INCREASING RAIN IN THE DESERT:
From three continents come new ways of solving an old problem
Scientists believe it may be possible to increase rainfall in arid areas. (Photo by Digital Vision/Getty Images.)
Because of a population boom in the United Arab Emirates (UAE), government leaders are facing a fundamental challenge: keeping up with demand for water. The mostly desert country, which has grown from about 50,000 residents in 1975 to more than 3 million today, relies on desalination plants and underground aquifers. But desalination is very costly, and the aquifers are quickly becoming depleted.
In the past few years, the UAE has begun to explore an innovative solution. What if modern technology could produce more rain?
Scientists at NCAR, the UAE Department of Water Resource Studies, University of the Witwatersrand in South Africa, and elsewhere are analyzing the potential for cloud seeding. They hope to find storm clouds that can be induced to release rain over regions where the water would most benefit society by falling on crops or replenishing aquifers.
“This is a multidisciplinary analysis that considers hydrology, cloud science, atmospheric chemistry, and other disciplines,” explains NCAR scientist Roelof Bruintjes, who oversees the project. “Increasing the rainfall is just one aspect. We also have to consider what the impact would be. It might not help to seed clouds over a desert. If 90% of the rainfall evaporates, it may not be worth it.”
Making droplets bigger
NCAR is building on weather modification projects it has led or participated in over the last few years in Mexico and South Africa. The center has refined a technique to increase the size of particles in clouds and promote the coalescence of water droplets. Called hygroscopic seeding, this technique uses flares mounted on aircraft to seed clouds with small salt particles. Water droplets can bond to the particles and grow large enough to fall out of the cloud as rain.
Initially, researchers used airplanes and a network of radars to examine clouds that form along the UAE’s coast during the winter. But only about 10 frontal systems form during a typical winter, and fewer than half contain the convective motions needed to produce rain.
Researchers next turned to the Oman Mountains, which form the boundary between Oman and the UAE. Although the mountains had received little attention from climate scientists in the past, the team discovered that clouds there typically form and release rain during about 40 days in the months of June, July, and August.
NCAR’s Roelof Bruintjes (left) with Abdulla Al Mangoosh, director of UAE’s Department of Water Resources Studies. (Photo by Brant Foote, NCAR.)
The research team has launched a randomized experiment to seed clouds over the mountains, measure the resulting rainfall, and trace the movement of the water once it reaches the ground.
If cloud seeding produces significantly more rain in the area, the UAE can compare the costs and benefits with desalination and decide whether to launch a multiyear cloud seeding program.
In the near future, NCAR is likely to expand its research on weather modification to other regions as well. Oman is considering working with the center to build on the UAE program, and officials as far away as Thailand may explore the technology.
The African nation of Burkina Faso, where many rely on subsistence farming, may also benefit from weather modification. With technical assistance from NCAR, Burkina Faso has implemented a pair of state-of-the-art software systems to support cloud seeding efforts. The software is used to display and analyze radar data about cloud systems and precipitation, thereby guiding cloud seeding operations and helping scientists evaluate the results.
Bruintjes cautions that weather modification is still a developing field. In Mexico and South Africa, hygroscopic seeding trials produced more rain 30 to 60 minutes after seeding. But researchers need to conduct more experiments to evaluate the extent to which overall precipitation was increased.
Even if hygroscopic seeding proves effective in the UAE, that does not assure its success somewhere else. Only certain types of clouds produce rain. And air pollution may complicate the situation by changing the dynamics of clouds and precipitation.
Bruintjes stresses that nations interested in weather modification need to conduct thorough research before launching a full-scale program.
“If cloud seeding works in one area, it may not work in another,” Bruintjes says. “We shouldn’t just go out there and seed clouds blindly and hope for the best.”
More information about the UAE rainfall enhancement project
Accurate weather forecasts are much needed in Africa, especially where tropical cyclones and floods pose an ongoing threat. But the continent has relatively few observing stations for monitoring the skies, and forecasters are limited by lack of access to data and models appropriate for the weather conditions in their regions.
Instructor Emmanuel Kploguede of the African School of Meteorology and Civil Aviation. (Photo ©Daily Camera, Boulder, Colorado.)
To improve the situation, UCAR is working with collaborators in Europe and Africa on an initiative known as the African Satellite Meteorology and Training Project (ASMET). The goal is to train African meteorologists to interpret data from European satellites that gather atmospheric information over Africa.
UCAR’s Marianne Weingroff and the rest of the ASMET team, including instructors at regional meteorological training centers in Kenya, Niger, and South Africa, produce educational modules on topics such as forecasting tropical cyclones and integrating satellite imagery with model data. The modules are used at the training centers to teach hundreds of African meteorologists each year. They are also disseminated to forecast offices to permit self-paced training. EUMETSAT, the European Organisation for the Exploitation of Meteorological Satellites, funds the project and distributes the modules on compact discs and the Web.
Better forecasts, including daily and seasonal rainfall predictions, are critical to Africa, where millions of lives depend on the current year’s crops from farms of all sizes. “ASMET modules are making a real contribution to the improvement of forecasts in Africa,” says Emmanuel Kploguede, a member of the ASMET team and instructor at the African School of Meteorology and Civil Aviation in Niamey, Niger. “This is particularly important because most African countries are in the tropics where the weather can change quickly—either helping farmers by distributing rain widely or hurting society with strong storms that can flood croplands, livestock areas, and houses.”
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