The 2021 Central Texas summer has been noticeably mild, with temperatures in the Hill Country cooled by rainy and overcast days. This summer, Camp Mabry in Austin counted 31 days with measurable rain. That makes it the third rainiest summer when it comes to days of rainfall in the 123 years of record keeping. Between early June and Late September we received a rainfall total of 10.5 inches with July and August reporting above-average numbers.
While the above-average rainfall over the summer provided enough to keep vegetation on the surface nice and green, it wasn’t enough to generate substantial aquifer recharge to keep Edwards water levels at the Lovelady monitoring well from falling. Upper Trinity levels saw a substantial rise due to a combined 11 inches in April and May and have maintained elevated levels since. Middle Trinity levels have been declining since late June.
Aquifer levels in the Edwards and Middle Trinity continued to decline through a particularly dry September until heavy rain fell on September 9th. The heaviest amounts were seen in central Hays County, recording between 1 to 6 inches (texmesonet.org). The Austin area saw between 0.5 to 4 inches. Even this amount of rain didn’t generate much recharge because the very dry surface soils soaked up most of it. With increased soil moisture due to that rainfall, the stage was set for the next rain event to produce more runoff to recharge.
That rain came on October 13th as an average of 4.2 inches spread across the Hill Country. Some areas received up to 6 inches. This brought considerable recharge as stream gauges on all area creeks showed rises. This includes the Blanco River at Wimberley, where flow peaked at 11,400 cubic feet per second (cfs), Jacobs Well Spring & Cypress creek peaked at 361 cfs, Onion creek near Driftwood saw peak flow of 2,400 cfs and Barton Creek above Barton Springs reached 950 cfs just to name a few. Water levels as of October 19th in Edwards, Upper Trinity and Middle Trinity aquifers have seen a positive response to the rains (Figure 1). As of October 19th Lake Buchanan is 89% full and Lake Travis is 73% full.
So far in 2021 we have received a total of 33 inches of rain, just 2.5 inches below the annual average, which means we could finish 2021 with an above-average year. This may be due to a 6 month ENSO-neutral (neither La Nina or El Nino) period from March to October 14th. This neutral period has allowed for sufficient rainfall to bring us close to the 35.5 annual average.
According to the latest advisory from the Climate Prediction Center, La Nina officially developed on October 14th and is expected to continue into 2022. Remember that La Nina typically brings a warmer and drier climate to Central Texas. For more on La Nina visit here.
It was 10 years ago, in 2011, that climate experts blamed one of the worst droughts since the 7-year drought of the 1950s on the La Nina phenomenon. 2011 was the driest year ever for Texas with only 14.8 inches of rain.
Hopefully we can expect more rainfall before the end of the year even with the recently developed La Nina. As drought conditions always loom in Central Texas, it’s important that we continue our community effort to conserve water.