Climate impacts and future trends of hailstorms in China based on millennial records

Understanding how hailstorm trends have changed in the context of climate change is a persistent challenge, mainly because of the lack of long-term consistent observations of hailstorms. Here, we leverage hail damage records from Chinese historical books and extend hailstorm records to approximately 2890 years ago, exploring variations in the number of hailstorm days between 1500 and 1949 based on reliable and consistent data. We show that the number of hailstorm days was constant before 1850, but has increased significantly afterwards. This increase in hailstorm days seems to be associated with the increase in surface temperature after the population effect is removed. In addition to the trend, hailstorm activity is found to display both quasicentennial and multidecadal variability, with the former (later) dominating before (after) the 1850s, driven by the Pacific Decadal Oscillation (PDO). These results suggest that long-term changes in hailstorm days in China are modulated by climate warming and natural variability, via the PDO. Future projections based on different climate change scenarios and a convolutional neural network model show a further increase in the number of hailstorm days in the 21^st century.