Why did the Deep South have devastating tornadoes?
The 13th January 2023 saw a devastating swarm of #tornadoes (at least 35) sweep through the US’s Deep South, killing at least 9 people and leaving behind a trail of destruction in #Georgia and #Alabama. As this article is being written, recovery efforts are on-going and unfortunately, it is likely that more bodies will be recovered. Such events are not rare in this part of the US, but they do seem to be increasing. Most tornadoes until now, in North America, have happened a little further to the northwest in a region called Tornado Alley, centred largely on Texas, Oklahoma, Nebraska and Kansas (remember the Wizard of Oz?)
Tornado destruction in Alabama (13 January 2023). Source.
Tornado Alley. Source.
So why are these regions so prone to tornadoes and are we getting more?
In North America, tornadoes usually form from large storms called “Supercells” and these are common over the Midwest United States (i.e. including Tornado Alley) for a couple of reasons. Firstly, the region is flat, meaning that wind speeds can build up rapidly given that there are few obstacles in the way. Secondly, the region sits right at the meeting point of warm, moist air from the Gulf of Mexico (to the south) and cool, dryer air from the Rocky Mountains to the west and the Canadian Plains to the north. This meeting causes the warmer, moist air mass to rise, generating supercell storms and, where the wind speed difference between the surface and the upper levels (termed wind-shear) becomes significant, rotations in the atmosphere can form that lead to tornadoes when uplifted (see below).
Wind shear and generation of atmospheric rotations that lead to tornadoes. Source.
Given that tornadoes are a meteorological phenomenon influenced by the prevailing climate, it is possible that as the climate changes, we could get more of them. The science behind such a hypothesis is simple: a warmer climate will lead to more evaporation and water entering the atmosphere and, in turn, more potentially tornado-forming storms. The conclusions based on evidence linking a changing climate and tornado frequency, however, are not clear cut, as not all storms generate tornadoes, although the evidence does seem to point towards an increased frequency in severe storms (Lapore et al. 2021). Other recent research (Haberlie et al. 2022) in contrast, has shown that the southeast US (including the Deep South and the region affected by yesterday’s tornadoes) is likely to experience an increased frequency of thunderstorms while the Midwest may experience a reduction. The reason for this is directly related to a warming climate: if the air-masses from the Rockies and Canadian Plains are warmer (and also dryer), temperature contrasts will be lower and storms will be less intense and/or fewer in number. Such conditions will result in higher pressure conditions over the Midwest, forcing storms further towards the southwest and the Deep South.
Is there anything we can do to reduce the impact?
Short of stopping climate change (that’s a whole other story), the best thing that can be done is to ensure that regions not used to experiencing tornadoes so frequently are better prepared for them. Most US weather-monitoring organisations monitor storms for intense conditions that could lead to tornadoes developing, and they have access to Doppler Radar facilities which are capable of detecting tornadoes once they have formed. Such detections however, need to feed directly into warning systems so as to give the public time to take appropriate actions; facilities in turn, need to be available for the public to allow for such appropriate actions (e.g. the provision of tornado shelters for mobile-home parks).
Tornado shelter in Kansas. Source.
So the tragic swarm of tornadoes affecting the Deep South yesterday may, unfortunately, become a more common event as the climate continues to change. The region may need to adapt to this increased risk and people become more prepared for such eventualities.