Page:OMB Climate Change Fiscal Risk Report 2016.pdf/29

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5. FEDERAL FACILITY FLOOD RISK
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Climate Change and Flood Risk
Just as American homeowners and businesses face growing flood risks due to climate change, so does the Federal Government. The NCA found that climate change may intensify flooding in many U.S. regions, even where total precipitation is projected to decline. Increasingly heavy downpours can cause flash and urban flooding and, along with more rapid spring snowmelt, can exacerbate river flooding. Climate-related sea level rise from thermal expansion of ocean water and melting of glaciers and ice sheets can cause coastal flooding and compound damages from storm surges (Melillo et al., 2014).

A common measure of flood risk for a given structure is whether it would be inundated by flood hazards that have at least a one percent annual chance of occurring based on historical hydrological patterns— the so-called “100-year floodplain.” With climate change, the current 100-year floodplain is expected to widen, while structures in the current 100-year floodplain are generally expected to see more frequent and severe flooding (AECOM, 2013). While FEMA has mapped the 100-year floodplain in the areas of the United States with the majority of the population, the projected 100-year floodplain area as influenced by climate change is not readily available.

However, changes in risk are more easily identified in coastal areas, where sea level rise projections have been mapped. The 2014 NCA considered 1-4 feet of additional sea level rise as the likely range by