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1.7 Cloud Seeding

The technology of cloud seeding is based on the principle of introducting artificial frost nuclei to the already-existing natural frost nuclei within clouds. Several countries, especially those in arid and semi-arid regions, have used this technology to try to increase rainfall volumes. Experiments in Russia, United States of America, Australia, China, India, Morocco, Syria and other countries have demonstrated that artificial cloud seeding can increase the quantity of rainfall between 5-20% over large areas and relatively long durations (monthly or over the rainy season).

There are regions in West Asia that could potentially benefit from this technology, including the coastal mountains in the eastern Mediterranean, Yemen and Saudi Arabia highlands along the Red Sea, and some internal regions. Despite the diversity of opinions on the feasibility of the technology, primarily because of the difficulties in assessing its results, the prevailing opinion is that it has reached a relatively advanced stage of application, and it can be considered one of the technologies capable of contributing to the augmentation of freshwater supplies in semi-arid regions.

Technology Description

Cloud seeding requires advanced equipment and facilities, including aircraft, a meteorological station network to monitor the clouds, a rainfall monitoring ground network, a network for data collection and processing, and a satellite image transmission networks.

Materials used for cloud seeding include silver iodide (in the form of Pyrotechnic), azotic cooling liquid, dry ice (CO₂) and propane. Cooling material and silver iIodide are usually used at a concentration of 2%, for seeding clouds with graded microstructures. Dispensing the material from the top of the cloud produces better results than dispensing it from the bottom. This is typically done by airplanes or ground generators, with the goal of facilitating the optimal distribution of the seeding material among the cloud components containing the largest portion of supercooled water.

Cloud-seeding projects require establishment of a technical and administrative organization containing (1) a radar and electronic maintenance division, (2) an aviation affairs division, (3) a data collection and processing division, and (4) an education and training division. Cloud-seeding technology also requires cooperation and coordination between relevant water resources, irrigation, civil aviation and meteorology authorities.

Extent of Use

Cloud-seeding experiments were carried out in the Asir Mountains of Saudi Arabia, United Arab Emirates, Jordan and Syria. Field studies were conducted in the Sultanate of Oman. Cloud-seeding experiments in Syria continued between 1991-1997 (Table 8), and the project carried out by the Ministry of Agriculture and Land Reclamation is considered one of the most important projects carried out on this topic in the West Asia region, as well as being a pioneering project on the Arabic and international level. The project’s objectives included (1) improving the rainfall distribution in the Balia agricultural regions (to ensure that the economic return on rain-fed agriculture did not rely only on the quantity of rain during the agricultural season), and (2) improving the rainfall distribution at different plant growth stages. Additional objectives included increasing the volumes and intensities of rainfall for charging groundwater aquifers, as well as increasing the water volume stored in surface dams. The estimated additional rainfall attributable to cloud seeding ranged between 7-16% of the natural annual rainfall (estimated to be about 45 billion m³). The use of this technology is in an experimental stage in the other Arab countries, but generally is exhibiting encouraging results.

Table 8. Summary of cloud-seeding operations in Syria

Operation and Maintenance

Use of this technology includes long-term monitoring of rainfall and other meteorological parameters, based on conventional and satellite meteorological recording networks. Information from weather-predicting centers is typically used in the initial operation of this technology in specific target areas. Because available prediction methods are inadequate, artificial tracers are typically used to follow the development and motion of clouds. This is done with the use of infrared rays, visual images and water-pressure images. Meteorological radar is generally used to determine cloud microstructure, and especially cloud heights. Radar is used to monitor precipitation from the clouds, as well as the cloud development prior to and after the seeding process.

The cloud-seeding plane is usually dispatched when suitable clouds are available. It conducts an aatmospheric investigation, measuring such meteorological paramaters as temperature, humidity, dew point, and wind speed and direction. A radiometer is used to measure cloud content of supercooled water. The operation base on the plane and the meteorological radar stations cooperate to ensure that the cloud-seeding exercise is based on accurate knowledge of the cloud base and height, temperature, uplift currents and humidity. All navigational, meteorological and seeding information is recorded on the plane’s computer for later analysis.

