Methods to Estimate the Annual Exceedance Probability (AEP) of the 1-day Probable Maximum Precipitation

Estimating probabilities of extreme-weather events is critically important for avoiding weather-related disasters. Quantitative risk-based decision making is becoming an accepted methodology in dam safety evaluations. Traditionally, deterministic procedures such as the Probable Maximum Precipitation (PMP) and Probable Maximum Flood (PMF ) are used to design critical infrastructure such as dams. An important input for dam safety would be the probability of occurrence of extreme events such as the PMF and PMP. Several methodologies are identified in the literature for estimating the annual exceedance probability (AEP) of extreme precipitation.
Applied Weather Associates (AWA) conducted a site-specific PMP study for the Catawba basin using a deterministic storm based approach. After the PMP study, several methods were used to develop magnitude-frequency curves for annual 1-day peak precipitation events up to and including PMP magnitude. The curves were used to estimate the AEP of the PMP for three sub-basins in the Catawba basin. The 1-day PMPs were determined to have AEPs between 10-5 and 10-7. The estimated AEPs are site-specific and are a function of storm location, storm duration, basin area, and terrain.
This presentation will discuss methods used to estimate the site-specific PMP and the associated AEP for the 1-day PMP for three sub-basins in the southeastern United States. Methods discussed will include: i) site-specific statistical curve extension, ii) regional L-moment statistical approach, and iii) stochastic storm transposition approach.