Black Water Rising The Growing Global Threat of Rising Seas and Bigger Hurricanes

摘要

Hew Orleans is a sort of American Venice, built on a watery site ideal for commerce and surrounded by a huge delta assembled over millennia by the Mississippi River. Levees intended to contain the river's floods have coincidentally eliminated the annual silt deposits; as a result, along with the effects of oil and gas extraction, the area is subsiding. In New Orleans the problem has been compounded by groundwater use and the immediate pumping of rainwater after storms. Without rainwater's slow percolation into the soil, aquifers are never recharged, and the land compacts still further, especially under heavy structures. The coastal parishes of Louisiana are sinking, on average, about 11 millimeters each year. At the same time, global sea level has been slowly rising over the last century, at 1.0-2.5 millimeters per year. The two trends have consigned half a million hectares of South Louisiana to the sea since 1932; the ongoing rate is about one and a half football fields every hour. Much of the lost land was coastal wetlands, which historically protected New Orleans by slowing and soaking up storm surges (the sudden rises in sea level that occur as hurricanes come ashore). The remaining wetlands are increasingly fragile, fragmented by canals built for navigation and access to the area's oil and gas.