When all the physical information on the cloud is obtained, it is seeded with silver iodide. The required maintenance work focuses on the mechanical and electronic equipment, which requires a skilled staff with multiple specialties.

Level of Involvement

Cloud seeding in the West Asia region is conducted by government institutions, with contributions from such executing organizations as civil aviation, meteorology, water resources and agriculture. The main beneficiary is the Ministry of Agriculture, and its institutions, central directorates and municipalities. The private sector has not yet shown significant interest in this technology. This lack of attention is attributed to the fact that, in addition to the high capital costs, private companies will not achieve their economic goals unless they are established on a regional level.

Costs

Cloud-seeding technology is generally an expensive process, dependent on its efficiency and effectiveness. The seeding equipment used in Jordan included C-B and VRC 74 weather radars, and an aircraft equipped with meteorological recording instruments. The aircraft also contained a computer, satellite station (METEOSAT NOAA), qualified radar technicians, engineers, meteorologists and pilots. In Syria, the cloud-seeding project was initiated in 1992, involving similar equipment and staff. Six aircraft were used for seeding purposes during 1993-1994, with the project costs reaching 156 million Syrian lira. The operation costs reached 25 million Syrian lira (US$ 0.5 million) in 1998. The cost per cubic meter of water for the years 1991-1997 were previously highlighted in Table 8. Based on the regression method is used to estimate increased rainfall, the costs range between US 0.026-0.181 cents/m³ of water, and between US 0.016-0.113 cent/m³ if the ratio method is used.

Effectiveness of the Technology

Under certain circumstances, data suggest that natural rainfall can be increased through the use of orographic clouds. Statistical analysis of rainfall records of several projects suggests a rainfall increase of about 10% over the natural level. Nationwide experiments in Syria suggest that the rainfall increase ranged between 7-16% during 1991-1997. The average increase was about 3.02 km³ over a period of 4 months (11.1%) using the regression method, and 3.75 km³ (12.5%) using the ratio method.

Cloud-seeding experiments are still limited in the countries of West Asia, and the technology is currently undergoing analysis and scientific research. Because the cloud-seeding technology is still in a developmental stage, its fruitful applications are still limited. Further, ongoing research currently concentrates on the meteorological aspects, with inadequate attention being given to the hydrogeological aspects.

Due to increasing water shortages in the West Asia region, this technology is nevertheless considered promising under suitable conditions for facilitating increased rainfall, resulting in improved water resources and economic benefits. The most promising regions for application of this technology can be determined by conducting the necessary cloud survey and assessment work, and interest in this technology currently exists in Iraq, Jordan, Syria, Saudi Arabia, Yemen and Oman.

Suitability

The proper and beneficial use of the technology requires certain appropriate conditions, including (1) suitable sites, (2) suitable cloud-seeding material, (3) a means of dispensing the seeding material in the supercooled clouds, and (4) sufficient quantities of vapor and supercooled water, as well as sufficient time for the rain particles to achieve a suitable size to cause it to fall to the land surface.

Based on current knowledge, cloud seeding gives the best (and most economically-feasible) results when the target cloud systems flow over mountains, or the air masses are affected by a series of mountains to form the clouds (orographic clouds). Most cloud-seeding experiments in the region were conducted under these conditions, including the experiments in the Asir hills in Saudi Arabia, Emirates and Jordan. Cloud-seeding efforts in Syria have been carried out over the whole country, therefore being conducted under different methological and topographical conditions. The importance of cloud-seeding experiments in these regions rests in its potential hydrological contributions and positive impacts on water resource management. In the eastern Lebanon mountains of Syria, for example, cloud seeding contributes to increased snowfall which, in turn, contributes to the recharge of the underground reservoir (especially the grand Karstic springs) supplying the city of Damascus and its suburbs.

Cloud seeding efforts in Syria , in addition to contributing to aquifer recharge, has the following objectives:

• Improving the required rainfall distribution for rain-fed agriculture (especially grains);
• Increasing dam storage volumes.

