CORPUS CHRISTI, Texas — As has been the case during other devastating weather disasters, the topic of cloud seeding has again become popular. Claims that humans caused the deadly flooding in the Texas Hill Country quickly began circulating as news of the tragedy gained attention. While weather modification is a real activity, it should be understood that it is not possible for it to have caused the Texas Hill Country floods. This Science Snippet isn't focused on that claim, but instead on what cloud seeding is, and why scientists are researching it, and why/how it happens. Hopefully, this knowledge will help to further explain why the aforementioned claim is false.
What is 'cloud seeding'?
Cloud seeding is a type of weather modification. According to the National Oceanic and Atmospheric Administration (NOAA), weather modification is defined as 'any activity performed with the intention of producing artificial changes in the composition, behavior, or dynamics of the atmosphere.' There are federal laws governing this activity. Globally, the World Meteorological Organization provides "guiding best practices for research and operational projects" related to weather modification, but does not promote or discourage the practice.
The goal is to provide 'seeds' to alter the small-scale physics of a cloud.
How do clouds form?
In order to understand cloud seeding, you'll need to know how clouds form and what makes them precipitate.
NOAA defines clouds as 'the visible aggregate of minute particles of water and/or ice that form when water vapor condenses in the atmosphere'. Water vapor is the gas form of water, and in order to be visible, the gas needs to condense onto a surface. These surfaces or particles become what's known as "cloud condensation nuclei" (CCN) or in this case, the 'seeds'.
You've likely seen how water vapor condenses into water when you bring out a cold soda can on a hot summer day (note how this doesn't happen when the can is warm or similar to the outside temp.) The same process happens in the air above us. Water vapor in the air (at the right temperatures) will condense onto little particulates: specks of dust, smoke, soot, and salt. Together, these tiny cloud droplets can make a visible cloud. It may surprise you, but clouds can be pretty massive! According to NOAA, clouds are heavy and "can weigh tens of millions of tons yet float in the atmosphere". You can learn all about clouds here.
What's used to 'seed' a cloud?
Typically cloud seeding will use the following agents:
- Silver Iodide
- 'Dry ice' or Solid Carbon Dioxide
- Salts
- Liquid Propane
Less commonly used or experimental:
- Potassium Iodide: Similar to silver iodide, but less commonly used
- Electric Charges: Research into using electrical fields to promote coalescence
- Infrared Laser Pulses: Lasers could help create a better environment for CCN
- Nanomaterials: Research into other small agents that could be more effective or environmentally-friendly
What makes a cloud precipitate (rain, snow, etc.)?
When the smaller water droplets that make up clouds bump into each other, the grow! This is merge is a physical process called 'coalescence'. As the droplets grow bigger, and bigger, they fall to the ground as liquid rain. The process of making snow or other frozen precipitation is more complicated. Water vapor has to condense onto a speck of something in the atmosphere and grow into ice (here, that speck is the "ice condensation nuclei"). This is a very complicated process that requires the right environment; the coalescence needs to happen at the right temperatures, height, pressure, etc.
What does cloud seeding do?
Did you know water can be colder than 32ºF and still be liquid? These water drops are known as "super-cooled" water droplets. Cloud seeding can bridge the gap between cloud and precipitation but giving that very cold water not only a surface to cling to, but a surface to freeze onto and become ice. This is where cloud seeding can be useful.
Clouds can be seeded for a few purposes: promote more rainfall, promote more snowfall, or hinder/suppress hail and disperse fog.
To promote rainfall and snow
The 'seed' can boost the precipitation process by providing enough CCN in the right part of a cloud. This helps the precipitation process by promoting growth of bigger water droplet and/or ice and snowflakes— once big enough, they fall! This is desirable to maximize rainfall in arid places or in times of drought. More snowfall can help snowpack in mountainous regions which is desirable for communities that depend on snowpack as a water source as well as tourism.
To hinder fog and hail
Seeding can help disperse fog by providing more CCN in a layer of fog. Fog is a ground-level cloud and seeding fog can help the cloud droplets coalesce into bigger droplets that "rain" to the ground. This is desirable to improve visibility.
To supress hail growth, seeding adds more CCN. As opposed to having fewer, but bigger hailstones, cloud seeding provides more CCN; this makes more hailstones that are much smaller in size. Small hailstones are more likely to melt before reaching the ground, causing less damage and/or injury.
What's the controversy?
Cloud seeding has been studied for decades. The controversy seems to arise over its effectiveness and the environmental impact of the materials used (called "seeding agents").
A popular example is project called 'STORMFURY' that was conducted between 1962-1983 to find out it cloud seeding could weaken hurricanes. NOAA conducted cloud seeing in four hurricanes to see if they could reduced the strongest winds by triggering a eyewall replacement cycle. When a hurricane undergoes an eyewall replacement cycle, there is a brief period of time when the strongest winds (located in the storms eyewall) weaken as the eyewall weakens during a replacement cycle. While researchers initially thought they had an effective way to weaken these destructive storms, further analysis concluded that the observed decrease in winds may have happened naturally without seeding. Ultimately, the project was scrapped because researchers couldn't prove the cloud seeding made any difference.
These projects have been misunderstood by the general public, with many in the Coastal Bend suggesting that cloud seeding made Hurricane Celia worse. The irony is that cloud seeding was not performed during Celia, but it was performed during Hurricane Beulah— in 1963. This is often confused for Hurricane Beulah in 1967 which moved over the Coastal Bend (no cloud seeding with this storm). Today, storm names repeat every 6 years but that was not the convention decades ago. The name 'Beulah' has been used for three tropical cyclones in the Atlantic Basin: 1959, 1963, and 1967 (the most destructive). The name was retired and replaced with 'Beth' as the 'B' storm in 1971.
Why don't we use it to fix our drought?
For better or for worse, cloud seeding has only been proven to increase precipitation by 20% at most. The process is very complex in that the perfect conditions must be present to yield the best results. It's also costly and wouldn't produce enough rain to be a drought-buster for South Texas. Texas is one of nine states that allow cloud seeding. At least ten states have banned or have considered banning weather modification entirely. There are cloud seeding operations ongoing in Texas, as regulated by the Texas Department of Licensing and Regulation (TDLR). In fact, one of the biggest operations in Texas operates in Bee County. The last time cloud seeding operations happened in Bee county was June 15,2025.
Want to learn more?
The U.S. Government Accountability Office report on cloud seeding technology is a helpful summary of cloud seeding in the United States.
While NOAA does not regulate weather modification, those performing such activities must report to the agency. Here is an article 'debunking' and fact-checking many common misconceptions about the practice.