Cloud seeding in India has been garnering attention due to its potential to alleviate drought conditions. A two-year study dedicated to understanding the microphysics of convective clouds and their characteristics for rainfall enhancement has yielded some promising results.
About The Study
- IITM Pune conducted a cloud seeding experiment in Solapur city, a region that typically receives low rainfall due to its location on the leeward side of the Western Ghats.
- The total rainfall in this city was 384 mm and 422 mm during June to September in 2018 and 2019, respectively.
- The experiment resulted in an 18% relative increase in rainfall, equivalent to an additional 8.67 mm of rainfall.
- This increase in rainfall was observed two hours post cloud seeding.
- The overall boost in water availability through the cloud seeding experiments was 867 million litres.
- These findings have been recently published in the Bulletin of the American Meteorological Society journal.
Key Findings Of CAIPEEX Phase 4
- The Cloud Aerosol Interaction Enhancement Experiment (CAIPEEX Phase 4) took place in Solapur city in 2018 and 2019, during the summer monsoon period.
- The main goal of this scientific study was to examine the efficiency of hygroscopic seeding in deep convective clouds and create a cloud seeding protocol.
- Two aircrafts were utilised in this experiment to research various cloud parameters and for the actual cloud seeding.
- It was concluded that cloud seeding can successfully increase rainfall in an area when conditions are right.
- A randomised seeding trial was conducted to specifically investigate the impact of cloud seeding on rain production.
- In this trial, 276 convective clouds were chosen. Out of these, 150 were seeded and the remaining 122 were not.
Understanding The Process Of Cloud Seeding
- The study identified convective clouds likely to transform into deep cumulus clouds. These clouds were over a kilometre deep.
- The seeded clouds, those treated with cloud seeding, generated more rain than unseeded ones.
- We used flares containing calcium chloride for cloud seeding. Upon activation, these flares release particles.
- Seeding was strategically done at the base of warm convective clouds during their growth stage. This timing and location minimised particle dispersion.
- Convective cloud bases are at altitudes of 500-1500 metres during summer monsoons. During monsoon breaks, they rise to 2000 metres or higher, depending on lower atmospheric moisture.
- The base of these convective clouds is relatively warm, around 15 degrees C.
Challenges And Success Rates In Inducing Rainfall From Cloud Seeding
- The two-year study focused on understanding the microphysics and characteristics of convective clouds for rainfall enhancement.
- Comprehensive protocols and technical guidance for planning and executing seeding in India were developed.
- The study resulted in a high-resolution numerical model, beneficial for stakeholders in identifying target locations, clouds suitable for seeding, and proper seeding strategies.
- Not every cumulus cloud yields rainfall from cloud seeding.
- The study found that only 20-25% of cumulus clouds result in rainfall when seeded correctly.
- There is a wide variance in the micro-physics of clouds, which accounts for the variable success rates in cloud seeding inducing rainfall.
- Cloud seeding can’t eliminate droughts but can boost rainfall by up to 18%. This can partially meet water needs.
- Running cloud seeding projects at the catchment scale could help manage drought conditions.
Convective Clouds
- Convective, or cumuliform, clouds resemble cotton balls.
- They originate when warm, humid air rises in the cooler air of the atmosphere.
- The buoyancy of the warm air creates strong updrafts.
- Buoyancy refers to how objects rise or sink due to differences in their density compared to their surroundings.
- This buoyancy increases when water vapour in the air becomes cloud droplets through condensation.
- This process releases latent heat, the energy needed for a phase change – here, condensation.
- These clouds usually have flat bases about 1 km above the ground, but this distance can vary.
- The vertical depth of these clouds also varies widely.
About Cloud-Seeding
- Cloud seeding is the process of introducing substances into clouds to cause precipitation.
- It’s controversial, with some government officials advocating for it while some scientists and meteorologists question its effectiveness.
- The technique originated in 1946 with research by American chemist and meteorologist Vincent J. Schaefer.
- Cloud seeding can be conducted from various platforms including aircraft, rockets, cannons, and ground generators.
- A variety of substances have been used, but dry ice and silver iodide have proven most effective.
- These substances work best in supercooled clouds, where they create nuclei for water droplets to evaporate around.
- The evaporated water turns into ice crystals, which grow as more water droplets attach.
- In warmer clouds, calcium chloride particles can be used to form raindrops.
- Cloud seeding has been attempted to prevent damage from hailstones to crops and buildings.
Source: The Hindu