Amplification of the North American “Dust Bowl” drought through human-induced land degradation

Abstract

The ''Dust Bowl'' drought of the 1930s was highly unusual for North America, deviating from the typical pattern forced by ''La Nina'' with the maximum drying in the central and northern Plains, warm temperature anomalies across almost the entire continent, and widespread dust storms. General circulation models (GCMs), forced by sea surface temperatures (SSTs) from the 1930s, produce a drought, but one that is centered in southwestern North America and without the warming centered in the middle of the continent. Here, we show that the inclusion of forcing from human land degradation during the period, in addition to the anomalous SSTs, is necessary to reproduce the anomalous features of the Dust Bowl drought. The degradation over the Great Plains is represented in the GCM as a reduction in vegetation cover and the addition of a soil dust aerosol source, both consequences of crop failure. As a result of land surface feedbacks, the simulation of the drought is much improved when the new dust aerosol and vegetation boundary conditions are included. Vegetation reductions explain the high temperature anomaly over the northern U.S., and the dust aerosols intensify the drought and move it northward of the purely oceanforced drought pattern. When both factors are included in the model simulations, the precipitation and temperature anomalies are of similar magnitude and in a similar location compared with the observations. Human-induced land degradation is likely to have not only contributed to the dust storms of the 1930s but also amplified the drought, and these together turned a modest SSTforced drought into one of the worst environmental disasters the U.S. has experienced. dust aerosols ͉ land surface feedbacks

A 1,200-year perspective of 21st century drought in southwestern North America

“…Conversion of desert and grassland to cropland, grazing, fire suppression, introduction of invasive species, disturbances leading to soil erosion and blowing dust, and the development of urban areas have all likely had impacts on regional climate. No systematic studies on these land cover changes and their impacts on climate or drought have been undertaken (68), but these changes are another important reason that droughts of the past are unlikely to be an exact analogue for current and future droughts. In addition, from an impacts standpoint, droughts have a much broader range of impacts on human activities today than in the past because of today's greater demands on limited water resources.…”

Intensification of North American Megadroughts through Surface and Dust Aerosol Forcing*

“…While several papers have speculated that these landscape changes may have amplified these droughts (Feng et al 2008;Seager et al 2008b), only one study to date has explicitly tested surface impacts on the megadroughts within a modeling framework (Cook et al 2011). They found that vegetation mortality alone (i.e., without wind erosion or dust feedbacks) was insufficient to amplify the modelsimulated droughts or reproduce the drought persistence seen in the paleorecord.…”

“…Despite the JJA focus of the NADA, PDSI has a memory time scale of about 12-18 months (Guttman 1998;Vicente-Serrano et al 2010), allowing it to incorporate information on temperature and precipitation throughout the year. PDSI from the NADA has been used with good success to validate and inform a variety of modeling studies investigating historical and paleo-droughts over North America (e.g., Cook et al 2011;Herweijer et al 2006Herweijer et al , 2007Oglesby et al 2012;Seager et al 2008a). …”

“…For example, the central plains has long been considered a ''hot spot'' for positive soil moistureprecipitation feedbacks (e.g., Findell et al 2011;Koster et al 2004;Meng and Quiring 2010). More recently, work on the Dust Bowl drought of the 1930s demonstrated that land degradation, in the form of vegetation mortality, wind erosion, and dust aerosols, could amplify regional drought over the central plains when these processes were included in a suite of climate model experiments (Cook et al 2008(Cook et al , 2009). Specifically, these two studies found that dust aerosols and reduced vegetation cover caused significant warming and drying, increasing the fidelity of their simulated Dust Bowl temperature and precipitation anomalies.…”

“…They found that vegetation mortality alone (i.e., without wind erosion or dust feedbacks) was insufficient to amplify the modelsimulated droughts or reproduce the drought persistence seen in the paleorecord. Here, we expand on the experiments of Cook et al (2011), presenting a new ensemble of simulations including wind erosion and dust aerosol forcing. We frame our analysis around two questions: 1) can forcing from dune mobilization, conceptualized as reduced vegetation coverage and a dust aerosol source, intensify simulated megadroughts over the central plains and 2) does inclusion of these surface factors increase the simulated persistence of these megadroughts?…”