State of Statewide PMP-Where We've Been and What's Next

ABSTRACT ONLY - 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, led by Ed Tomlinson, 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. Sixteen statewide and regional PMP studies have been completed in the last ten years, with three 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, funding in the PRECIP act may provide an avenue for a public-private partnership that will utilize this work to support continual updates and improvements of a national database. Exciting improvements in the PMP estimation process continue to be in development, including meteorological modeling of PMP storms, leveraging advancements in Geographic Information Systems (GIS), and evaluating climate change impacts. Given all the work and funding states have committed to PMP updates and implementation, it is imperative they have a seat at the table to ensure their important work is utilized to help build the foundation for future PMP development in any national programs.