Yahoo - Research from the University of California, Irvine revealed that many of the planet's most populated coastal regions are subsiding faster than the oceans are rising.
In the study, published in the journal Nature, researchers analyzed satellite radar data across 40 major river deltas, including the Mississippi, Nile, and Yellow River deltas.
They found that land in these regions is constantly shrinking and that more than 236 million people now face increased flooding risk due to delta subsidence alone.
The researchers said human activity is the main driver. According to the University of Southampton, which was involved in the study, about 35% of the 40 studied deltas were primarily sinking due to groundwater extraction, while others were impacted by sediment loss and urban development.
"The dominance of subsidence over sea-level rise was more pervasive than anticipated," said Leonard Ohenhen, lead author of the study, in a statement. "In every delta we monitored, at least some portion is sinking faster than the sea surface is rising."
In the U.S., the Mississippi River Delta is sinking at an average of 3.3 millimeters per year, with some areas dropping more than 3 inches per decade.
Why is delta subsidence happening?
River deltas support massive populations, major ports, agriculture, fisheries, and ecosystems that people and wildlife rely on, yet they make up less than 1% of Earth's land surface, according to the Geological Society of America.
As deltas sink, flood exposure worsens, storm surges become more destructive, and drinking water sources are increasingly contaminated by saltwater. Entire communities may eventually be forced to relocate, as has already begun in parts of coastal Louisiana.
This sinking is made even more dangerous by rising seas driven by human-caused pollution from burning oil, coal, and gas. Meanwhile, warming temperatures are melting polar ice and expanding ocean water.
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