Belfast, Londonderry and Newry are most at risk of coastal flooding from the global climate change threat, it has been revealed.
Downpatrick and Newtownards have also been identified as potential flood flashpoints.
The risk assessments were ordered by Agriculture Minister Michelle O'Neill, whose department (DARD) includes the Rivers Agency.
The exercise was undertaken as a result of the EU floods directive which required flood management plans which are now in place.
In a written Assembly answer, the Sinn Fein Minister said the agency has developed an interactive map-viewer 'Flood Maps (NI)' that enables the public to access the latest flood hazard information available from government.
"The viewer highlights the areas throughout the north of Ireland that are prone to flooding and its potential adverse impacts. The flood assessments, undertaken as part of the EU Floods Directive, have identified Belfast, Derry and Newry at significant risk of coastal flooding.
"Other areas at risk, albeit to a lesser extent, include Downpatrick and Newtownards."
The disclosure came as Environment Minister Mark H Durkan, whose department is responsible for climate change policy, claimed the Executive had "sat on" plans to extend emergency relief for flood victims for a year. "Having sat on it for over a year, the Executive decided that it would be better progressed by DARD and the Department of Finance (in January)," he told the Assembly's environment committee.
The SDLP Minister argued his request to have the financial assistance scheme extended to include churches, businesses and community groups "just kept bobbing along".
Then the Executive secured an extra £1.3m of money from Westminster to fund preventative measures and prepare for future flood incidents.
Mr Durkan also claimed that money could have ended up being spent elsewhere.
"After asking and asking and asking, we elicited the response, 'Yes, there will be £1.3m'," he told the Environment committee.
"I believe that, had it not been for me asking and asking, that money would not have been used to deal with flooding here."
Ms O'Neill also set up the £1m homeowner flood protection grant scheme to help people who wish to protect their homes from flooding - providing 90% of funding to install physical barriers and equipment to reduce the impact of flooding.
Four 'action groups' overall have been set up by Stormont to attempt to tackle future flooding crises.
They include one team to investigate land which is prone to flooding but where ownership is unclear and another that will be focused on reducing specific flooding risks.
Regional Development Minister Michelle McIlveen has warned flooding flashpoints like the Erneside Shopping Centre in Enniskillen will not be quickly resolved.
"I have been advised by officials from Rivers Agency that they are providing flood alleviation measures to help protect the Erneside Shopping Centre and Derrychara Link," said Ms McIlveen.