechanism and potential predictability. A record-breaking heatwave event occurred in the YRB in July and August 2022, posing significant risks on human health, power supply, and social economic activities. Recognizing the importance of such an event, our study aims to identify key factors influencing its prediction using the SINTEX-F2 system. The central Pacific La Ni & ntilde;a, negative Indian Ocean Dipole and the resultant warming in the TWP_EIO provide the dominant predictability, but accounts only about 26% of the heatwave strength. However, internal variations in the anomalous warming in the TWP_EIO and Europe, surplus precipitation in Pakistan, and local land-air interaction collectively explain about 65%. Our results suggest the necessity of large-ensemble prediction in capturing this kind of unprecedented extreme event. The SINTEX-F2 initialized on 2022 early May captures the warmer-than-normal air temperatures in Yangtze River basin The model successfully predicts co-occurrences of CP La Ni & ntilde;a and negative IOD in 2022 However, the direct SST forcing contributes only 26% to the 2022 extreme event in Yangtze River basin