July 10, 2023

Climate Shift Index™ alert

CSI alert archive: Southwestern July 2023

Climate Central analysis finds that human-caused climate change continues to make persistent, dangerous heat in places in Texas, the Southwest, and Mexico at least 5 times more likely.

This ongoing heat event started in mid-June, leading to significant health and safety impacts across Texas and Mexico. The heat and climate change signal is forecast to continue through at least Friday, July 14. 

Note: This is an ongoing event that will likely continue beyond July 14. Use the U.S. Climate Shift Index map to stay updated on the latest climate-related heat, as well as to download custom daily graphics for specific U.S. cities. The Global Climate Shift Index map provides daily forecasts for the entire globe. 

CSI alert archive: Southwestern July 2023

Forecast: extreme heat wave across Mexico and U.S. Southwest

  • An almost week-long stretch of extreme and potentially record-breaking heat is forecast across large areas of Mexico and the U.S. Southwest from Sunday, July 9 to Friday, July 14, 2023. 

  • Temperature anomalies during the latter part of the week, from July 12-14, are forecast to reach more than 15°F hotter than normal across most of California. Additionally, large parts of the Southwest (including Nevada, Arizona, and New Mexico), along with a majority of Texas and the state of Chihuahua, Mexico, will experience temperatures 10-15°F hotter than normal.

  • Daytime temperatures are forecast to exceed 100°F in major U.S. cities. Daytime high temperature records in the region for July 13 include: 104°F (Austin, in 2022), 112°F (Laredo, 1998), 114°F (Phoenix, 2020), 114°F (Las Vegas, 2005), 85°F (San Diego, 1984), 110°F (Fresno, 1983).

  • Many cities will experience extended periods of extreme heat. The most intense 3-day periods for impacted cities are listed below. Each of these cities is at Climate Shift Index (CSI) level 5 for at least three days (more on CSI below).

    • Bakersfield, CA: peak on 7/13, 17°F above normal

    • Austin, TX: peak on 7/12, 12°F above normal

    • San Antonio, TX: peak on 7/12, 11°F above normal

    • Chihuahua, Mexico: peak on 7/13, 8°F above normal

    • Monterrey, Mexico: peak on 7/12, 10°F above normal

  • Data for over 200 cities in the U.S. and Mexico is available here.

  • The extreme heat will be combined with high humidity across extensive portions of Texas, leading to dangerous daytime heat index values of up to 115°F. 

  • Overnight low temperatures will not fall below 90°F in some desert valley regions in California and Arizona, thereby exacerbating the threat of heat-related illnesses and stress placed on regional electricity systems. 

Attribution science analysis: climate change makes this event at least 5x more likely

  • From July 9-11, daily maximum temperatures are expected to reach Climate Shift Index (CSI) levels of 5 in central Texas, parts of New Mexico and Colorado, large parts of the Mexican state of Chihuahua, and most of the Gulf Coast of Mexico. 

  • A CSI level 5 indicates that human-caused climate change made this excessive heat at least 5 times more likely, signifying an exceptional climate change event. 

  • During this same period (July 9-11), CSI levels 1 to 4 are forecasted in the following locations, indicating that climate change made the high heat in these regions at least 1.5 to 4 times more likely: large parts of Texas and New Mexico, eastern locations in Arizona, and the majority of Mexico, stretching nearly down to Mexico City. 

  • Forecasted daily highs are 7-15°F hotter than the average in the locations where CSI is forecast to reach the maximum level of 5. The most extreme temperature anomalies are expected in eastern Texas, New Mexico, and Chihuahua, Mexico.

  • From July 12-14, CSI levels of 5 will become more widespread, covering the vast majority of Texas, large parts of New Mexico, Colorado, the Mexican state of Chihuahua, most of central to western Mexico, much of the Gulf Coast of Mexico, as well as some locations in Utah, Arizona, and central California. 

