New Delhi: With pollution levels in the capital showing no sign of improvement, the Centre is planning to induce artificial rain to clean the air.
Union minister Mahesh Sharma said that the government should issue a notification to induce artificial rain, in case air quality dips further. "Increasing menace of air pollution is a big concern for a developing country like India. The Centre has decided that if the air quality crosses 500-mark then they will ask authorities to induce artificial rain or cloud seeding over the capital," he said.
An AQI of over 500 is past the 'severe' category and into the 'Hazardous' category – presently, the AQI is at 352, falling under 'Very Poor' category due to favourable wind conditions. But what is artificial rain? Will it really work?
Cloud seeding
Rain occurs when supercool drops of water, which are still in liquid form but below freezing point (zero degree Celsius), become ice crystals. These water droplets become too heavy to remain suspended in the air and they fall, melting on their way down and become rain.
Even in places drier than Delhi (present humidity in the capital is at around 40%), there is water in the air.
What seeding could do is mimic this process and change the amount of precipitation by dispersing substances into the air, which can trigger the process of forming ice crystals by condensing available water in the air. These chemicals may be dispersed either by aircraft or by dispersal devices on the ground.
Finding the right cloud
Whether it is warm or cold, polluted or clean, over a mountain or a city—ultimately, it is the characteristics of the cloud that is key to success of cloud seeding efforts. According to a 2017 bulletin by the World Meteorological Organisation, "New tools are enabling meteorologists to study and understand clouds and their modification with greater precision than ever, while new technologies such as nanotechnology are expanding possibilities in this field."
Finding the "right" cloud depends on both temperature and location, the report adds. In 'cold clouds' agents such as silver iodide help initiate formation of ice crystals. While in "warm clouds, scientists can use hygroscopic seeding, generally with a simple salt. The salt helps water droplets to collide and produce rain," the report says. As far as the location is concerned, clouds in tropics are different from clouds in mid-latitudes because temperature influences cloud processes, it says, adding that "different levels of pollution can also develop precipitation differently."
How Effective is it?
Over the years, there has been growing evidence that has contested the effectiveness of cloud seeding.
In 2003, the US National Research Council released a report stating that "scientifically acceptable proof for significant seeding effects has not been achieved" although in the past five decades "substantial progress" was made in understanding the natural processes that led to changes in weather.
A 2010 study by the Tel Aviv University's Department of Geophysics and Planetary Sciences, published in the journal Atmospheric Research looked at over fifty years’ worth of data on cloud seeding, with particular emphasis on the effects of seeding on rainfall amounts in northern Israel. The research concluded that it was changing weather patterns that were responsible for the higher amount of precipitation during these years and not seeding, as was initially thought.
Past instances
In 2016, 56 countries had cloud seeding operations, compared to 42 in 2011, as estimated by the World Meteorological Association. China had, for the 2008 Beijing Olympics, turned to cloud seeding to try and keep rain away, by inducing rain prior to the games. Most recently, the National Cloud Seeding Research Centre in Iran started its project in the highlands of the central province of Yazd, with other provinces in the pipeline.
In 2015, the UAE launched the Research Programme for Rain Enhancement Science with a budget of US $ 5 million, to advance research and technology of rain enhancement. It has two primary goals: boosting research in rain enhancement globally, and to increase rainfall in UAE and other arid and semi-arid areas of the world.
Will it work in Delhi?
Union minister Mahesh Sharma assured that, "Our scientists and authorities are working round the clock to curb this. All requisite preparation for artificial rains are underway." The government's plan to seed clouds and trigger rain in 2016 had failed. Last year too, the government had proposed ‘watering’ Delhi with the help of helicopters to reduce the prevalent dust haze and smog that turns the National Capital Region into a toxic gas chamber. This proposal too had failed.
This year, though, scientists remain optimistic. "We have been mulling this for a long time and this is an emergency step we will take if need arises," a CPCB official said.
Will it actually work? Only time will tell.
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