Improved Practical Methods for Considering Climate Change in Design Flood Estimation

In practice, methods arbitrarily increasing probable design rainfall or return periods have been adopted to derive design flood increases due to climate change. However, the method of arbitrarily increasing probable design rainfall is inadequate because probable rainfall estimated by the common frequency analysis method usually cannot be accepted in trend tests, meaning there is no increasing trend due to climate change. In addition, the method of increasing return periods to increase design flood is problematic. Rising flood damages—an opportunity to recognize climate change—are caused by concentrated flooding due to urbanization rather than increased probable rainfall. Thus, we proposed new methods for considering climate change in design flood estimation, by changing the temporal distribution of design rainfall or adjusting parameters in the rainfall-runoff process. Furthermore, the method of raising the freeboard criteria is proposed as an alternative for considering climate change.