Cloud Seeding – An Overview

Cloud Seeding - ProcessExploding demand of water resources and continued population growth has giving rise to the problem of water scarcity in many regions of our planet. To meet the demand of water resources scientist have started using weather modification commonly called as cloud seeding.  Cloud seeding is a weather modification technique which involves the introduction of material into a cloud (using aircraft or ground-based generators) with a view to encouraging the formation and growth of ice crystals or raindrops and, in turn, enhancing the precipitation (snow and/or rain) falling from the cloud.

There are two basic types – cold and warm:

  • Cold cloud seeding (glaciogenic seeding) involves adding particles such as silver iodide crystals or dry ice pellets to the super-cooled (below freezing point) water already present in clouds to promote the formation of ice crystals. The ice crystals grow, fall and melt to below the freezing level to become raindrops.
  • Warm cloud seeding (hygroscopic seeding) involves adding salt particles (sodium, magnesium and calcium chlorides), which attract water into or just below the base of suitable clouds to enhance the growth of cloud droplets by coalescence.

Historically, most seeding experiments and operational programs have involved cold cloud seeding. Warm seeding is a more recent development, which has extended the range of potentially seedable clouds as it can be used on warmer clouds than those suitable for seeding with silver iodide

Cloud Seeding | It’s Effects

One major problem is that it is difficult, if not impossible, to quantify the impact of a cloud seeding operation over a wider area, without expensive, time consuming and detailed experimentation and evaluation. Natural variability in rainfall is high, both in spatial and temporal terms, and it is difficult to predict what would have happened in an area had cloud seeding not taken place, despite the use of controlled experiments. It is difficult to design a practical cloud seeding campaign that has sufficient statistical rigour to prove or disprove the effectiveness of the seeding. Experiments using appropriate statistical design criteria may need  to run for many years in order to detect with reasonable certainty a rainfall enhancement signal against the ‘noise’ of the natural variability of rainfall. Many cloud seeding trials have suffered because of the inability of the design to produce unequivocal signals of the effect of cloud seeding. In addition, clouds amenable to seeding may not be present for a significant fraction of the time – for example the 1979-1980 Victorian experiment was abandoned due to a lack of suitable clouds.

Another disadvantage with cloud seeding is the high operational cost without commensurate assurance of success or economic return. Other issues include the possibility of downwind effects (decreased rainfall downwind from the target area), possible ecological impact of minute traces of seeding chemicals on sensitive terrestrial ecosystems, legal challenges, and overselling the technology without supporting scientific understanding and robust evidence. Experience has shown the importance of community engagement and consultation.

Overall we can say that Cloud Seeding is a mixed bag with it’s own pros and cons and so far is being treated as a controversial issue.

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