Trends in hail and severe weather activities in China over the past 30 years under the changing monsoon climate

Based on exclusive station-by-station hourly-to-daily records of hails, lightning, damaging winds and heavy precipitation, we examine the frequency changes of severe and extreme convective weather activities in China over the past 30 years. In particular, it is found that there is a decline trend in the total number of hail and severe weather events over China over the past few decades but the changes vary from region to region. In particular, hail frequency in northern China and Tibetan Plateau decreases by 42 and 53 percent, respectively since the early 1980s while no clear trend in southern China. It is also found that hail duration, as well as intensity (in terms of maximum hail diameter) in China showed a significant decreasing trend in the northern China and Tibetan Plateau, while no rend in southern China from 1982 to 2012. The variation in hail activity is found to be associated with the variation of severe weather events across China. Preliminary analysis shows that the overall decreasing hail activity and severe convective weather over northern China might be attributable to the weakening Asia summer monsoon while the reduction of hail activity in Tibet Plateau might also be due to the increase in freezing-level height that is associated with global warming.