Fire (plus) flood (equals) beach: coastal response to an exceptional river sediment discharge event

Wildfire and post-fire rainfall have resounding effects on hillslope processes and sediment yields of
mountainous landscapes. Yet, it remains unclear how fire–flood sequences influence downstream
coastal littoral systems. It is timely to examine terrestrial–coastal connections because climate
change is increasing the frequency, size, and intensity of wildfires, altering precipitation rates, and
accelerating sea-level rise; and these factors can be understood as contrasting accretionary and
erosive agents for coastal systems. Here we provide new satellite-derived shoreline measurements of
Big Sur, California and show how river sediment discharge significantly influenced shoreline positions
during the past several decades. A 2016 wildfire followed by record precipitation increased sediment
discharge in the Big Sur River and resulted in almost half of the total river sediment load of the
past 50 years (~ 2.2 of ~ 4.8 Mt). Roughly 30% of this river sediment was inferred to be littoral-grade
sand and was incorporated into the littoral cell, causing the widest beaches in the 37-year satellite
record and spreading downcoast over timescales of years. Hence, the impact of fire–flood events on
coastal sediment budgets may be substantial, and these impacts may increase with time considering
projected intensification of wildfires and extreme rain events under global warming. Wildfire is an important factor in hillslope erosion and sediment yields of mountainous and forested