Scientists plan to produce rain in sub-tropical areas during the cloudless summer months by altering air currents using a unique thermal material developed in Israel.While scientists have made great strides in recent years in understanding and predicting the weather, the idea of taking control of the weather and making it rain has remained within the realm of mysticism and religion.

Now Israeli researchers are part of an international team along with American and Belgian colleagues gearing up to perform one of the greatest and most elusive tricks of all by causing the heavens to bring rain. With the potential to alleviate the hunger problem in the world, the Geshem Project (named for the Hebrew word for rain) hopes to turn myth into science.

Scientists plan to produce rain in sub-tropical areas during the cloudless summer months by altering air currents using a unique thermal material developed in Israel.

Led by Professor Leon Brenig of the University of Brussels Department of Physics, Project Geshem partners desert researchers from Israel’s Ben Gurion University of the Negev with computer analysts at UCLA in California, and space imagery from NASA.

The technique involves spreading a large black solar-absorbing surface over several square kilometers of land to generate intense and asymmetrical thermal emissions. Energy from sunlight is absorbed by the material and then radiated back into the air to heat the lower atmosphere with minimal loss into the ground. The heated air rises taking water condensation high enough to form clouds and produce out-of-season rain.

“It will make a huge difference.” Brenig told ISRAEL21c. “In a region where there is 150 mm. a year it would go up to 600-700 mm. a year.”

Eli Zaady, a researcher on the project and ecologist from the BGU Open Space Agriculture Research organization, explains the technique could increase crops for a given area by 40 percent.

“It all depends on the amount moisture in the air,” said Zaady.

Sub-tropical climates are vulnerable to drought during the summer due to an atmospheric phenomenon know as the Hadley Cells. First described by their namesake George Hadley in the 18th century to explain the Trade Winds, Hadley cells are convection cycles of air that affect the weather in tropical and sub-tropical climates.

The hot equatorial sun heats air in the low atmosphere causing it to rise and flow away from the equator towards the North and South. The air thermals carry water condensation up until it forms clouds that produce rain and the humid equatorial climates. However, as the air-currents reach sub-tropical regions they cool and descend preventing local water condensation from rising high enough to form clouds.
The effect deprives sub-tropical areas of rain during the warm months of spring and summer.

“The object is to locally fight against that descent,” Brenig says and estimates that air above the black surface could be raised by 40-50 degrees centigrade above the surrounding temperature creating a ‘chimney’ of rising air currents. The artificial thermal will boost water vapor to around 3000 meters where it can condense into water droplets that create clouds.

Materials with the required asymmetric thermal properties are hard to find. Mirrors, for example, although highly reflective would concentrate the heat in a small area whereas the Geshem project requires heating a wide expanse of air.

The search for the ‘ideal’ black surface brought researchers to Acktar, an Israeli company that specializes in making custom materials with unique surface properties. Founded in 1994, Acktar, is a world technology leader in the development, and production of black, light absorbing coatings that deliver unique performance due to their high specific surface area.

The coatings are based on vacuum deposition technologies that use a flow of atoms or ions directed towards a surface to build specific layers or crystalline phases on an atomic level.

Whereas there are other materials that absorb and reflect heat – such as road tarmac for example – the Acktar panels are unique in their highly asymmetrical properties and easy deployment.

“You aren’t going to put down tarmac over large areas,” jokes Acktar CEO Zvi Finkelstein from the company’s manufacturing site in Kiryat Gat.

The Ackerman material is so light that the company will be able to wrap several kilometers of material onto rolls for easy deployment and relocation. The material will be laid out on panels in long modules allowing maintenance crews to service the panels from vehicles driving between the rows.

By covering an area of between five to nine square kilometers with the black material researchers estimate rainfall on an area of 40-100 square kilometers downwind. Clouds will form along a strip as wide as the black surface and up to 30 kilometers long during the hours from midday till five in the afternoon.

The cost of setting up a full-size black surface would run at over 80 million Euros, about comparable to establishing a desalinization plant. However, the operational costs are minimal and the technology simple to operate. Whereas desalinization requires a safe method of disposing with the saline by-products and energy to drive the process the Geshem method is environment-friendly and powered by the sun.

“Solar energy is free,” Brenig notes.

The method can be applied to any dry region located in subtropical or tropical latitudes within 150 km from an ocean, sea, or large lake.

In coastal regions with high solar radiation intensity, the dominant wind during the day is a steady sea breeze that flows from the coast inland. The predictable wind will cause rains on accurately determined culture zones on the continent almost each day during sunny seasons. Adapted agricultural and water-collecting techniques could then make best use of the predictable rain.

The idea of using a large solar-heated surface to make clouds has been around since the 1960s. However, at that time the only suitable black-surface material was asphalt and the computing power required to test the theory was still decades away.

Brenig first toyed with the idea of playing with the weather in the 1980s but was also hampered by limited computer power.

“It is hard to simulate because meteorological predications are often not very good,” Brenig explains. “We need very accurate predications such as how much rain will be produced to evaluate the efficiency of the system. The problem is that the mathematical models for cloud formations are still in their infancy.”

The project was put on hold until 2003 when Brenig contacted the Jacob Blaustein Institute for Desert Research at BGU. Brenig chose Israel because of its arid regions and BGU’s worldwide reputation for desert research.

Armed with space images from NASA Brenig turned to the number-crunching super-computers at UCLA to run simulation on models in order to determine the optimal size and shape for the black surface.

“Meteorological simulations are the most complex in the world and require the fastest computers,” he notes.

Initial simulations confirmed the theory was reasonable and the search began to find an efficient and environment-friendly material to create the black surface.

Now researchers are putting the finishing touches to the computer-simulations and hope to garner the financial support for a trial within in a year on an area of 3000 square meters in Israel?s Negev desert that will use water vapor and breezes from the nearby Mediterranean Sea. Finklestein estimates the trial will cost around two million euros and Brenig is seeking support from the European Commission, NATO’s Science for Peace, and various water authorities to fund the trial. Israeli authorities are keen to back the project and have already indicated that they will approve the required land area.

Zaady says that if the experiment is a success a larger trial will follow and Brenig is confident that if the technique works according to the simulation the idea will be adopted in various sub-tropical regions around the world that are suffering from desertification.

Northeastern Brazil, North Africa, the Kalahari and Sahara deserts could all benefit from the method. In southeast Spain where desertification is claiming large swathes of agricultural land authorities have already shown great interest in the project and have indicated they would finance a large trial in that country.

“It can bring water to a place where there is no water,” Finklestein says. “Where there is water there is life, and then there is no limit to the imagination.”