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Water and Weather for May 2021 Posted on June 09, 2021



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 in the Surface Water Division here at the agency. And today, we'll be taking a look at conditions for our state at the end of May 2021. 

May, which is historically our wettest month, brought above-average precipitation to large areas of the state. At the end of the month, drought conditions covered 25 percent of the state, down 40 percentage points from the end of April. Statewide, storage in our water supply reservoirs was up significantly, almost two percentage points, to end the month at 84.6 percent of capacity—within half a percentage point of what is considered normal for this time of year. And La Niña conditions, which are at least partially responsible for drought in Texas, have dissipated and are not expected to return this summer.

Let's take a closer look at May precipitation relative to what is considered normal for the month. The grays, greens, blues, and purples on this map show areas where precipitation was above normal. The yellows, oranges, and reds were below normal. Notice that May precipitation has been well above average for most of the state. And May is typically the wettest month of the year for Texas, averaging more than 3.3 inches of rainfall statewide. If you were trying to reduce drought in Texas, you couldn't pick a better month to have above-average rainfall. 

The results of above-normal rainfall in May have been pretty dramatic, as shown in the U.S. Drought Monitor map for Texas. This map for conditions on May 25 shows a 40-percentage-point decrease in drought from the end of April. Since this map was released, the last few days of May and the first few days of June have brought additional rainfall, setting us up for additional improvements in coming weeks.

The rainfall we got in May wasn't just good for the landscape; it also provided a welcome increase in the volume of water stored in our water supply reservoirs. 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. We began 2021 at 82 percent of capacity, right about normal for the time of year. In a normal year, we'd start to see a buildup in our reservoir storage beginning in mid-February thanks to increased inflows, cooler temperatures, and lower water supply demands. This year, there was no such increase. Instead, due to reduced precipitation, we stayed right about 82 percent of capacity well into April; that's about three percentage points lower than normal for that time of year. But thanks to a wetter-than-average May, our reservoir storage has now climbed to 84.6 percent of capacity, within about half a percentage point of normal, and a much nicer place to be as we head into summer. That concludes our report. Until next time, I hope you all stay healthy and safe.       

This article is posted in Weather / Water Data .