Chan Ngai Weng of Universiti Sains Malaysia (USM) said climate change, which likely caused the extraordinarily heavy rains, was only partly to blame. The other main factor is anthropogenic or human activities, such as forest clearing, construction, agriculture and conversion of virgin forests to built-up areas.
“One could even fault humans for climate change since they are the culprits causing it.
“We should look in the mirror and point the finger at ourselves and not blame nature, the weather or God,” he told FMT.
Rain fell intensely for more than six hours on Wednesday afternoon. According to the meteorological department, 278mm of rainfall was measured on the mountain range, exceeding a 70-year average recurrence interval.
The rainfall on the summit of Gunung Jerai sent massive amounts of water gushing through streams in its valleys and rapidly bursting into towns at the foothills like a tsunami.
The towns of Merbok and Gurun saw water levels of 0.2m to 0.3m high. In smaller towns in the coastal Yan district, waters rose to 1.5m, about the height of a Perodua Myvi.
The waters receded on Thursday, leaving layers of mud everywhere. At least 3,000 people were out of clean water supply due to broken pipes. Some were left without electricity because a fallen tree had torn down a power supply pole.
The Kedah government said the incident was caused by “fenoma kepala air”, a kind of water surge.
Sahabat Alam Malaysia (SAM) said the muddy water was a sign that land clearing was rampant, but the state government swiftly denied this.
Chan said it was likely that many streams on the hill converged to form a river filled with debris and rocks, holding the water up like a small dam.
“This volume of water has nowhere to go except burst downstream in a terrifying giant water surge.”
He said the clearing of forests could be blamed for the rapid surge since barren land could not hold back rainwater, let alone act as a sponge to absorb excess moisture.
He added that the clearing of forests could also cause a river to become shallow. This is because the soil loosened from the cleared area would accumulate on the riverbed, thus reducing its carrying capacity.
The other cause could be development close to rivers, giving these rivers no space to release their energy in the event of a rapid surge.
“Rivers need their floodplains to disperse their energy,” Chan said. “By their nature, they need to meander and should not be straight.
“However, when humans build too near to rivers, they block them from releasing their energy. This energy then builds up. When it bursts, the result would be flash floods.”
Chan made these suggestions:
- the building of check dams or small retention points along the rivers to divert rainwater;
- the clearing of natural dams or debris holding up rivers;
- the dredging of shallow rivers; and
- satellite or drone monitoring on the hills to check for cleared forests.
He also said future development on the land surrounding the Jerai range should allow for at least 50% of absorbable surface to enable rainwater to seep underground.