Abstract
The United States of America (USA) experiences the most tornadoes of any nation in the world, with these extreme weather events causing many deaths and billions of dollars of damage each year. With the recent warming of the climate due to human activity, it is likely that the occurrence of USA tornadoes will be affected. However, exactly how the spatial and temporal distribution of tornadoes in the USA will be affected by climate change is still an area of active research. The trends in the literature show that as the climate has warmed, there has been an observed clustering of USA tornadoes onto fewer, more active tornado days, as well as an eastward movement of the average centre of USA tornado activity. This review shows that these observed changes could be explained by shifts in environmental parameters related to tornado formation due to anthropogenic climate change. This research will allow for better tornado preparedness and prediction in tornado-affected areas as the climate warms. Future research may focus on more precisely modelling the impacts of global warming on USA tornado occurrence by using higher-resolution climate models.
Highlights
A tornado is a violently rotating column of air, originating from a thunderstorm, that makes contact with the ground (Guo et al, 2016), with supercellular tornadoes being the most powerful and destructive type
Strong tornadoes occur in the south-eastern United States of America (USA), outside of the Great Plains, where they tend to form from high wind shear, low-convective available potential energy (CAPE) supercells; these remain poorly understood in the literature (Wade and Parker, 2021)
Moore (2017a) found that this overall increase was primarily due to a statistically significant increase in the number of tornado days with 30+ tornadoes, with a corresponding decrease in tornado days with 1–10 tornadoes per day in the USA from 1974 to 2014. These concurrent trends have caused the mean number of tornadoes per tornado day to have increased from 3.75 from 1975 to 1980 to 5.46 from 2010 to 2014 (Moore, 2017a). These findings indicate that, since the 1970s, tornadoes in the USA have been tending to cluster together on fewer tornado days, with each tornado day producing more tornadoes on average
Summary
A tornado is a violently rotating column of air, originating from a thunderstorm, that makes contact with the ground (Guo et al, 2016), with supercellular tornadoes being the most powerful and destructive type. Central plains of the USA allow for warm, moist air from the Gulf of Mexico to be overlain by cooler, dryer continental air from higher elevations to the west, causing temperatures to decrease rapidly with height (Schultz et al, 2014) This strong vertical temperature gradient results in a high convective available potential energy (CAPE), which is a measure of how likely air is to rise and form a thunderstorm, with higher CAPE values generally resulting in stronger storms (Brooks et al, 2014). At the mid-latitudes where the USA is located, there is a large change in wind speed with altitude called ‘wind shear’, which is essential for generating the rotating mesocyclone that characterises supercells This combination of high CAPE and high wind shear in the Great Plains of the central USA makes the area well suited to generating powerful tornadoes. It will analyse recent research to uncover possible mechanisms for how anthropogenic climate change could be causing the observed changes in the tornado record
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