By Mike Ekberg, manager of water resources monitoring and analysis
One year ago, I wrote a blogpost summarizing the year 2017 as “another wet year.”
Now I’m summarizing water conditions for 2018, and I could pretty much copy and paste what I posted last year. And, with some minor changes, it would ring true. Last year reflects a continuation of the trend in rising precipitation for our region. If it continues, we’ll see more rain, more runoff, and more high-water events in the future.
The chart below shows how the 30-year average annual precipitation for the Great Miami River has changed since 1945. Note the upward trend in precipitation that began sometime around the late 1980s to early 1990s.
Significant weather events in 2018 included record high precipitation in February, a large high-water event in April, significant showers and thunderstorms in August, the remnants of Tropical Storm Gordon in September, a much warmer-than-normal October, and a cold and very wet November.
Precipitation for 2018 was much above average for the Great Miami River Watershed at 50.68 inches. This is 10 inches above the 30-year average annual precipitation of 40.30 inches. The Miami Conservancy District (MCD) observation station in Dayton recorded 48.70 inches of precipitation in 2018, which is the sixth highest since record-keeping began in 1883.
Monthly precipitation was more than 1 inch above average in February, April, August, September, and November. May, July, and October were the dry months, recording more than 1 inch below-average precipitation. February set an all-time record high for the month with an average of 5.35 inches of precipitation for the Great Miami River Watershed.
The greater-than-average amounts of precipitation in 2018 led to above-average runoff. Runoff is that portion of precipitation which flows downhill or seeps into aquifers, and enters streams, rivers, lakes or ponds. Runoff in the Great Miami River Watershed ultimately ends up in the Great Miami River. Annual runoff for the Great Miami River was 23.26 inches in 2018, which is 8.69 inches above average. MCD recorded 13 high-water events last year – well above the 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 MCD’s Emergency Action plan.
The largest high-water event in 2018 took place from April 3-9 and resulted in a total peak storage of 65,050 acre-feet (21.2 billion gallons) of water behind all five MCD dams. This event ranked as the 12th largest high-water event in MCD history. MCD also recorded its 49th and 55th largest events in 2018.
There is evidence that rising global temperatures are increasing the amount of water or humidity in the atmosphere. Satellites have measured a 4-percent rise in water vapor in the air column. The more humid atmosphere seems to be making storms wetter. Many weather stations in the United States are showing increases in extreme precipitation. Our region seems to be showing signs of this trend.