One way in which FEMA updates flood hazard maps is to conduct a Government-funded detailed reevaluation of flood hazards, referred to as a flood study. The flood study process is very costly and can take up to 5 years to complete. Because of the time and expense involved in conducting a restudy, FEMA bases its decision on whether to conduct a restudy on a benefit-cost analysis. Through this analysis, FEMA weighs the expected benefits to existing and future development against the funds to be expended. In this way, the flood studies that will yield the most benefit are performed first. However, the number of flood studies needed far outweighs the funds available to perform them.
As an alternative, FEMA established procedures by which an interested community may compile appropriate data and request a map revision. Map revisions are often completed in less than 90 days from the date all data are received.