The Impacts of ‘Business as Usual’ Climate Change on Supercell Thunderstorms

Supercell thunderstorms tend to occur most frequently in the Great Plains of the United States and are often responsible for extreme severe weather, including the majority of violent tornadoes. The influence of anthropogenic climate change (ACC) on severe weather is the subject of much ongoing research, which has linked ACC with generally higher convective available potential energy (CAPE) and lower vertical wind shear over the Great Plains, resulting in a net increase in favorable severe weather days. However, the covariance between CAPE and shear changes with ACC is not fully understood, nor are changes in convective initiation. Crucially, the impacts of ACC on supercell characteristics such as intensity, lifetime, ability to produce severe hazards, or their governing dynamical processes, is not clear.

This study explores how ACC’s impact on the mesoscale environment around future supercells will influence supercell frequency, storm scale characteristics, behavior, and dynamical processes through examination of output from two 13 year dynamically downscaled convective resolving simulations following the Pseudo Global Warming methodology. One simulation is governed by ‘modern’ climate conditions, while the second contains ‘future’ conditions at the end of the 21st century following the high end RCP8.5 scenario (‘business as usual’) emission projection. Uniquely, each individual model-resolved supercell was identified and tracked throughout its lifetime in both datasets, providing a modern and future supercell ‘climatology’. Corresponding climatological attributes and mesoscale environmental data were collected for each supercell in these datasets, as well as a variety of supercell characteristics, including supercell lifetime and intensity. A series of statistical tests were conducted to compare the distributions of these characteristics and the local inflow environments of the modern and future supercells. Initial results suggest future supercells are seen more frequently in March-April with little change in May-June, in line with previous research. A strong eastward shift in occurrence of springtime supercells is also identified, but this is not collocated with strongest increases in severe weather parameters; a change in initiation mechanism is hypothesized to cause this shift. Thus, this research will identify how ACC will cascade down to the convective scale, thus providing a more explicit picture into the sensible impacts of climate change.