Ohio Nowcast.
How did the nowcast system perform in past years?

Huntington - How did the nowcast perform in past years?Nowcasts were provided to the public at 8 beaches during the recreational season of 2014. Performance of the nowcast model was compared to using the persistence method (using the previous day’s E. coli to predict the current day’s E. coli concentration) at 6 of those beaches..

  • At 5/6 beaches, the nowcast model performed better than the persistence method in terms of overall percent correct and specificity. Specificity is the percentage of non-exceedances of the E. coli bathing-water standard (235 colonies per 100 milliliter) that were correctly predicted.
  • At 4/6 beaches, the nowcast model performed better than the persistence method in terms of sensitivity. Sensitivity is the percentage of E. coli exceedances of the bathing-water standard that were correctly predicted.
  • The model performed especially well at Huntington, where three subseason models were used.
  • Because sampling was not done on any consecutive days at Fairport Harbor and Headlands, comparison to the persistence method could not be done.
  • The Maumee Bay State Park model sensitivity was lower than expected because the Berger Ditch stream gage was removed mid-season and a backup model was used.
  • The model performed poorly at Nickel Plate. Work will continue in 2015 to test new models at this beach.

At Huntington, we have been providing nowcasts to the public the longest— 756 days during the recreational seasons of 2006-14.

Huntington Beach Nowcast Results (2014).

  • The nowcast provided a correct response 85.4 percent of time.
  • The sensitivity of the nowcast was 61.9 percent. That means that the nowcast correctly predicted that the standard was exceeded on 83 out of 134 days that the standard was actually exceeded.
  • The specificity of the nowcast was 90.5 percent. That means that the nowcast correctly predicted that the standard was NOT exceeded on 563 out of 622 days that the standard was actually NOT exceeded.

The Huntington nowcast continues to provide more accurate information and better estimates of public health risk than the use of the previous day’s E. coli (the current method used by most beach managers.), especially in regard to sensitivity. In addition, nowcast results have been consistent from year-to-year.

Huntington Beach Nowcast Results (2006-2014).

Having many years of data at Huntington afforded the opportunity to test a non-observation model. A non-observational (NOD) model is a model that can be run remotely with available data and doesn’t require a visit to the beach. During 2014, performance of the NOD model was compared to the standard model and prior day E. coli method. The standard model was the model used for the Huntington nowcast and requires a visit to the beach to measure model parameters. Although the NOD model did not perform as well as the standard model, it still performed better than using the prior day E. coli method (see donut graphs below).

Standard and non-observational (NOD) models at Huntington Beach, 2014.

At Edgewater, nowcasts were provided to the public for 693 days during the recreational season of 2008-13.

  • The nowcast provided a correct response 75.6 percent of time.
  • The sensitivity of the nowcast was 59.2 percent. That means that the nowcast correctly predicted that the standard was exceeded on 90 out of 152 days that the standard was actually exceeded.
  • The specificity of the nowcast was 80.2 percent. That means that the nowcast correctly predicted that the standard was NOT exceeded on 434 out of 541 days that the standard was actually NOT exceeded.

The Edgewater nowcast provided more accurate information and better estimates of public health risk than the use of the previous day’s E. coli (the current method used by most beach managers.). Although the sensitivity of the nowcast was greatly improved over the previous day’s E. coli, the specificity was about the same using the nowcast and the previous day’s E. coli concentrations.

  • The previous day’s E. coli provided a correct response 71.4 percent of time.
  • The sensitivity of using the previous days E. coli was 34 percent. That means that the current method correctly predicted that the standard was exceeded on only 49 out of 144 days that the standard was actually exceeded.
  • The specificity of using the previous days E. coli was 81.6 percent, about the same as using the nowcast.
  • Work will continue in 2014 to improve the accuracy of the Edgewater nowcast. These include measurements of foreshore head and photosynthetically-active radiation and qPCR results.
Edgewater Beach Nowcast Results (2008-2013).  

 

At Maumee Bay State Park, nowcasts were provided to the public for 49 days during the recreational season of 2013. The nowcast was able to provide more correct responses (79.6%) than the use of the previous day’s E. coli (64.7%) and both a higher sensitivity and specificity.
 Maumee Bay Beach Nowcast Results (2013).  

 

At Cuyahoga Valley National Park, nowcasts were provided to the public for 139 days during the recreational season of 2013. On 37 of these days, samples were taken to check nowcast results. The nowcast was able to provide more correct responses (89.1%) than the use of the previous day’s E. coli (77.8%) and both a higher sensitivity and specificity.
 Cuyahoga River Nowcast Results (2013).

At Villa Angela, nowcasts were provided to the public for 197 days during the recreational seasons of 2012-13. The nowcast was able to provide more correct responses (74.1%) than the use of the previous day’s E. coli (61.0%) and both a higher sensitivity and specificity.
 Villa Angela Beach Nowcast Results (2013).

For comments or changes regarding this Web page, please contact:
Donna Francy, USGS Ohio Water Science Center, 6480 Doubletree Avenue, Columbus, OH 43229; Phone: (614) 430-7769