Eighty-five percent of the world's largest deltas have experienced severe flooding over the past decade, according to the authors of an overview article published online in Nature Geoscience. The authors predict that the amount of deltaic land vulnerable to flooding could rise by 50% if sea-level rise occurs as projected for the twenty-first century.
James Syvitski and colleagues assessed the overall state of 33 major delta systems across the globe from satellite measurements and historical maps. They found that only nine of these deltas were keeping up with sea-level rise, and, of those, four were barely breaking even. They attribute the relative sinking of delta surfaces primarily to human interference ― the sinking deltas were affected by upstream damming and river diversions, which limited the amount of new sediments carried to the delta. At some sites the recovery of oil and gas also led to sediment compaction.
Increasing rates of sea-level rise in response to greenhouse gas emissions will only increase the likelihood that swollen rivers and storm surges will flood these vulnerable areas.