The Mexican Ministry of Agriculture announced in July 2021 the start of a "rain stimulation" project in Coahuila, Zacatecas and Durango, as an extension of previous trials in Sinaloa, Chihuhu and Sonora. Now, the Mexican Ministry of Agriculture, through the National Commission for Arid Zones (Conaza), has expanded the release of silver iodide particles into the skies of Tamaulipas and Baja California at the request of farmers affected by a new episode of drought.
Mexico thus joins a practice that countries such as China or the United Arab Emirates have used in recent years. In all known cases, despite the self-praise data published by the governments involved, artificial rain by bombardment or sowing of silver iodide (terms also used to refer to this technique) has had little or no results.
A newspaper article published in the journal Nature explains some details of the artificial rain plan in Mexico, noting that various "scientists warn that there is little evidence that cloud seeding works, despite the fact that the Mexican government says it has been successful." .
Mexico is experiencing its second most severe drought in a decade, and farmers fear for their crops and livestock. So they have asked the Mexican government to use cloud seeding technology to help them. In China, this method was used, for example, in the summer of 2021 in the Beijing area with the aim of reducing pollution; causing the rain to precipitate the particles in suspension.
La Conaza announced last March that it would begin to implement a rain stimulation program in the states of Tamaulipas and Baja California, in the northeast and northwest of the country, respectively.
The method consists of dispersing crystalline silver iodide particles in the clouds and, since the particles have ice-like structures, they attract water droplets that are concentrated in a nucleus around them; eventually, the droplets become heavy enough to fall as rain or snow.
Nature magazine mentions Fernando García, a cloud physicist at the National Autonomous University of Mexico (UMAM) in Mexico City, to downplay the results of this technique. "Mostly there is 'theoretical proof' that cloud seeding can increase precipitation, but some rigorous experiments have resulted in modest increases in precipitation, so there is arguably no evidence that it will work every time." , indicates this expert. “I can modify [a cloud]. What I don't know is if I am going to increase the rainfall or even suppress it, because it may also happen that it rains less than expected”, according to statements released by the magazine Nature.
Mexico has carried out precipitation modification experiments on several occasions but the data obtained have not been published in scientific journals. On the contrary, some of Conaza's own reports, without verified data, assure that they have achieved notable successes in the tests in demarcations such as Chihuhua, Sinaloa or Sonora. This is indicated, for example, by a presentation signed in 2022 by Ramón Antonio Sandoval, general director of Conaza.
Instead, through a transparency request in Mexico, Nature asked Conaza for documents showing how the institution evaluates the successes of the program. Conaza delivered 150 pages about the program, with information from 2020 to 2022, in which he declares that he is not a technology research or regulation institution, and that he chose Startup Renaissance because the company promised efficiencies greater than 90% with its RainMate technology. The documents also show that Conaza assesses success by comparing measurements captured by rain gauges after cloud seeding with the amount of precipitation predicted in the region in advance.
The problem with this approach is that the weather forecasts are not entirely accurate. It is possible that the clouds would have produced rain anyway without seeding them, Garcia says.
Trueba confirmed to Nature that the company is "measuring [on the] impacts, and not on a scientific meteorological basis."
Sarah Tessendorf, a cloud physicist at the US National Center for Atmospheric Research in Boulder, Colorado, says there is some evidence that cloud seeding works. She is the principal investigator for the Seed and Natural Winter Orographic Clouds: The Idaho Experiment (SNOWIE) project, which in 2020 reported ice crystal growth and snowfall during three cloud seeding events1. Tessendorf and her colleagues calculate that, over an area of about 2,000 square kilometers, those experiments generated snowfall equivalent to the water needed to fill 300 Olympic-size swimming pools.
However, Nature points out, Tessendorf does not suggest using cloud seeding to end a drought: "Because you need to have clouds and storms that can be seeded to begin with,"
There are ways to measure whether cloud seeding has worked, Tessendorf says. One is by using a control group of clouds — seeding some clouds, but not others, where conditions are similar — and running a statistical experiment “for years and years — ideally decades,” she says.
The other way is with simulations. Current computer models can predict how clouds behave with and without seeding. The researchers compare the results of those models with measurements of how much water the clouds hold before and after they were seeded with silver iodide, he adds.
In 2022, a scientific advisory committee of the National Civil Protection System (Sinaproc) recommended that Conaza not implement cloud seeding projects without first completing a series of tasks such as a cost-benefit analysis, a verification of the successes of the technology on increasing rainfall and studies to assess the environmental impacts of silver iodide. "Otherwise, large local, state, and federal economic losses are caused by allocating resources to weather modification projects whose precipitation increase hypotheses could not be validated," the recommendation said.
