By Mike Ekberg, Manager of water resource monitoring and analysis
At MCD, we track water movement into and out of the Great Miami River Watershed over long periods of time, spanning decades. The records generated at precipitation stations, stream gages, and observation wells enable MCD staff to track long-term trends in water resources.
Water enters the watershed as precipitation (rain, sleet, hail, and snow), and it exits the watershed through evaporation, plant transpiration, and runoff.
2021 precipitation was above average, despite a slow start
In regards to precipitation, the year 2021 got off to a slow start. January through April experienced below-average precipitation however, June, July, September, October, and December saw significantly above-average precipitation.
Annual precipitation for 2021 in the Great Miami River Watershed totaled 44.15 inches. This total was 2.23 inches above average, continuing a long-term trend of increased annual precipitation.
2021 annual runoff was below average
Despite the above-average precipitation, the runoff amounts recorded were below average. Annual runoff for the Great Miami River was 15.45 inches in 2021. That is 0.76 inches below average. The reason for the below average runoff has a lot to do with a process called evapotranspiration.
Evapotranspiration happens when water is transferred from the land to the atmosphere by evaporation from soil and other surfaces, and by transpiration from plants. Evapotranspiration is low during winter and early spring months. Much of the precipitation that falls during these months ends up as runoff in rivers and streams.
In 2021, precipitation was generally below average during the low evapotranspiration months. This resulted in less runoff during the time of the year when conditions are most favorable for high runoff to occur.
15 high water events occurred during 2021
There were 15 high-water events last year. That is well above the average of eight. MCD defines a high-water event as a time when one or more of the following occurs:
- When any one of MCD’s five flood protection dams goes into storage. That happens when the conduits slow the flow of water. This is approximately when the conduits are flowing full.
- When the Great Miami River, in any one of the 10 cities MCD’s system protects, reaches an action stage. The action stages for each city are defined in MCD’s Emergency Action plan.
The largest high water event in 2021 took place from March 18 to 23 when all five MCD dams together stored a peak of 8.2 billion gallons (25,295 acre-feet) of water. The event ranked as the 79th largest high-water event in MCD history.
Changes in precipitation and runoff are striking
The transition from 1981 – 2010 to 1991 – 2020 for establishing monthly and annual averages in precipitation and runoff is remarkable. Annual precipitation increased by 4% and annual runoff increased by 11%. All of these changes occurred over a period of just 10 years! While no monthly or annual records were set in 2021, MCD precipitation and runoff data continue to provide evidence of a changing climate in southwest Ohio.
This trend is likely to continue and if it does, our region can expect to experience an increase in urban flooding and an increase in streambank erosion that could result in damages to infrastructure, loss of property, and potential loss of life.
Adapting to a wetter climate
What can our region do to adapt to wetter climatic conditions? Here are four things to consider.
- MCD’s priority is to maintain the flood protection infrastructure so that it will continue to keep the Great Miami River from overflowing its banks in the protected areas, just as it has the past 100 years.
- Homeowners can take steps to manage stormwater infiltration and runoff on their properties. Installing rain gardens can reduce, or slow down, runoff. Ensuring that sump pumps are working properly and have backup power can keep basements dry.
- Communities may need to retrofit existing stormwater infrastructure to accommodate larger storm events. Installing green infrastructure practices such as rain gardens, drainage swales, and pervious surfaces increases the resilience of their stormwater systems.
- Developers should consider water resource protection a priority in new development and infill projects. Increasing the desirability of homes and businesses and resiliency can occur by restoring natural features, preserving floodplains, and protecting stream channels.
Identifying new normals for precipitation and runoff averages
Southwest Ohio’s climate is rapidly changing and getting wetter. The differences in the amount of water that falls as precipitation and flows in rivers and streams compared with a decade ago are striking. This may mean we’ll experience more urban flooding and more streambank erosion, if our region doesn’t adequately adapt to the changing conditions.
Every 10 years, MCD staff redefines “normal” when it comes to 30-year averages for monthly and annual precipitation and runoff for the Great Miami River Watershed. Precipitation is any moisture that falls to the ground and runoff is that portion of precipitation which ultimately ends up in the Great Miami River.
In 2021, MCD transitioned from the 1981 – 2010 time period to the time period of 1991 – 2020 for establishing 30-year averages in monthly and annual precipitation and runoff. This transition is consistent with the approach used by the National Oceanic and Atmospheric Administration (NOAA) as well as the World Meteorological Organization for establishing climate normals. The transition also gives the public a standard way to compare today’s conditions with “normal” conditions. MCD will not update 30-year averages for precipitation and runoff again until the year 2031. At that time the 30-year averages will be updated to the time period of 2001–2030.
The charts below show the month by month change in the 30-year averages between the two time periods.
Average monthly precipitation and runoff increased for most months of the year when comparing the time interval of 1981 – 2010 with 1991 – 2020. In fact, average monthly precipitation increased for 9 out of the 12 months of the year and average monthly runoff increased in 11 of those month. Likewise, the 30-year average annual precipitation for the Great Miami River Watershed increased from 40.30 to 41.92 inches, and the 30-year average runoff increased from 14.57 inches to 16.21 inches.
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.