Uncertainty analysis of regional flow duration curves

Flow duration curves (FDCs) are useful tools for many water resource development and management purposes. Many water resource projects are located at ungauged sites, however, for which FDCs are required but unavailable due to the lack of observed flow records. Both the polynomial and area-index methods are introduced herein to synthesize FDCs at ungauged sites and estimate their uncertainties for the upper catchments of the Cho-Shuei Creek in Taiwan. The major difference between these two methods is that the area-index method only uses drainage area to explain regional variation, whereas the polynomial method uses annual rainfall, altitude, and drainage area. Results obtained by using cross validation at 15 stations indicate that the polynomial method produces better estimates of synthetic FDCs at ungauged sites than the area-index method. Furthermore, uncertainty analysis through bootstrap resampling reveals that the polynomial method has less uncertainty in synthesizing FDCs than the area-index method.