outlook+water: Drought expands, reservoirs fuller, drought expected to expand in West Texas

SUMMARY:

• Drought conditions expanded to 27% of the state (D1–D4); statewide reservoir storage rose to 75.1% full but still about ten percentage points below normal for this time of year.
• El Niño has a 95% chance of extending through the March-April-May season, with La Niña favored in June-July-August and through at least November-December-January.
• Drought is expected to remain and expand in West and Far West Texas and improve in parts of the Hill Country.

I wrote this article on May 5, 2024.

I continue to focus on the levels in Travis, Buchanan, Canyon, and Medina lakes and flows in the springs this month since they remain at or near record lows. As I write this on May 5, several good storms moved over the Colorado River watershed over the weekend, particularly upstream of Lake Buchanan and Lake Travis. Thus far, the rains and resulting run-off have not resulted in higher water levels in Canyon Lake (Figure 1a) or Lake Medina (Figure 1b). Lake Buchanan shows a “fake bump” in percent full with a seasonal contraction of the conservation pool (water for use) due to a seasonal expansion of the flood pool (Figure 1c). However, recent rains have also brought up the real levels of the lake. So far, Lake Travis doesn’t show much of a benefit from the rains, although levels are slightly up (Figure 1d). Sometimes, it takes time for run-off to route to the reservoirs, so watch those hydrographs!

The Edwards Aquifer, under the jurisdiction of the Edwards Aquifer Authority, remains at Stage 3 drought with flows at San Marcos Springs at about 116 cubic feet per second (Figure 1e), down from a long-term average of 160 cubic feet per second and flows at Comal Springs at 152 cubic feet per second (Figure 1f), down from a long-term average of 320 cubic feet per second. The Edwards Aquifer, under the jurisdiction of the Barton Springs Edwards Aquifer Conservation District, remains at Stage 2 drought, with flows at Barton Springs at about 37.5 cubic feet per second (Figure 1g), down from a long-term median of 66 cubic feet per second.

Figure 1a: Reservoir storage in Canyon Lake since 2022 as of May 5, 2024, with the median, min, and max for measurements from 1990 through 2023 (graph from Texas Water Development Board).

Over the past month, we’ve had the usual more rain in the east and northeast (with large areas receiving 10, 15, and more than 20 inches) and less rain in the west (El Paso to Big Bend along the Rio Grande receiving less than 0.01 inches) (Figure 2a). The percent of normal rainfall over the last month looks just like the rainfall map (Figure 2b). The percent of normal rainfall over the 90 days looks just like the rainfall map for the last 30 days (Figure 2c). All these rains, particularly over the past week, have resulted in flooding in the Houston area that has gained attention from national news.

The amount of the state under drought conditions (D1–D4) increased from 23% four weeks ago to 24% today (Figure 3a), with a mixture of drought improvements and developments across the state (Figure 3b). Extreme drought or worse stayed the same as four weeks ago at 2% of the state, with exceptional drought remaining at 0% (Figure 3a). In all, 45% of the state is abnormally dry or worse (D0–D4; Figure 3a), up from 43% four weeks ago.

The North American Drought Monitor, which runs a month behind current conditions, shows drought in New Mexico, Southern Colorado, and Mexico, among other places (Figure 4a). Parts of the Rio Grande watershed in Colorado and New Mexico show higher-than-normal rainfall over the last 90 days (Figure 4b).

Conservation storage in Elephant Butte Reservoir—an important source of water for the El Paso area—rose slightly from 21.9% four weeks ago to 22.0% more recently (Figure 4c), slightly below median storage since 1990.

The Rio Conchos basin in Mexico, which confluences with the Rio Grande just above Presidio and hosts the largest tributary to the Lower Rio Grande, remains in Extreme to Exceptional drought (Figure 4a). Combined conservation storage in the Amistad and Falcon reservoirs decreased to 19.9% full from 22.6% four weeks ago, almost 40 percentage points below normal for this time of year (since 1990) and the lowest in at least the past 33 years (Figure 4d).

Basins across the state continue to host flows over the past week below historical 25th, 10th, and 5th percentiles (Figure 5a). Statewide reservoir storage is at 75.1% full, up about 900,000 acre-feet from 72.3% four weeks ago and about 10 percentage points below normal for this time of year since 1990 (Figure 5b). Recent rains have not topped up most of the reservoirs in the central part of the state (Figure 5c).

The reservoir marked in yellow in the Dallas-Fort Worth area (the lemon in a sea of blueberries) is New Terrell City Lake and has dropped from full in early March (Figure 5c). I could not discern the cause, but I suspect it is for maintenance on the reservoir and/or dam.

My (drumroll, please) “Hydrograph of the Month” is Stillhouse Canyon Lake due to its quick rise out of record-low territory over the last month. However, it continues to be almost 30 percentage points lower than average (Figure 5d).

Sea-surface temperatures in the Central Pacific that, in part, define the status of the weather phenomenon known as the El Niño Southern Oscillation, still remain in El Niño conditions; however, temperatures are dropping (Figure 6a). Projections suggest El Niño conditions continuing with a return to neutral conditions in the March-April-May season. This month’s projection is similar to last month’s except for a cooler La Niña (Figure 6a; these end-of-projection bumps appear to be due to uncertainty). The official probabilities, a month newer than the projections in the graph, give El Niño conditions a 95% chance of extending through the March-April-May season, giving way to strongly favoring (>80%) neutral conditions in April-May-June and odds favoring La Niña conditions starting in June-July-August (Figure 6b). Accordingly, we remain under a La Niña Watch.

The U.S. Seasonal Drought Outlook through March projects drought persistence and development in West and Far West Texas with drought improvement and even removal in the Hill Country (Figure 7a).

The three-month temperature outlook projects above-average temperatures for the state (Figure 7b) while the three-month precipitation outlook favors drier-than-normal conditions for West and Far West Texas (Figure 7c).