Climate-risk assessment for winter wheat using long-term weather data

Temperature and water deficit stresses cause large year-to-year yield variability, and matching crop phenology with periods less prone to stresses can improve yield stability. We used 30 years of daily weather data from 69 stations in the U.S. Great Plains to quantify the risk of water deficit and temperature stresses for winter wheat (Triticum aestivum L.) cultivars differing in maturity, and to evaluate whether the selected variables explained variability in yield and area abandonment. Crop phenology was estimated using a simple temperature-based model based on 282 field observations. A difference between the 15-d running sums of reference evapotranspiration (ETo) and precipitation greater than 40% of the soil's available water holding capacity (AWHC) determined atmospheric water deficit (AWD). Heat and freeze stresses occurred when maximum temperatures >27 degrees C and minimum temperatures <0 degrees C occurred around heading. Probabilities of AWD in the spring was greater in the west and in the south; however, latitudinal AWD gradients dissipated when crop maturity was considered. The day of year (DOY) for last freeze increased from south to north and from east to west; and the DOY for onset of heat stress increased from south to north but did not follow a longitudinal gradient. Early maturing varieties avoided heat and AWD stresses during heading but were more likely to experience freezing conditions. Regional yield decreased and area abandonment increased with early onset of spring AWD and heat stresses. This conceptual framework for evaluating the risk of environmental stresses can be applied to other regions and cropping systems.