Assessment of Chen and other methods for estimating intensity-duration-frequency functions

Estimation of intensity-duration-frequency (IDF) functions at ungauged locations is sometimes done using the method introduced by Chen in 1983 [Chen, C. 1983. "Rainfall intensity-duration-frequency formulas." J. Hydraul. Eng. 109 (12): 1603-1621.], with local rainfall statistics as input. This study applied the Chen method at 9,264 gauged locations in 44 states. The results were used to assess the validity of the fundamental assumptions of the Chen method, and to quantify the accuracy of IDF functions estimated using this method. It is shown that the two fundamental assumptions incorporated in the Chen method are not universally valid across all regions of the United States. Average statewide relative errors are in the range of -17.2 to 3.4%, with standard deviations in the range of 5.4-34.6%. Alternative approaches were investigated that will likely yield more accurate estimates of IDF functions.