High-Resolution Simulations of Decadal Climate Variability Impacts on Water Yield in the Missouri River Basin with the Soil and Water Assessment Tool (SWAT)

Abstract

he Missouri River basin (MRB) is the largest river basin in the United States and is 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 SST variability (WPWP)?substantially influence hydrometeorology in the MRB. The authors report on a simulation study with the Soil and Water Assessment Tool (SWAT) to estimate impacts on water availability in response to realistic values of PDO, TAG, and WPWP indices in approximately 13 500 hydrologic unit areas covering the MRB. SWAT, driven by hydrometeorological anomalies associated with positive and negative phases of PDO and TAG, indicated major impacts on water yields and streamflows, as much as ±40% of the average in many locations. Impacts of the WPWP index were smaller. Consistent with observations during 1949?2010, SWAT showed water flow increases of as much as 80% of the average, causing very wet periods when the positive phase of the PDO and the negative phase of the TAG at extreme amplitudes were superposed. Water flows decreased by a similar amount, resulting in severe to extreme droughts when the negative phase of the PDO and the positive phase of the TAG at extreme amplitudes were superposed. Thus, the combined and cumulative effects of these DCV phenomena on water flows, droughts, and wet periods in the MRB can be dramatic, with important consequences for all water-consuming sectors as well as for feedbacks to the climate system.