Simulated Impacts of Three Decadal Climate Variability Phenomena on Water Yields in the Missouri River Basin1

The Missouri River Basin (MRB) is the largest river basin in the United States (U.S.), and is one of the most important crop and livestock-producing regions in the world. In a previous study of associations between decadal climate variability (DCV) phenomena and hydro-meteorological (HM) variability in the MRB, it was found that positive and negative phases of the Pacific Decadal Oscillation (PDO), the tropical Atlantic sea-surface temperature gradient variability (TAG), and the west Pacific warm pool (WPWP) temperature variability were significantly associated with decadal variability in precipitation and 2-meter air temperature in the MRB, with combinations of various phases of these DCV phenomena associated with drought, flood, or neutral HM conditions. Here, we report on a methodology developed and applied to assess whether the aforementioned DCVs directly affect the hydrology of the MRB. The Hydrologic Unit Model of the U.S. (HUMUS) was used to simulate water yields in response to realistic values of the PDO, TAG, and WPWP at 75 widely distributed, eight-digit hydrologic unit areas within the MRB. HUMUS driven by HM anomalies in both the positive and negative phases of the PDO and TAG resulted in major impacts on water yields, as much as +/- 20% of average water yield in some locations. Impacts of the WPWP were smaller. The combined and cumulative effects of these DCV phenomena on the MRB HM and water availability can be dramatic with important consequences for the MRB.