Cloud seeding is a weather-modification method. It was discovered by Vincent J. Schaefer, an American chemist in 1946 after WWII. Its purpose is to induce rain and snowfall which may lead to reduced droughts. The efficiency of cloud seeding can be calculated by evaluating the ratio of rains that happened naturally and with this method. There are three principal techniques for cloud seeding that are static, dynamic, and hygroscopic.
Note that the cloud seeding technique is still in the research and development phase. When it was started back in the 1940s, many scientists and government departments did a number of physical experiments on cloud seeding.
The purpose was to remove the droughts and hunger from areas where rains are very rare. Some people mentioned cloud seeding as artificial or fake rain but the more appropriate way to define it is that it is the induction of rain from clouds by increasing the property of precipitation of clouds. In other words, clouds are condensed to precipitate by using some mechanical and physical techniques.
Working principle of cloud seeding
It works on the principle of nucleation. The intent of seeding mountaineers’ clouds is to introduce aerosol or nucleating particles into a cloud. That introduction may influence the natural development of cloud particles. Here the aim is to enhance odd-time precipitation in targeted areas. It is initiated with the introduction of silver iodide aerosol into cloud regions containing supercooled liquid water, leading to the nucleation of ice crystals. When they become large enough, they fall down as rain or snowfall.
Cloud seeding agents (CSA)
Chemicals that are used to induce precipitation are known as cloud seeding agents. The most common of these substances is silver iodide. It has a hexagonal crystal structure that aids clouds to freeze around it. Some other chemicals which are frequently used as CSAs are given below:
- Liquified propane
- Dry ice (frozen carbon dioxide)
- Potassium iodide
- Sodium chloride
- Calcium chloride
Cloud seeding methods
Various techniques to influence clouds are evolved with time, some of the most vastly used methods are described below:
Static method
It was discovered by the atmospheric scientist Dr. William R. Cotton. In this method, The efficiency of rain formation is enhanced by using CSAs. The chemicals used for this purpose such as silver iodide are ice-nucleating agents. They are introduced at the base of the clouds through airplanes. They interact with moisture and act as ice crystals because silver iodide has hexagonal crystals, similar to ice.
Dynamic method
This method comprises 11 different stages to encourage precipitation in clouds. It was found to be more complex as compared with the static method because it uses 100 times more cloud seeding agents.
Hygroscopic Method
In this method, CSAs are dispersed through mechanical means and explosives near the base of the clouds. Hygroscopic salts such as sodium cloud are used in this process. The size of salt particles ranges from 5 to 100 micrometers in diameter. These particles grow by vapor deposition and initiate rain formation by collision.
Physical experiments of cloud seeding and their outcomes
In the USA
In recent years, American states such as California, Idaho, Nevada, Utah, and Wyoming have started their own winter cloud seeding programs. Texas and North Dakota have summer programs that aim to increase rain and decrease hail.
On average, the random results have positive and negative outcomes, but overall 10 to 15% increase in rainfall in the summer season is observed.
In South Africa, by using hygroscopic methods
It was started in 1990 and persued for long 15 years. Its main objective was to control rains and storms. in this experiment, hygroscopic flares were introduced at the bases of clouds.
The results are somehow convincing as the main purpose of decreasing the rain in targetted regions was achieved. The storms were significantly reduced from a predicted 126 to 97 only.
United Arab Emirates (UAE) cloud seeding program
In 2001, the UAE Met department started a weather modification program in collaboration with the National Centre of the Atmospheric Research (NCAR) in the United States, the University of the Witwatersrand, Johannesburg, South Africa, and the National Astronomy Space Agency in the United States (NASA). It got a huge success in May 2008 when unexpected rain and thunderstorms hit many parts of Dubai and Abu Dhabi.
Factors that affect cloud seeding
In any weather modification operations or experiments with convective clouds, a situation will arise when seeding will not be effective. The factors which may affect the seeding are as follows:
- Clouds study: Not every type of cloud can yield rain. The clouds should be taken into consideration before commencing the physical experiment.
