Mapping the Extent of the Devastating July 4 Texas Flash Flood Event

CISESS
July 14, 2025
Highlights

The July 2025 flood event in Texas Hill Country, fueled by remnants of Tropical Storm Barry, resulted in, to date, 135 fatalities, including 28 children at riverside camps, the deadliest U.S. inland flood since 1976.

The Flash Flood Alley’s landscape features narrow valleys with thin, clay-rich soils overlying fractured limestone bedrock. This geology forces >70% of rainfall to become surface runoff (minimal infiltration). Valleys like the Guadalupe River basin constrict floodwaters and accelerate flow velocities. Even moderate rain can trigger rapid rises. Two hundred and fifty-four mm of rainfall fell in three hours, midnight July 3–4 at Hunt (500% of the July average), exceeding a 1,000-year recurrence interval. On 4 July, the Guadalupe River rose 8 m in 45 minutes, overwhelming Camp Mystic (152 m from the channel). The unique atmospheric-topographic nexus enabled rapid runoff amplification. It was cloudy on 4 July, and the Visible Infrared Imaging Radiometer Suite (VIIRS) daily 375-m floodwater product was unable to provide usable flood inundation information.

ESSIC/CISESS Scientist Qingyuan Zhang and the NOAA STAR Flood team have been working to order synthetic aperture radar (SAR) images and produce SAR flood inundation products. One Sentinel-1 image on 4 July was acquired and processed, and the NOAA STAR Flood team produced a SAR flood inundation map based on this image (see figure). The 4 July SAR map captured some flood inundated areas. All flood products are delivered to the RealEarth platform at the Space Science and Engineering Center at the University of Wisconsin-Madison for public use.

This article was put together by the CISESS coordinators based on scientist input.

Debra Baker

Debra Baker is the Coordinator for the Cooperative Institute for Satellite Earth System Studies (CISESS) at the University of Maryland. She received her M.S. in atmospheric science from the University of Maryland, College Park. Before joining ESSIC in 2013, she worked on air quality issues at the Maryland Department of the Environment. Debra also has a law degree from Harvard Law School.

Kate Cooney

Katherine Cooney is a part-time faculty assistant at the Cooperative Institute for Satellite Earth System Studies (CISESS). Kate received a B.S. in environmental science and policy from the University of Maryland (UMD), College Park. She later earned a M.S. in geology from UMD, while investigating the isotopic fractionation of precipitation nitrate under the guidance of Distinguished University Professor James Farquhar. After graduation, she worked as an air-quality specialist at the Mid Atlantic Regional Air Management Association in Baltimore, Maryland. While her family was stationed in Tokyo, Japan, she dedicated her time serving military families and the local community. She is grateful for the opportunity to return to earth system studies, supporting the CISESS Business Office and assisting the CISESS Coordinator Deb Baker since January 2021.