Extreme winter-spring drought in Southwest China in 2023: response to the phase transition from La Niña to El Niño

Abstract During January–May 2023, an extreme prolonged drought dominates Southwest China, which caused a severely damage of local water availability, power supply and productivity in Yunnan Province. It is noted that the initiation and maintenance of this extreme drought was concurrent with phase transition from La Niña into El Niño. We demonstrate that this severe drought event was partly attributed to the relay influences of La Niña and El Niño evolution. The anomalous enhanced cyclone over the western North Pacific (WNP) associated with mature La Niña triggered anomalous downwards motion and reduced moisture supply to Southwest China, contributing to drought initiation. As the La Niña decay, the anomalous WNP cyclone gradually weakened in late winter and early spring. Moreover, the eastwards shifting of anomalous WNP cyclone intensified by the El Niño developing and maintained anomalous northerlies in this region. The preceding winter La Niña favored the prolonged MJO activities over the tropical western Pacific in late spring, which re-intensified anomalous WNP cyclone and aggravated drought in Yunnan. The local extreme droughts are a footprint over Southeast Asia, showing a few months predictability as a possible response to the transition from the phase of La Niña to El Niño. This is supported by the similar extreme droughts in history during phase transition from La Niña into El Niño.