The Delhi government’s attempt to alleviate severe pollution in Delhi by resorting to artificial rain or cloud seeding is an experimental endeavour with no evidence so far that it will be successful in non-monsoon months. Though cloud seeding has been attempted since the 1940s and was pioneered by the United States military, having clouds deliver enough rain over a desired region continues to be a nebulous endeavour.
With air quality ‘severely’ bad, the Delhi government met experts from the Indian Institute of Technology (IIT)-Kanpur earlier this week, who plan to submit a proposal to the government, who in turn will submit it to the Supreme Court. The plan, the full details of which are not known, is to fly aircraft into rain clouds — which are anticipated in north India around November 20 — and litter them with a proprietary salt solution. Much like seeds sprayed onto fertile soil, the hope is that these salts will interact with existing water droplets in the clouds, make them bigger and heavier, and they will eventually condense as rain.
In principle, this works, but many factors must align for it to succeed, as the most exhaustive analysis of cloud seeding in India has found. Such an experiment in Solapur, Maharashtra over two monsoons in 2018 and 2019 , the results of which were published in the Bulletin of the American Meteorological Society in October, concluded that seeding resulted in 18% more rainfall or about 8.67 mm more rainfall (or 867 million litres of water) than in the absence of it. Solapur was chosen because it is a rain-shadow region that normally receives little monsoon rain. Even so, the research team, consisting largely of atmospheric-research scientists from the Indian Institute of Tropical Meteorology, Pune, could find 276 “convective clouds”. These are clouds with a minimum of 0.5 gm of water per sq. cm. of cloud.
