In a capital that every winter is under a persistent haze, the authorities have activated their first cloud seeding trial with an eye toward precipitation capable of removing some of the smog. The idea is simple on paper: take advantage of favorable weather windows to force rain that cleans the air, even knowing that its effect will be limited in time.
The plan comes after several days of very high air quality indices and the post-Diwali spike, when fireworks and firecrackers Measurements are worsening. With more than 30 million inhabitants, Delhi is among the most polluted cities in the world, and the cold months aggravate the situation due to the thermal inversion that traps contaminants close to the ground.
Delhi turns to cloud seeding to clean the air
The capital carried out a test flight over Burari The mission was carried out by a Cessna aircraft, coordinated by the Indian Institute of Technology Kanpur (IIT Kanpur) and the local Department of Environment. According to official communications, the objective was to verify procedures and atmospheric conditions before larger-scale operations.
If the weather is good, the authorities are considering activating the induced rain on immediate dates; the exact compound used in the test has not been specified, which is common until the testing phase is completed. In this type of operation, salts like silver iodide or sodium chloride, although the choice depends on the microphysics of the clouds.
The background pressure is known: every winter, the mix of emissions from traffic, industry and agricultural burning It is trapped by a layer of warmer air at higher altitudes, acting as a "lid" and preventing smog from dispersing. This pattern repeats itself year after year and requires additional measures when the air becomes unbreathable.
At some moments, the particles PM2,5 —capable of penetrating the bloodstream—have reached peaks that multiply the daily threshold recommended by the WHO by up to 60, with readings of ICA above 300 and even around 400 at specific stations. These values ​​require the activation of protocols to reduce the exposure of the vulnerable population.
How it works and when it can be useful
Cloud seeding introduces particles that act as condensation nuclei, promoting the formation of ice droplets or crystals in existing clouds. It doesn't create water out of nothing; it simply tries improve the eficiency from precipitation when humidity, temperature and atmospheric dynamics allow it.
Commonly used compounds include silver iodide and sodium chloride. The release can be done from airplanes—as in the case of Delhi—as well as drones or flares, or by means of surface generators. Deployment is scheduled during very limited weather windows to maximize the chances of success.
For it to work, they must come together suitable clouds with sufficient water content. In the colder months of northern India, this does not always occur, hence the importance of coordinating with meteorological services the selection of times with greater probability of precipitation.
Effectiveness, limits and doubts
The scientific evidence is heterogeneous: there are studies that point to increases in rainfall 10% to 20% in very specific scenarios, while in other cases the effect is marginal or difficult to isolate from natural variability. In air quality, the relief is usually temporary (1-2 days), enough to reduce severe peaks but not to solve the underlying problem.
Experts recommend instrumental monitoring before, during, and after operations, with transparency regarding compounds, dosages, and outcomes. Although the toxicity associated with these salts in the atmosphere is generally considered low at the quantities used, it is still necessary to evaluate the long term impact and publish the data.
In parallel, Delhi maintains more well-known measures —Water spraying on roads, construction monitoring, anti-smog cannons and burn controls—and has reported occasional decreases in the ICA (for example, from 353 to 305 in one day). Cloud seeding is intended as a complement, not a substitute, for structural policies on transport, industry and waste management.
European perspective: what Spain and the EU can learn
Time modification is already used in China, Gulf countries, and western US states, for purposes ranging from drought relief to supporting firefighting. Its use for air quality is more controversial, but Delhi's experience will serve as a reference for its use. operational feasibility in dense urban environments.
For Europe - and Spain in particular - it could be explored in episodes of anticyclonic stability that trigger smog in large cities, always under strict regulatory frameworks and with AEMET and environmental agencies at the center of design and evaluation.
Any pilot in the European context should be accompanied by environmental assessments, cross-border coordination and public information protocols. It is also worth remembering that, in the Old Continent, the main focus remains reduce emissions at source (mobility, heating, industry) and improve urban planning.
If trials are conducted, it is prudent to publish comparable metrics —PM2,5, PM10, ICA— before and after, define clear trigger thresholds and combine the technique with time restrictions on emission sources. Avoid the techno-optimism It is key: it can provide short-term relief, but it does not replace fundamental solutions.
Delhi opens a path of action that aims to offer occasional breaths when the air becomes especially harmful. Cloud seeding can be a useful tool if applied with rigor, open data, and as part of a broader strategy that prioritizes sustained reduction in emissions.
