Eolian processes and heterogeneous dust emissivity during the 1930s Dust Bowl Drought and implications for projected 21st-century megadroughts

摘要

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 dustemissive 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 PM2.5 and PM10 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 mu g 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.