Biological Systems Engineering, Department of


Date of this Version

Summer 7-2011

Document Type



Dr. Denis Mutiibwa’s dissertation is no longer published online, by his request and by request of his advisor Dr. Suat Irmak.

Interested parties may contact Dr. Mutiibwa and request a copy of the dissertation, at


A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Engineering, Under the Supervision of Professor Suat Irmak. Lincoln, Nebraska: June, 2011

Copyright 2011 Denis Mutiibwa


Human activities such as conversion of natural ecosystem to croplands and urban-centers, deforestation and afforestation impact biophysical properties of land surface such as albedo, energy balance, and surface roughness. Alterations in these properties affect the heat and moisture exchanges between the land surface and atmospheric boundary layer. The objectives of this research were; (i) to quantitatively identify the High plains’ regional climate change in temperatures over the period 1895 to 2006, (ii) detect the signatures of anthropogenic forcing of LULC changes on the regional climate change of the High Plains, and (iii) examine the trends in evolving regional latent heat flux under the changing climate during the past thirty years.

We investigated the regional climate change by comparing two trend periods, the reference period (1895 – 1930) and the warming period (1971 – 2006), using the base period as 1935 – 1965. For the objective (ii) the study developed an enhanced signal processing procedure to maximize the signal to noise ratio by introducing a pre-filtering technique of ARMA modeling, before applying the optimal fingerprinting technique to detect the signals of LULC change. For the objective (iii), we estimated ETc using the widely accepted two-step approach. We developed a linear model to estimate spatial crop coefficient (Kc) from AVHRR-based NDVI. The Kc estimates were used to adjust spatial ETo estimates, thereby yielding spatial ETc estimates that are representative of the summer latent heat fluxes of years 1981 to 2006.

The results from the study show that, the overall warming trend in the High Plains was about 0.11oC/decade. The minimum temperature had the strongest warming at a rate of 0.19oC/decade. Due to LULC changes attributed to increase in irrigation application and vegetation surfaces, more surface energy in summer is being redistributed into latent heat flux. Therefore, there is a significant influence of evaporative cooling on regional temperatures during summer season. As a result, the greenhouse warming effect in the region is being surpassed.