Although population change in the United States has been widely researched, most studies have focused on social and economic reasons for population shifts. The research that does exist on environmental factors for the most part has looked at temperature and seasonal relationships. To provide more depth to known impact of environment on US population shifts, Maxwell et al. (2011) set the primary research goal of identifying the main reasons for population shifts in six counties in three geographic regions. Secondarily, the researchers were interested in finding the relationship between drought from the 1800s to the present and population change. Furthermore, the study sought to assess the spatial variability between the six locations in the study. The study found that traditional variables for population change–unemployment, education, technological advancement, etc.–had the largest impact on population change. Through correlation and regression analysis drought was determined to cause a small variance in population change with significance in three of the six counties. Spatially, without other measures of climatic variables, counties in the same region tended to experience similar results. –Adriane Holter
Maxwell, Justin T., Soule, Peter T., 2011. Drought and Other Driving Forces behind Population Change in Six Rural Counties in the United States. Southeast Geographer 51, 133 – 148
The three regions observed in the study were: the Southeast, Ohio Valley, and Great Plains. The counties within these regions shared similar urban structures and economic makeups. All counties were predominately rural and agricultural. Studied counties did not have a metropolitan center, a highway that passed through the region, corporate owned farms, or substantial irrigation. Per capita income, agricultural prices, and manufacturing prices were acquired from census data and adjusted for inflation in order to analyze economic elements of population change. Additionally, variables such as birth and death rates, educational attainment, and unemployment were standardized by country population in the same year for use in developing a full social picture of each county. Climatic variables were retained from the National Climatic Data Center from 1985 to 2000. Drought was quantified through the study of tree rings in the Palmer Drought Severity Index (PDSI), which included an 11-year moving average to account for the extreme yearly variations in temperature and moisture. A multiple regression model was used to analyze which factors were the biggest drivers for population change in each county.
In the Southeast, the primary drivers for population change in Sampson County, North Carolina were manufacturing value with other significant factors in agricultural and educational sectors. In Bedford County, South-Central Tennessee the primary drivers were college attainment and temperature, with secondary influencers of agricultural value, manufacturing value, and high school attainment. Drought had a significant impact on population change, while population was inversely related to temperature. Increased level of educational attainment indicated an increase in population. In this area, the intuitive tie between drought and agriculture is evident – lower amounts of moisture negatively affect crops.
In the Ohio Valley, Adams County in Northeast Indiana the most successful model for population change included high school attainment, PDSI, and the death rate. Converse to the findings in the Southeast and Ohio Valley, Pottawatomie County, Northeast Kansas in the Great Plains had a negatively correlated relationship between college attainment and population. Similar to Adams County, PDSI has a significant impact on population change in Pottawatomie. Also in the Great Plains, Tillman County, Southwest Oklahoma had the key population change drivers of high school attainment and death rates with birth rates, college attainment, and annual income also possessing a strong influence. Finally, population change in Douglas County in southeastern South Dakota was most strongly linked to high school attainment and birth rates. Like Tillman County, the levels of death rates, college attainment, and annual income were also important factors.
The fact that population changes in three of the six counties researched in this study were positively related to the availability of moisture signals the need for more research in the relationship between drought and population size. Currently in the United States, the Southeast and the Southwest have the highest rate of population growth in the country. Furthermore, many of the counties in these regions still rely heavily on agriculture. With the increase in climate change, it is likely that droughts will become more frequent and intense today than the measures found in this study. The relationship between drought and threats to agricultural sustainability make these field a crucial realm of research.