outlook + water: May 2018

By Robert Mace, Chief Water Policy Officer at The Meadows Center for Water and the Environment

SUMMARY:

  • Rainfall deficits continue to afflict most of the state.

  • La Niña is expected to fade into neutral conditions (La Nada) by the end of May; there’s a growing chance of El Niño conditions arriving by winter.

  • Drought conditions in west and south Texas are expected to persist and expand over the next three months, but wetter conditions are expected for the fall.


Most of the state remains bitterly dry, especially in West Texas, but recent rains have reduced 90-day rainfall deficits for much of the state. Nonetheless, sizable areas around Amarillo, Midland-Odessa and Big Bend have seen less than 25 percent of average rainfall over the past three months (Figure 1). The north-east, the El Paso-area, and smatterings in the central part of the state have enjoyed greater than normal rainfall over the same period.

Figure 1. Rainfall as a percent of normal for the past 90 days (as of May 17, 2018). [source]

Figure 1. Rainfall as a percent of normal for the past 90 days (as of May 17, 2018). Source.

The North American Drought Monitor looks much worse than the one from February with drought worsening overall in the American Southwest including the headwaters of the upper Rio Grande (Figure 2).

Figure 2. The North American Drought monitor for April 20, 2018. Source.

Figure 2. The North American Drought monitor for April 20, 2018. Source. 

For the state, reservoir storage has moved to below normal for this time of year (below the median as measured since 1990) at about 84 percent full (Figure 3). This is the second time this year that statewide reservoir storage has been below normal, and we are about to head into out typically dry, summer months. As has been the case since the late-1990s, many West Texas reservoirs have been less than 50 percent full (Figure 4).

Figure 3: State-wide reservoir storage since 2016 compared to statistics (median, min, and max) for state-wide storage since 1990. Source.

Figure 3: Statewide reservoir storage since 2016 compared to statistics (median, min, and max) for state-wide storage since 1990. Source.

Figure 4: Reservoir storage as of May 17, 2018, in major reservoirs of the state. Elephant Butte Reservoir in New Mexico is shown because it is an important source of water to the El Paso area. Source.

Figure 4: Reservoir storage as of May 17, 2018, in major reservoirs of the state. Elephant Butte Reservoir in New Mexico is shown because it is an important source of water to the El Paso area. Source.

Looking forward, the Climate Prediction Center says that we will be coming out of La Niña conditions (which generally result in dryer-than-normal and warmer-than-normal conditions for Texas) by next month—good news for those weary of drought. Furthermore, the Center projects a 50 percent chance of El Niño conditions appearing this fall (which generally result in wetter-than-normal and cooler-than-normal conditions for Texas). A 50 percent chance sounds like a coin flip, but in this case, it’s a three-sided coin with La Niña conditions on one side, La Nada (neutral conditions) on the second side and El Niño conditions on the third side. Equal probability across the sides is therefore 33 percent, so 50 percent favors El Niño conditions (with a 40 percent chance of La Nada and a 10 percent chance of Niña). Winter outlooks for Texas show wetter-than-normal conditions but warmer-than-normal conditions (everything seems to be warmer than normal these days…). Stay tuned as we get closer to the end of the year.

Figure 5. Forecasts of sea surface temperatures anomalies for the Nino 3.4 Region as of April 19, 2018. Modified from source.

Figure 5. Forecasts of sea surface temperatures anomalies for the Nino 3.4 Region as of April 19, 2018. Modified from source.

The U.S. Seasonal Outlook through the end of August projects drought remaining but becoming less severe in the Panhandle with drought remaining and developing in south Texas (Figure 5). The National Weather service projects warmer-than-normal temperatures and normal rainfall over the next three months for Texas (source).

Figure 5. The U.S. Seasonal Drought Outlook for May 17 through August 31, 2018. Source.

Figure 5. The U.S. Seasonal Drought Outlook for May 17 through August 31, 2018. Source.

The National Weather Service has not yet published its hurricane outlook for 2018 (one is expected later this month); however, early predictions by others suggest a more active season this year (the lack of El Niño conditions supports this). Colorado State University (safely nestled away from tropical systems) projects 14 named storms, 7 hurricanes and 3 major hurricanes.