Missouri River Drought Picture Improves
Active rainfall patterns across the Midwest provided much-needed moisture to several portions of the Missouri River Basin, the Corps of Engineers reported June 4. Large areas of Montana, North Dakota, Wyoming, eastern South Dakota and eastern Nebraska received more than 200 percent of normal precipitation for the month of May. However, central South Dakota, western Nebraska, and eastern Colorado received as little as 25 percent of normal precipitation.
“The month of May brought significant rainfall to the northern and eastern portions of the Missouri River Basin, resulting in slightly above average May runoff,” said John Remus, chief of the Corps’ Missouri River Basin Water Management Division. “The runoff was higher than forecast last month.”
May runoff for the basin above Sioux City, Iowa, was 3.5 million acre-feet (maf.), which is 104 percent of average.
The division updated the forecast for whole-year runoff to 21.0 maf., 82 percent of average and 1.8 maf. higher than last month’s forecast.
“While the precipitation provided relief for some portions of the basin, drought remains a concern as we move into the summer months,” Remus said. “The western portion of the basin received very little rain last month. As we enter the summer months, we will continue to serve all congressionally authorized purposes while dealing with the ongoing drought.”
Currently, 31 percent of the basin is experiencing abnormally dry or drought conditions with predictions showing persisting drought conditions through the end of August. Soil moisture is below normal in Montana, North Dakota, eastern Wyoming and Colorado and near normal in South Dakota and northern Nebraska.
The mountain snowpack was below normal all season long and peaked approximately one week earlier than normal. However, additional late season storms have extended the anticipated snow melt season and increased the overall volume expected from snowmelt.
Total system storage is currently 55.0 maf., 1.1 maf. below the top of the carryover multiple use zone. During May, system storage increased 1.0 maf. The improved forecast and increased storage in the reservoir system indicate the navigation flow support for the second half of the navigation season will be higher than earlier forecasts.
“The June 1 reservoir studies indicate navigation flow support for the second half of the navigation season, will be reduced to 1,000 cfs. below full service,” Remus said. “However, the official navigation flow support level for the second half of the navigation season will be based on the July 1 system storage check.”
