Assessment of irrigation use on crop yield and water supplies in the Midwestern U.S.

摘要

Climate plays an important role in many aspects of hydrological and agricultural systems. Temperature and precipitation are usually the main forcing inputs for hydrological and agricultural simulations, while wind effect has generally been neglected in previous research. Wind speed is, however, an important factor for many physical processes, including evaporation from soil, and transpiration from plants. In order to investigate how climate variability impacts agricultural production, there are three hypotheses addressed in this dissertation. Hypothesis 1 is that the representation of changing wind speed will play an important role in the simulation of hydrological processes, and that the effect of wind speed will directly affect soil hydrology and evapotranspiration. Hypothesis 1 is tested using a factor separation analysis to quantify the contribution of projected future wind speed to hydrologic change under future climate. The result showed that changes in wind speed affected soil hydrology and evapotranspiration directly.;Hypothesis 2 is that the application of irrigation will be significantly beneficial for crop productivity in the future as it will mitigate risk associated with water deficits in the growing season, Regional farmers are expected to rely more on irrigation to mitigate risk due to increased climate variability in the future, resulting in a substantial increase in its use. This hypothesis is tested through the analysis of changes in crop (corn and soybean) yield due to climate change between historical and future periods using the VIC-CropSyst model, which incorporates a cropping system model, the CropSyst, model, into a large-scale hydrology model, the VIC model. First the effect of climate change on non-irrigated crop yields is quantified, then the ability of irrigation to mitigate crop yield losses due to changes in climate are quantified. Application of irrigation is found to improve corn yield by up to 5% and soybean yield by 20%, compared to the non-irrigated future scenario. In addition, irrigation is found to have significantly mitigated the impact of climate uncertainty on crop yield, with more benefits for soybean yield than for corn yield. This analysis addressed Hypothesis 2 and showed that irrigation is significantly beneficial for crop productivity and mitigates the impact of future changes in temperature and precipitation, meaning risk associated with water deficits in the growing season can be decreased using irrigation.;Hypothesis 3 is that the increased use of irrigation on historically rain-fed crops will affect regional water use significantly, increasing the risk of water supply deficits in the crop growing season. The assessment of water footprint in addition to the previous analysis of irrigation impact on crop yield, found that irrigation leads to significant increases in the blue water footprint. The assessment addressed Hypothesis 3 and suggested that irrigation on traditional rain-fed crops will affect regional water use significantly. However, we cannot assess the risk of water supply deficits because irrigation use is unrestricted in the model.