- Drought conditions remain in much of the interior of the state with drought conditions developing in north-east Texas.
- Much of Texas can expect warmer-than-normal and drier-than-normal conditions over the next three months.
- Statewide reservoir storage is near median levels.
I wrote this article on August 25, 2020.
So last month the cats and I waited for the outer rings of Hurricane Hanna to arrive in Austin, but they never came (although the hurricane certainly paid a visit to the Lower Rio Grande Valley). This afternoon (as I write this), the cats and I are waiting for Hurricane Laura’s path to reveal itself (which seems to be creeping more and more toward Houston and Galveston).
We are still on the upswing to the busy season for tropical systems in the Atlantic (Figure 1), and earlier this month, the Climate Prediction Center updated their hurricane season outlook. The revised outlook has an 85% chance of an above-normal season (up from 60% in May) with a significant chance of an extremely active season. The updated projection also holds that there’s a 70% chance of (1) 19 to 25 named storms, (2) 7 to 11 hurricanes, (3) 3 to 6 major hurricanes, and (4) an accumulated cyclone energy of 140 to 230% of the median. The number of named storms is considerably greater than the 13 to 19 projected in May. Increases in the projections are due to atmospheric and oceanic conditions and the growing likelihood of La Niña conditions, which tend to reduce vertical wind shear.
Figure 1: Number of tropical cyclones per 100 years in the Atlantic (source).
Most of the state received at least one inch of rainfall over the past 30 days with parts of coast getting six or more inches of rainfall, much from Hurricane Hanna (Figure 2a). Much of the Trans Pecos/Big Bend area received less than a tenth of an inch of rain over the past 30 days (Figure 2a). Despite these rainfalls, most of the state received less than normal amounts of rainfall over the past month with much of the Trans Pecos/Big Bend/Far West Texas areas getting less than 10% of normal (Figure 2b). Almost the entire state has received less than normal rainfall over the past 90 days (Figure 2c).
Figure 2a: Inches of precipitation that fell in Texas in the 30 days before August 25, 2020 (source). Note that cooler colors indicate lower values and warmer indicate higher values.
Figure 2b: Rainfall as a percent of normal for the 30 days before August 25, 2020 (source).
Figure 2c: Rainfall as a percent of normal for the 90 days before August 25, 2020 (source).
The amount of the state under drought conditions (D1-D4) increased from 36.4% four weeks ago to 47.6% today (Figure 3a) with a general intensifying of conditions in the western half of the state (Figure 3b). Numerous pockets of Extreme Drought conditions confetti’d across West and Trans-Pecos Texas with a pocket of Exceptional Drought in Presidio County (Figure 3a). In all, about 64% of the state is abnormally dry or worse (D0-D4; Figure 3a), slightly down from 66% four weeks ago.
Figure 3a: Drought conditions in Texas according to the U.S. Drought Monitor (as of August 18, 2020; source).
Figure 3b: Changes in the U.S. Drought Monitor for Texas between July 21, 2020, and August 18, 2020 (source).
The North American Drought Monitor for July now shows are large regional drought that stretched from Washington state down through Texas and deep into Mexico showing short-term and long-term effects (Figure 4a). Precipitation in much of the Rio Grande watershed in Colorado and New Mexico over the last 90 days is less than normal with the Sacramento Mountains at less than 25% of normal (Figure 4b). Conservation storage in Elephant Butte Reservoir decreased from 10.2% full on July 24 to 6.1% on August 25, approaching historic lows (Figure 4c).
The Rio Conchos basin in Mexico, which confluences into the Rio Grande just above Presidio and is an important source of water to the lower part of the Rio Grande in Texas, is now showing severe drought conditions (Figure 4a). Combined conservation storage in Amistad and Falcon reservoirs increased over the past month from 41.9% on July 24 to 42.9% on August 25, about 15 percentage points below normal for this time of year (Figure 4d).
Figure 4a: The North American Drought Monitor for July 31, 2020 (source).
Figure 4b: Percent of normal precipitation for Colorado and New Mexico for the 90 days before August 25, 2020 (source). The red line is the Rio Grande Basin. I use this map to see check precipitation trends in the headwaters of the Rio Grande in southern Colorado, the main source of water to Elephant Butte Reservoir downstream.
Figure 4c: Reservoir storage in Elephant Butte Reservoir since 2018 with the median, min and max for measurements since 1990 (source).
Figure 4d: Reservoir storage in Amistad and Falcon reservoirs since 2018 with the median, min and max for measurements since 1990 (source).
A number of river/stream basins in the state have flows over the seven days less than 25% of normal with four catchments with flows less than 10% of normal, two less than 5% of normal and one in extreme hydrologic drought (Figure 5a). Statewide reservoir storage is at 80.8% full as of July 24, down from 84.0% a month ago, and a few percentage points below normal for this time of year (Figure 5b). Storage in individual reservoirs dropped from last month with a number of reservoirs dropping below 90% full (Figure 5c).
Figure 5a: Parts of the state with below-normal seven-day average streamflow as of August 24, 2020 (source).
Figure 5b: Statewide reservoir storage since 2018 compared to statistics (median, min and max) for statewide storage since 1990 (source).
Figure 5c: Reservoir storage as August 25, 2020, in the major reservoirs of the state (source).
Sea-surface temperatures in the Central Pacific remained in neutral conditions but dropped more toward La Niña conditions (Figure 6a), so we remain in La Nada (neutral) conditions. The Climate Prediction Center increased the chance of La Niña conditions from 50 to 55% last month to ~60% this month with a ~55% chance of La Niña continuing through the winter (Figure 6b).
Figure 6a. Forecasts of sea-surface temperature anomalies for the Niño 3.4 Region as of July 20, 2020 (modified from source).
Figure 6b. Probabilistic forecasts of El Niño, La Niña and La Nada conditions (source).
The U.S. Seasonal Drought Outlook through November 30, 2020, continues to project drought persistence and development along much of West, Far West and Central Texas (Figure 7a). The Outlook also shows the drought consolidating across the western United States. The three-month temperature outlook projects (yawn) warmer-than-normal conditions statewide with greater warming to the west (Figure 7b) while the three-month precipitation slightly favors drier-than-normal conditions for much of the state (Figure 7c).
Figure 7a: The U.S. Seasonal Drought Outlook for July 16, 2020, through October 31, 2020 (source).
Figure 7b: Three-month temperature outlook from August 20, 2020 (source).
Figure 7c: Three-month precipitation outlook from August 20, 2020 (source).
Executive Director & Chief Water Policy Officer at The Meadows Center for Water and the Environment
Robert Mace is the Executive Director and the Chief Water Policy Officer at the Meadows Center. He is also Professor of Practice in the Department of Geography at Texas State University. Robert has over 30 years of experience in hydrology, hydrogeology, stakeholder processes, and water policy, mostly in Texas.