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Posted: February 1, 2021

2020 Precipitation: Up, Down and All Around

By Mike Ekberg, manager of water resources monitoring and analysis

Note: At MCD, we track water movement into and out of Great Miami River Watershed over long periods of time, spanning decades. The records generated by our observer precipitation stations, stream gages, and observation wells allow MCD staff to examine 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.

2020 will go down in history as anything but a normal year. And that goes for our region’s precipitation, too.

The Great Miami River Watershed started the year wet, with four of the first five months experiencing above-average precipitation. And then the tide turned, and the watershed saw drier-than-normal conditions for five of the last seven months.

Drought conditions existed in parts of the watershed from early July until mid-August and returned to parts of the watershed in mid-September, lingering until late October. October was uncharacteristically wet, averaging 5.02 inches of precipitation or 2.06 inches above average.

Despite the many drier months, total precipitation for the year was 2.26 inches above normal for a total of 42.56 inches, continuing a long-term trend of increased annual average precipitation.

The chart represents an average of 42 precipitation stations MCD operates.

Average Annual Precipitation Increasing

The chart below shows how the 30-year average annual precipitation for the watershed has changed since 1945. Note the upward trend in precipitation that began sometime around the late 1980s to early 1990s.

This graph shows the moving average 30-year precipitation for the Great Miami River Watershed.

Runoff

The higher-than-average amounts of precipitation in 2020 led to above-average runoff. Runoff is that portion of precipitation which ultimately ends up in the Great Miami River. Annual runoff for the Great Miami River was 16.01 inches in 2020—1.4 inches above average.

Two High-Water Events in the Top 100

MCD recorded 12 high-water events last year—well above the average of eight. MCD defines a high-water event as a time when one or more of the following occurs:

  • Any one of MCD’s five flood protection dams goes into storage—when the conduits slow the flow of water. This is approximately when the conduits are flowing full.
  • The Great Miami River in any one of the 10 cities MCD’s system protects reaches an action stage as defined by MCD’s Emergency Action plan.

The largest high-water event in 2020 took place from May 19-23 when all five MCD dams together stored a peak of 9.2 billion gallons (28,200 acre-feet) of water. This event ranked as the 69th largest high-water event in MCD history. MCD also recorded its 96th largest event in 2020.

While no monthly or annual records were set in 2020, we did experience two top 100 high-water events. The above-average total precipitation and runoff as well as the higher-than-average high-water events continue to provide evidence of a changing climate in southwest Ohio. A climate that seems to be getting wetter with time.