New research confirms that the land under the Chesapeake Bay is sinking rapidly and projects that Washington, D.C., could drop by six or more inches in the next century—adding to the problems of sea-level rise. This falling land will exacerbate the flooding that the nation’s capital faces from rising ocean waters due to a warming climate and melting ice sheets—accelerating the threat to the region’s monuments, roads, wildlife refuges, and military installations. For sixty years, tide gauges have shown that sea level in the Chesapeake is rising at twice the global average rate and faster than elsewhere on the East...