People don't really understand stored wealth (like in buildings), but the big difference is that the buildings become useless and not available for trade, when the oceans rise. This is very different from many other scenarios.
This means that the refugees will have lost a major portion of their assets. I don't know if anybody has moved due to employment, but it's expensive and highly inefficient. If you couple that with a loss of assets, it's nigh-near devastating.
The economy does not mind when poor people migrate to find work. But it terribly minds when people with assets have their assets taken away, and then they're forced to migrate.