La Nina gets most of the blame for the prolonged drought. “For the past 20 years Texas has fit the pattern of La Nina/El Nino,” Nielsen-Gammon said. That pattern shows that when waters in a specific area of the Pacific Ocean are cooler, the Southern United States experiences warm and dry conditions. That’s La Nina. When those waters are warmer, El Nino comes into play and conditions are cool and damp in the Southern United States.

“Most climatologists credit La Nina for the current drought,” he said.

But other factors also contribute to Southwestern weather patterns. Tropical storms in the Gulf of Mexico may break drought cycles as may storms coming across the Sierra Madre.

Nielsen-Gammon said drought contributed to the unusually high temperatures in the Southwest last summer. “Because of dry conditions, we also had high temperatures,” he said. “Most of the excess heat was due to lack of rainfall and lack of evaporation.”

He said evaporation from soil and plants helps cool temperatures. With drought, plant growth is diminished and evaporation reduced. “Solar energy goes into the soil instead of into evaporation, so it gets even drier.”

He said temperatures in Texas have been “unusually warm over the past decade. Except for the Panhandle, Texas’ coolest decade was the 1970s.”