Ocean and land forcing of the record-breaking Dust Bowl heatwaves across central United States

Tim Cowan,Friederike E L Otto,Robert Vautard,Aglaé Jézéquel,Andrew Schurer,Simon F B Tett,Gabriele C Hegerl,Luke J Harrington,Pascal Yiou,Benjamin Ng

doi:10.1038/s41467-020-16676-w

Abstract

The severe drought of the 1930s Dust Bowl decade coincided with record-breaking summer heatwaves that contributed to the socio-economic and ecological disaster over North America’s Great Plains. It remains unresolved to what extent these exceptional heatwaves, hotter than in historically forced coupled climate model simulations, were forced by sea surface temperatures (SSTs) and exacerbated through human-induced deterioration of land cover. Here we show, using an atmospheric-only model, that anomalously warm North Atlantic SSTs enhance heatwave activity through an association with drier spring conditions resulting from weaker moisture transport. Model devegetation simulations, that represent the wide-spread exposure of bare soil in the 1930s, suggest human activity fueled stronger and more frequent heatwaves through greater evaporative drying in the warmer months. This study highlights the potential for the amplification of naturally occurring extreme events like droughts by vegetation feedbacks to create more extreme heatwaves in a warmer world.

Highlights

The severe drought of the 1930s Dust Bowl decade coincided with record-breaking summer heatwaves that contributed to the socio-economic and ecological disaster over North America’s Great Plains
The underlying decadal sea surface temperatures (SSTs) anomalies in the 1930s resembled the warm phases of the Atlantic Multidecadal Oscillation (AMO)[16,17] and the Pacific Decadal Oscillation (PDO)[18,19] (Fig. 1b)
Supported by the Hadley Centre Global Environment Model version 3 (HadGEM3) results (Fig. 2) and consistent with unforced Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations (Fig. 1), this study reveals that Atlantic SSTs were an important factor in the Dust Bowl heatwaves, enhancing spring drought, and allowing heat to develop earlier over the central US3,6

Summary

Introduction

The severe drought of the 1930s Dust Bowl decade coincided with record-breaking summer heatwaves that contributed to the socio-economic and ecological disaster over North America’s Great Plains. Using idealised AGCM simulations, we find that warm Atlantic SST anomalies lead to more frequent Dust Bowl heatwaves over southern–central US than in simulations forced with historical Pacific SST anomalies This results from a stronger drying in the spring months, stemming from weaker moisture transport from the Gulf of Mexico, leading to a preconditioning of the land surface for extreme summer heatwaves. We use a set of baresoil simulations to analyse the extent to which 1930s land-use changes amplified the heat This reveals the strong sensitivity of heatwaves to increasing bare soil, and supports the hypothesis that the Dust Bowl heatwaves (and partly the drought) were amplified by rapid devegetation and exposed soil from human activities

Methods

Results

Conclusion