Director, Centre for Environmental Studies,
Gitam University, Visakhapatnam-530 045
http://www.climatechange.qld.gov.au/response/cloud_seeding.html [Queensland,Australia Expts.]http://jcsepa.mri-jma.go.jp/outreach/symposium20070131e.html [Japanese Int'l Conf.]
Many meteorologists, scientists, engineers, bureaucrats and politicians are sometimes arguing that cloud seeding operations are not scientific, successful and effective. Such arguments are not at all correct from the point of view of promoting public health, agricultural and industrial development and the economic prosperity of the people. Management consultants say that cloud seeding project sponsors may be classified typically either as those who “Do things right” or who “ Do the right things”. The project sponsors of cloud seeing who “Do things right” produce results with high efficiency and thereby obtain the best possible output from the resources. Similarly the sponsors of cloud seeding who employ the right people for the job which means doing the right things also contribute for the effectiveness of the operations. It means the project sponsors are setting the right goals and right objectives in terms of the additional rainfall needed for different crops or other purposes during different seasons at different places .They are also making sure that the right experts and right instruments and machinery like the right aeroplanes and the right ground generators in sufficient numbers are employed and the timely assistance from thedifferent authorities issuing permits for operations is secured and thereby make sure that the set targets of the operations are accomplished. Some experts say that it takes firstly the organisational efficiency in terms of engaging the right experts and right equipment and secondly an enlightened leadership to produce effectiveness of the operations. Thus effectiveness is a measure of the ability of the cloud seeding project operators to produce the specific desired effect or the result that can qualitatively or quantitatively be measured. However effectiveness must be distinguished from “Efficiency” which is measured by the volume of the output produced for the input used. Hence efficiency is closely related to “Productivity”as set by the target. Either due to inefficiency or vested interests if the sponsors are not able to employ the most qualified and experienced experts as managers and scientists and efficient aeroplanes are not employed,naturally efficiency suffers and the effectiveness of the project falls down.
There should be high levels of integrity,service motive,empowered employees and organisational cooperation to ensure high level success to produce a specific desired result that can be measured in terms of people's prosperity.
In the case of cloud seeding operations no worthwhile scientist ever questioned about the scientific basis of cloud seeding because Vincent Schaefer and Irwing Langmuir have established the scientific basis both by laboratory work and field operations conducted in 1946 in New York suburbs in United States. Some people are also questioning cloud seeding operations saying that they are not successful and effective and that they cause adverse effects.see web pages:
some people also question whether the rain that is claimed due to cloud seeding is due to natural causes or only due to cloud seeding and how can one distinguish between them?
To the several pessimistic questions raised on cloud seeding by the Experts of the US National Science Academy,the Academic and Field Experts of the American Weather Modification Association,Fresno,California furnished their reasoned replies in the web pages:http://www.weathermodification.org/images/FinalReport.pdf
Prof.Roland List,another giant among world experts on weather Modification has also made an an indepth analysis of the Report of the Experts of the US Academy of Sciences on Critical Issues in Weather Modification[October,2003] and presented very cogent arguments in favour of large scale promotion of cloud seeding operations in a scientific paper under the web pages:
Most of these unfounded fears about cloud seeding operations are answered in the form of Questions and answers
1.What are the statistical methods used for checking the results of cloud seeding operations? Are there other methods for evaluation of the success of cloud seeding operations ?
Expert scientists of the National Academy of USA in their report of 2003 concluded that we have still to employ methods of cloud seeding that produce credible and repeatable changes in precipitation and that there is no still convincing scientific proof of the efficacy of man made weather modification efforts. It is stated that in some cases like mixed phase hygroscopic seeding and Orographic cold cloud seeding there are strong indications of positive effects but such evidence of encouraging result has not been subjected to tests of significance and reproducibility. The experts affirmed that this does not challenged the scientific basis of weather modification concepts. They stated that despite this lack of scientific proof of cloud seeding programmes to increase snowfall and rainfall and to suppress hail formation are continued in several countries in the world on the basis of cost benefit analysis.
