Regulated river modeling for climate change impact assessment: The Missouri River

The Great Plains of the United States, drained primarily by the Missouri River, are very sensitive to shifts in climate. The six main stem dams on the Missouri River control more than one-half of the nearly 1.5 million square kilometer basin and can store three times the annual inflow from upstream. The dams are operated by the U.S. Army Corps of Engineers using a Master Manual that describes system priorities and benefits. The complex operational rules were incorporated into the Soil and Water Assessment Tool computer model (SWAT). SWAT is a distributed parameter raintfall-runoff model capable of simulating the transpiration suppression effects of CO2 enrichment. The new reservoir algorithms were calibrated using a 25-year long historic record of basin climate and discharge records. Results demonstrate that it is possible to incorporate the operation of a highly regulated river system into a complex rainfall-runoff model. The algorithms were then tested using extreme climate scenarios indicative of a prolonged drought, a short drought, and a ten percent increase in basin-wide precipitation. It is apparent that the rules for operating the reservoirs will likely require modification if, for example, upper-basin precipitation were to increase only ten percent under changed climate conditions.