Is cloud seeding preventing further flooding in Indonesia?

Scientists claim rainfall has reduced since the project began, but experts call for more evidence
Dyna Rochmyaningsih guardian.co.uk 19 Feb 13;

Indonesia is banking on an unusual strategy to prevent further flooding in its inundated capital Jakarta, and officials claim that they are already seeing positive results.

They are using 'cloud seeding' — a weather modification technology often resorted to during drought. The method involves injecting clouds with substances that encourage the formation of ice crystals heavy enough to fall, thereby speeding up the production of rain.

Rain is the last thing that Indonesia needs now, as it has been experiencing heavy rainfall since mid-January.

But Indonesian scientists believe that inducing rains to fall over the ocean before the rainclouds reach the city will help prevent further flooding in Jakarta.

"We are mimicking nature. It is easy to make rain in most clouds above the sea. We found out that salt from sea water, which evaporates from the sea, accelerates the rain process because it encourages the cloud particles to adsorb water," Tri Handoko Seto, a top official of the Weather Modification Technical Unit of the Agency for the Assessment and Application of Technology, tells SciDev.Net.

Last month (26 January), military planes carrying tonnes of salt started the cloud seeding operation scattering salt onto rainclouds across the ocean. The operation is expected to last two months.

The operation has come into the national spotlight recently because of the Indonesian government's claims that it had succeeded in decreasing Jakarta's rainfall rate, particularly from 26­-29 January when local meteorologists had predicted heavier rains and flooding.

"We have conducted an evaluation using the data in our radar device, which records cloud development and movement. From our analysis, cloud seeding contributed to the decrease of rainfall in Jakarta during this period," says Seto.

But Zev Levin, chair in atmospheric physics at Tel Aviv University in Israel, says that it is difficult to prove how much rain would have fallen before reaching the city had the clouds not been seeded.

To prove the effectiveness of cloud seeding, Levin says, well designed experiments must be conducted based on robust statistical design with an unseeded control area and random allocation of seeding.

"In this case, Indonesia can't prove the success of their cloud seeding operation because they have no control area," says Levin.

He adds that cloud seeding in Indonesia will do nothing or very little to modify the weather because tropical clouds are not easy to modify.

"The dynamics of the clouds dominate the rain process and any attempt to modify it will only play secondary role at best," says Levin.

But Seto defends their programme and says that they will submit their work for publication in international journals to refute claims that their operations are not scientific.

Scientists produced the first evidence that cloud seeding can boost long-term rainfall in 2009. But they also urged caution over the technique due to unrealistic claims about its success and difficulties faced in comparing clouds to prove if the technique really works.