The experts agreed with the conclusion of Silverman(2001) that the experiments of the past 4 decade have not yet provided either the statistical or physical evidence required to establish their scientific validity.
Seeding effects are assessed by comparing the amounts of rainfall in a target area as compared with that from a control area and there is no randomization. Measurements were made over the same fixed geographical areas and comparisons were made between measurements taking during the seeding period and those from a period without seeding. Alternatively control area is selected adjacent to the target area with similar meteorological and geographical characteristics and results compared from the 2 areas during the same time periods. This does not allow for biases arising from temporal or spatial trends occurring during the trial period. But a more statistically robo studies design known as a cross-over design uses two similar fixed areas so that for each test one out of the two fixed areas is chosen for treatment by a random process while the other areas serves as the control. It is inferred from these experiments that the seeding effects were based on physical measurements but the data were not sufficient to reach the statistical conclusions and new statistical methods need to be explored.
2.How are chemical tracers useful in proving that cloud seeding works effectively?
During the last 4 decades cloud seeding operations have been conducted with some consultants injecting chemical tracers to study the effectiveness of operations. Warburten in his research work in Central Sierra, Nevada (1978-1992) estimated the background concentration of silver in snow samples at 2 parts per trillion so that silver from AgI seeding from ground generators can be easily detected while silver detection in snow fall is the useful measure it is done by using ground generators and hence it may be more useful to make in-cloud measurements of the seeding clouds themselves. Sometime sulfur hexafluoride was used for making quantitative measurements with less than a 1-second time length. Subsequently indium and silver were used as tracers that provide the possibility of calculating directly the amount of enhanced precipitation. Indium Oxide In2 O3 is a non-water soluble and a non-ice nucleating agent with about same particle size as the ice-nucleating silver iodide (AgI) these 2 agents are released at the same place and time by the ground generators. The snow is sampled from the snow gauging stations down wind for detection and analysis of Indium and Silver. The excess amount of silver over indium in the sample is a measure of the additional amount of precipitation due to seeding and in the case of sampling at lake Almanor , California the Ag/I ratio indicated 4 times as much silver as indium and this ratio is used to estimate the quantity of additional precipitation. According Warburten one ground generator is required to seed 40 sq.miles in the Sierra, mountains and one gram of AgI precipitates 420 cubic meters of water on the ground. AgI in snow is non-toxic since its concentration is very small, that is 4 orders of magnitude below the toxic levels specified. The purpose of simultaneous release of Indium Oxide and silver iodide from the ground generators is to differentiate between the silver content present from ice nucleation and that present from the scavenging of the silver iodide and also the concentration of indium present from scavenging of the chemical. According to aerosol emission rates from ground generators it is found that if AgI is captured only by scavenging, the silver to indium ratio (Ag:In) would be 0.8 but experiment shown that analysis of snow samples collected from cloud seeding operations produced ratios of AgI/Indium above 1.10, thereby showing that some of the snowfall occurred by artificial nucleation. In one of the experiments recorded silver concentration was 180 parts per trillion (background concentration 2 to 4 ppt) and silver to indium ratios were the order of 20:1 indicating that cloud seeding is not only a success but also has a strong scientific foundation.
3.Will chemicals used for cloud seeding cause damage to public health and environment?
Chemicals like Sodium Chloride, Calcium Chloride, Silver Iodide and dry ice are used as nuclei to seed the warm clouds and cold clouds. It is necessary to know what will be their short term and long term effects on the environment. Estimates made in USA indicate that due to the use of silver iodide for cloud seeding operations in 1977 the amount of silver iodide worked out to 1500kgs. According to EPA reports of 1973 about 360mg of silver enters into the atmosphere over USA. In the rain water samples obtained by cloud seeding operations silver concentration is estimated at 10-12 that is one part per billion (ppb). Since AgI is not soluble in water it does not readily get into the sea but tends to be deposited in the soil and the bottom of stream beds. The research investigations conducted up to 1977 indicate that this chemical has not posed any threat to the ecological systems. Silver has been detected at 10 nano-grams to less than 0.1 micro grams per litre in the rain water samples collected from the cloud seeding operations. The US authorities specified drinking water standards with the safe concentration of silver at 50 micrograms per litre. The values of silver in the precipitation samples in the Montana project was 1/50 to 1/500 of the limiting values set by the US public health service for silver in drinking water.
