By Mike Ekberg, manager for water monitoring and analysis

Last year was a wet one for the Miami Valley region, continuing a trend we’ve been seeing for a while now. The chart below shows how the 30-year average annual precipitation for the Great Miami River has changed since 1945. Note the upward trend, especially since about 1995.

Fig 6 30-yr Mean Precipitation

Noteworthy Weather

Notable weather came through our region in 2017, including a very warm February, outbreaks of severe weather in March and May; intense thunderstorms and localized flash flooding in July, a solar eclipse in August, and a cold December. By the end of December, La Niña conditions had developed in the Pacific Ocean, promising to influence the weather we are getting in 2018.

Precipitation for 2017 was well above average for communities across the Great Miami River Watershed at 48.27 inches. This is almost 8 inches above the 30-year (1981–2010) average annual precipitation of just 40.30 inches. One of the Miami Conservancy District (MCD) observation stations in Dayton recorded 46.28 inches of precipitation, the 18th highest since records began to be kept in 1883.

Monthly precipitation was significantly above average in March, May, June, July, October, and November. The months of February, August, September, and December were drier than normal. No record highs or lows were set in 2017.

Fig 5 Max and Min Precipitation Bar Graph

More high water events but only one in the Top 100

Above average precipitation led to above average runoff in 2017. Runoff is the portion of precipitation which flows downhill and enters streams, rivers, lakes or ponds. Annual runoff for the Great Miami River was 19.12 inches, which is 4.55 inches above average.

MCD recorded 16 high water events in 2017 – well above the annual average of eight. A high water event is defined by MCD as a time when one or more of the following occurs:

  • Any one dam goes into storage—when the conduits slow the flow of water. This is approximately when the conduits are flowing full.
  • The river at any one of the cities we protect reaches an action stage as defined by the MCD Emergency Action Plan.

The largest high water event in 2017 took place from May 4–10 and resulted in peak storage of 30,500 acre-feet (9.9 billion gallons) of water behind MCD dams. All of the dams except Huffman were storing floodwaters.This event ranked as the 60th largest high water event in MCD history.

All in all, 2017 was a continuation of the rising trend in precipitation for our region. What can we expect in the future? If the trend continues, more rain, more runoff, and more high water events.