Why cloud-seeding trial to produce rain in Delhi was bound to fail

The Delhi government on Tuesday (October 28) claimed in a report that there had been two precipitation events in Noida (0.1 mm) and Greater Noida (0.2 mm) after two rounds of cloud seeding experiments to tackle air pollution. They also claimed that air pollution had marginally decreased in certain areas, ostensibly indicating success.

However, scientists The Federal spoke to questioned this narrative, saying that such low levels of rain or drizzle — if they occurred at all — were ineffective in combating air pollution, and could in fact worsen it.

Absence of seeding clouds

Meteorologist Gufran Beig, founder of the System of Air Quality and Weather Forecasting and Research (SAFAR), said it was a “foregone conclusion” that the artificial rain trial would fail.

“Seeding clouds are not present at this time of the year. Even if they are, there is a 5 per cent possibility for rain, and there is no guaranteed that they will be properly seeded. I had said much before the trial itself that such kind of a shortcut solution is not going to make any difference. It is more of a fun fair rather than a serious attempt,” he said.

Beig also questioned whether it rained at all, pointing out that IMD (India Meteorological Department) data did not indicate any rainfall.

Also read: Delhi cloud seeding trial put on hold due to insufficient moisture: IIT Kanpur

“Even if there was any rainfall, it has not come to the ground; it must have washed away on the upper side of the atmosphere, which doesn’t make any difference as far as air quality is concerned. Success can only be measured if particulate matter washes away when there is rain. And they wash away only when there is heavy rain, which has not been seen anywhere,” he said.

Conditions not suitable

Thara Prabhakaran from the Indian Institute of Tropical Meteorology (IITM), an expert in cloud seeding, said her team has studied nearly 267 clouds and done a “controlled experiment” whereby some clouds were seeded and some left unseeded. She told The Federal that her studies showed “rain enhancement of about 18 per cent in the seeded clouds”.

Prabhakaran, however, said the cloud conditions in Delhi were not suitable for such trials.

“In Delhi, we have different layer clouds, or occasionally we have some convective storms in the layer. In the layer clouds, some of the clouds are very high up in the atmosphere. There is a very dry layer between two cloud layers, and even if the upper layer rains, it will evaporate in the subsequent layer,” she explained.

She added that the shallow clouds lacked sufficient liquid water content.

“Another limiting factor is the amount of already available aerosol particles in the atmosphere. The cloud droplets are formed, but they are too many and too small in size. They don’t grow large enough to make collisions to form larger raindrops,” she said.

AQI declined naturally

Beig also disputed the Delhi government’s report on rain and reduction in pollution, which claimed that before cloud seeding, “the PM 2.5 level was 221, 230, and 229 in Mayur Vihar, Karol Bagh, and Burari, respectively, which reduced to 207, 206, and 203, respectively, after the first seeding”.

Also read: Delhi cloud seeding fails to produce rain, but govt claims air quality improved

“If it (AQI) declined a little bit or increased a little bit, that is natural variability, which would have happened even without cloud seeding,” he said.

“Drizzle, in fact, tends to increase the pollutants because it will make the air heavy, and then particles will sit on that and react and then multiply. So, drizzling during the winter is not good for air pollutants,” Beig added.

Drizzle does not help

IITM Scientist Sachin Ghude concurred that drizzling does not help with air pollution and questioned the use of artificial rain as a solution.

“We looked at the cloud presence during many of the peak pollution days, and our data showed that whenever there were peak pollution days, clouds were largely absent. The data of the last five to seven years shows that there are only 20 per cent of days when we have a cloud covering over Delhi-NCR,” he said.

Ghude noted that there is occasional rain in Delhi during winter, even without the trial, but it is too weak and localised to make any lasting difference. “During winter, there is rain, but even there, we see that within 8-10 hours, you regain the same air level because pollution is vast. It is not just centric to Delhi. It covers Delhi NCR and outside the NCR region also,” he said.

“Drizzle will not help because in drizzle, the washout will be less, and to clean the pollution, you need rain over the entire Delhi-NCR to get a substantial reduction in air quality levels. Washout means that when raindrops are falling on the surface, the pollution particles get dissolved in the raindrops and then are removed from the atmosphere. Those chances are only possible when you have WDs (western disturbance) and large cloud bases are present, and then eventually you get rain twice or thrice,” he said.

Not a viable or long-term solution

All experts agreed that artificial rain is not a viable or long-term solution to Delhi’s worsening air pollution.

“It (artificial rain) is not really a viable solution because too much infrastructure is needed right now. We have to develop so many things, and we have to have a very sound research strategy for implementing any such programmes,” said Prabhakaran.

Also read: Delhi conducts first cloud-seeding trial to tackle air pollution

According to Ghude, “there are no short-term options”.

“You have to shut down the sources. We need proper management of emission sources, and not just targeting Delhi, but Delhi NCR and also beyond NCR,” he said.

The only solution

Beig stressed that vehicular emissions remain one of the major sources of pollution that need urgent attention.

“More than the number of vehicles, it is the stagnation of the traffic or rampant stagnation, not running and not running at an optimal speed, that is one of the largest reasons for resuspended dust,” he said.

Earlier, D Raghunandan, former president of the All India People’s Science Network (AIPSN), had told The Federal that the government was looking for “silver bullet solutions” instead of addressing the core issue.

The solution is staring you in the face — which is to reduce the number of vehicles on the road. We know that more than 60 per cent of air pollution in Delhi is caused by vehicles. If that is the case, all policies must be directed to reduce the number of vehicles on the road and the only way to do that is to substitute personal vehicles with public mass transport,” he had said.