AFTER A YEAR OF EXTREMES, WHAT DOES MOTHER NATURE HAVE IN STORE FOR THE START OF 2019?
On August 30, 2018, 99 percent of the Brazos River basin was experiencing drought conditions. Then rain began to fall.
Gates were opened at Possum Kingdom Lake’s Morris Sheppard Dam for what would be one of the longest releases from the uppermost reservoir in the Brazos River Authority system. Within 6 weeks, the basin was entirely drought free.
Possum Kingdom Lake had released continuously for 30 days, moving more than 720,000 acre-feet of water downstream, adding an extra 210,000 acre-feet in the watershed above Lake Granbury, sending more than 930,000 acre-feet to Lake Whitney.
At the beginning of November, Lake Limestone, located on the eastern edge of the Brazos basin on the Navasota River filled for the first time in 17 months. By January 1, the BRA’s three reservoirs (Possum Kingdom Lake, Lake Granbury and Lake Limestone) combined have released over 2.4 million acre-feet of floodwaters. This amount was sufficient to fill all 11 BRA system reservoirs from empty to full.
After a summer of intensifying drought conditions, we ended the year in a very wet pattern that is expected to continue for the next several months. According to the NOAA Hydrologic Prediction Service, model data suggests prospects for higher than normal rain events. “The outlook for January calls for near normal temperatures and above normal precipitation,” the organization announced in a monthly email. “Soil moisture conditions should remain moist for the foreseeable future. For the 90-day January through March period, near normal temperatures and above normal precipitation is forecast.”
So, what happened to turn our weather situation on end? The answer is El Niño – and a weak one at that.
“We began (2018) with a mild La Niña, which contributed to dry conditions over the winter and spring,” said Texas State Climatologist, John Nielsen-Gammon, Ph.D. “The tropical Pacific gradually warmed, and presently El Niño conditions are in place, but enhanced rainfall from El Niño really wouldn't have kicked in until November. So, I think Texas weather is mostly to blame.”
Nielsen-Gammon added that Central Texas saw the most dramatic changes. “Waco, in particular, had a roller-coaster ride. The 12 months through August 2018 were the second-driest September-August on record at 14.34" (of rainfall), just 0.11" behind the drought precisely one century ago and more than twenty inches below normal. But then, 25.38" inches of rain followed in September through December 2018, the third-wettest September-December on record, and Waco ended up slightly wetter than normal!
As of mid-December, NOAA’s Climate Prediction Center said an El Nino was 90 percent likely, with a 60 percent chance it would persist into the spring. We're still waiting to see whether the El Niño conditions will stay around long enough to make this officially a full-blown El Niño event. Probably they will, so wetter than normal conditions would be slightly favored through April,” Neilsen-Gammon said.
We’ve heard a lot about El Nino in the past several years; so, what is the big deal?
According to NOAA, El Niño (which brings rainfall to Texas) and its companion, La Niña, “form a natural cycle that can last from a few months to two or three years. When they occur, weather patterns around the world can be affected, producing a range of impacts on crop yields, famine, heating, and cooling demands of homes and buildings, fire risks, coral bleaching, and extreme weather.” The last El Nino ended in 2016, and fortunately, the current cycle is not expected to be as severe as the last.
“With saturated soils over most of the basin, particularly upstream of Possum Kingdom Lake, any rain over the next several months will produce runoff, associated inflows into reservoirs, and reservoir releases,” said Aaron Abel, Water Services manager for the BRA. “During the winter months with dormant vegetation and lower evaporative rates due to shorter days with less sunlight, water losses in the watershed are much lower than during the remainder of the year. So, soils stay wet,” he said. Any additional rainfall at this point will result in runoff.
As we continue into the winter and early spring months, Abel adds it is likely that additional gate operations at Possum Kingdom Lake will be required to pass inflows if the rains continue.
Over and above rainfall, El Nino also effects seasonal temperatures, the potential for tornados, and hurricane season as well. According to NOAA’s Climate Prediction Center, there is an 86 percent chance of 2019 being among the top-five warmest years on record. Moreover, the organization states that “should El Nino develop as forecast into the summer months, it could have a suppressing effect on 2019’s hurricane season.” They add that it “remains to be seen whether spring 2019 will also give parts of the typically tornado-prone U.S. another breather.”
What will 2019 bring for the Brazos River basin?
“As of late December, NOAA's three-month outlook indicated above normal rainfall probabilities for all of the Brazos basin over the months of January, February, and March,” Abel said. “If we receive average or even below average rainfall over the next several months, reservoir levels will remain full. The rain that has already fallen over the last several months has caused streamflow and reservoir inflows to stay above normal and it will take some time for them to recede even if we get into a drier pattern.”
Abel added that as we head into the spring, typically our wettest months of April – June, it is anticipated that water supply storage will remain healthy into the spring and summer months.
“From a water supply perspective, we will definitely be in good shape regarding storage as we head into the summer months,” said Abel, suggesting the reservoirs will be full for the spring and into summer months. “However, when we do get into a period like we’ve seen over the last several months with above normal rainfall and numerous reservoir releases downstream, flood impacts are definitely a concern,” he said. “We strive to do everything possible to minimize those impacts.”
The latest seasonal drought outlook calls for no drought development in Texas through March of 2019, outside of the areas outside the Brazos basin where drought currently exists over the far west and the panhandle.