(A) Subsidence map for coastal Louisiana based on geostatistical interpolation (kriging) of 274 observations (black dots) of land-surface subsidence rates over the past 6–10 years. Areas in white and gray are agricultural and urban, respectively, and located outside of the wetlands. (B) Semivariogram of the data using 100 draws from different kriging options (gray), the data mean (black), and the kriging model (red). (C) Uncertainty (standard deviation) of the kriging estimate. Black squares show GPS stations. (D) Uncertainty (standard deviation) of the underlying data. Black squares show National Oceanic and Atmospheric Administration (NOAA) tide gauges. Note that the subsidence map can easily be converted into a relative sea-level rise map by adding the climate-driven sea-level component. Graphic: Nienhuis, et al., 2017 / GSA Today

By Chelsea Harvey
15 June 2017

(The Washington Post) – It’s common knowledge that the coast of Louisiana is quietly sinking into the balmy Gulf waters. But new research suggests we may have been underestimating how quickly it’s happening.

A new paper, published Wednesday in the Geological Society of America’s bulletin GSA Today, includes an updated map of the Louisiana coastline and the rate at which it’s sinking into the sea, a process scientists call “subsidence,” which occurs in addition to the climate change-caused process of sea-level rise. The new map suggests that, on average, the Louisiana coast is sinking at a rate of about 9 millimeters, or just over a third of an inch, per year — a faster rate than previous studies have suggested, according to the authors.

“I think it’s a point worth making that we are finding here that what people recently have considered worst case scenarios are actually conditions that we already see right now,” said Torbjörn Törnqvist, a geologist at Tulane University and a co-author on the new paper.

Scientists have long known that Louisiana is sinking. Subsidence is believed to be a natural process, which has likely been occurring in the region for thousands of years. But scientists believe the process has been enhanced by a variety of human activities in the Mississippi Delta over the past century, including oil and gas extraction, as well as the building of levees and other actions affecting the flow of the Mississippi River, which carries mud and sediment down toward the Gulf and helped build up the delta in the first place. [more]

Scientists say the rapid sinking of Louisiana’s coast already counts as a ‘worst case scenario’

ABSTRACT: Coastal Louisiana has experienced catastrophic rates of wetland loss over the past century, equivalent in area to the state of Delaware. Land subsidence in the absence of rapid accretion is one of the key drivers of wetland loss. Accurate subsidence data should therefore form the basis for estimates of and adaptations to Louisiana’s future. Recently, Jankowski et al. (2017) determined subsidence rates at 274 sites along the Louisiana coast. Based on these data we present a new subsidence map and calculate that, on average, coastal Louisiana is subsiding at 9 ± 1 mm yr−1.

A New Subsidence Map for Coastal Louisiana



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