Development and evaluation of an ensemble forecasting system for coastal storm surges

Flowerdew, Jonathan; Horsburgh, Kevin ORCID: https://orcid.org/0000-0003-4803-9919; Wilson, Chris ORCID: https://orcid.org/0000-0003-0891-2912; Mylne, Ken. 2010 Development and evaluation of an ensemble forecasting system for coastal storm surges. Quarterly Journal of the Royal Meteorological Society, 136 (651), Part B. 1444-1456. https://doi.org/10.1002/qj.648

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Abstract/Summary

The overtopping of flood defences by coastal storm surges is a significant threat to life and property. Like all forecasts, storm surge predictions have an associated uncertainty, but this has not been directly predicted by previous operational systems. The Met Office Global and Regional Ensemble Prediction System (MOGREPS), which has recently become operational, provides an explicit sample of the range of atmospheric evolutions consistent with the latest observations. The storm surge ensemble derives a storm surge forecast for each MOGREPS ensemble member, giving an explicit estimate of the risk of reaching significant water levels. The system has now been running for over two years in trial mode, with positive feedback from both Met Office and Environment Agency forecasters. For the surge on 9 November 2007, which received significant media coverage, it produced a clear signal of an abnormal event at the full 54-hour lead time, with a useful indication of the range of possible water levels. Statistical verification covering two winters demonstrates that the ensemble spread is indeed a reliable indicator of the significantly increased uncertainty associated with large surge events, although the error in more normal situations is dominated by inaccuracies in the separate harmonic tide prediction which is used to convert surge to water level. Probabilistic verification shows some advantage over climatological error distributions, particularly for larger thresholds and longer lead times. Following this successful trial, the system was made operational in December 2009

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1002/qj.648
Programmes:	Oceans 2025
ISSN:	0035-9009
Additional Keywords:	PROBABILITY FORECASTING; COASTAL FLOODING; THRESHOLD EXCEEDANCE; RISK ASSESSMENT; PREDICTION SYSTEM; BIG FLOOD; ECMWF
NORA Subject Terms:	Marine Sciences
Date made live:	23 Jun 2011 15:30 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/13911

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