High-resolution Simulations of Decadal Climate Variability Impacts on Spring and Winter Wheat Yields in the Missouri River Basin with the Soil and Water Assessment Tool (SWAT)

Abstract The Missouri River Basin (MRB) encompasses one of the most important agricultural regions in the world. Three decadal climate variability (DCV) phenomena — the Pacific Decadal Oscillation (PDO), the tropical Atlantic sea surface temperature (SST) gradient variability (TAG), and the West Pacific Warm Pool (WPWP) variability — substantially influence hydro-meteorology and, consequently, spring and winter wheat yields in the MRB as indicated by data from 1961 to 2010. We applied the Soil and Water Assessment Tool (SWAT) to simulate DCV impacts on wheat yields in response to realistic values of the DCV indices in approximately 13,500 hydrologic unit areas covering the MRB. SWAT, driven by scenarios of past hydro-meteorological anomalies associated with positive and negative phases of the PDO and TAG, indicated major impacts on wheat yields, as much as ± 40% of the average in many locations, with smaller impacts of the WPWP variability. SWAT showed much larger wheat yield increases when the positive phase of the PDO and the negative phase of the TAG are superposed, and an equivalent decrease in yields when opposite phases of the two DCV phenomena are superposed. Thus, combined effects of DCV phenomena on wheat yields in the MRB can be dramatic with important consequences for food production and security. The usefulness of this inter-disciplinary study to farmers and other stakeholders for adapting MRB agriculture to DCV, and the applicability of the methodology to other agricultural regions are described. The results’ implications for detection and attribution of climatic change impacts are also described.