Similarly the iodine concentration in the rain water samples collected at the end of cloud seeding operation is found to be far lower in concentration than that found in the common iodized table salt used by the people.
During the experiments conducted for 11 years at Baramati, warm cloud seeding operations were done by sprinkling common salt powder into the clouds from the aeroplanes. The analysis of the rain water samples collected after the experiments indicated the concentration of chloride at 10mg/litre while sodium was present at 4.5 mg/litre. Hence these chemicals are not at all harmful to the public health and the environment.
4.Does cloud seeding in one area affect precipitation in another down-wind side region ?
In other words, does cloud seeding amount to Robbing Peter to pay Paul?A common wrong impression regarding cloud seeding is to consider the atmosphere as a static pool of cloud water passing over the earth, which is a limited steady state supply of water.
With this conceptual model, it is easy to argue that because this supply is limited and we remove a percentage of the water by cloud seeding in the form of precipitation from the
atmosphere in one area, there will be less moisture available to fall as precipitation from the cloud at other (downwind) locations because a larger fraction of this fixed supply of water in the cloud was already
removed at the first instance in another (upwind) location.
Common man does not know that the atmosphere does not behave in this simplistic manner. Clouds are fortunately the systems that continuously process moist air from the atmosphere. They are created when tiny water droplets get formed when the cooling rising air with moisture ascends into the sky.
In a typical precipitation cap-cloud ascending over a mountain, if it is assumed that the ascending water vapour mass is cloud-free, about 20% of the water vapour in the ascending air mass condenses and forms a cloud. Out of this about 20% comes down as rainfall from the cloud. Hence only 4% of the atmospheric water vapour amounting to 100(0.20 x 0.20) = 4% is thus removed. If it is assumed that the cloud seeding operations increase the rainfall by 20% then the additional water vapour removed from the ascending cloud vapour in the sky works out to 100 (0.20 x 0.04) =0.8% and this is a relatively insignificant amount and hence only a trivial reduction in the total atmospheric reservoir of water vapour would occur in the region downwind of a target area. According to scientists of South Africa about 6 million cubic meters of moisture passes over the country every day in its sky out of which 5% gets precipitated as rainfall. Out of this rainfall 60% is returning to the sky through evaporation from the rivers, lakes and plants. It means that 40% of the rain amounting to 2% of the atmospheric moisture (1,20,000 m3) is left in South Africa. But cloud seeding operations produce about 25% additional rainfall. Out of this additional rainfall only 40% remains over land while 60% again returns to the atmosphere due to evaporation. Thus cloud seeding operations are capable of squeezing only a very small fraction of the atmospheric moisture flow in the skies. This inconsequential small fraction of the atmospheric moisture obtained through cloud seeding operations cannot cause adverse impacts on the normal rainfall anticipated in the areas downwind of the target area selected for the operations.
Depending upon its size the life of a cloud may be 30 minutes to 60 minutes. If we are not able to use the cloud in proper time for seeding operations and squeeze its water content in the form of precipitation this cloud may dissipate as moisture. Hence there is no guarantee that this cloud will remain in tact for such a long time beyond its life time to give rain in another region downwind of the target area. Based upon local environmental conditions like meteorology and topography the cloud downwind of a mountain may descend and get dissipated without giving rain in the rain shadow area. However if the area downwind contains good forests or mountains the moisture gets replenished again and the newly formed cloud may provide more rainfall to the areas down wind of the target areas.
Precipitation data from many cloud seeding projects in the USA have been examined in detail for evidence of extra area effects. There are not statistically significant indications of rainfall/snowfall decreases downwind from any long term cloud seeding project.so,there is no question of robbing Peter to pay Paul
5. Is the NRC panel report on Weather Modification of the US Academy of Sciences of 2003 justified in adversely commenting on the conduct of cloud seeding operations?
