Probable Maximum Precipitation: What Is It, How Is It Calculated, and How Do I Apply It?






Join us on December 10, 2024, from 12:00 PM - 2:00 PM Eastern for Probable Maximum Precipitation: What Is It, How Is It Calculated, and How Do I Apply It? This webinar will provide detailed discussions related to the development of Probable Maximum Precipitation and its application for dam safety. Detailed information will be provided regarding the history of PMP development and its use in dam safety design, the current standard of practice for calculating PMP estimates, the uncertainties and subjective aspects of PMP, how deterministically derived PMP depths relate to risk analyses, and where climate change factors into PMP estimates and dam design. Specific examples will be provided of site-specific and statewide PMP studies that demonstrate the calculation process from start to finish and include examples of the results that are used as input for Probable Maximum Flood (PMF) development. This will include discussions on how the PMP depths have changed through time and how to address differences across study domain, as well as trends in PMP depths, future expectations, and how to address situations where PMP information has been updated versus locations that have not been updated. The examples will include an explanation on the proper selection of the magnitude, spatial, and temporal distribution of a major precipitation event. Discussion on the future development of PMP and potential federal involvement will also be provided. Note: A companion webinar is planned that will provide training on the use of the PMP to generate the PMF, including a walk through the rapidly evolving Army Corps’ HEC-HMS and HEC-RAS modeling processes to transform rain into the runoff.

Learning objectives attendees will receive from this webinar:

  • Understand what PMP is, where the concept came from, why we use it, and how it is calculated.
  • Learn when to consider a site-specific study for your location.
  • Understand how to address differences between adjacent locations that have updated PMP versus those that don’t have updated information.
  • Discuss why PMP depths have changed through time, what those trends are, and why they occur.
  • Comprehend the areas of uncertainty in the PMP development and how those affect design decisions and dam safety.
  • Discuss the application of PMP outputs and the importance of temporal and spatial patterns for PMF, what temporal rainfall distributions to use, and where to find them.
  • Learn how to determine which durations are most important for your location and dam design.
  • Understand when to consider rain-on-snow flood runoff scenarios.
  • Learn how climate change may affect PMP estimates today and in the future.
  • Explore the integration of deterministically derived PMP estimates within the risk-informed decision process and risk analysis needs.
  • Discuss the future of PMP and what‘s next.


  • This course qualifies for 2 PDHs.



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