Flooding
Flooding is one of Rhode Island’s most common and dangerous natural hazards. A flood is the overflowing of the normal confines of a stream or other body of water, or the accumulation of water over areas that are not normally submerged.
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Flood Return Periods
The term 100-year flood is sometimes used to describe rare and extreme flooding events. What do these terms really mean? Flood return periods are described by the annual exceedance probability (AEP); a statistical estimate used to place floods within a historical context. AEP is estimated from annual peak streamflow values measured at U.S. Geological Survey stream gauges. Thus, a 100-year flood for a waterway is a unique value.
Annual Exceedance Probabilities
- 1-year flood = 100% chance of annual occurrence
- 2-year flood = 50% chance of annual occurrence
- 3-year flood = 33% chance of annual occurrence
- 5-year flood = 20% chance of annual occurrence
- 10-year flood = 10% chance of annual occurrence
- 25-year flood = 4% chance of annual occurrence
- 50-year flood = 2% chance of annual occurrence
- 100-year flood = 1% chance of annual occurrence
- 500-year flood = 0.2% chance of annual occurrence
- 1,000-year flood = 0.1% chance of annual occurrence
Rhode Island STORMTOOLS
The University of Rhode Island (URI) and the Rhode Island Coastal Resources Management Council (CRMC) developed the online platform STORMTOOLS to map coastal flood inundation along the state’s coastline. STORMTOOLS can be viewed with or without projected sea level rise for various flood return periods. Inland flood projections that consider climate change-induced extreme precipitation will eventually be integrated into STORMTOOLS.