The adverse comments of the mass media in the United States on the report f the NRC panel of National Academy of Sciences of 2003 are not justified because the report has made many positive comments on the promotion of cloud seeding under suitable conditions. The experts themselves stated that the science behind cloud seeding is well founded and that the results for fog dispersal in the airports, warm cloud seeding in some regions and cold cloud seeding under orographic conditions have shown positive results. Inspite of these basic positive aspects of cloud seeding still the experts panel demanded for reproducibility of results to establish the soundness of the programmes presently under execution in different states in USA and in different countries in the world. It must be admitted that Weather systems are subject to very many variables and hence the conclusion made in 2003 by NRC panel of the US Academy of Sciences that there is no convincing scientific proof of the efficacy of weather modification efforts in USA is highly damaging to the very survival needs of man and Nature. Simultaneously, the NRC report frankly admits that this does not challenge the scientific basis of Weather Modification concepts. Further they admit that recent hygroscopic experiments showed increases in precipitation and lifetime of rain-producing systems and that positive seeding effects occured in clouds systems over mountainous terrain. Hence their demand for reduction of basic scientific uncertainities before proceeding for conducting cloud seeding operations amounts to their blocking the pathways for securing proofs for minimising the so called innumerable scientific uncertainities.In fact the scientists of the Chinese academy of sciences have done adequate research work to affirm that by cloud seeding operations they can fight the droughts to promote public welfare which is the basic objective all scientific investigations.
see the following web sites for detailed information on the success stories:
Hence cloud seeding operations should not be stopped to merely satisfy the theoretical curiosity of a few unaccountable scientists of US Academy of sciences by sacrificing the interests of the millions of people who suffer irreparable losses including their right to safe water, right to health, right to life and the right to livelihood.Since water is BLUE GOLD that promotes the public welfare any attempts by any group of scientists will amount to promotion of poverty, disease, unemployment and social unrest and terrorism that disturbs peace in all countries of the world and so the responsible scientists must reconsider their negative approach to cloud seeding.
But the field and academic experts of Weather Modification Association of USA in their response to NRC expert panel report of 2003 have observed as follows: The NRC panel was asked to identify critical uncertainties limiting advances in weather modification science and operations and to identify future directions in weather modification research and operations for improving the management of water resources and the reduction in severe weather hazards, among other things. They were to do this even though the panel members collectively had very limited experience or knowledge in weather modification operations, especially in recent years. But in the Snowy Mountains cloud seeding operations, the results of 2004 snow chemistry analysis confirmed that the primary target areas were effectively seeded during most of the storm events.Snow samples after seeding indicated silver concentrations of 180ppt[as against back-ground levels of 2ppt,parts per trillion] and Silver-indium ratios were of the order of 20:1 over the target areas.In the light of this new evidence and in view of the results of the Chinese Academy of Scientists,it is essential for us to realize that cloud seeding has attained the stage of passing the operational tests and hence cloud seeding must be treated as an effective weapon to fight the Droughts,floods,hurricanes,hail storms,fogs and impacts of global warming.
6.How can you prove that the precipitation at a given place occured due to natural causes or due to cloud seeding operations?
This is a common question raised by many people.since early days of cloud seeding operations,the tha managers of the operations tried to prove this fact that cloud seeding augments precipitation.For the purpose,they used to select in a given area two sets of similar clouds and treat one set with chemical seeding and kept the second set of clouds as controls.At the end of the experiment,they found that the seeded cloud gave about 50% more precipitation than the non-seeded cloud used as the control.such observations were confirmed by both the radar observations and by collecting precipitation samples which were checked for the presence of trace concentrations of the chemicals used for cloud seeding.
statistical methods were also used by demarcating one area for seeding,another for control and yet another for non-seeded area by establishing rain gauges in all these areas for collecting samples of precipitation and calculations were made to establish the degree of additional precipitation in the seeded area by statistical basis by randomisation.The latest methods apply the Indium tracer method.
