INCREASING RAIN IN THE DESERT:
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
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
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
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
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
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.
Emmanuel Kploguede of the African School of Meteorology
and Civil Aviation. (Photo ©Daily
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
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,
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