Wednesday, September 27

We have been “seeding clouds” for decades to combat drought. Now we know that it was used for rather little

If the Cherokee dances and the egg baskets for Santa Clara have something in common, it is that they both show that humanity has long dreamed of changing the climate. We dream of it raining when we want. And to stop doing it when it doesn’t suit us. Now to that aspiration, as old as humanity itself, a new incentive is added: drought. Over the last few decades, the lack of rain has taken on historical overtones, a problem that will only get worse.

Against this backdrop, some territories are betting on “cloud seeding.” It sounds futuristic, but the technique dates back to the middle of the last century and we have enough data to assess its effect with perspective. The question is, with all that accumulated baggage: Does it work or doesn’t it work?

Sow the skies to generate precipitation. Cloud seeding consists of releasing silver iodide particles or other aerosols in clouds that meet certain characteristics with a clear objective: to cause rain or snowfall. On The Conversation Professor William R. Cotton details that the system operates with several approaches that differ, basically, by the type of cloud: if it is supercooled or warm and requires hygroscopic materials, capable of absorbing moisture. When it comes to acting, experts can spray with planes, from the ground or even use rockets.

Although some scientists had theorized about ice crystals before, the origins of the system date back to the 1940s and the investigations of Vince Schaefer of General Electric. Following tests of it in the laboratory, in 1946 Schaefer sprayed crushed dry ice onto supercooled stratus clouds. The project soon attracted the interest of the US military.

On the table for decades. The promise to increase rainfall almost on demand, when it is most needed, has long captured the interest of governments. And it continues to do so today. In the United Arab Emirates (UAE) they use fleets of drones to seed clouds and generate artificial rains and in China they want to have 5.5 million square kilometers covered, more or less 60% of its territory, with programs of this type by mid of the decade.

On the other side of the Atlantic, in the US there are different states, such as Idaho, Utah, Colorado or California, that have opted for similar operations to combat the drought. The same strategy is followed in the west, where the NOAAA agency expects the problem to worsen this spring.

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…Also in Spain. The system has not been used only in the desert regions of the Middle East, America or Asia. In Spain we have also experimented with weather modification techniques. In the Community of Madrid or Aragon, for example, they have been applying a similar philosophy for a long time with a somewhat different objective: to avoid hailstorms that can destroy crops. Four decades ago, between 1979 and 1981, in Valladolid they were also thinking about a project with the World Meteorological Organization (WMO) to intensify rainfall.

Artificial cloud seeding: who and how can you make it rain?

neither simple nor magical. With the experience of almost half a century of tests, experts warn: cloud seeding is not a simple or magical solution. “It’s not as simple and may not be as promising as people would like,” warns Professor Cotton: “Experiments that produce snow or rain require the right kind of clouds with enough moisture and the right temperature and wind conditions. percentages are small and it is difficult to know when the snow or rain fell naturally and when it was triggered by planting.”

Encouraging, yes; but still far from expectations. Cotton goes further and acknowledges that, although “encouraging” experiments have been developed, they have not reached “the level of importance” that Schaefer and his colleagues predicted decades ago. “Most studies aimed at evaluating the effects of cumulus seeding have shown little or no effect. However, the results of seeding orographic winter clouds (clouds that form when air rises over a mountain) have shown increases in precipitation”, specifies the expert.

The professor emeritus of the Colorado State University (CSU) provides some data for reflection. For example, the disparity in figures produced by studies that try to measure how much rain or snow is attributable to cloud seeding. In an experiment in Australia they have even pointed out that snowfall has increased by 14%. Other 2014 research focused on the mountains of Wyoming noted that despite the region being suitable for cloud seeding for much of the year, snow cover increase would not exceed 1.5%.

Ferdinand Stohr Hzscr9frfd0 Unsplash

Neither magic wands nor resounding failures. Does that mean cloud seeding is useless? Absolutely. In his article, Cotton himself details the results and cites a 2020 study in which it was found that just 20 minutes after planting, a snowfall was recorded that left a tenth of a millimeter of snow in just over an hour. The key, as he also indicates, is that it may not be as “promising” as was thought on his day, years ago.

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There is research that strongly concludes that cloud seeding is effective, although they agree that there is still work to be done. Katja Friedrich, atmospheric scientist and author of the SNOWIE study, which sought to show precisely, unambiguously, that planting can help increase snowfall.

Long periods of drought are going to be more and more normal.  It's time to get used to them

A key moment to resolve doubts. “In terms of research, this is a really exciting time for cloud seeding,” agrees Sarah Tessendorf, another of the authors of SNOWIE, a study that, despite its conclusions, has certain shortcomings, such as not covering all contexts , that their results for a territory may not be extrapolated or that during their tests an increase in snowfall was not always observed after the planting cycles.

Your field of study is benefiting in any case from advances in other areas of knowledge. Dr. Linda Zou, a professor at the Khalifa University of Science and Technology, recently explained to the magazine IMT Technology Review how it is taking advantage of advances in the area of ​​nanotechnology and nanoscience to create seed materials that ensure that vapor condensation occurs in an “effective way and maximizing precipitation.”

It is not (the only) answer to drought. What does seem clear is that cloud seeding should not be our only recourse in the fight against drought. “It’s just another tool in the box,” Mikel Eytel, a water resources specialist for the Colorado River District, told the magazine. Yale Environment 360: “It’s not the cure-all some people think it is.”

There are other handicaps that advise against entrusting everything to the artificial modification of time. For example, as the same Yale newspaper recalls, during a prolonged drought it is likely that experts will have fewer storms that can be “seeded”. And even when there are, specialized companies calculate that the increase in rainfall is 10% in specific areas.

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Reasonable costs and with the confidence gained. In its favor, planting has some relevant factors. Perhaps the most important is that it has already earned the trust of a good number of countries and institutions. According to the data handled by the WMO, in 2017 there were more than 50 countries with climate modification programs underway, initiatives that sought to induce an increase in rain and snow to suppress the effects of hail on crops. Over the last 20 years, NOAA alone has received dozens of proposals totaling around 800 reports.

Another of its strengths is that although cloud seeding programs obviously require funds, their costs are relatively low when compared to the results. Even, they remember from Yale, in the event that the reports exaggerate the effect of the campaigns. Over time, this strength could be even greater thanks to work such as that carried out by Dr. Linda Zou, from the University of Khalifa, which seeks to “scale production and reduce cost.”

Minor impact in the middle and… on cue. As well as being reasonably cheap, seeding doesn’t seem to have much of a detrimental impact either. Cotton himself acknowledges that, despite what is commonly believed, “the negative effects appear to be minor”: “The silver ion is a toxic heavy metal, but the amount of silver iodide in the seeded snow cover is so small that extremely sensitive instrumentation must be used to detect its presence.”

Although if it is about looking for strengths, without a doubt the main one, both for planting and for any other strategy that wants to combat drought, is that the problem seems to have entered the public agenda. The reason: a reality that tightens more and more. The report presented in 2021 by the Ministry of Ecological Transition on the impact of climate change shows that throughout the second half of the 20th century, a reduction of between 10 and 20% of available water resources and more than 75 % of the Spanish territory is at risk of desertification.

Pictures | Lisanto 李奕良 (Unsplash), Ferdinand Stöhr (Unsplash) and Wikimedia

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