Such experiments have highlighted the suitability of this technology for the prevailing environmental conditions in the eastern Mediterranean region.

Advantages

The advantages of this technology are as follows:

• It contributes to augmenting freshwater resources to meet water demands, particularly in arid and semi-arid regions. It holds promise for regions facing water deficiencies. Its efficiency can be increased through research, experiments, and a better understanding of precipitation and cloud systems;
• There is growing recognition that cloud seeding under certain conditions can produce positive results, using either stratus clouds (formed by the collision of moist air masses over mountainous heights) or connective clouds. Under these conditions, cloud seeding can contribute to increasing shallow underground storage water;

• It allows successful dissipation of fogs and low stratus clouds that can be an obstacle to aviation traffic at airports;
• It contributes to improving the productivity of rain-fed agricultural areas, either by increasing rainfall volumes or sometimes by controlling the spatial and temporal distribution of rainfall.

Disadvantages

The disadvantages of this technology are as follows:

• The effectiveness of this technology in drought situations is very limited, primarily due to inappropriate climatic conditions during such periods;
• Positive benefits from a cloud-seeding process for one group of a community may be accompanied by negative effects on other groups;
• For countries of limited areas, or along national boundaries, cloud seeding could result in problems relating to possible negative effects that might occur in neighboring countries. Cooperation in such cases is therefore essential, and may require issuance of legislation regulating the legal aspects of cloud seeding;

• Cloud seeding requires advanced and costly equipment, as well as the recording, collection and analysis of relevant information. The seeding process also required qualified professional staff and modern equipment. Thus, the benefits may ultimately not be sufficient to cover the costs. A cloud-seeding program also will not produce effective results without accurate weather data, or an inability to carry out the seeding process at the suitable time or place;
• Although planning of cloud-seeding programs may be successfully and efficiently carried out, accurate and practical assessment of the results may be hindered by the lack of physical and statistical evidence. The assessment process also may require the use of modeling techniques.

Cultural Acceptance

There are different opinions on the acceptability and effectiveness of the cloud-seeding process. Due to an increasing need to increase water resources and supplement existing supplies in the arid and semi-arid areas of West Asia, the technology has received increasing attention from the public and government institutions. This increasing attention is accompanied by the need to be wary of any negative impacts that may occur in some rain-fed agricultural areas as a result of positive results in other areas, thereby resulting in unstable agricultural grain production. The technology is nevertheless acceptable among all levels of officials and the public in regard to its goal of increasing water resources. There are questions about the economic feasibility of the technologies used, as well as the seeding methods (ground generator, airplanes) used to deliver the seeding materials to the clouds.

The acceptance of cloud-seeding experiments depends on local subjectivity to analyze the results and illustrate the benefits, especially the confidence of the statistical methods used in the assessment.

Some fear still exists in regard to potential changes in the rainfall system outside of the experiment areas. Thus, provision of accurate quantitative information about such efforts may reduce the fear of negative impacts in neighboring areas.

Future Development of the Technology

The most obvious issue in cloud-seeding technology is the potential importance of its development as a means of contributing to solutions of water scarcity in arid and semi-arid regions. Because their rainfall characteristics undergo tangible changes throughout the year, semi-arid areas are the areas with the greatest need for this technology. These changes also change the productivity of agricultural systems, as well as shortages of water for drinking and other basic needs.

Some of the promising ways to develop and improve the technology are as follows:

• Implementation of joint projects between neighboring Arab countries, as well as promotion of cooperation between countries and organizations interested in developing the technology, coordinating international programmes in this field and utilizing the results of successful experiments;
• Conducting cloud surveys for monitoring and measuring the basic elements in the clouds, quantitative determination of precipitation and analysis of cloud-seeding methods;

• Collection of accurate information about cloud characteristics and cloud seeding. The results of such efforts also should be publilshed and distributed among the institutions and countries involved in research on cloud-seeding programs;
• Promoting participation of beneficiaries, particularly farmers, for the technology. This is especially important because the technology can simultaneously achieve positive results in some areas and negative impacts in other neighboring or distant sites. Thus, legal complications can arise when cloud seeding is conducted near national boundaries. Because the impacts of weather modification on society are tangible and multifacted, attention on this topic must not only focus on metoerology and water, but also consider the prevailing ecological, hydrological, social and economic conditions. The legal aspects of cloud-seeding experiments, therefore, are worthy of attention from different institutions. There also may be a need to compensate adversely-affected groups, or at least inform decision-makers and the public of the current weather modification process.

