Water Watch Penang president Prof Dr Chan Ngai Weng said logging in the earmarked area, reportedly twice the size of Singapore, would drastically impact water supply, irrigation and power, while raising temperatures in the whole region.

"It is certainly one of the most important water catchments in northern Peninsular Malaysia, if not the most important," he said.

"The effects would not only affect Penang but also Kedah itself as Sungai Muda is shared by both states."

Chan, a professor in Universiti Sains Malaysia's geography department, said even if the Kedah government did not care about Perlis and Penang, it should consider the consequences to its own people.

"Is the Kedah government fair to its thousands of farmers?" he asked.

"Kedah also has expanding industries in Kulim and many towns and settlements that depend on the water from Sungai Muda."

Kedah Mentri Besar Azizan Abdul Razak announced on June 18 that the state had approved logging in the Pedu, Muda and Ahning dam catchment areas.

Chan explained that the Kedah forest acts like a sponge, soaking up between 30% and 70% of rain.

Any logging would not only pollute water resources, but also initially increase water quantity due to less forest to retain rain, resulting in more downstream flooding.

"Eventually, total water resources would be drastically reduced because of lack of water catchments to retain and trap the rain," he said.

Chan stressed that the forest acts as a "carbon sink" in that the trees, flora and soil store carbon dioxide absorbed from the atmosphere.

"When these forests are gone, there will be localised warming of temperature which will add to global warming," he said.

He pointed out that the Cabinet had rejected a proposal to log the forest some years ago after studies were carried out when the previous Kedah government made such plans.

"Malaysia is always talking about its commitment to control global warming. Cutting forests is definitely not the way to go," he said.

"The Kedah government should not be short-sighted by merely looking for short-term profits which will dry up once the forest is gone."