Asheville rainfall extremes

Earlier this year on September 27^th Asheville, NC was the center of the devastation brought by hurricane Helene, with record-breaking rainfall which resulted in extreme flooding. The flooding inundated homes, businesses, and roads, displacing hundreds of residents and leading to billions of dollars in damages and hundreds of houses destroyed in Buncombe County. With 227 fatalities Helene became the deadliest hurricane to hit the US since Katrina in 2005.

With one of the longest daily rainfall records in the U.S., dating back to the 1870s, Asheville’s historical data highlights the peculiar nature of this event. The figure shows, for each year in the historical record, the maximum 24-hour (blue) and 72-hours (yellow) rainfall totals. While Helene’s 1-day rainfall (and peak rainfall rate) were significant but not unprecedented and were exceeded at least twice in the historical record, the 3-day total far exceeded anything in Asheville’s history. This record-breaking 3-day rainfall was fuelled by two days of heavy rain before Helene’s arrival, caused by a unique meteorological setup. The precursor rain saturated the ground and raised river levels, leaving the region vulnerable to catastrophic flooding once Helene made landfall.

This event highlights the growing challenge of preparing for extreme weather. The sequence and intensity of rainfall, rather than daily peaks alone, proved decisive in causing the devastation. At Inigo, we’re prioritizing the evaluation of flood risk models and maximizing our learning from these events to improve our preparedness and resilience in the face of increasingly severe weather patterns. Asheville’s experience underscores the urgency of better understanding flood risk and adapting to a changing climate to mitigate future risks.