Mid-20th century land-use change greatly reduced flood intensity in the Southeastern US

Abstract Land cover and land use influence hydrologic processes, but their impacts on flooding remain obscure amid intensifying land-use changes and the global increase in heavy precipitation. Instrumental records are short relative to the long history of land-use change and inadequate for discerning regional flood changes attributable to land use. Here we integrate a new high-resolution paleoflood discharge record spanning the past ~200 years from the largest basin in the Southeastern United States with regional stream gage data and hydrologic modeling. We find that flood magnitudes in the region exhibit a substantial decrease beginning in the 1950s CE. The high magnitudes in the early 20th century correspond to widespread forest clearance and soil erosion, while the mid-20th-century reduction corresponds to soil conservation measures and reforestation in the region. We evaluate the role of land-use change on flood intensity by testing the sensitivity of Hurricane Florence’s (2018 CE) flood to different land-use configurations using the WRF-Hydro model. Our findings indicate that river floods are sensitive to land-use change — even on large river systems. Further, our work implies that aggressive agriculture expansion and ongoing rapid urbanization, together with climate change, will generate substantial increases in flood hazard without mitigation measures.