(a)

To provide reliable information about the probabilities of successful artificial intervention in meteorological processes with the object of increasing the amount of precipitation over an area of the order of 10,000 km. The size of the target and nearby control areas should be somewhere around 50,000 km2, a scale large enough to provide adequate evaluation of scientific feasibility and economic benefit, but small enough to permit the use of adequate methods for seeding and observations;

(b) To demonstrate at a satisfactory statistical significance level over a relatively short experimental period (5 years) that any increase observed is not a chance event but is associated with the seeding. The principal evaluation of this project will be in terms of precipitation at the ground;

(c)

To obtain sufficient understanding of the meteorology and cloud physics in the area of the project to ensure that the statistical association of seeding and any increase in precipitation will be generally acceptable as a cause-and-effect relationship;

(d) To make an examination outside the target area in order to determine whether any effects of seeding extend over areas greater than the target area, or whether there has merely been a comparatively local redistribution of precipitation;

(e)

To make systematic measurements varying from meso-scale to cloud microstructure in order to develop additional covariates to strengthen the power of the statistical analysis;

(f) To obtain well-documented scientific evidence that may lead to the optimization of the effects of seeding. For this purpose a series of systematic cloud physics measurements should be taken on a routine basis. This would allow the application of statistical stratification techniques to relevant physical parameters, and could shed more light on the quantitative aspects of the seeding technique;

(g) To be able to make some recommendations about the applicability of the PEP procedures to other areas of the world.

(h)

To make an assessment of the environmental impact of precipitation enhancement activities both within and outside the experiment target area.

Preliminary planning for PEP has begun with initial emphasis on site selction for the experiment.

The Seventh Congress also endorsed the text of a statement entitled "Present state of knowledge and possible practical benefits in some fields of weather modification" given in appendix C of the WMO report (1975).

This statement stresses that "weather modification is still largely at the research stage and, for this reason, operations should be undertaken only after the most careful study by experts of the particular situation, and on the understanding that the desired end results may not always be achieved". Brief summaries of the current status of precipitation stimulation, fog dissipation, hail suppression, and hurricane modification were included in the statement.

An informal meeting of WMO and United Nations Environmental Program (UNEP) representatives was held in Geneva on November 17-21, 1975, to discuss legal aspects of weather modification. The rationale for the discussions was the need to consider international legal principles and guidelines in conjunction with the scientific advancement of weather modification. Even though the present state-of-the-art of weather modification is not yet adequate to permit developing formal legal instruments for regulating activities, it is feasible to begin to establish certain principles (World Meteorological Organization and United Nations Environmental Program 1975).

The WMO held a conference on typhoon modification in 1974 at Manila in the Philippines (World Meteorological Organization 1975). Subjects of the sessions included characteristics of tropical cumuli, typhoons, and storm surges; modification hypotheses, models, and experiments; operational activities; and the design and evaluation of tropical cyclone seeding experiments. An example of the latter session was an experimental study by Heng and Yuen (1975) of flood control by seeding maritime warm clouds over the South China Sea so that they may precipitate at sea instead of over land thereby reducing flooding on the east coast of Malaysia. The seeding agent used was a saturated calcium chloride solution dispensed from an airplane. The authors concluded (a) that radar and visual observations confirmed that seeding induced cloud dissipation over the sea and (b) that a 25-percent decrease in rainfall occurred over the land area.

Conference participants adopted a statement on typhoon moderation with recommendations that WMO encourage and support any work to increase knowledge of the nature and properties of typhoons (hurricanes), to reduce wind damage with the help of seeding, and to distribute rainfall over a wider area. The statement also recommended that typhoons should be seeded on an experimental basis only if they are not expected to reach land within 24 hours.

On July 3, 1974, the President of the United States and the General Secretary of the Communist Party of the U.S.S.R. issued a joint statement at their summit conference, calling for representatives of the two nations to meet and explore effective measures to overcome the dangers of the use of environmental modification techniques for military purposes. A year later, after several bilateral meetings, a US/Soviet draft convention was presented to the United Nations Conference of the Committee on Disarmament (CCD). Article I of the draft states that each State Party to the Convention would not "engage in military or

any other hostile use of environmental modification techniques having widespread, long-lasting or severe effects as the means of destruction, damage, or injury to another State Party". The proposed treaty is not intended, however, to interfere with the development of modification techniques for peaceful purposes, such as increasing rain for agricultural needs. Further action on this proposed international treaty will be undertaken in the CCD in 1976.

An agreement between the United States and Canada was signed on March 26, 1975, relating to the exchange of information on weather modification activities, both governmental and non-governmental, carried out within 200 miles of their border. This unique agreement provides for transmittal of relevant information prior to commencement of activities, if possible; it does not require transmittal of proprietary information or that which is prohibited from disclosure by law. Furthermore, nothing in the document relates to or shall be construed to affect the question of responsibility or liability for weather modification activities. In addition, both nations agreed to consult, at the request of either, regarding particular weather modification activities of mutual interest or to review the implementation of the agreement. Since both countries have on-going reporting programs, the exchange of information was initiated immediately.

Foreign Programs

Documentation of foreign weather modification activities is not readily available. Some papers are given at meetings in the United States and a few are published in journals of the AMS and the WMA. Reports presented at international meetings are also sources of information as are newspaper and magazine articles. Translations of foreign technical documents are often made, but they were not used as references herein. The following brief items, therefore, are only samples of the types of weather modification efforts in other countries.

