Recent unusually dry weather in Malaysia and Singapore is probably the result of recent volcanic eruptions in Indonesia, says a Hong Kong earth scientist.
And the same volcanic activity may cause a severe drought in southern China too, climate-change veteran Wyss Yim Wai-shu says.
The honorary professor of earth sciences at the University of Hong Kong said two eruptions in Indonesia moved a large amount of ash, water vapour and other gases in Southeast Asia. The ensuing dry spell in Singapore lasted a record 27 days.
“Water vapour in the region has effectively been drawn into the direction of the volcanoes in Indonesia that began erupting in November, so that has redistributed much of the water vapour in the region’s air,” said Yim, who was deputy chairman of a Unesco climate change team between 2007 and 2009. He said his conclusions were supported by extensive weather records.
“It is likely to affect southern China too … I am sticking my neck out by only drawing on past events to deduce what’s happening and what’s going to happen, but I’m pretty confident there is a corollary … Time will tell if I am right.”
One of two eruptions Yim thinks is prompting droughts in parts of Southeast Asia – that of Indonesia’s Mount Kelud – began violently on February 13, killing two people, sending ash plumes several kilometres into the air and causing over 100,000 people to evacuate parts of Java. Mount Sinabung – another of Indonesia’s 150 volcanoes – saw sporadic activity from November until last month.
Yim said that when volcanoes erupt, gas and ash form a column that streams into the air above the volcano. In the most explosive eruptions, the column may rise more than 50 kilometres, penetrating the stratosphere. Its aerosols are then carried elsewhere by the jet stream.
The Kelud eruption formed a column 26 kilometres high, and that of Sinabung a column 12 kilometres high. Both entered the stratosphere and changed the normal circulation pattern.
In 1963, when Indonesia’s Mount Agung erupted mightily, southern China had one of its worst droughts on record. In Hong Kong, water rationing became necessary and water supplies were available for only four hours every four days. The eruption of Mount Pinatubo in the Philippines in 1991 was followed by a period of significantly lower rainfall. The year was also Hong Kong’s 11th driest.
In both cases, the eruptions’ rising thermal plumes caused the surrounding cooler air to be drawn in. Because of Hong Kong’s coastal location at the margin of the world’s largest continental land mass, the change from the normal wind direction to predominantly offshore winds was conducive to drought, Yim said.
Depending on an eruption’s explosivity, location and timing, it can also cause flooding, he said. In 1982, when Mexico’s El Chichon erupted, spreading its volcanic cloud to the South China Sea, Hong Kong recorded its second wettest year.
In Malaysia, authorities in Selangor – its most populous province – have started water rationing after river and reservoir levels reached critical lows. In Singapore, rain fell on just seven days last month, typically the driest month of the year, leaving the lush city-state parched and prompting officials to warn residents to conserve water. The environment agency expects the dry weather to last until mid-March.
“Volcanoes don’t erupt a lot, but when they do, they make a huge impact on the climate. Yet not a lot of scientists are studying this,” Yim said.
Meteorologists look at things like air flow, so there’s a gross underestimation of the importance of water vapour during volcanic eruptions.
“It is like a detective story. And we, earth scientists, are the detectives.”