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Browse History: Home (2009)

Chesapeake Bay Summer Forecast:

For the past several years, Chesapeake Bay scientists have collaborated with EcoCheck (NOAA-UMCES partnership) to forecast Chesapeake Bay summer ecological conditions, weeks to months in advance, based on flow and nutrient loading conditions through mid-May. Ecological forecasts provide resource managers with information that can be used to guide restoration, enable proactive communication of Bay conditions, and help direct research activities.

The forecast focuses on two important elements of Bay health — dissolved oxygen and harmful algal blooms. The dissolved oxygen forecasts predict the volume of both anoxic (dissolved oxygen levels ≤0.2 mg·L‑1) and hypoxic (DO ≤2 mg·L‑1) water in the Bay's mainstem. The harmful algal bloom forecasts predict the occurrence and intensity of Microcystis in the Potomac River and Prorocentrum within the Maryland region of the Bay. Microcystis is a type of cyanobacteria (also referred to as blue-green algae) that can form a green scum on the water surface. Prorocentrum is a dinoflagellate that can cause the water to turn reddish-brown and form what are called mahogany tides. Future forecasts may include additional elements. All ecological forecasts are built from a foundation of environmental monitoring data gathered over more than two decades.

Click on the items below for the 2009 summer ecological forecast:

Forecast Overview

Overview graphic

Anoxia Forecast

forecast Map

Hypoxia Forecast

Hypoxia Forecast graphic

Nutrient Loading was Unique in Spring 2009

This year’s forecast may provide a unique opportunity to understand important dynamics of the relationship between Chesapeake Bay health and input of nutrients (nitrogen and phosphorus loading). The 2009 forecasts for volume of hypoxia, anoxia, and Prorocentrum are relatively low (see indicator pages for forecast details), based primarily on loading estimates from the Susquehanna River provided by the US Geological Survey (USGS).

The Susquehanna River is the single largest source of nitrogen and phosphorus discharging into Chesapeake Bay. These nutrients have a significant effect on the dissolved oxygen and Prorocentrum forecasts. Susquehanna River flows during the first five months of 2009 were characterized by two large peak flows in late February and mid-March, which were higher than normal. Following the mid-March peak, Susquehanna river flows were substantially lower than average (see Overview page for Susquehanna River flow data).

The precipitation patterns in the northeastern United States during May and June are likely a result of positioning of the jet stream. This year the more southerly orientation of the jet stream generated precipitation along the Maryland and Pennsylvania border. For more information on the spring jet stream location see the AccuWeather website

According to USGS, for example, “May rainfall was the second highest rainfall on record in Baltimore. The abundant rainfall has… resulted in normal to above normal monthly mean streamflows across the region." For more information, visit the USGS for Maryland and Virginia/West Virginia streamflow data. While Maryland and Virginia/West Virginia experienced very wet conditions in late May, this rain does not appear to have had a significant effect on the low Susquehanna River streamflow noted above.

Although the 2009 forecasts for hypoxia, anoxia, and Prorocentrum blooms are relatively low, it seems likely that the very wet conditions in the southern portion of the watershed from late May through mid-June may have created substantial Chesapeake Bay nutrient loading that is not fully accounted for in the forecast models. It will be interesting to evaluate summer hypoxia, anoxia, and Prorocentrum results given these differences. This spatial rainfall variability provides us a unique opportunity to observe the major contributions from Maryland and Virginia tributaries, somewhat independently from the Susquehanna.

Similar to the hypoxia, anoxia, and Prorocentrum forecasts, the 2009 Microcystis forecast is relatively low. Potomac River streamflow through mid-May was moderate, and the wet conditions in late-May and June were not included as input to the modeled Microcystis forecasts. Future improvements to each of the forecast models may include methods to account for spatial and temporal variability of rainfall and loading, as well as methods to adjust forecasts as new streamflow data become available, similar to weather forecast updates by the NOAA National Weather Service.


These web pages have been produced in collaboration with members of the Chesapeake Pay Program's Tidal Monitoring and Analysis Workgroup (TMAW). The following individuals are acknowledged for their contributions: Don Scavia (Univ. of Michigan), Peter Tango (USGS/CBP), Jeni Keisman (UMCES/CBP), Dave Jasinski, and Jon Anderson (Morgan State). We would also like to thank Joel Blomquist from USGS for providing the provisional nitrogen loads estimates needed to forecast hypoxia.