Tropical Pacific Ocean Influence on Recent Changes in Summer Rainfall Over the Yangtze–Huai River Valley

Abstract

Summer rainfall over the Yangtze–Huai River valley (YHRV) exhibits prominent decadal variability, and understanding the underlying mechanisms of this variability is essential for improving climate predictions and disaster prevention strategies in the region. Despite extensive research, the recent changes in YHRV's summer rainfall since the late twentieth century and their driving factors remain unclear. Analysis of observational precipitation data reveals a three-stage decadal variation over the past three decades, with two major shifts occurring in the late 1990s and mid-2010s. These variations are strongly influenced by the tropical central and eastern Pacific Ocean, which has experienced a “warm–cold–warm” decadal variation during this period. During the 1990s, warming in the tropical central and eastern Pacific induced a meridional wave train extending from the western North Pacific to East Asia through the Pacific–East Asia teleconnection, leading to a weakened East Asian summer monsoon (EASM) and enhanced summer rainfall in the YHRV. Since the late 1990s, the tropical central and eastern Pacific has turned from warm to cold, intensifying the EASM and resulting in a substantial shift in rainfall toward a pattern opposite to that of the 1990s. By the mid-2010s, as the tropical central and eastern Pacific cooled again, the rain belt retreated southward to the YHRV, leading to widespread summer rainfall increases across the YHRV since the mid-2010s. Pacemaker simulations, nudging observed time-evolving sea surface temperature (SST) anomalies in the tropical Pacific Ocean, capture well the two major rainfall shifts, providing compelling evidence that the tropical Pacific Ocean plays a key role in driving recent decadal changes in summer rainfall over the YHRV.