While irrigation effects on LST and EVI (i.e., lower LST and higher EVI), which peaked in July, were found in the majority of Nebraska counties, there were exceptions and markedly spatial variations (Figure \ref{436149}). First, a few counties showed the opposite irrigation effects on LST and EVI, particularly in June and to a less extent in other months. The location of those exceptions differed in different months and years (Figures \ref{121733} to \ref{879569}). The exact reason for these exceptions is not clear, but might be related to the minimal irrigation in June, the accuracy of irrigation map and remote sensing data, or some unobserved local factors at the field level. 
Second, there was a clear spatial transition in the irrigation effects from west to east Nebraska. The irrigation effects were greatest in southwest Nebraska, with an LST cooling and EVI increase in July by up to -4°C and +0.2°C, respectively. These effects were weakened towards northeast Nebraska as the \(\Delta LST\) and \(\Delta EVI\) shrank to close to zero. Irrigation effect is more pronounced in western Nebraska, because irrigation is required in that area to achieve high yields under a drier climatic regime. By contrast, eastern Nebraska is much wetter, so that irrigation is not a necessity for crop growth, therefore, irrigation effects are rather small. See \cite{V_Sharma_2012,V_Sharma_2012a} for a description of the climatology and net irrigation requirements across Nebraska ranging from ~450 mm/yr to 50 mm/yr. These results reveal that the baseline climate condition is an important factor in determining irrigation effects.