Water + Weather for August 2021 Posted on September 03, 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 August 2021.
Let's take a look at some of the big water and weather headlines. August was cooler than normal for most of the state and wetter than normal for about half the state, continuing a trend since May of cooler and wetter-than-average conditions. At the end of the month, drought conditions covered 1 percent of the state, about the same as at the start of the month. Storage in our water supply reservoirs ended the month at 84.1 percent of capacity, about two percentage points more than normal for this time of year. At the end of August, 75 percent of the state's major water supply reservoirs are holding more water compared to last year.
The two weather variables that drive water conditions in our state are temperature and precipitation. So far this summer, we've benefited from cooler and wetter-than-normal conditions. While not quite as good as previous months, August has continued that trend. Let's take a closer look. On the map on the left, we're looking at average temperature relative to what is considered normal. On the right, we're looking at precipitation relative to what is considered normal. Note the color scheme is reversed on these maps. From a water supply perspective, greens, blues, and purples are preferred on both maps. They show areas with below-average temperature on the left and above-average precipitation on the right. Not all areas benefited from both below-average temperature and above-average rainfall, but many areas benefited from at least one of these conditions during the month. Thanks to generally cooler and wetter conditions, we're ending August with very little of the state impacted by drought.
The U.S. Drought Monitor map for conditions as of August 31 shows less than 1 percent of the state in drought, down slightly from the end of July. Having this little of the state impacted by drought this time of year is unusual. Over the last 22 years, we've averaged about 40 percent of the state in drought by the end of August. Since 2000, we've only had two other Augusts that ended with less drought area: 2004 and 2007.
Cooler and wetter conditions this summer have also benefited our water supply reservoirs. The dark line on this chart shows how statewide 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. As you can see from the dotted red line that represents median conditions, storage in our water supply reservoirs typically declines about three percentage points from the end of May to the end of August. This year, the cooler and wetter conditions have reduced demands on our reservoirs while keeping evaporation low and inflows high. As a result, we ended August at 84.1 percent of capacity, down half a percentage point from how we ended May. In fact, at the end of August 2021, three out of four water supply reservoirs around the state are holding more water compared to last year.
That concludes our report. Until next time, I hope you all stay healthy and safe.