The NOAA 2014 U.S. Spring Flood Risk Assessment provides an important first look at some of the factors that influence summer hypoxia (low dissolved oxygen) in the Gulf of Mexico and the Chesapeake Bay. This year’s predicted elevated flood risk in the Upper Midwest and the Ohio River Valley may result in a larger hypoxic zone in the northern Gulf of Mexico than the average size in recent years. If flooding occurs, then higher than normal springtime discharges of nutrients and freshwater from the Mississippi River into the Gulf of Mexico may also occur, conditions that promote the formation and spread of hypoxia.
Hypoxia in the Chesapeake Bay has also been linked to nutrient loadings and river discharge, especially from the Susquehanna and Potomac Rivers. The spring flood outlook for portions of these basins indicates a slight risk for minor flooding, with an average-size hypoxic zone expected for the bay. Both forecasts assume typical summer conditions and the absence of major disruptive events such as tropical storms and hurricanes.
In early June, the actual river discharge rates and corresponding nutrient concentrations will be available from the U.S. Geological Survey. This information will be used by NOAA’s National Ocean Service to release its annual dead zone forecasts for the Gulf of Mexico and the Chesapeake Bay, which will provide hypoxic zone size estimates based on the available data. In June and July, the dead zone sizes will be measured and compared against the predictions. NCCOS has provided hypoxia data for the U.S. Spring Flood Risk Assessment since 2012, when hypoxia data were first added to the assessment.
For more information, contact David.Scheurer@noaa.gov.