Abstract
Understanding the trend of localized severe weather under the changing climate is of great significance but remains challenging which is at least partially due to the lack of persistent and homogeneous severe weather observations at climate scales while the detailed physical processes of severe weather cannot be resolved in global climate models. Based on continuous and coherent severe weather reports from over 500 manned stations, for the first time, this study shows a significant decreasing trend in severe weather occurrence across China during the past five decades. The total number of severe weather days that have either thunderstorm, hail and/or damaging wind decrease about 50% from 1961 to 2010. It is further shown that the reduction in severe weather occurrences correlates strongly with the weakening of East Asian summer monsoon which is the primary source of moisture and dynamic forcing conducive for warm-season severe weather over China.
Highlights
It clearly shows that South China is the most-prolific thunderstorm-producing region with some stations reporting an average of more than 80 days per year
Motivated by the apparent positive correlations between the changes in local severe weather occurrence and the change in the East Asian summer monsoon index, we further examine the mean changes in the large-scale circulation and thermodynamic environmental conditions during the warm season derived from the same global reanalysis dataset
Consistent with changes in the low-level monsoonal trough, jet and moisture, and more pertinent to productivity of localized severe weather, there are considerable reductions over broad areas of China in the moist instability (indicated by convective available potential energy (CAPE) in Fig. 4c) and dynamic forcing (indicted by the 0–1-km low-level vertical wind shear in Fig. 4d) from the first half (1961–1985) to the second half (1986–2010) of the study period
Summary
The large decreasing trend occurs over almost every month but in particular during the peak season from May to September (Fig. 2b); these warms-season months account for 84% of the annual mean total number of thunderstorm events.
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