From CNN:
"The strongest thunderstorms, the strongest severe storms and tornadoes are likely to happen more often and be stronger," Del Genio said in an interview Thursday from his office at the Goddard Institute for Space Studies in New York. The paper he co-authored was published online this month in the journal Geophysical Research Letters. Other scientists caution that this area of climate research is too difficult and new for this study to be definitive. But some upcoming studies also point in the same direction.
Study: Global warming could bring more severe U.S. storms
Presumably, similar scenarios can be expected for other places – inc China, say, which this year has experienced several major thunderstorms associated with summer flooding.