Karachi authorities plan 'cloud seeding' to scale down effects of lethal heatwave

Rains are the only natural way to supply water to the megapolis, but the absence of these and scorching weather for past few days have seriously troubled Karachi’s residents with the death toll now at over 500.

Authorities today hinted at using artificial rain in Karachi. Under this process a chemical will be sprinkled on clouds via airplanes, which will force the clouds to rain.

Director General of Pakistan Meteorological Department (PMD), Dr Ghulam Rasul has that artificial rain was meant to overcome the heat wave.

Sources quoted Dr Ghulam Rasul as saying that “Most favourable weather for artificial rain is monsoon season. Success rate of such rains are higher than the procedures done during the non-monsoon days. Monsoon days in Pakistan fall from July to September.”

The process of generating artificial rain is called Cloud Seeding – a form of weather modification – an attempt to change the amount or type of precipitation that falls from clouds, by dispersing substances into the air that serve as cloud condensation or ice nuclei, which alter the microphysical processes within the cloud. The usual intent is to increase precipitation (rain or snow).

But the question is whether this method is inexpensive and sure-shot?

It is pertinent to mention that many developed countries have utilized the method of artificial rain during drought. Middle East countries are also using this technology to convert deserts into green land.

 

Questions regarding such a proposal

Scientists say the process will require a huge sum, which our government does not have, secondly there is no assurance whether it will rain.

If it rains even then the city is so vast that it is not possible for anyone to get it rained over completely.

Artificial rain also requires temperature at 5 degrees Celsius and 70 percent moist air – where will the authorities get these conditions from?

Former president Pervez Musharraf had also once excused from one such attempt.

However, it is yet another thing if such a plan is being pondered over only to waste the money of tax-payers, otherwise a tank-full of water can also be supplied to every house in Karachi with this amount.

What is ‘cloud’ seeding and how effective is it?

Cloud seeding or the practice of making rain involves the use of silver iodide, potassium iodide and dry ice (solid carbon dioxide). Table salt has also been used in industrialized countries. The procedure is based on the fact that the equilibrium vapour pressure is lower over ice than over water.

The formation of ice particles in super cooled clouds allows those particles to grow at the expense of liquid droplets. If sufficient growth takes place, the particles become heavy enough to fall as precipitation from clouds that otherwise would produce no precipitation. This process is known as “static” seeding.

Seeding of warm-season or tropical cumulonimbus clouds seeks to exploit the latent heat released by freezing. This strategy of “dynamic” seeding assumes that the additional latent heat adds buoyancy, strengthens updrafts, ensures more low-level convergence, and ultimately causes rapid growth of properly selected clouds.

 

Environmental impact of ‘cloud seeding’

Silver iodide can cause temporary incapacitation or possible residual injury to humans and mammals with intense or continued but not chronic exposure. However, there have been several detailed ecological studies that showed negligible environmental and health impacts