Understanding Inundation Risk
Sea Level Rise
In the State of Maryland, permanently inundated land is no longer real estate, the title is invalid. In Charles County, sea level rise is a risk for land loss particularly around Blossom Point and Cobb Island. This map indicates the present elevation of low lying areas in meters.
There is uncertainty in expected sea level rise and its timing, not only owing to uncertainty in future greenhouse gas emissions (stuff we can fix) but also owing our incomplete understanding of how abruptly ice can enter the oceans from the big reservoirs in Antarctica and Greenland.
This next figure needs some unpacking. It comes from this government report.
The blue line in (a) is the intermediate scenario reaching about 3 ft of sea level rise in 2100. But that is average over the globe. The orange patches around where we live indicate that the sea level rise we would see would be around one to two feet higher than that. Similarly, where the blue line gives about a foot for the average in 2050, we would be closer to 2 feet by then. This would make tidal encroachment on the new sewage treatment facility for Cobb Island a fairly regular occurrence by mid-century. Beach erosion for the island itself could be a serious problem for property owners even sooner.
By the end of the century, Cobb Island would be overwashed by moderate storms with some frequency bringing damage similar to that brought by Isabel, perhaps annually. The sewage treatment facility would have to have modifications to prevent inundation and roads and bridges would need serious improvements. The red line in (a) which combines everything extra bad scientists have considered thus far (worst case) gets us to this situation fifty years earlier around 2050. At the close of the next Charles County Comprehensive Plan, 2036, we’d see what we would expect in 2050 for the intermediate scenario.
Storms
This government report anticipates how often very strong rainfall events will occur as a consequence of climate change. As can be seen above, a trend is already strong in our region as Ellicott City can attest. With continued greenhouse gas emissions, the trend could grow to close to a 300% increase in our region. Strong, slow moving rain events put great pressure on our stormwater management infrastructure and may make emergency services unable to respond to calls during flooding emergencies when roads are overwhelmed. Management of this change in conditions may require enlarged culverts, strengthened water retention facilities and even raised roads. Participation in the national flood insurance program may need to be broadened as well as flood maps are revised to include more property within the 100 year flood contours.