Delays Irk The Rainmakers

Press, Volume CV, Issue 31042, 23 April 1966, Page 14

Delays Irk The Rainmakers

[By NOEL LINDBLOM, science correspondent of the “Sydney Morning Herald.“J

gpHE 30 OR SO Australian scientists interested in making artificial rain did not share popular enthusiasm for the dramatic rain-making flights of two aircraft in the central-west earlier this month.

They have known to their own satisfaction since February 5, 1947, that they could seed clouds and cause them to deposit rain. On that day they achieved a far more spectacular result than the CobarNyngan falls.

On that day all along the Pacific coast -of New South Wales it was fine and cloudless. Inland, banks of cumulus covered nearly eight-tenths of the country but hung tantalisingly high and dry. Rain Came Just before 2 p.m. a C.5.1.R.0. experimental DC3 dropped 150 pounds of “dry ice” into the top of a 23,000 ft cloud west of Lithgow. Within 16 minutes rain tumbled from :he base of the cloud and persisted for the rest of the afternoon. No other rain was observed within 100 miles of the aircraft.

This was one of the most exciting demonstrations that man could make rain fall where none was likely to fall unaided. A report of the test by two young Australian scientists named Kraus and Squires was seized on by Russian, American and Japanese colleagues who had also started work on the artificial stimulation of clouds.

It was a practical experiment on a theory first put forward in 1933 that, if crystal “germs” could be planted in clouds which contained no ice crystals, then the “germs” might grow into large snowflakes at the expense of the water drops and eventually fall as rain or snow. In America and Australia (and we now know in the Soviet Union) scientists began a series of large, controlled experiments to compare the effects of cloud-seeding Operations in different areas. Trouble Began Silver iodide replaced “dry ice" as the chosen stimulant for the clouds. Instead of 200 pounds of the ice the seeding aircraft needed to carry only 20 grammes of silver iodide—enough to precipitate a million tons of water from a suitable cloud formation.

But something started to go wrong. By the mid-1950s the rainmakers in Australia and America were bogged down in a bewildering statistical mess which seemed to show that the benefits from cloud-seeding dropped off progressively year by year. For example, the C.S.LR.O. did a four-year trial in the Snowy Mountains which gave a 26 per cent increase over natural rainfall in the first year, a 27 per cent increase in the second year, a 12 per cent increase in the third and only 8 per cent in the final year.

Other large-scale field trials to Israel and Arizona produced the same depressing graphs, so that by 1955 the optimism of the rainmakers was at its lowest. The scientists kept on with their experiments and their arithmetic, however while many incompetent groups, particularly in America, played at rain-making and rather brought the whole business into disrepute. Persistency Effect Then about three years ago the scientists found a real possible reason for the depressing percentage drop-offs as the area experiments progressed. It was what an economist would call the law of diminishing returns. In the argot of the rainmakers it is known as persistency effect. In other words, the reason why there seemed to be less percentage increase from year to year was because the artificial rain-making had raised the over-all level of the natural rainfall. Some effect of the artificial rain persisted and caused more natural rain to fall as well as further falls of man-made rain. There is no satisfactory explanation for this persistency effect. It may be that some particles of the silver iodide crystals live on, but this is doubtful.

Perhaps the simplest reason may be the old bushman’s saying that water begets water. The initial downpour of artificial rain may be enough to change the ground conditions and the vegetation so that more natural rain clouds will form over the area. Total Fall Up The answer to this largely statistical question should be answered by the end of next year is the result of a series of controlled rain-making experiments which the C.5.1.R.0. has been carrying out in Tasmania Since 1964.

The target area has been the hydro-electric installations, with two similar areas north and south acting as the controls.

After producing percentage increases of up to 25 per cent in the target area in 1964, the rain-makers found an apparent drop down to 5 per cent But in real terms the rainfall of the whole area had gone up. The area was rested throughout 1965 and the observed rainfall was found to go back gradually to the natural, historical level by about August.

Seeding will continue through this year and a similar check on natural rainfall throughout 1967 will be taken. If the figures follow the 196465 pattern the effect of persistency will be well established. Australian scientists are confident that they will be able to provide this final statistical evidence of the benefits of artificial rainmaking. They believe they can provide percentage increases of 20 to 25 per cent. But they are impatient with delays in putting into practical effect what they have already demonstrated of their rainmaking abilities. They say it can not be doubted that they can make individual clouds rain and that in drought conditions it is worth “giving it a go.” The Americans, largely prodded by Russian, successes with rainmaking, are certainly going to give it a go in a big way.

Rising Budget Two weighty reports by the National Academy of Sciences and • the National Science Foundation within the last year have achieved a remarkable volte face after a decade of indecision. The over-all consensus is that rainmaking can produce economically usefull increases. Along with these reports newly formed United States Bureau of Reclamation has a $3,000,000 budget for cloudseeding operations this year. And there is a bill now before Congress which would boost this to $3O million in 1967, $5O million in 1968 and $75 million in 1969. Some of this International enthusiasm is bound to rub off on Australian Federal pol-icy-makers. They are the ones who must make the final decision to invest in -large-scale cloud-seeding operations. To farmers and graziers desperate for rain it does not matter much that nobody is 100 per cent certain yet whether silver iodide crystals produce rain from clouds as they can in a laboratory. Nor does it matter that scientists have a long way to

go before understanding what really goes on in a cloud. The best of computers are still 50 times too slow to model the complexity of a rain cloud. They want rain and cloudseeding seems to be the answer. In central N.S.W. they may be forgiven for impatience with officials who have to wait on statistics from Tasmania before ordering out the men in the flyingmachines.