The variations of summer days and frost days in the Yangtze River Basin and their influencing factors

The Yangtze River Basin has always been one of China's most densely populated regions and one of the most active in agricultural activities. Although previous studies have examined extreme climate events in the Yangtze River Basin, the main factors influencing the long-term changes in the region’s key agricultural frost days (FD) and summer days (SU) are unclear. In this study, we analyze the variations of FD and SU in the Yangtze River Basin and explore the dominant factors driving the long-term changes in these two climate indices. The key findings are as follows: FD and SU show a downward and upward trend, with rates of − 0.88 days/decade and 0.65 days/decade in the Yangtze River Basin during 1961 − 2020, respectively. The significant weakening of the Asian Polar Vortex and the strengthening of the Northwest Pacific Subtropical High Pressure reduce FD and increase SU, respectively. In addition, the less FD in winter is closely linked to more SU in summer. We highlight that Kuroshio Current Sea Surface Temperature serves as a crucial connection between the less FD in winter and the more SU in summer over the Yangtze River Basin. Furthermore, global warming will significantly amplified the extreme temperature changes observed during the winter and summer.