The wish to control rain is ancient and has a prominent place in many religions. In Viking mythology, several gods had the power to control rain and in America, the Hopi people still perform rain dances centred around antelopes and snakes. The dance is rooted in the belief that the thundering sound of running antelopes brings rain clouds and that snakes have the power to suck the rain out of them. And in 2007, when Australia faced a severe drought crisis, Prime Minister John Howard urged his fellow citizens to pray to the Christian god for rain.
Modern rain makers rely more on high tech and science than chanting and prayers. They use radar systems to track the weather and when dark clouds form, they turn on their engines, take off and head straight into the storm with small planes. Instead of snakes, they base their approach on the practical application of science and use ice-like particles to suck rain out of the clouds: silver iodide. This process is known as cloud seeding.
“The interest in cloud seeding is extremely high right now,” says Neil Brackin, president of Weather Modification Inc.
“We are currently offering full package solutions to four hydro power companies in the US, and we have a number of customers in process for starting seeding programmes outside the country. We are also operating to replenish groundwater and lakes for drinking water and for agricultural irrigation in California, Wyoming and North Dakota.”
The rain-making properties of silver iodide were first explored by Bernard Vonnegut (brother of novelist Kurt Vonnegut) in the mid-1940s. After a series of more or less random experiments he was struck by an idea that would prove to be fruitful: why not trick the clouds? The reasoning was to supply them with a substance similar to the ice particles that allow moisture in the clouds to condense and form rain drops. Now that Vonnegut knew what he was looking for, a look in the “Handbook of Chemistry and Physics” revealed that silver iodide had a hexagonal crystal structure almost identical to ice. This suitable ice core doppelganger could be sprayed into the clouds, either from a plane or from the ground.
In water-scarce California, cloud seeding has been practised since the 1960s to feed the state’s hydro power reservoirs. Sacramento Municipal Utility District, SMUD, spends an average of 150,000 US dollars a year on it.
“Most studies place the boost in the neighbourhood of four to ten per cent – even just a 1.5 per cent increase in precipitation makes cloud seeding a worthwhile investment,” Assistant Chief Dam Safety Engineer at Sacramento Municipal District Dudley McFadden III says.
“In a dry year it is especially valuable because the price of energy is so high.”
But in a state still recovering from a severe drought, issues around the precious resource are sensitive. Here, every drop counts. So what if the extra water extracted means that someone else gets less?
“The most efficient storms precipitate out on the order of 10 per cent of the moisture in the clouds. And with cloud seeding maybe 11 per cent. So, yes, the water must be taken from somewhere, but there is still plenty of moisture left in the clouds,” McFadden argues.
“There is no stealing from one area to another,” Brackin claims. “A cloud is in a continuous process rather than being a static object that moves from, let’s say, west to east. It is continually condensing and regenerating, and it is that process that is enhanced. Cloud seeding has proven to not have any negative downstream effects in the redistribution of precipitation at all.”
Further, there seems to be little effect of cloud seeding on the environment.
“Over several decades, there have been more than 30 environmental impact studies conducted by various groups, including the US Environmental Protection Agency, and none of them have found any negative effects from cloud seeding. There is even one study that showed lower levels of silver iodide after the cloud seeding which was explained by the cleansing effect of the additional fresh water,” Brackin says.
There has been a scientific debate about whether cloud seeding actually works. Sceptics think that using silver iodide for making rain might be no more effective than praying or worshipping animals. They claim that although the theory is valid, there is no proof that the technique actually works.
“It is often not possible to say if it would have been raining the same amount without the seeding. The basic mechanism on how clouds are created is relatively well understood, but in practice it is hard to determine if the mechanism can really be significantly altered,” says Anna Rutgersson, professor of meteorology at Uppsala University in Sweden.
But Brackin believes that proof of the concept has been strengthened by using new technologies such as high resolution radars and weather forecast models. “Several studies by universities and federal government have confirmed that modern targeted cloud seeding is effective,” he says.
“The radar allows you to track moisture in the clouds. And the high resolution models give a very detailed forecast that can demonstrate how much rain actually fell after seeding. These studies also use a high number of precipitation gauges to confirm the results.”
Could the cloud seeding technique also bring more precipitation to Nordic reservoirs? One could argue that in the rainy and snowy climate of the Scandinavian mountains there is already enough water available for hydro power. But on the other hand, hydro power is considered a clean and valuable source of power that is likely to become even more important in the future. So could cloud seeding increase hydro power output in the Nordic countries?
According to Brackin, there are also examples of effective cloud seeding in wet and cold climates.
“It is all about setting up the right program and using the right methods. As an example, Idaho Power Company, with 17 hydro-electric dams in operation, has seeded in the winter time for over a decade. They are normally not short of water but seed proactively to enhance their current production and for the reliability of future power supplies. By doing so they have increased their average annual streamflow in the rivers by 14 per cent,” he says and refers to a report from Idaho Power Company.
But Anna Rutgersson is more uncertain to whether the cloud seeding technique would add any value for Nordic hydro power.
“The conditions for cloud seeding in Sweden are not much investigated. But my assessment is that the atmospheric conditions here are not so good for cloud seeding. The technique might be effective if there is a deficit of ice particles high up in the atmosphere, but I don’t think that this is the case in the Nordics.”
Weather Modification Inc. is now preparing to approach several hydro power companies in Europe. Vattenfall so far has no plans to start cloud seeding.