NOAA Spring Flood Outlook and Hypoxia

15 March 2012

Draining over 40% of the contiguous United States, precipitation patterns in the Mississippi River Basin have a impact on the delivery of nutrients to the Gulf of Mexico. High levels of these nutrients cause a large area of low-oxygen in the Gulf, known as the dead zone, to form each summer. The Upper Mississippi and Ohio Valleys supply the majority of the nutrients to the Gulf, so examining spring flood risk in these basins can provide a useful indicator of the possible size of the summer dead zone. The predicted above-normal flood risk in the lower Ohio Valley would serve to increase the severity of the dead zone. However, this increase may be countered by below-normal flood risk in the Upper Mississippi Valley. It is the net result of these forces that may determine whether the dead zone is above or below normal this summer. In early June, NOAA will be releasing its annual dead zone forecast based on observed river discharge rates and nutrient concentrations provided by the USGS.