https://doi.org/10.1177/0959683617702235 The Holocene 1–11 © The Author(s) 2017 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0959683617702235 journals.sagepub.com/home/hol Introduction The 1930s Dust Bowl Drought (DBD) on the Great Plains, US, was an environmental crisis with agricultural and economic col- lapse, poor air quality, heightened respiratory illness, and the ultimate out migration of >350,000 people (Egan, 2006; Greg- ory, 2004; Hurt, 1981). There were hundreds of continent-wide dust storms during the 1930s with scores of individual storms that deposited soil-derived dust as far as Washington, DC (Hand, 1934), on ships 800 km off shore (Hurt, 1981), and increased tropospheric dust loads across the Northern Hemisphere, with likely dust deposition onto the Greenland ice cap (Donarummo, 2003). Recent climate modeling underscores the vulnerability of the Great Plains in the 21st century to extreme droughts, with drying forecasted to exceed historic conditions and with severity similar to decadal-scale megadroughts during the Medieval Cli- mate Anomaly (Cook et al., 2015; Dai, 2013) when many dune systems reactivated on the Great Plains (e.g. Forman et al., 2008; Halfen and Johnson, 2013; Hanson et al., 2010; Miao et al., 2007a, 2007b). The DBD was most severe between 1934 and 1936 with an average annual Palmer Drought Severity Index (PDSI) of -4 (Burnette and Stahle, 2013; Cook et al., 2014) which encom- passed the panhandle areas of Texas and Oklahoma, and adjacent lands in eastern Colorado and western Kansas. Climate modeling of the DBD indicated that higher dust loads resulted in stability of the boundary layer, suppressed warm season precipitation, and thus expanded the footprint and magnitude of drying (Cook et al., 2008, 2009, 2013). Furthermore, summer temperatures across Kansas were the hottest in the past 180 years with daily maxima exceeding 41°C (Burnette et al., 2010). A long-standing assumption is that the dusty conditions during this drought were a direct response to large-scale crop failure of a succession of small farms, which left fields barren and exposed sandy soils to eolian erosion (Bennett and Fowler, 1936; Cook et al., 2008, 2009, 2013; Hansen and Libecap, 2004; Johnson, 1947; Lee and Gill, 2015; Peters et al., 2007; Schubert et al., 2004; Worster, 1979), and these denuded soil surfaces were sources for atmo- spheric dust loading. Particularly severe dust storms, referred to as ‘black blizzards’, formed during passage of cyclones, Eolian processes and heterogeneous dust emissivity during the 1930s Dust Bowl Drought and implications for projected 21st-century megadroughts Kasey Bolles, 1 Steven L Forman 1 and Mark Sweeney 2 Abstract The 1930s Dust Bowl Drought on the US Great Plains was an environmental crisis with failure of agricultural systems, landscape denudation, and elevated atmospheric dust loads. Poor agricultural practices were implicated for triggering widespread eolian erosion and heightened dust emissions, but this assumption is called into question. This study classified land surface changes in southwest Kansas from aerial images taken in 1936 and 1939 to infer surficial processes, dust sources, and associated emissivity. In total, seven distinctive surface classes were identified from an ArcGIS analysis of spectral reflectance values connected to surface vegetation cover and eolian activity, demonstrating a strikingly heterogeneous landscape response to the drought. Stratigraphic studies indicate accumulation of up to 4 m of eolian sand in places with erosion of a subjacent silty pre-1930s soil surface. Potential dust emissivity estimates for particulate matter were derived from the distribution of classified land surfaces and from empirical relations on analogous dust- emissive surfaces in the western US. Over 60% of total suspended particles in 1939 were inferred to be derived from uncultivated sandy surfaces and eolian landforms within the study area, with the remainder from human-modified surfaces. The PM 2.5 and PM 10 emissivity estimates for a single dust event with winds over 6 m s −1 in the study area were 510–4514 and 4700–41,607 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 Dust Bowl and may be associated with magnitude increase in atmospheric dust loads. Keywords dunes, Dust Bowl Drought, dust emission, dust sources, eolian processes, human–environment interaction Received 11 November 2016; revised manuscript accepted 23 February 2017 1 Department of Geosciences, Baylor University, USA 2 Department of Earth Sciences, University of South Dakota, USA Corresponding author: Kasey Bolles, Department of Geosciences, Baylor University, One Bear Place #97354, Waco, TX 76798, USA. Email: kasey_bolles@baylor.edu 702235HOL 0 0 10.1177/0959683617702235The Holocene Bolles et al. research-article 2017 Research paper