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There is increasing concern that local severe storm occurrence may be changing as a result of climate change. The Tibetan Plateau (TP), one of the world's most sensitive areas to climate change, became significantly warmer during recent decades. Since 1960 (1980), storm (hail) days have been decreasing by 6.2%/ decade (18.3%/decade) in the region. However, what caused the frequency changes of storm and hail in the TP is largely unknown. Based on 53-year continuous weather records at 48 TP stations and reanalysis data, we show here for the first time that the consistent decline of storm days is strongly related to a drier midtroposphere since 1960. Further analysis demonstrated that fewer hail days are driven by an elevation of the melting level (thermodynamically) and a weaker wind shear (dynamically) in a warming climate. These results imply that less storm and hail may occur over TP when climate warms.

Plain Language Summary How the severe storm, such as hail and thunderstorm, will respond to climate change remains uncertain. Particularly, the Tibetan Plateau, which experienced greatest hail frequency and also has one of the most frequent occurrences of severe storms in China, has been found to be one of the most sensitive areas to global climate change. In this work, we tried to explain the connection between the change of severe storm and the change of climate in the Tibetan Plateau. To do this, we used continuous and persistent weather phenomena reports recorded by professionally well-trained observers over the Tibetan Plateau and analyzed storm-related parameters using both sounding data and reanalysis data over half a century. We demonstrated that there was consistent decline of severe storm which is strongly related to a drier midtroposphere. Further analysis demonstrated that recent years with less hail days present higher melting level and weaker wind shear than those years with more hail days. These results provide us a better understanding of the response of severe storm to climate change and imply that there would be much less severe storm if warming continues in the near future in the Tibetan Plateau.