Scientists in Indonesia are experimenting with cloud seeding, or firing salt-based chemicals into clouds to force out rain, to try and prevent flooding in the capital Jakarta, home to increasingly destructive rains.
On 27 January, aircraft began dropping salt onto rain clouds to induce rain over the Java Sea before the clouds could reach the mega-capital of more than 10 million people. The operation, which cost US$1.3 million, ended on 28 February.
“We have yet to conduct a full evaluation, but in general we have seen a significant reduction in rainfall in Jakarta,” Heru Widodo, head of the Artificial Rain Unit at the Agency for Assessment and Application of Technology under the Ministry of Research and Technology, told IRIN.
“People seem to have forgotten about floods already,” he said, referring to January flooding in Jakarta that brought parts of the city to a near standstill, killing an estimated 20 people and displacing another 40,000.
Cloud seeding has been carried out in West Africa to boost rainfall in the drought-prone edge of the Sahara desert. And while it has been used regularly in Indonesia to fight forest fires that frequently spread in Sumatra and Borneo during the dry months from May-October, this was the first time the technique has been to prevent flooding.
After Jakarta, Widodo’s team is turning to Central Java Province, where heavy rains have caused a dam to overflow in Bojonegoro District and cold `lahar’ (rainwater mixed with volcanic rock and sand) from the still-active Mount Merapi volcano to slam into residential areas, destroying homes and bridges.
A series of eruptions on Mt Merapi killed more than 300 people and displaced hundreds of thousands in 2010.
The team will conduct cloud seeding in Bojonegoro and the region of Yogyakarta (also on Java Island and home of Mt Merapi) until the end of March.
“Volcanic eruptions [in 2010] left 80 million cubic metres of mud and sand, and when it rains these materials can wreak havoc [in] neighbourhoods,” Widodo said. In the latest mudflow incident, one person was killed when volcanic debris swept away vehicles in a Yogyakarta village last month, local media reported.
“Our plan is to reduce the intensity of rains that fall in these areas,” he said.
Widodo said cloud seeding, though not a mainstream strategy, may be able to mitigate the effects of increasingly erratic weather the country has seen.
The National Disaster Management Agency said floods, rain-triggered landslides, cyclones and forest fires killed nearly 300 people and displaced more than 700,000 in 2012.
A dissenting voice
Thomas Djamaluddin, head of the Centre for Atmospheric Sciences at the National Aviation and Aerospace Agency, discounts seeding as a tool to control weather. “An analysis of the dynamics and growth of [seeded] clouds showed that the favourable weather was only accidental,” he said. “Satellite images showed that movements of clouds never threatened Jakarta during [February].”
He said cloud seeding operations only affected clouds at the height of 12,000-15,000 feet (3.6-4.5km), which did not contain much rain anyway.
“Cumulonimbus clouds that are as high as 10km are too difficult and too risky to reach,” he said. “For a large area like Jakarta where floodwaters also come from other areas, don’t ever think of relying on weather modification technology to prevent flooding.”
Mahally Kudsy, an official at the Centre for Weather Modification Technology, said salts dropped from 3.6km can reach clouds at greater heights because they strengthen the upward current of moist air.
Whether or not cloud seeding proves capable of diverting rain, it can only be part of the solution, said Syamsul Maarif, head of the government’s National Disaster Management Agency.
“Cloud seeding is only a supplementary method in our flood prevention efforts. Maintaining the drainage system, dredging rivers and strengthening dams and dykes should be the main priority.”