What is cloud seeding and does it work?

CNN
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A torrent of rain on Tuesday flooded parts of Dubai, turned roads into rivers and temporarily closed the world's second-busiest airport. The deluge of water prompted the question: Was this disaster caused by the UAE's cloud seeding program?

Officials at the National Weather Service were quoted as saying the rain was not caused by cloud seeding. CNN has reached out to the center for comment.

But even if the program had flown its planes through the skies leading up to the storm, it's unlikely that the effort would have produced more rain than would fall naturally.

These understandable attempts to squeeze more moisture out of clouds have been around for decades, but with little evidence of success.

But that hasn't stopped some countries, including the United Arab Emirates, China and the US, from trying to modify the weather.

Here's what you need to know about cloud seeding.

Cloud seeding is a weather modification concept that attempts to extract more rain or snow from a cloud than would occur naturally.

Cloud droplets do not form spontaneously. Moisture needs something to condense on like water forming on the side of a cold glass on a hot day. In a cloud, so-called condensation nuclei are small, tiny particles in the air on which moisture can condense.

Cloud seeding adds more of those particles to the air. The planes fly through existing clouds and inject tiny particles, such as silver iodide, with the goal of creating more water or ice droplets.

In any cloud, once enough droplets coalesce, they become heavy and fall to Earth as rain or snow.

Small natural particles, such as dust and dirt, usually serve as the driving force for clouds to condense and shed their moisture. Silver iodide could theoretically serve the same purpose.

It is extremely difficult to determine what impact cloud seeding has on precipitation. Experimentation and efforts to evaluate its effectiveness have been fraught with challenges.

How do you know how much precipitation that may actually end up falling from that cloud has occurred because of the seeding? Or how much would have fallen without planting? Daniel Swain, a climate scientist at UCLA, previously told CNN. This is not a setting where you can do a truly controlled experiment.

Researchers have tried. A 2020 study published in the Proceedings of the National Academy of Sciences showed that a cloud seeding experiment could have produced up to 10% more precipitation than would have fallen naturally.

But skepticism still remains in the scientific community.

There have to be controlled studies that actually show that it was the planting that increased rainfall in a meaningful way, Swain asserted.

As the climate continues to warm due to human-caused climate change, some parts of the world are becoming hotter and drier. Cloud seeding can be perceived as a solution to bring more water to areas that need it, but it can also make other areas drier in the process.

Water, like any other substance, cannot be created or destroyed. It can only transform as it moves through the closed loop of the water cycle.

It is possible that you are actually stealing water from someone else when you do this (cloud seeding) because it can be, at least on a regional basis, a zero-sum game where if water falls from the cloud in one place , is even drier by the time it makes it downwind in the next watershed, Swain said.

The heavy rain that caused unprecedented flooding in the United Arab Emirates, Oman and Iran didn't just appear out of nowhere. It also didn't just affect areas participating in cloud seeding.

The torrential rain was driven by a large, slow-moving storm that crossed the Arabian Peninsula and tracked into the Gulf of Oman over the course of several days. This storm was able to pick up deep, abundant tropical moisture located near the equator and discharge it as a firehose over the region.

Regardless of whether cloud seeding occurred, the storm was part of an extreme setup that showed up in forecast models days ago.

Heavy rainfall events like this will become more frequent as the atmosphere continues to warm, allowing it to absorb more moisture like a towel and show it up as flooding precipitation.

CNN's Rachel Ramirez and Angela Fritz contributed to this report.