- Delivery techniques: A proper propeller homogenizer should be used to get accurate dispersion of CSAs.
- Seeding material (CSAs): The quality and shape of the molecule are really important in cloud seeding. Silver iodide with hexagonal crystal, similar to ice, can only be used to trigger the nucleation.
- Radar Monitoring: The monitoring of CSAs by using advanced radar techniques is highly recommended.
Benefits
- Weather modification
It seems one of the best methods to modify the local weather of a region as per requirement. For example in desserts where rain is much-needed cloud seeding may help to produce it.
- It can be used to halt the hailstorms
In Alberta, cloud seeding is used to decrease the hailstorms in the summer seasons. These storms are responsible for severe damage to agriculture.
- Booster to economy
This method directly impacts the people of certain regions where the weather has been modified by cloud seeding. For example, this method enhances crop yield.
- Tourism
The weather is one of the key factors to promote tourism. Extreme weather does not attract tourist to spend their time in that region. Cloud seeding is a local weather modifier. In 2008, during the Beijing Olympics China used this method to maintain the temperature range from 25C to 30C and it was proven quite effective.
Related topics
Impacts on the environment and living organisms
Cloud seeding uses some dangerous chemicals to aid rain formation. Though it is used in very minute quantities still it has the potential to react with other volatile chemicals such as chlorofluorocarbons (CFCs) in the troposphere. Moreover, breathing problems are also reported in the regions where those physical experiments are conducted due to air pollution.
Below is the overview of the impact of the cloud seeding:
Concepts Berg
Does cloud seeding work?
The efficiency of cloud seeding is still debatable. In the last 70 years, different research institutes designed various methods. All these methods somehow show some potential, but this still requires a lot of research. Hence we can say that cloud seeding is in its research phase and it cannot be used to save the world from droughts.
How do we cloud seed?
Clouds can be seeded through different methods, such as static, dynamic, and hygroscopic. In the static method, clouds are seeded via chemicals such as silver iodide. while the dynamic method uses vertical air currents which aid nucleation. The hygroscopic method of cloud seeding involves the introduction of hygroscopic particles such as salts to enhance precipitation.
Why is the state of Utah involved in this process?
The State of Utah involved in cloud seeding since the 1950s. The reason is it wanted to rise water reservoirs.
What is a cloud?
When water evaporates it rises up in the air these vapors condense in the sky when passes from a cold region. The water vapors or ice particles form an aerosol and when it gets that required temperature and nucleation conditions, it starts gathering to form heavy particles that cause snow and rain.
Is it safe to do cloud seeding?
Cloud seeding involves chemical substances such as silver iodide which is sometimes found to be harmful to the environment. But in recent studies, it has been proven that the concentration is around 50 microgram/liter (50 ppb) and is not harmful to live organisms.
What are the disadvantages of cloud seeding?
Cloud seeding doesn’t get the importance it sought due to some disadvantages which are listed below.
- It can cause water pollution.
- This method requires chemicals that are so costly. Hence, the environmental budget may be compromised.
- It works with certain types of clouds and between a specific range of temperatures.
- Health problems such as skin and breathing issues are also caused by cloud seeding.
Who invented this technique?
Vincent J. Schaefer, an American chemist invented this method. In 1946, he performed the first experiment on cloud seeding and created artificial rain.
How much does cloud seeding cost?
In America 5 million dollars per year is spent on research and development of cloud seeding. It is very expensive because the efficiency is not so good so far. The cost needed can be used to plant more trees and reduce harmful gases getting into the atmosphere. This is a cost-effective way to reduce global warming.
What are the required conditions for cloud seeding?
Cloud seeding requires specific conditions such as -20 to -4°C temperature for static methods.
What is the most advanced cloud seeding technique to date?
The static method is the most advanced technique used to date.
References
- Design of physical cloud seeding by Arizona dept of water sources, (USA)
- Environmental sciences Bachelor Level Course by Dr. Zahidullah (AIOU Pakistan)
- Cloud seeding program (dri.edu)
- What to Know about cloud seeding (webmd.com)
- Precipitation formation from orographic cloud seeding (pnas.org)