  • Additionally, the rest of Texas and New Mexico, as well as Louisiana, Oklahoma, most of Mexico, Arkansas, Missouri, Kansas, California, Arizona, and parts of Nevada and Utah will reach CSI values of 1 to 4 during July 12-14, indicating that the high heat in these regions have been made at least 1.5 to 4 times more likely.

  • Over the entire period (July 9-14), 34 million people in the U.S. (22 million) and Mexico (12 million) will experience at least one day with CSI level 5. It is possible that 11 million people (4 million in the U.S., 7 million in Mexico) may experience at least five days at this level.

Looking back: heat impacts in Texas and Mexico during June 2023

This week’s heat is a continuation of the significantly impactful heat across a broad region from Central America to the southern U.S in June 2023. The heat in this region had a strong climate fingerprint: climate change increased the probability of the sustained extreme temperatures experienced during this event. Over 100 million people in Mexico and the U.S. experienced five or more days with temperatures that were made at least five times more likely by human-caused climate change. 

Impacts in Texas:

  • Since the beginning of the heat wave, at least 13 deaths were reported in Texas due to heat-related illness (as of June 28), 11 of which occurred in Webb County, which includes Laredo where the CSI was at or above level 3 from June 13-27. The CSI was at level 5 from June 18-23 when Laredo set a series of daily records. 

  • Heat-related fatalities include many older adults between the ages of 60 and 80, as well as outdoor workers and inmates, many of whom did not have access to air conditioning. [Other sources: 1, 2]

  • On June 20, there were at least 350 ER visits due to heat illnesses across Texas, the highest number of single day visits in 2022 and 2023 so far. 

  • The Electricity Reliability Council of Texas (ERCOT) reported a record electricity usage of 80,828 MW on June 27.

  • Wind and solar energy have helped meet the extra demand in electricity. Renewable energy generation reached a record of 31,498 MW on June 28, enough to power more than 6 million homes. ERCOT reports that 1MW could power about 200 homes during peak demand.

Impacts in Mexico:

  • Mexico registered at least 112 heat-related deaths so far this year, 64 of which were in the state of Nuevo León, which borders Texas. In the same period, at least 1,559 people received medical treatment due to heat-related issues.

  • Mexico’s electricity system was under emergency operational status as the country’s reserve reached a historic low. Electricity demand peaked at 52,993 MW on June 20, 2023.

  • The city of Chihuahua, in Northern Mexico, reported that increased electricity demands led to power failures that affected 30% of the city’s water supply in June, leaving some residents with no water.

  • In total, only 16% of households in Mexico are equipped with air conditioning (as of 2018), according to the International Energy Agency (IEA).


Dr. Andrew Pershing, VP of Science at Climate Central, said: 
“This is a dangerous heat event that will impact tens of millions of people. Carbon emissions from burning coal, oil, and natural gas made this event more likely, longer, and more intense.”

To request an interview with a Climate Central scientist, please contact Peter Girard at pgirard@climatecentral.org

Reporting resources as this heat event unfolds:

Health & Safety

  • Populations most vulnerable to high temperatures include older adults, young children, pregnant people, individuals with chronic conditions, members of low income and historically marginalized communities, athletes, and outdoor workers.

  • Exposure to risky heat can trigger heat-related illnesses, including heat exhaustion and heat stroke, a life-threatening condition. For more information on heat safety, visit the National Integrated Heat Health Information System’s Planning and Preparing guide.

  • For more information on heat and the related human health implications refer to the follow  Climate Matters briefs

Attribution Science

About the Climate Shift Index 

Climate Central’s Climate Shift Index, grounded in the latest peer-reviewed science, maps the influence of climate change on temperatures across the globe, every day. 

Climate Shift Index levels indicate how much human-caused climate change has altered the frequency of daily temperatures at a particular location. Level 1 indicates that climate change is detectable in that day’s temperature. Level 2 means that climate change made exceptionally warm temperatures in a given location at least twice as likely. Level 5 is the maximum and indicates temperatures at least 5 times more likely because of climate change.

For this analysis, temperatures come from NOAA’s Global Forecast System model.

Previous Climate Shift Index alerts