Texas heat is not letting up at night

The heat wave in Texas has offered little reprieve. 

For two straight weeks, high temperatures in Del Rio have exceeded 100 degrees Fahrenheit each day — rising at its highest to 115 F. 

Just as worrisome — nighttime temperatures have set records and offered no relief. On all but one day, Del Rio’s lowest temperature was at least 80 F, according to National Weather Service data. 

Heat at night disrupts sleep and prevents the body from recovering and cooling down, making minimum temperatures a critical indicator of a heat wave’s severity, experts said. In many parts of the country, nights are warming faster than days — a sneaky risk to people’s health.

“There are a number of studies on health impacts that show nighttime temperatures are particularly important,” said Ben Zaitchik, a professor in the Earth and planetary sciences department at Johns Hopkins University who studies extreme heat. “The body’s accumulated heat stress can lead to all kinds of complications and the ability of the body to relax at night can be critical.”

Texas State Climatologist John Nielsen-Gammon said temperatures during this heat wave in the state have threatened records at both ends of the spectrum — including maximums and minimums — in its urban centers.

“We’ve had a couple stations, mostly urban ones, that have come close to having periods of time with record minimum temperatures — San Antonio and Houston,” he said.

Nielsen-Gammon said several areas, including Midland, San Angelo and Del Rio, have set records for weekly average temperatures, an indicator of the length and severity of this heat wave, which was triggered by a prolonged stretch of high pressure.

Kristie Ebi, a professor at the Center for Health and the Global Environment at the University of Washington who specializes in heat and climate change research, said deaths during heat waves typically start after the 24-hour mark as stress accumulates on the body.

“It takes a while for our heart to become hot, before you see something like a heart attack,” she said. “We have behavioral mechanisms — it’s hot, we try to find a place to cool down. We have physiological mechanisms — sweating. There’s a real effort to bring that core temperature down on the behavioral and physiological side.”

Ebi said the high nighttime temperatures and the prolonged nature of the Texas heat wave are particularly concerning. 

The toll of heat is often underestimated in part because its cumulative stresses can exacerbate underlying health conditions. After a heat wave is complete, researchers will compare death data to prior years, control for other factors and then tally the number of “excess deaths” — people who would not have otherwise died if not for extreme temperatures. 

“A very small percentage of death certificates during a heat wave put down, ‘heat’ as an underlying cause,” Ebi, who studies heat deaths, adding that about half of excess deaths, on average, are from cardiovascular diseases. 

Climate change is causing temperatures to rise in Texas. Average daily minimum temperatures have risen from 51.9 F in 1970 to 54.2 F in 2020 — a change of about 2.3 F, which is roughly in line with the overall pace of warming in the state. 

“Everything’s been going up at about the same rate — daily minimums, daily maximums, winter versus summer,” Nielsen-Gammon said. “We’re now 2 degrees above the 20th century average in all seasons.”