Despite the irrigation effects that reduce LST and increase EVI identified from satellite remote sensing data, the direct and most important effect of irrigation is to increase crop yield. In this regard, irrigation increased maize yield in Nebraska by ~80 bu/acre (+81%) relative to rainfed maize (103 bu/acre) when averaging from all counties where both irrigated and rainfed yields were available. The yield effect could be up to ~+180 bu/acre in very dry and hot counties (Figure \ref{786634}). Such yield effect of irrigation (i.e., delta Yield) can be well predicted by our statistical models (r=0.86, Figure \ref{282712}), and the averaged predicted yield gain (79 bu/acre) was close to the observed effect (80 bu/acre, Figure \ref{793326}). We note the land evaluations also reflect these large yield differences, with center pivot irrigated crop being assessed at $2700/acre and rainfed being evaluated at $700/acre in 2018 for Northwest Nebraska \cite{stokes2018}.
Following the quantification method in Section \ref{300462}, we found that 16% of irrigation yield increase in Nebraska was due to irrigation cooling, whereas 84% of yield increase was due to water supply (Figure \ref{793326}). Although the relative contributions of these two varied in different years, the irrigation yield effect was still dominated by water supply while cooling contribution was relatively stable. In particular, irrigation effect was the largest in the extreme drought year of 2012. This suggests that irrigation can effectively buffer the negative impact of extreme weather on crop yield, as suggested by previous studies \cite{Troy_2015,Thiery_2017}. These results reveal that irrigation cooling has as a non-negligible contribution to crop yield gain of irrigation besides water supply. 

4. Discussion

4.1 Irrigation cooling on air temperature from flux tower sites