Information Sources

Contacts

Abdel Rahaman Tamimy Al-Omrah
Director, Palestinian Hydrological Group
P.O. Box : 565- West Bank- Ram Allah
Tel: 972-2-6565887
Fax: 962-6-5857688
e-mail: phg@palnet.com

Aly Abbas
Director, Cloud Seeding Project
Ministry of Agriculture and Reclamation
Damascus, Syria
Tel: 2235137 – 2224201

Nabil Kafwin
Head, Cloud Seeding Division
Directorate of Meteorology
P.O. Box : 341011, Jordan
Fax: 962-6-894409

References

Abba,s A. and S. Halabi. 1994. Cloud seeding project in Syria, 1991-1993. Efficiency Six, WMO Scientific Conference on Weather Modifications, vol. 1, WMO/TD-n 596, Geneva, Switzerland. p. 325-322.

Abbas, Aly, Bedour Al-Bana, and Mohamed Al-Bana. Statistical analysis of the rainfall in Syria. Workshop on Statistics and Planning in Syria, October, 1980, Damascus (in Arabic).

Abbas, Aly. 1982. Effect of irrigation projects on the local climate in Syria. Results of Workshop for Agricultural Meteorology in the Arab World, May 1982, T-20, ACSAD/DX, Damascus, Syria. p. 230-247 (in Arabic).

Abbas, A. and A. Mustafa. 1999. Syrian rain enhancement project, 1991-1998. 7^th WMO Scientific Conference on Water Modification, February 1999, Chiang Mai, Thailand.

B.Sh. Kadyrov and V.P.Kurbatkin. 1999. On methodological issues of the assessment of cloud modification effects in desert areas. Rainfall enhancement research and operation in South Africa: Past, present and future, 7^th WMO Scientific Conference on Water Modification, February 1999, Chiang Mai, Thailand.

Chen, Zhiyu. 1999. A general introduction to weather modification in China. 7^th WMO Scientific Conference on Water Modification, February 1999, Chiang Mai, Thailand.

Deone,Terblanche. 1999. Rainfall enhancement research and operation in South Africa: Past, present and future. 7^th WMO Scientific Conference on Water Modification, February 1999, Chiang Mai, Thailand.

Gabriel, K. R. and D. Petrondas. 1983. On using historical comparisions in evaluating cloud seeding operations. Jour. Climate Appl. Meteor. 22:626-631.

Howell, W.E. 1984. Comments on using historical comparisons in evaluating cloud seeding operations. Jour. Climate Appl. Meteor. 23:850-845.

Remalal, K.H.M.S. 1999. Sri Lankan experience in cloud seeding. Advantages of weather modrification for agriculture. 7^th WMO Scientific Conference on Water Modification, February 1999, Chiang Mai, Thailand.

Sami, Al-Juboory. 1999. Data analysis of Iraqi cloud seeding project. Rainfall enhancement research and operation in South Africa: Past, present and future, 7^th WMO Scientific Conference on Water Modification, February 1999, Chiang Mai, Thailand.

Seder GAF. 1977. Linear Regression Analysis. John Wiley & Sons, Inc., New York. 456 p.

Shipilov, O.I., B.P. Koloskov and A. Abbas. 1994. Statistical evaluation of cloud seeding operation in Syria (1991-1993). 6^th WMO Scientific Conference on Weather Modification, vol. 1, WMO/TD-N 596, Geneva, Switzerland. p. 341-344.

Wathana, Sukarnjanse. 1999. The Applied Atmospheric Resources Research Program (AARRP) of Thailand. 7^th WMO Scientific Conference on Water Modification, February 1999, Chiang Mai, Thailand.

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