Reconstructing land surface processes of the 1930s Dust Bowl drought, U.S. Great Plains.

Abstract

Mineral dust aerosols are a key component of the Earth system and a growing public health concern under climate change as levels of dustiness increase. The U.S. Great Plains is particularly vulnerable to dust episodes, but land-atmosphere feedbacks contributing large-scale dust particle transport are poorly constrained, introducing uncertainty in future dust-borne risks to air quality and drought persistence. The 1930s Dust Bowl drought (DBD) is a well-studied, historical example of extreme climate variability. A leading hypothesis to explain the intensity of the DBD is landscape denudation associated with agriculture. However, historical reanalysis indicates that ~30% of the Great Plains was cultivated in the 1930s, thus human agency as the ultimate cause of degradation has been questioned. This work explores the surface processes and meteorological conditions influencing dust particle emission and eolian transport from historical aerial photographs and archival records of the Soil Conservation Service, combined with contemporary field surveys using a Portable In-Situ Wind Erosion Laboratory (PI-SWERL). Over 40% of the variance in DBD dust storms is explained by air temperature at the surface and 850 hPa and relative humidity at 850 hPa, highlighting the impact of elevated temperatures and spring precipitation deficits associated with 1930s heatwaves. The dominant sources of degradation found for sites east of the 100th meridian are cultivated fields and fluvial deposits. For sites to the west, denuded surfaces are predominantly eolian sandsheets and dunes, correlated with intensity of drought conditions and reduced plant diversity. Discrete spatial signatures of the drought are observed not only within the classically recognized southern Dust Bowl area, but also in the northern and central plains. The PM₂.₅ and PM₁₀ emissivity estimates for a single dust event with winds over 6 m s⁻¹ in the study area were 510-4,514 μg m⁻³ d⁻¹ and 4,700-41,607 μg m⁻³ d⁻¹ respectively, similar in magnitude to current dust storm events from North Africa and East Asia. Drought frequency is forecast to increase in late 21st century, potentially with greater severity than the DBD, and may be associated with magnitude increase in atmospheric dust loads.