Analyzing Long-Term Changes in Precipitation and Temperature in the Midwest United States

This study focusses on evaluating the long term changes in four hydrologic variables, i.e., precipitation, temperature, minimum temperature, and maximum temperature in the Midwest United States. Annual averages of hydrologic variables for 106 climate divisions in the 12 Midwest states are analyzed for trends and steps for a period of 120 years (1895–2014). Nonparametric Mann-Kendall (MK) Test and Pettit’s Test are used to evaluate the changes in hydrologic data at a significance level of p≤ 0.05. The study also takes in to consideration the effect of short term persistence (STP) on the trends. The results from the MK test indicated increasing trends in the hydrologic variables for majority of the climate divisions in the Midwest. An increasing trend in mean temperature was detected in the eastern Midwest and it ranged from 0.04 to 3.09 °F/century. The climate divisions showing increasing trend in mean temperature also showed an increasing trend in precipitation (0.03 to 0.57 mm/century). While minimum temperature showed an increasing trend throughout the Midwest (0.25 to 3.8 °F/century), maximum temperature showed an increasing trend only in the northwest region of Midwestern states (0.01 to 3.46 °F/century). The Pettitt’s Test results indicated that shift, which were statistically significant, in all hydrologic variables occurred in the decades of 1980s and 1990s. Overall, the analysis from the current study provides a detailed view of changing temperature and precipitation in Midwest and the results are expected to aid water resources managers to effectively manage the available resources in the agriculture dominated region.