Tropical storms have big raindrops that hit surfaces hard.
Trees and undergrowth soften the impact of raindrops on the soil.
Forest soil absorbs and stores rain.
Groundwater is a key water supply source as it replenishes rivers in drier times.
But without forests, a different process happens.
Clearing forests exposes the soil.
Raindrops pummel the ground like a million hammers.
The force hardens the soil surface; broken bits clog up the pores below.
Most of the rain runs into rivers, carrying dirt and debris.
Floods hit areas downstream.
Meanwhile, forest soil absorbs less water.
Groundwater supply shrinks and cannot replenish rivers in drier times.
In December 2014, Kelantan was ravaged by its biggest flood on record. Called 'bah kuning' locally, the flood came in the wake of historical rainfall.
Subsequent studies pinned widespread forest loss as a major cause of the flood.
The flood killed 13 people and displaced more than 200,000.
Evacuavees returned to find their homes destroyed. Scenes like this in Kampung Kemubu, taken 3 weeks after, were common.
Photo: Khalilah Mohd Nor/Shutterstock
The hardest hit areas were those along the rivers Sungai Galas and Sungai Lebir. Parts of the rivers rose as much as 18 metres.
Flood researcher Edlic Sathiamurthy surveyed Dabong after the flood. “It was a shocker when we saw [signs that] the flood reached the 3rd floor of a school. That is almost unimaginable.”
The flood swept away a railway bridge in Kampung Kemubu, south of Dabong.
Photo: Zanariah Salam/Shutterstock
The torrential rains “makes it very easy to blame [the flood] on the rain,” says Edlic. But “flood is also caused by changes in land cover.”
And there had been warning signs of the flood risk.
In the years before 2014, loggers and planters cleared lots of forests upstream of Sungai Galas.
This map shows satellite-detected forest loss in 2010-2014 which mostly occurred inside forest reserves.
Upstream of Sungai Galas, in the Batu Papan and Ulu Galas forest reserves, more than 5,000 ha were cleared.
But in Forestry Department statistics, these forest reserves remained mostly intact, with only about 2,000 ha removed in 2014.
The horror of the 2014 flood had not stopped forest-clearing. More forest loss in 2015-2021 was detected by satellites.
Another severely damaged town was Kuala Krai where chairs were washed up into trees.
The devastation is evident in photographs taken 3 weeks after the flood.
Photos: Muhd Fuad Abd Rahim/Shutterstock
Just like Dabong with Sungai Galas, Kuala Krai also sat at the end of Sungai Lebir that saw a lot of forests upstream cleared.
Forest-clearing continued after the flood.
"Once you [remove] forest cover, you get more surface runoff and less groundwater,” says Edlic.
“Sad to say that if we keep changing things like this, we will get floods in the rainy season and droughts in the dry seasons. Things will go the extreme."