Water + Weather for September 2021 Posted on October 11, 2021
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Dr. Mark Wentzel – Hydrologist, Texas Water Development Board
Hi everyone, and welcome to the Texas Water Development Board's latest Water and Weather report. I'm Dr. Mark Wentzel, a hydrologist here in the Surface Water Division at the agency. And today, we'll be taking a look at conditions for our state at the end of September 2021.
Let's take a look at some of the big water and weather headlines. September was warmer and drier than normal for most of the state, a big change from the cooler and wetter conditions we experienced earlier this summer. At the end of the month, drought conditions covered 7 percent of the state, up six percentage points from the end of last month. Storage in our water supply reservoirs ended the month at 81 percent of capacity, about one percentage point more than normal for this time of year. After being almost washed out of the state in early September, drought is expected to cover more than two-thirds of the state by the end of the year. Earlier this summer, conditions were cooler and wetter than normal. That began to change in August and disappeared almost completely in September.
Let's take a closer look. On these maps, we're looking at average September temperature and precipitation relative to what is considered normal. From a water supply perspective, reds, oranges, and yellows mean trouble on both maps. They show areas with above-average temperature on the left and below-average precipitation on the right. September was the first month since March of 2021 that was both warmer and drier than normal for most of the state. That's a recipe for increasing drought and decreasing water supplies. One month of warmer and drier than normal conditions does not make for a statewide drought, but it's a step in that direction.
The U.S. Drought Monitor map for conditions as of September 28 shows the switch from drought reduction early in the summer to drought expansion recently. We ended the month of August with 1 percent of the state in drought, but by the end of September drought covered 7 percent of the state. This map doesn't reflect the influence of rain that fell on September 29 and 30, but the trend is clear. Without sustained widespread rainfall soon, Texas is headed for more, not less, drought.
Statewide, our water supply reservoirs were also impacted by the warmer and drier than normal conditions. The dark line on this chart shows how storage this year compares to minimum, maximum, and median values for the day of the year from data going back to 1990. Also displayed are lighter lines that show how we did in 2020 and 2019. Storage in our water supply reservoirs typically declines about two percentage points during the month of September. This year, with the hotter and drier than normal conditions, storage declined three percentage points. Fortunately, we started the month about two percentage points more than normal. At the end of September, with storage just under 81 percent of capacity, we still have about one percentage point more stored water than is considered normal for this time of year.
Where are things headed? The next few months are expected to follow the pattern of September, warmer and drier than normal. According to the latest seasonal drought outlook from the National Weather Service, that will lead to drought expanding to cover all but the eastern edge of the state by the end of the year.
That concludes our report. Until next time, I hope you all stay healthy and safe.