Much needed rain could prompt flash floods, experts warn

The weeks of drought means there is now a risk - albeit slight - of flash floods following sudden downpours on baked hard ground which has low moisture content, according to authorities.

Keith Lambkin, an agricultural meteorologist with Met Éireann, said any downpour or heavy rainfall which falls now “is for the large part going to run off the surface”.

He said a localised torrential downpour could see run-off quickly swelling rivers and causing flash flooding.

The problem with occasional light showers he said, was that moisture is subjected to “evapotranspiration” a process that combines evaporation of the rain as it lands on the surface, and plant transpiration.

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Transpiration involves moisture carried through plants from roots to small pores on the underside of leaves, where it changes to vapor and is released back to the atmosphere.

Ideally, Mr Lambkin said what should happen in a period of consistent showers over the medium period is a return to normal soil conditions.

‘Short, sharp floods’

Mark Adamson deputy chief engineer of the Office of Public works said “localised short, sharp floods” could occur in small rivers as a result of run off from high ground such as the Dublin mountains.

He said urban areas with run-off from roads, footpaths and roofs which prevented natural absorption were more likely to be affected by sudden intense rainfall.

He said rivers such as the Shannon and the River Suck in Ballinasloe were more likely to be able to absorb short, summer downpours as there was not a sharp fall in these rivers.

Waterways Ireland which administers the Shannon and many of the State’s navigable waterways said water levels were currently at “normal summer levels”.

Dr Conor Muprhy of the Department of Geography, Maynooth University said the decade to 2015 had been the wettest on record, and the wettest for at least 300 years.

He said wetter winters and drier, warmer summers were in line with climate change.

But “even taking climate change out of the equation for the moment these events pose significant challenges” as the State deals with an over supply of water in the winter and a shortage in the summer.