My research partners conducted statistical
regression analysis to identify which of our thousands of county-level variables was most correlated with the decision to move out of a county. Meanwhile, I constructed a series of county-level chloropleth maps to explore the spatial variation of these various factors. The map below, for example, plots the rate of emigration for each county in the United States, between 1935 and 1940. Laid over this map are outlines of the regions devastated by the wind and dust storms of the "Dust Bowl." The most interesting thing to note is that the Dust Bowl region - the focus of most research on environmental disaster and migration during the 1930s - forms just one small part of a much larger region experiencing high-outmigration during the period. As can be seen here, counties from the Texas-Mexico border to northeastern Montana saw high proportions of their residents move out, with many counties losing 20% or more of their
residents in 1935.
The explanation for the wide-spread emigration became clear after examining climate maps. These maps showed that drought and high temperatures plagued all of the Plains states from Texas to Montana. Much earlier scholarship focused on the Dust Bowl region, whose experiences were widely publicized by journalists, photographers, and later authors. A larger, quantitative analysis - with the aid of digital mapping - makes evident the much wider extent of this environmental disaster.