The challenge of quantifying risk in the face of climate change on the east coast
High in the Appalachian Mountains of Western North Carolina, there is a hydrologic ‘four corners’ where the headwater boundaries of four major river basins converge – the New, Watauga, Yadkin and Catawba Rivers. I live nearby, along the upper reach of the New River, in the small college town of Boone, NC. As a hydrologist, moving into a house along a stream in the mountains was, in part, a dream-come-true - my science, my source of fascination, and the centerpiece of my preferred pastimes were right outside my door. Rather than checking the nearest gauge data online, I could peer out my door to judge if the river was prime for canoeing; rather than driving across town to dip my feet in cool swirling eddies in the summer, I could scramble down the bank at the edge of my yard; and rather than dragging my kids in the car to see raging streams after downpours, I could drag them to the bedroom window (and endure far fewer renditions of – “can we PLEASE go home now Mom?”).
That said, as a hydrologist, I also knew all too well that moving into a house on a riverbank came with risks. Like most others in my field, when I hear the words “mountain stream,” I promptly think “flash flood.” Before we moved in, the owner told us the river had not risen above its bank since his family built the house in 1955. I checked historic records and FEMA maps, confirming the house was outside of the 500-year floodplain, thanks to the height of the streambank. This was reassuring, but I also knew such maps are fraught with uncertainty and assumptions of stationarity. Nevertheless, indulgence and family pleas prevailed.
Perceptions of Flood Risk
Talking with others around town, we quickly learned that certain spots within the community flood on a regular basis – the Boone Mall, Deerfield Rd, portions of App State campus, and many more. Sure enough, within a few weeks of moving into town, we got the chance to see the flooding for ourselves. A few months later it happened again…. then again… and again. Each time, I watched the water level like a hawk, checked downstream data, and made rough forecasts of peak flow at our house. In most events, the river peaked between three to five- feet higher than baseflow, but still well below the top of the bank.
Then came October 2017, when nearly six inches of rain fell over a few hours. Two weeks earlier, five inches had fallen in one day, and it had rained on and off since. The ground was saturated. Large sections of town were underwater. The damage was significant. Our house stayed dry, but the river swelled uncomfortably close to bankfull. It was one of the worst floods in Boone in recent years, but it was not the result of one of the many recent hurricanes to hit this State.