Climatic Changes in the Twenty-Four Solar Terms Based on Temperature Observations Back to 1873

Twenty-four Solar Terms (24STs) have been widely used for guiding human activities in China over more than 2000 years. However, the implication of the conventional 24STs has been changing under global warming. The climatic 24STs proposed recently impose a time-varying characteristic on the conventional 24STs, thus they can better serve as guidance for people under current situation. Previous studies only focused on linear trend of the 24STs since 1960. In this study, climatic changes in the 24STs back to 1873 are analyzed based on homogenized daily temperature series at Beijing station for the period 1940-2017 and at Shanghai station for the period 1873-2017. The results show that the annual mean temperature as well as temperatures of the 24STs at Beijing station for the period 1941-2016 and at Shanghai station for the period 1874-2016 all show warming trends, thus resulting in advancing trends during the warming stage (around spring) and delaying trends during the cooling stage (around autumn) in the timings of the climatic Solar Terms in the seasonal cycle. Most of these trends are statistically significant. The occurrence of extreme cold days shows a significant decreasing trend at both stations of Beijing and Shanghai, whereas the occurrence of extreme hot days at Shanghai station shows a significant increasing trend. In addition to the long-term trend, there exists apparent multi-decadal variability with a period of 60-80 years in both the occurrence of extreme hot days and summer temperature at Shanghai station, which is correlated with the Atlantic Multi-decadal Oscillation. These results can provide an important scientific base for climate change adaptation and benefit the understanding of modern climatic warming in China from a perspective of fine evolution of the seasonal cycle.