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Crop yields can be negatively impacted by excess water as well as insufficient water. The northwestern portion of the Corn Belt, including South Dakota, North Dakota, Minnesota, and Iowa, is situated in a transition zone from moist subhumid to semiarid climates, and is, therefore, susceptible to both floods and drought. Precipitation has increased in the upper Midwest over the last 50 years, but less is known about changes in evapotranspiration (ET), which, along with precipitation, determines water excess or deficit. The objective of this research was to evaluate patterns of precipitation and ET in the four-state region over the last 49 years. The results confirm that precipitation has increased over much of the region in the last two decades, particularly outside the growing season. Fall and winter precipitation increases were more pronounced in the Dakotas, while precipitation increases in the spring were more common in Iowa. Areas of increased summer precipitation corresponded to areas of expanded row crop production. Reference ET has generally declined slightly over the region. However, more information is needed to fully evaluate the impact of changes in reference ET on actual ET. A better understanding of the impacts of these precipitation and ET patterns may help to evaluate potential mitigation and adaptation strategies for future crop production in the region under projected climate change.