Evidence of Increasing Nonstationary Flood Risk in the Central Himalayas

Extreme floods provide a design basis for flood-sensitive infrastructures. There is strong evidence of climate change to alter the characteristics of extreme floods in the central Himalayan region, Nepal. However, current infrastructure design practices rely on the assumption of stationary flood peak records. Given the nonstationary behavior in extreme floods, traditional infrastructure design specifications may yield poor outcomes. Here we show that assuming climate stationarity can drastically underestimate extreme floods. We find that the uncertainty in extreme flood estimates is driven by complex interaction between uncertainties associated with data record length, model priors and model structures. Our results highlight the importance of incorporating climate nonstationarity into extreme flood estimates, and are of practical use for keeping infrastructure reliable over the service life.