The Mississippi River is the largest commercial waterway in North America and one of the most heavily engineered rivers in the world. Future alteration of the river’s hydrology by climate change may increase the vulnerability of flood mitigation and navigation infrastructure implemented to constrain 20th century discharge conditions. Here, we evaluate changes in Lower Mississippi River discharge from 1920-2100 C.E. by integrating river gauge observations and climate model simulations under different greenhouse gas emissions scenarios. We show that the Lower Mississippi River’s flood regime is highly sensitive to emissions scenario; specifically, the annual probability of discharge exceeding existing flood mitigation infrastructure increases from 0.08% to 3.3% by the year 2100 under high greenhouse gas emission forcing (RCP8.5), primarily driven by increasing precipitation and runoff within the basin. Without aggressive reductions in greenhouse gas emissions, flood mitigation infrastructure may require substantial retrofitting to avoid catastrophic disruptions to industries and communities along the Lower Mississippi River.
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