Estimation of the effects of climate variability on crop yield in the Midwest USA

Crop yield is strongly affected by climate variability. When applying ecohydrologic models to study climate impacts on crop yield, especially interannual yield responses to climate stresses, the model simulation of plant available soil moisture must be constrained in order to reproduce plant production variation via moisture related bio-climate variables. In this study, the Soil and Water Assessment Tool (SWAT) is used to investigate the relationship between climate variability and crop yield at four sites (Boone, Woodbury, Madison, and Mason) in the Midwestern USA. The model was first calibrated for soil moisture at the plot scale. The calibrated model was then used to extend the observational records between 1991 and 2010 to better capture the effect of climate variability on crop yield over a longer period (1941-2010). We also explored the relative yield reduction due to individual stresses. Our results indicated that annual observed yield from 1991 to 2010 is correlated with drought stress intensity in the early and middle reproductive stage at most sites. The early and middle reproductive periods were thought more critical than other stages, because severe drought stress in those periods is substantially correlated with low observed yields. No significant relationship between crop yield and aeration stress was found at any of the four sites, due to their different impacts under different spatial scales, as well as low frequency of events in the historical record. Long term simulation of yield reduction indicates that drought stress was the dominant factor affecting yield in the historical period when compared with aeration stress both at short and long return periods (high/low probability of exceedance). For a 70-year period, the total yield reduction due to drought stress is 8.1%, 17.5%, 15.2% and 9.7% respectively for Boone, Woodbury, Madison and Mason. (C) 2015 Elsevier B.V. All rights reserved.