Norwich has been identified by government experts as an area at particular risk of flooding, with some 11,000 properties deemed to be under threat.
The Environment Agency says the city is an indicative flood risk area - one of 60 across the country - because of the number of properties deemed at risk from surface water flooding.
The Environment Agency assessed the risk to all properties and critical services in Norfolk of the sort of flooding event which occurs once in 100 years.
In Norwich, 9,323 residential properties were identified as being at risk, along with 1,731 businesses and 92 key services (including schools and electrical substations) - a total of 11,146.
Council bosses stressed the city's inclusion is not because more homes are now at risk of flooding, but because criteria to identify such areas has changed.
A Norfolk County Council spokeswoman said: 'Although Norwich is now an indicative flood risk area, it should be noted the number of properties at risk has not changed and remains the same at around 11,000.
'The thresholds, set by the Department for Environment, Food and Rural Affairs, for identifying whether an area is at risk has gone down from 13,000 to 3,000 properties, which is why Norwich as an area is now included.
'Having the status does not change the risk to the property, it merely changes the way an area is classified.'
More than £10m is already being spent to improve drainage in Thorpe St Andrew, Taverham, Drayton, Sprowston, Hellesdon and Old Catton.
The county council added £1.2m to government money awarded after almost a hundred properies were hit by flooding in 2014, causing an estimated £2m damage.
But the new classification will not automatically bring more money.
The council spokeswoman said: 'No extra funding is linked directly to the identification of the flood risk area, but Norwich will remain a focus for funding bids and flood mitigation schemes for the flood management team at Norfolk County Council.
'As the risk of flooding has not changed for the individual property the reclassification should not affect individual householders.
'The insurance industry will have access to all the same flood risk information as they always have.'
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here