The area burned by wildfires has increased in recent decades and is expected to increase in the future for many watersheds worldwide due to climate change. Burned areas within watersheds increase soil erosion rates, which can increase the downstream accumulation of sediment in rivers and reservoirs. Using an ensemble of climate, fire, and erosion models, we show that post-fire sedimentation is projected to increase for more than ¾ of watersheds by at least 10% and for more than ¼ of watersheds by at least 100 % by the 2041 to 2050 decade in the western USA. In this region, 65% of the water supply originates from forested lands that are prone to wildfire, and many of the watersheds with projected increases in sedimentation are important headwaters of rivers and reservoirs that meet water demands of downstream users.