By Mike Ekberg, manager of water resource monitoring and analysis
Any community that needs to replace or build a bridge, culvert, stormwater system, or conduct a floodplain analysis must compute peak stream flows during the design process. Understanding peak stream flows ensures the infrastructure will be designed large enough to handle rainfall and runoff.
In order to be certain that future hydraulic infrastructure is adequately designed for the climatic conditions that exist now and into the foreseeable future, it may be necessary to update rainfall frequency estimates for our region using a different methodology.
Who does this impact?
- A city, municipality, local or state government getting ready to design infrastructure such as stormwater management systems, culverts, roadways and bridges, or wastewater treatment plants.
- An engineer in the design phase for any type of infrastructure listed above.
- A local, state, and federal government, as well as engineers, mapping floodplain and regulating development in floodplains.
- A meteorologist or climatologist looking to estimate the severity of historic events.
Infrastructure planning and future rainfall amounts
Peak stream flows are computed using rainfall frequency estimates determined by the National Oceanic and Atmospheric Administration (NOAA). Unfortunately, the NOAA Atlas 14 rainfall frequency estimates (more detail on Atlas 14 below) for southwest Ohio are only based upon rainfall records through December 2000. Since that time, the monthly and annual rainfall in our region has increased, possibly making those estimates too low.
Many climate models indicate that the increasing trend in intensity and frequency of precipitation will continue in the future. Therefore, using only statistics from past observations could underestimate future rainfall frequency, which could result in the design of undersized engineering water infrastructure.
How can our region increase resilience?
NOAA has a new methodology that accounts for precipitation trends due to climate change. They published a report titled Analysis of Impact of Nonstationary Climate on NOAA Atlas 14 Estimates. The report recommends future precipitation frequency analysis use an approach that will account for historical trends and changes in climate. This new methodology should be applied to an updated rainfall frequency analysis for our region. In doing so, our region can help to ensure that hydraulic infrastructure is resilient to the climatic conditions of tomorrow.
As far as we know, NOAA doesn’t have a date for updating the Atlas 14 rainfall frequency estimates for southwest Ohio. Until this happens, new infrastructure could be designed too small. Please encourage NOAA to speed this process along. Otherwise we might wait another decade or more before these necessary updates occur.
Meanwhile, we can each do our part to reduce the negative effects of increased rainfall:
- Give streams and ditches more space to handle increased flows.
- Manage more water where it lands through green infrastructure like rain gardens, filter strips, rain barrels, etc.
- Slow down the flow of water to the storm system by implementing pervious paver systems on driveways, parking lots, and patios. More ideas and examples here.
More detail on Atlas 14: Atlas 14 is an ongoing study used to analyze historical rainfall data in order to update statistical hypothetical rainfall events. Based on historical data, Atlas 14 will assign probabilities to rainfall volumes to estimate the likelihood of a rainfall event, like a 100-year storm, occurring in any given year. Since the statistical data for storms in Ohio has not been updated in many years, this may cause significant changes in some regions’ projected rainfall volumes. For example, what is now considered a 100-year storm, may actually occur more frequently, the land area that floods during such a storm may be greater, and the volume of water that flows through a channel during that probability of rainfall might be some percent greater than current calculations. Commissioned by the National Oceanic and Atmospheric Administration (NOAA) and implemented by the Hydrometeorological Design Studies Center (HDSC) with the Office of Water Prediction (OWP), Atlas 14 has been completed across the majority of the United States but is outdated for Ohio.
Mike Ekberg is MCD’s Manager of water resource monitoring and analysis. A hydrogeologist, Mike has been with MCD since 2000. He is responsible for all MCD operations concerning collection of water quantity and quality data. He holds a Bachelor of Science degree in geology from Lehigh University in Pennsylvania, a Master of Science degree in geology from the University of Cincinnati and an MBA from Wright State University with an emphasis on project management.