Spatial representation of agroclimatology in a study of agricultural drought

Agricultural drought is the leading cause for crop failure throughout the world. In the USA, significant impacts of recent droughts on agricultural production indicate the continuing vulnerability of the country to drought. This paper presents a methodology for spatial representation of the agroclimatic component of agricultural drought vulnerability. This methodology was developed as a part of an integrated assessment of drought vulnerability. For the spatial analysis, the state of Nebraska was selected as a study area because of the considerable variation in climatology, soil characteristics, land use, and cropping patterns. The underlying approach assumes that the best spatial characterization of the state's agroclimatology 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 grain yield data were analysed to define an economically viable threshold for wheat. Seasonal ET thresholds determined for the crops were used to calculate area-weighted mean ET for the combination of crops in every county. The threshold values and long-term precipitation data were used for calculating statistical probabilities of seasonal crop moisture deficiency. Probability values were analysed at 112 weather stations across Nebraska, spatially interpolated and classified using geographic information systems. The spatial pattern of probabilities of seasonal crop moisture deficiency reflected both seasonal precipitation across Nebraska and the distribution of crops and grasses.