25 of the 28 largest U.S. metropolises studied are sinking each year. Texas cities like Houston, Dallas, and Fort Worth are experiencing the most dramatic land subsidence–or sinking of land. Land subsidence can cause increased flood risks and structural damage, which is even more pronounced in urban centers. Groundwater extraction is the main driver of the sinking in most locations, according to the study. Other factors include the loading effect of urban development, oil and gas extraction, and glacial isostatic adjustment–the slow rise or fall of land caused by the melting of massive ice sheets.