Henderson (1975a) has provided an interesting account of Soviet hail suppression work, based upon a visit to operational areas in the U.S.S.R. during 1974. He inspected the Soviet systems that combine radar with ground-launched rockets or artillery shells to disperse the seeding agent (silver or lead iodide) into storm clouds. His evaluation of the capability of weather modification operations to reduce hail in the U.S.S.R. is guardedly positive. This optimistic view is based on his belief that "a significant economic benefit lies in the sheer numbers of projects treated and the length of the total historic period now logged for various operational sites. Numbers emerge which show that, (1) during eight years of hail suppression operations in many different regions, the area of damage is three to ten times less than average annual amounts prior to operations, and (2) damage in any single year within any single protected area continues to be less than in adjacent areas". Although the

reduction in hailfall has produced an economic benefit, Henderson notes that there is still room for argument as to the precise degree of the program's effectiveness.

An operational cloud seeding program was carried out to increase the rainfall in the Lualaba watershed in the Republic of Zaire from November 1974 through March 1975 (Colorado International Corporation 1975). For a number of years, the stream flow had been below normal in the rivers feeding the lakes that contributed to electrical power capacity in the area. To make up for this power loss, it had been necessary to import electrical energy from Zambia. Using radiosondes, radar, and -aircraft with silver iodide flares, the cloud seeders applied the concept of massive or dynamic seeding of convective cumulus clouds to increase rainfall over the watershed. On April 18, 1975, importation of electrical energy was discontinued as the two resevoirs were nearly filled.

During the period October 1967 through January 1975, an operational hail suppression program was active in an area northwest of Nairobi, Kenya, East Africa. The project was supported by private companies which have approximately 45,000 acres of select tea in production. Within the operational area, average precipitation is about 71 inches and hail on the ground is experienced on more than 200 days per year. Silver iodide was applied by aircraft at cloud base; a total of 1382 operational days and 2,910 seeding flight hours were logged (Henderson 1975b).

In May 1975, the Nelspruit South Africa Project completed its fourth year of hail suppression operations to reduce damage to tobacco crops. The project area experienced about 30-40 hail days per year and the target area is 8,000 km2. Jet aircraft were used for seeding. Simpson (1975) has reviewed the project and, on the basis of preliminary results, expressed cautious optimism. She noted that the tobacco farmers involved have a high degree of belief in the efficacy of the project, as does a major insurance company. However, many persons tend to discount the results of any weather modification effort unless a randomized, statistically significant experiment has been conducted.

A previous analysis of rainfall data in the project area by those conducting the operation indicated that hail suppression seeding substantially increased the total average daily rainfall (National Oceanic and Atmospheric Administration 1974). However, a separate investigation by the Weather Bureau of the Republic of South Africa, based on data from 94 rainfall stations, showed that rainfall was neither increased nor decreased in the target area (LaRoux 1975).

The prime objective of experiments in Rhodesia during 1973-1974 was to confirm the effectiveness of seeding the tops of single cumulus clouds. by aircraft using pyrotechnic cartridges (fired from a Very pistol). Randomized trials on 20 seeded and 16 non-seeded clouds resulted in

average rainfall about five times heavier on seeded occasions than on non-seeded occasions. A ranking test showed a nine to one probability in support of this five fold increase in rainfall, when measurements started 25 minutes after seeding (McNaughton 1975). McNaughton also reported that there was evidence of less seeding effect under wet conditions, the experiments having been carried out during one of the wettest seasons in Rhodesian history.

Scientists in India have continued their studies of warm cloud seeding. Ramachandra Murty et al. (1975) investigated the dynamic effect of massive seeding with salt in cumulus clouds. Their experiments showed a rise in temperature as well as a rise in liquid water content before onset of rain. Clouds also grew a few thousand feet. These characteristic features, which appear to be the dynamic effect of salt seeding, were noted in all the clouds with initial vertical thickness of more than 5,000 feet at the time of seeding.

In Canada, studies and experiments have been performed to examine the possibility of using cloud seeding techniques, similar to those used in the U.S.S.R., to control forest fires. About one-fourth of Canada's land has productive forests and $50 million are spent annually on forest fire control. If 1 mm or more rain could be artifically induced to fall on a fire, a very powerful control technique would be available. Results of observations and measurements of forest fires in 1974 and consideration of seeding methods were reported by Isaac et al. (1975). They concluded that silver iodide would be suitable for seeding cumulus clouds just before they drift over a forest fire and that cloud top seeding by aircraft with an ice nuclei generator would be the safest method. They also noted that dynamic or massive cloud seeding, which causes explosive cloud growth by releasing the latent heat of freezing, will not produce precipitation in the Canadian climate. In 1975, a Summer Cumulus Rainfall Experiment was initiated in the area of Yellowknife, Northwest Territory, to investigate further the concept of forest fire control by airborne cloud seeding.

A group of American meteorologists visited the People's Republic of China in 1974 and reported their findings (Kellogg et al. 1974). They described a program underway in Hunan Province of southern China to increase precipitation by seeding warm cumulus congestus clouds with pulverized salt when natural rain is deficient. Randomization was not used in the experiments, but the Chinese made efforts to determine seeding effects by visual observations, by studying raindrop spectra, and by comparing rainfall in seeded areas with that in adjacent areas. In addition, Kellogg et al. described some earlier dry ice seeding activities in cold clouds that had been discontinued. Hail suppression programs were still active in China, with blank cannon shells, rockets, and artillery shells being fired at hail storms. Rad the various experiments was also mentioned.