Delhi saw its first cloud-seeding trial on Tuesday as authorities explored ways to mitigate air pollution, using a technique that artificially modifies clouds to produce more rainfall. This method, known as cloud seeding, involves introducing specific particles or chemical solutions into clouds to act as “seeds,” around which water vapour condenses, eventually forming raindrops or snow.

Cloud seeding works differently depending on the type of cloud being targeted. In cold clouds, where temperatures are below zero degrees Celsius, silver iodide particles are typically used. These particles attract water and ice, forming larger fused droplets. As these droplets become heavier, they begin to fall, melting into rain as they pass through warmer layers of the atmosphere closer to the ground.

In warm clouds, with temperatures above zero, chemical solutions such as sodium chloride (NaCl) or potassium chloride (KCl) serve as the seeding agents. These compounds promote the fusion of smaller water droplets into larger ones, improving the efficiency of rainfall formation.

The natural formation of clouds is the starting point for cloud seeding. When air is saturated with water vapour, it cannot hold the moisture in gaseous form. Water molecules begin condensing onto tiny particles, forming visible droplets or ice crystals. Rainfall or snowfall occurs when these droplets or crystals grow heavy enough to overcome air resistance and fall to the surface. Cloud seeding accelerates this process artificially.

The origins of artificial rainmaking trace back to the 1940s. In 1946, American chemist and meteorologist Vincent Schaefer conducted experiments adding dry ice to a chilled chamber, observing cloud formation around the ice particles. This is considered the first documented instance of artificially created clouds in a laboratory. The following year, atmospheric scientist Bernard Vonnegut improved the technique by using silver iodide crystals, which produced more consistent results than dry ice.

Over the decades, the technique has evolved, with studies highlighting its potential benefits and limitations. For instance, cloud seeding in orographic clouds—clouds over mountainous regions where natural air lifting enhances cloud formation—has shown the ability to increase snowfall. However, global evidence regarding the effectiveness of cloud seeding remains limited, making it difficult to measure its true impact on rainfall reliably. A 2024 report by the US Government Accountability Office noted these challenges, emphasizing that observed increases in precipitation could not always be definitively attributed to seeding.

Environmental concerns have also been raised regarding cloud seeding. Seeding agents like silver iodide, which eventually fall to the ground with precipitation, have been flagged as potentially toxic. Studies have detected residual silver in areas near seeding operations, raising questions about environmental safety. Additionally, the use of dry ice, which is solid carbon dioxide, contributes greenhouse gases, potentially adding to global warming concerns.

In India, cloud-seeding research has a long history. The Indian Institute of Tropical Meteorology (IITM), Pune, conducted experiments as early as the 1970s, suggesting a potential 17% increase in rainfall in targeted areas. However, even these studies did not draw definitive conclusions about the overall efficacy of the method. Recent decades have seen more sophisticated efforts to analyze aerosol and cloud droplet behavior across India, in order to identify suitable regions and optimal conditions for cloud-seeding trials.

Practical implementation of cloud seeding involves a range of technical and logistical considerations. Accurate weather monitoring is essential, including pre-existing cloud conditions and any imminent severe weather that could interfere with operations. Flying restrictions and permissions must be secured in advance to ensure the safety and security of aircraft and personnel involved in the seeding process. During trials, data on cloud formation, droplet density, temperature profiles, and other meteorological parameters are continuously monitored. This information helps researchers determine which clouds are suitable for seeding and evaluate the success of the operation.

Aircraft equipped with dispersal mechanisms are used to introduce the seeding particles or solutions into clouds. Once released, these particles serve as nucleation points for water vapour to condense upon. In the case of cold clouds, silver iodide crystals mimic the structure of ice, promoting ice crystal formation and eventual precipitation. In warm clouds, salts like NaCl or KCl help small droplets coalesce into larger droplets capable of falling as rain.

Cloud-seeding trials also emphasize precautionary measures. Authorities need to account for flight safety, air traffic control, and coordination with meteorological services. Any misjudgment could endanger the aircraft, pilots, or ground populations. Observations collected during trials allow scientists to fine-tune the process and improve predictions of rainfall enhancement.

Despite its potential, cloud seeding is not a guaranteed solution for water scarcity or pollution control. Its effectiveness can vary based on cloud type, atmospheric conditions, temperature, humidity, and the precise timing of seeding. As the Delhi trial demonstrates, the technique is being considered as one of several measures to address seasonal challenges like air pollution, but it remains supplementary to broader environmental and urban planning strategies.

In conclusion, cloud seeding is a complex atmospheric intervention that artificially stimulates precipitation by introducing particles into clouds to act as condensation nuclei. While the technique has historical roots dating back to the 1940s and has been applied in various parts of the world, its effectiveness remains subject to scientific scrutiny. Environmental considerations, careful monitoring, and precise execution are essential to ensure that cloud-seeding experiments are safe, scientifically meaningful, and environmentally responsible. Delhi’s recent trial represents an ongoing effort to explore innovative solutions to environmental challenges such as air pollution, while continuing to balance technological feasibility with ecological and public safety concerns.