Needs to Update Probable Maximum Precipitation for Critical Infrastructure

Abstract:

Probable Maximum Precipitation (PMP) is theoretically the greatest depth of precipitation for a given duration that is physically possible over a given size storm area at a particular geographical location at a certain time of the year. It is used to develop inflow flood hydrographs, known as Probable Maximum Flood (PMF), as design standard for high-risk flood-hazard structures, such as dams and nuclear power plants. PMP estimation methodology was developed in the 1930s and 40s when many dams were constructed in the US. The procedures to estimate PMP were later standardized by the World Meteorological Organization (WMO) in 1973 and revised in 1986.

In the US, PMP estimates were published in a series of Hydrometeorological Reports (e.g., HMR55A, HMR57, and HMR58/59) by the National Weather Service since 1950s. In these reports, storm data up to 1980s were used to establish the current PMP estimates. Since that time, we have acquired additional meteorological data for 30 to 40 years, including newly available radar and satellite based precipitation data. These data sets are expected to have improved data quality and availability in both time and space. In addition, significant numbers of extreme storms have occurred and selected numbers of these events were even close to or exceeding the current PMP estimates, in some cases. 

In the last 50 years, climate science has progressed and scientists have better and improved understanding of atmospheric physics of extreme storms. However, applied research in estimation of PMP has been lagging behind. Alternative methods, such as atmospheric numerical modeling, should be investigated for estimating PMP and associated uncertainties. It would be highly desirable if regional atmospheric numerical models could be utilized in the estimation of PMP and their uncertainties, in addition to methods used to originally develop PMP index maps in the existing hydrometeorological reports.