Publication Date

2021

Document Type

Dissertation/Thesis

First Advisor

Changnon, David

Second Advisor

Gensini, Vittorio A.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Earth, Atmosphere and Environment

Abstract

In the Corn Belt region of the United States, the twentieth century saw many land use changes as the land had been converted from the natural landscape to cropland. As the twentieth century progressed, numerous advancements occurred to increase the crop acreage, crop density, and amount of irrigated land. All of these changes contributed to higher rates of evapotranspiration, which put more moisture into the low levels of the atmosphere. This additional moisture played a role in changing the radiative fluxes and, as a result, the surface temperature. The Diurnal Temperature Range (DTR) is examined across the 1900 to 2018 time period to determine if there are any spatial or temporal trends. The summer months are found to produce the strongest decreasing DTR trends across the Corn Belt. An analysis of seven stations indicated that the five stations experiencing a decrease in the summer DTR mean values decreased between 1.4 and 5.36°F, with most stations between 1.4 and 2°F. The two stations, Concordia, KS and Bismarck, ND, that experienced an increase were located outside the Corn Belt region, and the stations each had an increasing DTR mean value of 0.98°F and 1.9°F, respectively. The DTR is examined for the 1979 to 2018 time period for comparison with the related moisture variables, such as soil moisture content and dew point temperature at 2 m, during the same time period. The North American Regional Reanalysis (NARR) dataset moisture variables are examined in order to gain understanding of the contributions of the hydrologic cycle on the DTR. Since the increased presence of moisture in the lower atmosphere is found to increase the latent heat flux while decreasing the sensible heat flux, these variables have the potential to show the moisture contributions towards altering the DTR. The DTR is found to decrease by about 1 to 3°F during this time period for the most locations (eastern North Dakota, eastern South Dakota, eastern Nebraska, central Iowa, Wisconsin, Minnesota, Missouri, and western Illinois) within the study area. However, there are many stations in the 1979 to 2018 time period that have an increasing trend. The increasing trends are typically of a lower magnitude, around 2°F or less. This changing DTR trend pattern from 1979 to 2018 occurs as many moisture variables experience widespread dryness, particularly around the Great Plains region.

Extent

82 pages

Language

eng

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

Media Type

Text

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