The effectiveness of cloud seeding is confirmed by Indium Tracer as detailed below
Chai et al.  reported on chemical tracer studies conducted as part of the 1984-1985 winter cloud seeding program at Lake Almanor, California. In the technique originated by Warburton et al. , AgI aerosol and Indium sesquioxide (InO ) were released from collocated, ground-based generators. InO is a water insoluble, non-ice-nucleating substance. The purpose of making collocated releases was to differentiate between the silver content in the snow that was present from ice nucleation and that present from scavenging of the AgI. Based on aerosol emission rates, Chai et al.  computed that if AgI is captured only by scavenging, the silver to indium ratio (Ag:In) would be 0.8. Analysis of snow samples frequently produced ratios in excess of 1.1, thereby suggesting that some of the snowfall occurred by artificial nucleation. Further analysis showed that snowfall at sites closer to the generator had higher Ag:In ratios than could be explained by a contact-freezing mechanism. Chai et al.  suggested that the ratios could be explained if a condensation-freezing mechanism operated immediately after generation.
Results of the 2004 snow chemistry analysis, have confirmed that the primary target and upwind mountain ranges were being seeded effectively during most storm events, both in the concentrations of chemicals monitored and in the silver to indium ratio. Prevailing
winds in seeded storms were predominately from northwest counter-clockwise through southwest. The Recorded Silver concentrations were as high as 180 ppt and Silver-Iindium ratios of the order of 20:1, over the central part of the target area.
Thus,there are several methods to prove that cloud seeding alone augments the rain-fall or snow-fall.
Reasoning by Ian Searle to dispel the Doubts about negative impacts of cloud seeding
Snowy Hydro, the company running the Cloud seeding experiment at ns
A] Ian Searle , a true believer in the effectiveness of cloud seeding. , worked in the field for 37 years and until recently was Hydro-
B] “Let me first say that the cost of silver iodide, at $500 per kilogram, is a fairly minor part of the total cost. The aeroplane is expensive; we have staff costs and the like. So we end up paying about $1-million a year, or a bit more now .To run a successful cloud-seeding program. , how we do it, is really quite simple. The aeroplane is fitted with two tanks, which have at the rear end of them, a burning chamber, very much like a blowtorch. And we dissolve the silver iodide in acetone, and spray it out through these blowtorch-type devices and light it up with a sparkplug, so the acetone is burned away, the silver iodide is left in the cloud in very tiny crystals, they’re quite microscopic. But only tiny amounts of silver iodide are necessary to start the rain falling process. So in a whole day of cloud seeding, we might only use two or three kilograms of silver iodide, and that’s spread over many thousands of square kilometres of cloud.
we would spend about $1-million a year running the program, but it was worth, by my estimation, about $20-million extra to the company, in extra water storage or extra energy generated through the power stations”
C] To the Question if cloud seeding in one area deprives the down-wind areas of their normal rain-fall,Searle says,” From the very beginning, the first CSIRO experiments that were conducted in Tasmania, had within their design a program to analyse rainfalls in the downwind regions as well as in our target area and in control areas and other surrounding regions. And in every case, an analysis of the rainfalls in the downwind direction, showed no significant decreases in rainfall at all. In worldwide experiments, it has been discovered that the increased rainfall continues for 200 or 300 kilometres in the downwind direction generally, unless there is a major change in the topography; if there are mountain ranges or large valleys or somesuch that modifies the weather far more than the cloud seeding does. And so in
D] To the Question if Silver iodide will not damage the Environment,Searle states thus” Firstly, there’s been a tremendous amount of scientific work done on the toxicology of silver iodide. They’ve fed it to rainbow trout in high concentrations with no detrimental effect. They’ve planted all sorts of plant species in pots with high concentrations of silver iodide in the soil, with no detrimental effect.
The second thing is we use such tiny amounts of it; it’s distributed in the atmosphere at relatively high altitudes. Only a portion of it actually comes down in the rain, and when it does, it gets locked up in the soil, because silver iodide has an affinity for the clays within the soil.
The third thing is that it’s not soluble in water, and is generally for that reason, not taken up into biotic systems. So if you were to ingest silver iodide, as they did with the rainbow trout, it would pass through their alimentary canal without being taken up into the bloodstream, and it just does not have any detrimental effect, certainly not in the quantities which we use”.