The North Carolina Department of Environmental Quality’s Dam Safety Program, in collaboration with Applied Weather Associates, has introduced a new tool aimed at improving storm preparedness. This initiative marks the release of the state’s first Probable Maximum Precipitation (PMP) study and evaluation tool, which seeks to enhance readiness for future storms and their potential impact on dams across North Carolina.
“We know that storms will keep coming, with increasing frequency and intensity, and this new tool will help us better prepare for storms and their impact on dams,” stated DEQ Secretary Reid Wilson. He emphasized ongoing collaboration with federal and local agencies as a key strategy in disaster preparedness.
The PMP study analyzes data from 91 storms over the past 150 years in North Carolina and nearby regions. It examines storm types, severity, coverage area, and rainfall intensity. Notably, recent events like Hurricane Helene are part of this study. The tool aims to update the state’s response to severe rainfall impacts on hydraulic structures such as dams.
“Before the new PMP tool, the standard for storm preparedness was based on the Hydrometeorological Report 51,” explained Toby Vinson, Director of the Division of Energy, Mineral and Land Resources. “This new tool is based on the most current scientific methods.” He noted its significance given increasing storm intensity.
There are three major differences between the PMP Study and HMR51:
1. Local storms include smaller thunderstorm systems.
2. General storms cover multiple states.
3. Tropical storms include hurricanes covering large areas.
The PMP considers terrain characteristics and evaluates shorter rainfall durations affecting smaller high-hazard dams across North Carolina.
HMR51 evaluated only one type of storm with minimum six-hour durations for larger watershed areas. In contrast, the PMP assesses one-hour durations for watersheds as small as one square mile—relevant to most dams in North Carolina.
While not predictive of specific impacts from incoming storms, this new tool provides accurate data for preparation and hydraulic structure design.
The Dam Safety Program has made available the PMP study online along with an evaluation tool, user manual, tutorials, and additional information.
