The interannual variability of the day-night compound hot days in the Yangtze River Basin: dynamic origins and seasonal predictability

Abstract

Day-night compound hot days (CHDs) poses substantially greater risks to human health, ecosystems, and socioeconomic systems than that heat extremes occurring only during the day or night. Here, we investigate the spatiotemporal characteristics, physical mechanisms, and seasonal predictability of CHDs within the Yangtze River Basin (YRB), a recognized hotspot for CHDs in China. We show that CHDs are primarily associated with a local anomalous barotropic high-pressure/anticyclone, which is jointly influenced by a La Niña-like sea surface temperature pattern in the Pacific and a positive sea level pressure tendency over the North Atlantic through distinct atmospheric teleconnections. Based on these two physically interpretable ocean-atmosphere precursors, we develop a physics-based empirical model using data from 1980 to 2010. During the independent validation period of 2011–2022, the model exhibits substantial prediction skill, with a temporal correlation coefficient of 0.67. Nevertheless, it markedly underestimates the record-breaking CHDs in 2022. A comparison with 2013, when the second-highest CHDs was successfully predicted, revealed that land-atmosphere interactions, including the soil moisture-temperature positive feedback and the cloud-water vapor warming effects in the YRB, significantly amplified the CHDs in 2022. Because these land-atmosphere processes are not represented in the model, the exceptional severity of the 2022 CHDs is underestimated.