Geographic Shift and Environment Change of U.S. Tornado Activities in a Warming Climate

Zuohao Cao,Guang J Zhang,Huaqing Cai

doi:10.3390/atmos12050567

Abstract

Even with ever-increasing societal interest in tornado activities engendering catastrophes of loss of life and property damage, the long-term change in the geographic location and environment of tornado activity centers over the last six decades (1954–2018), and its relationship with climate warming in the U.S., is still unknown or not robustly proved scientifically. Utilizing discriminant analysis, we show a statistically significant geographic shift of U.S. tornado activity center (i.e., Tornado Alley) under warming conditions, and we identify five major areas of tornado activity in the new Tornado Alley that were not identified previously. By contrasting warm versus cold years, we demonstrate that the shift of relative warm centers is coupled with the shifts in low pressure and tornado activity centers. The warm and moist air carried by low-level flow from the Gulf of Mexico combined with upward motion acts to fuel convection over the tornado activity centers. Employing composite analyses using high resolution reanalysis data, we further demonstrate that high tornado activities in the U.S. are associated with stronger cyclonic circulation and baroclinicity than low tornado activities, and the high tornado activities are coupled with stronger low-level wind shear, stronger upward motion, and higher convective available potential energy (CAPE) than low tornado activities. The composite differences between high-event and low-event years of tornado activity are identified for the first time in terms of wind shear, upward motion, CAPE, cyclonic circulation and baroclinicity, although some of these environmental variables favorable for tornado development have been discussed in previous studies.

Highlights

Tornadoes, as one of the most severe weather phenomena on Earth, can occur globally [1,2] especially in the United States, Canada, northern Europe, Bangladesh, China, Japan, Argentina, South Africa, Australia, and New Zealand
The Intergovernmental Panel on Climate Change (IPCC) and the United States Climate Change Science Program have recently begun to pay close attention to how a warming climate affects localized severe weather such as tornadoes [11,12], even though it is challenging to identify the influences of global warming on tornado activity [13,14]
To take into consideration the tornado intensity (i.e., EF scales) in the composite analyses of high and low tornado activity years, we introduce the concept of intensity weighted tornado number (IWTN)

Summary

Introduction

As one of the most severe weather phenomena on Earth, can occur globally [1,2] especially in the United States, Canada, northern Europe, Bangladesh, China, Japan, Argentina, South Africa, Australia, and New Zealand. The United States is ranked number one in terms of the total number of tornadoes with annual occurrences of more than 1000 in recent years [3]. The Intergovernmental Panel on Climate Change (IPCC) and the United States Climate Change Science Program have recently begun to pay close attention to how a warming climate affects localized severe weather such as tornadoes [11,12], even though it is challenging to identify the influences of global warming on tornado activity [13,14]. We focus on long-term changes of tornado activities in the U.S and their associated large-scale environments. We attempt to examine whether tornado occurrence variability in the U.S has increased and/or shifted in recent decades. We will investigate the spatial changes of tornado activity (counts and days) and their association with regional climate warming over the continental U.S

Methods

Results

Conclusion