A nonstationary flood frequency analysis method to adjust for future climate change and urbanization

Many current flood management policies and designs are based on an estimate of the 100-yr flood, an event that has a 1% chance of occurring in a given year. Existing methods to estimate the 100-yr flood, however, assume flood records are stationary even though multiple nonstationary factors, such as climate change and urbanization, influence measured hydrologic data. The goal of this study was to develop and apply a nonstationary flood frequency analysis method that accounts for multiple nonstationary factors. The method adjusts a measured flood record to urbanization and climate conditions for a future design year to account for the effects of changes in conditions from the year that each flood was measured to a selected design year. The method was applied to the Little Patuxent River in Guilford, Maryland, and the results showed a 30.2% increase in the 100-yr flood for the design year 2100. The developed method is intended to begin a discussion among engineers, scientists, and policy makers in regards to incorporating the issue of nonstationarity due to multiple factors into future policies and designs.