Peaks-Over-Threshold Flood Analysis
Peaks-over-threshold (POT) flood analysis models every independent flood peak that exceeds a chosen high threshold, rather than only the single largest peak in each year. The number of exceedances in time is treated as a Poisson process and the amounts by which peaks exceed the threshold are modeled with the Generalized Pareto distribution — the extreme-value limit for threshold exceedances given by the Pickands-Balkema-de Haan theorem. Because a wet year may contain several damaging floods and a dry year none, POT (also called the partial duration series) uses the data more efficiently than the annual-maximum approach, which is why Lang, Ouarda, and Bobée's 1999 operational guidelines and USGS Bulletin 17C both treat it as a key complement to annual-maximum frequency analysis. The method delivers the same design-flood quantiles for chosen return periods, often with lower variance at short return periods.
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- Lang, M., Ouarda, T. B. M. J., & Bobée, B. (1999). Towards operational guidelines for over-threshold modeling. Journal of Hydrology, 225(3-4), 103-117. · DOI 10.1016/S0022-1694(99)00167-5
- England, J. F., Jr., Cohn, T. A., Faber, B. A., Stedinger, J. R., Thomas, W. O., Jr., Veilleux, A. G., Kiang, J. E., & Mason, R. R., Jr. (2018). Guidelines for Determining Flood Flow Frequency — Bulletin 17C. U.S. Geological Survey Techniques and Methods, book 4, chap. B5, 148 p. · DOI 10.3133/tm4B5
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