What is cloud seeding? A step-by-step chart shows how the weather modification technique works as experts question whether it was the cause of Dubai’s floods
On Tuesday, the United Arab Emirates was hit by a year and a half of rain in one day, leaving much of Dubai flooded.
Now experts are wondering whether the sudden flooding of the desert city could have been caused by climate interference.
Since the early 1990s, the UAE has used a technique called cloud seeding to increase annual rainfall and drinking water supplies.
This technique involves releasing specialized salt flares from aircraft before flying into the clouds to cause rain.
Now that Dubai is experiencing the heaviest rain ever, MailOnline takes a step-by-step look at how the controversial technology works.
Cloud Seeding works by releasing grains of salt or silver iodide into clouds. These cause water vapor to condense or freeze into droplets large enough to fall as rain
Since the early 1990s, the UAE has been using this controversial technique to increase rainfall by about 15-25 percent. Here, a UAE plane is shown releasing salt flares into a cloud
Controlling the weather may sound like a futuristic technology, but the principle was actually discovered in the 1940s.
Scientists at General Electric discovered that water cooled between -10°F (-10°C) and 23°F (-5°C) could not form ice crystals under certain laboratory conditions.
The water could not freeze because there was no ‘core’ around which the ice crystal could form.
However, when the scientists added silver iodide to the water vapor, they found that the ice crystals formed immediately.
In nature, clouds produce rain or snow when water vapor forms around natural nuclei such as bacteria or dust.
What the scientists had discovered was an artificial way to add nuclei to clouds, allowing the vapor to condense quickly.
Although technology has come a long way, modern cloud seeding uses the same basic ideas developed 80 years ago.
Dr. Brian Thomas, an expert in hydrology from UCL, told MailOnline that natural rainfall has four phases.
First the air is cooled to the ‘dew point’, while warm air rises into the cold atmosphere.
Secondly, that water vapor condenses around a ‘cloud condensation core’ (CCN).
Third, those drops grow larger until they are heavy enough to fall.
And finally, the atmosphere ‘imports’ more water into the area to keep the rain flowing.
Dr. Thomas said, “Cloud Seeding works from step two. Chemicals are dispersed in the upper atmosphere and act as CCNs, initiating the rain formation process.”
As long as there is cool moisture vapor in the atmosphere and more and more moisture is imported, the rain will continue.
Not every cloud can be seeded, so the UAE’s National Center of Meteorology has a fleet of aircraft (pictured) that can respond when a suitable cloud is spotted
Not every cloud is suitable for seeding, so the NCM has set up a sophisticated network of weather stations to monitor atmospheric conditions.
The UAE’s Rain Enhancement Program (UAEREP) said: ‘The NCM has established a national network of 86 automatic weather stations (AWOS) for weather monitoring, six weather radars covering the entire UAE, and one higher air station.’
Once the right type of cloud is spotted, specialized seed aircraft are deployed to respond.
Mark Newman, deputy chief pilot at NCMS, previously told MailOnline: ‘As soon as they see convective cloud formations they launch us on a flight to investigate.’
The planes are loaded with salt flares that can be burned to produce more rainfall
It is estimated that the UAE conducts around 1,000 hours of seeding flights each year, although it is uncertain how much this actually changes rainfall patterns
If conditions are believed to be correct, the pilots will fire hygroscopic flares that release a fine salt powder into the cloud.
While silver iodide is used elsewhere, salt works well in warmer climates and achieves the same effect.
The water vapor then condenses around the salt particles and becomes larger and heavier.
Once they reach a certain size, the water droplets fall in the form of rain, snow or hail, depending on the weather conditions.
It is believed that the AUE conducts approximately 1,000 hours of seeding flights each year to increase rainfall in this way.
In some cases, instead of flying planes into the clouds, seeding can also be done by firing seeding rockets from the ground.
In China, this technique has been used to divert rainfall away from rivers as part of an effort to combat drought and reportedly to prevent rain during the 2008 Olympics.
In China, seed rockets have been fired into the clouds to replace flying seed planes
On Tuesday, much of Dubai (photo) was under water due to the worst flooding ever
Cars have been swept away and transport paralyzed as the capital experiences a year and a half of rain within 24 hours
Immediately after the flooding occurred, questions began to arise as to whether cloud seeding was responsible.
Ahmed Habib, a specialist meteorologist, initially told Bloomberg that at least seven planes had landed from Al Ain airport between Sunday and Monday.
However, the NCM was quick to deny that any cloud seeding operations had taken place at all in the lead-up to the heavy rains.
Omar AlYazeedi, Deputy Director General of the NCM, said CNBC that the facility “did not conduct any seeding operations during this event.”
Mr AlYazeedi added: “One of the basic principles of cloud seeding is that you need to target clouds early on before it rains. If there is a severe thunderstorm, it is too late to carry out any seeding operation.”
Some have blamed cloud seeding for the increased rainfall, although the NCO denies that any seeding has occurred
Despite the heavy use of cloud seeding in the UAE, there are still doubts among some experts as to whether it could increase rainfall to this extent.
More than 17.5 centimeters of rain fell in Dubai between Monday morning and late Tuesday.
In an average year, Dubai International Airport receives 3.73 centimeters of rain, meaning the country received a year and a half of rain in 24 hours.
The country is one of the driest in the world, receiving between 140 and 200 mm of rain per year.
However, during this week’s intense downfall, the Emirate of Al Ain received more than 250 mm in one go.
Studies have suggested that cloud seeding generally increases rainfall by an average of five to 15 percent, far less than this week’s extreme flooding.
Additionally, cloud seeding generally takes place outside populated areas due to airspace restrictions.
This means it is not clear whether the increased rain over Dubai could have been caused by cloud seeding operations taking place elsewhere.