Defining agroclimatological factors influencing vulnerability to agricultural drought: a Nebraska case study

Agroclimatological factors of vulnerability to agricultural drought in Nebraska were defined by synthesizing crop and climate data. The underlying approach assumes that the best characterization of the climatology of the state from the agricultural drought vulnerability perspective is the probability of seasonal crop moisture deficiency. Seasonal crop water use thresholds for well-watered crops (e.g., corn, soybean and sorghum) were estimated using the evapotranspiration (ET) mathematical model. For wheat and grass, ET values were estimated based on the relationship between ET, water use efficiency and crop yield. Historical yield data were used to determine the economically viable threshold for wheat. Thresholds determined for the crops in the state were used to calculate area-weighted mean ET for the combination of crops in every county. Threshold values and long-term precipitation data were used for calculating statistical probabilities of seasonal crop moisture deficiency. Probability values were assigned to 112 weather stations across Nebraska, spatially interpolated and classified using Geographic Information Systems (GIS). The classifications included "low", "moderate", "high", and "very high" probability of seasonal crop moisture deficiency. The results of this study formed the basis for a comprehensive, GIS-based agricultural drought vulnerability assessment for Nebraska. The spatial pattern of probabilities of seasonal crop moisture deficiency reflected both the seasonal precipitation distribution across Nebraska and the distribution of the crops and grasses.