TODAY, a Singapore-based newspaper, has reported that Indonesia may use cloud-seeding in an attempt to increase rainfall in attempt to tackle the peat fires in Indonesia:
Indonesian forestry ministry official Raffles Panjaitan said the government planned to use [cloud-seeding] technology to try and put out the fires, that are mainly centred on peatlands in Riau province, reported AFP.
However, the earliest this could take place would be on Friday as preparations need to be made, the official said. Helicopters will be dispatched to inject chemicals into clouds, prompting the formation of heavy ice cystals which would speed up the production of rain.
The operation also depends on weather. “Hopefully there will be lots of clouds so that we can produce a lot of rain,” AFP quoted him as saying.
Heavy and persistent rainfall would indeed be desirable. It could help to extinguish or at least suppress the burning in Sumatra. Furthermore, rainfall would also help to remove many of the aerosol particles currently contributing to the haze. However, is rainfall something that people can really control?
What is cloud-seeding?
Water vapour is vital for the formation of clouds. However, water vapour on its own is not enough. The water vapour needs surfaces to condense onto. Aerosol particles act as these small surfaces, the so-called cloud condensation nuclei (CCN), which can grow to form cloud droplets. Rain drops may then form via two possible processes:
- Some of the cloud droplets may grow large enough to start colliding and combining with other droplets. These larger droplets are often formed by large aerosol particles known as giant CCN.
- Some of the cloud droplets may freeze. Liquid cloud droplets often exist in a supercooled state at temperatures below freezing. Freezing is often caused by aerosol particles known as ice nuclei. When freezing occurs, the ice crystals grow at the expense of the water droplets. These ice crystals can then form rain, snow or hail, depending on the specific cloud and whether or not they melt before they reach the surface.
The proposal to seed clouds assumes that the artificial introduction of specific types of aerosol may effect the ice formation processes, allowing the rainfall to be influenced to some extent.
Does cloud-seeding work?
Investigating possible aerosol effects is one of my favourite areas of scientific research. It is interesting partly because these effects are still poorly understood, particularly aerosol effects on convective clouds. Most rainfall in this region is formed by tropical deep convective clouds, the sort of clouds that produce lightning and thunder. These convective clouds are extremely complicated systems with many factors determining precipitation formation. So, do I think that cloud-seeding allows us to control deep convective precipitation? The short answer is ‘No’. On the one hand, the addition of specific types of aerosol particles to a cloud may well influence the precipitation to some extent. On the other hand, I do not believe that anyone can say how seeding will impact the precipitation in any one given cloud. In some cases it may enhance the precipitation, whereas in other cases it might suppress it. Hence, I do not believe that anyone can currently control precipitation in Southeast Asia.
A final word
The investigation of possible aerosol effects on precipitation is a fascinating area of scientific research. However, I am very skeptical that cloud-seeding allows us to control precipitation, particularly in this region. We should indeed hope for some heavy and persistent rainfall. But the Indonesian government cannot control when the rain will come. In the meantime, firefighters remain the most important human-controlled asset for fighting the fires that have already started. This firefighting, and the prevention of new fires, should remain Indonesia’s priority for the resolution of this current haze event.