Cloud Seeding | 30 Oct 2023

For Prelims: Cloud Seeding and Types, Artificial Rain, Convective Clouds

For Mains: Application of Cloud Seeding and Concerns, Atmospheric Circulation, Water Resources

Why in News?

Cloud seeding, a groundbreaking technique to enhance rainfall, has taken centre stage in a recent study published in the journal Bulletin of the American Meteorological Society, conducted by the Indian Institute of Tropical Meteorology, Pune.

The study unveils the potential of cloud seeding to boost precipitation in water-scarce regions, offering hope for tackling drought conditions.

What are the Key Highlights of the Study?

CAIPEEX Phase-4 Investigation:
- The Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX phase-4) was a two-year study in Solapur (Maharashtra), conducted during the 2018 and 2019 summer monsoons.
- Its primary objective was to assess the effectiveness of hygroscopic seeding in deep convective clouds and develop a cloud seeding protocol.
  - Researchers used calcium chloride flares for cloud seeding.
    - A cloud seeding flare releases these particles when triggered. The seeding was done at the base of the warm convective clouds and at a time when the clouds were in their growing stage so that the seed particles could enter the clouds with minimum dispersion.
- The experiment employed two aircraft for cloud parameter study and cloud seeding.
Cloud Seeding's Effectiveness:
- Cloud seeding is proven effective for enhancing rainfall under suitable conditions.
- A random seeding experiment selected 276 convective clouds, with 150 clouds subjected to seeding and 122 unseeded.
  - Specific cloud characteristics, including liquid water content and vertical motion, were used to identify clouds with potential for rainfall.
  - Targeted convective clouds were typically over one kilometer deep and likely to evolve into deep cumulus clouds.
Benefits:
- Cost-Benefit Ratio:
  - The approximate cost of producing water through cloud seeding was 18 paisa per liter during the research experiment.
  - Using indigenous seeding aircraft could reduce costs by more than 50%.
- Managing Drought Conditions:
  - Cloud seeding alone cannot fully mitigate droughts but can contribute to an 18% increase in rainfall, partially addressing water requirements.
  - Undertaking cloud seeding as part of catchment-scale projects could help in drought management.
- Practical Applications:
  - Cloud seeding can significantly benefit regions like Solapur which falls on the leeward side of the Western Ghats and hence gets low rainfall.
  - Additional water through cloud seeding has the potential to alleviate water scarcity issues in such areas.
Microphysics and Cloud Characteristics:
- The two-year study aimed to understand the microphysics and characteristics of convective clouds suitable for enhancing rainfall.
  - It provides comprehensive protocols and technical guidance for planning and conducting cloud seeding in India.
Cloud Variability:
- Not all cumulus clouds respond to cloud seeding; approximately 20-25% can produce rainfall if seeding is executed correctly.
- Cloud microphysics varies widely, leading to varied results with cloud seeding.

Convective Clouds

Convective clouds are clouds that form when warm, humid air rises through cooler air in the atmosphere.
- The warm air is less dense than the surrounding air, so it rises. This process is called convection.
- Convective clouds are also known as cumuliform clouds. They look like stacks of cotton balls.
There are two types of convective clouds: Cumulus clouds and cumulonimbus clouds.
- Cumulus clouds are fluffy, white clouds with a flat base and a rounded top. Cumulus clouds can develop into cumulonimbus clouds, which are associated with thunderstorms.
- Cirrocumulus Clouds are high-altitude clouds that appear as small, white, and fluffy cloud patches. They often have a wavy or honeycomb-like pattern.

What is Cloud Seeding?

About:
- It is the process of artificially generating rain by implanting clouds with particles such as silver iodide crystals.
- Cloud seeding uses planes to spray clouds with chemicals to condense smaller particles into larger rain droplets.

Cloud Seeding Methods:
- Static Cloud Seeding:
  - This method involves introducing ice nuclei, such as silver iodide or dry ice, into cold clouds that have supercooled liquid water droplets.
  - The ice nuclei can trigger the formation of ice crystals or snowflakes, which can grow at the expense of the liquid droplets and fall as precipitation.
- Dynamic Cloud Seeding:
  - Dynamic cloud seeding is a method of inducing rain by boosting vertical air currents.
    - The process is considered more complex than static cloud seeding because it depends on a sequence of events working properly.
- Hygroscopic Cloud Seeding:
  - This method involves spraying fine particles of hygroscopic materials, such as salts through flares or explosives into the base of warm clouds.
  - The particles can act as cloud condensation nuclei and increase the number and size of the cloud droplets, which can enhance the reflectivity and stability of the clouds.
Applications:
- Cloud seeding is done to enhance winter snowfall and increase mountain snowpack, which can supplement the natural water supply for communities in the surrounding area.
- Cloud seeding can also be done to prevent hailstorms, dissipate fog, induce rainfall in drought-prone regions, or reduce air pollution.
Challenges:
- Cloud seeding requires the presence of moisture-filled clouds, which are not always available or predictable.
- Cloud seeding does not occur during times when additional precipitation would be problematic, such as times of high flood risk or busy holiday travel periods.
- Cloud seeding may have negative effects on the environment and health, such as altering the natural water cycle, contaminating the soil and water with chemicals, or affecting the local climate.