Abstract:
Probable Maximum Precipitation-20 Years of Updating the HMRs
and What to Expect through 2100
Development of statewide and regional Probable Maximum Precipitation (PMP) studies has
accelerated over the past several years because of the need to update Hydrometeorological
Reports (HMRs), to include recent storm data, to apply current scientific understanding of
extreme precipitation, and to provide accurate meteorological information for hydrologic
analysis. HMRs currently in use were published from the 1960's to 1990's. Each of these
documents cover large regions varying from single states (HMR 59 California) to large regions.
At the same time, the need for updates and strain on state dam safety offices continues to
increase. To address HMR limitations, many states have chosen to update PMP information
through statewide and regional PMP studies. The first statewide PMP update was for the states
of Wisconsin and Michigan in 1993. This study provided a significant benefit to the two-state
region by improving the PMP development process and including additional storm data. The
next statewide PMP update, Nebraska, did not occur until 2008. The Nebraska study updated
the PMP storm database and provided significant improvements in the data and methods. The
utility of the statewide and regional PMP studies is that PMP are updated for hundreds or
thousands of dams at once, thereby saving millions of dollars, improving safety, and helping to
alleviate stress on state dam safety offices. Numerous statewide and regional PMP studies
have been completed in the last ten years, with several other states currently in progress. The
benefit of this work is enormous with improvements continuing to be realized during each
study. Going forward, data and information from these PMP studies is being consolidated into
an easily accessible user interface that will allow access to PMP results, will provide detailed
documentation, and will not have software specific requirements. In addition, evaluations of
how climate change may impact PMP development have been considered in many of these
studies. This presentation will discuss PMP through time and what to expect going into the
future.
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