Before the flood, a warning

After severe weather events in recent years, Ireland has joined a European forecast system that provides flood warnings

KNOWING THAT A severe flood is likely to hit your region in coming days has its advantages: if you are organised enough you can evacuate people from at-risk areas, protect structures and maybe even call for international assistance.

This month, Ireland officially signed up to a European system that can forecast serious flooding several days – sometimes up to two weeks – in advance by crunching enormous amounts of data twice a day about weather, ground and river conditions.

The European Flood Alert System, or EFAS, aims to remove the element of surprise from major flooding events, according to Dr Ad de Roo, who leads the EFAS team at the European Commission’s Joint Research Centre (JRC) at Ispra, near Milan.

Weather forecasts can predict the likely rainfall that’s coming down the track, but weather is a notoriously tricky beast, so the EFAS system hedges its bets and uses 120 forecasts from across Europe, and then looks at the variation to get a general picture.

The system also automatically mixes in data from satellites and more than 1,000 ground stations about soil and river conditions, land use and observed rainfall.

And what pops out is a flood risk level that can raise alarm bells about likely regional events ranging from high water levels to severe and extreme flooding.

“Our aim is to give a warning of magnitude and region,” says de Roo, who presented to Irish journalists at Ispra last week. “If you want a ‘centimetre’-type of prediction you need more [specific] data and that’s where the national agency comes in closer to the time of the crisis.”

It’s important to avoid triggering false alarms – the public will lose confidence in a system that cries wolf, according to de Roo – so if a risk emerges, the procedure is to wait for three 12-hour updates before deciding whether to alert the national agency.

But so far, EFAS and its team of hydrologists, meteorologists, geographers and IT experts has had a good hit rate, he notes. “With any forecast you can never be exactly right. But over the last five years we are right more or less two out of every three times.”

One of those “right” forecasts included late last year, when EFAS staff were surprised by the signals coming up for Ireland on November 13th, 2009, several days before flooding devastated regions of the country. “I still remember my staff coming in to me and saying look at Ireland, because we had never seen Ireland coming up like this – actually we had never seen Ireland coming up at all,” recalls de Roo.

The signal persisted, with the normal response being to issue an alert to a member country – but unfortunately Ireland was not a member at the time, he notes. “We can only disseminate our warnings if countries are members of the system, for all kinds of political and legal reasons.”

Ireland is a member now, and the formal contact point is the Office of Public Works. According to an OPW spokesperson, formal EFAS warnings are only issued for river basins of more than 4,000sq kms. In Ireland this restricts the coverage to the Shannon, the Erne as it flows through Ballyshannon to the sea, and the combined Barrow/Nore systems along the joint estuarine reach, but not for these rivers individually.

The JRC is developing forecasts for smaller catchments, but this is at development and testing stage, he adds. Meanwhile, 2010 has been keeping the experimental EFAS system on its toes, with about 20 serious alerts going out already, compared to about five in other years, according to de Roo.

Ultimately, the plan is to operate the system at the European Centre for Medium-Range Weather Forecasts at Reading, which has more powerful computing facilities. But the group in Italy will continue to improve EFAS, says de Roo. “And the long-term idea is to have a global system, but that will take time.”

See floods.jrc.ec.europa.eu