Two new studies by international experts on the future of the Tonle Sap Basin concluded that hydropower development and continuing climate change will cause major changes in its water flow system, disrupting ecosystems and livelihoods.
According to the studies, the Tonle Sap lake is expected to ex-perience a huge increase in discharge from the Mekong River due to climate change alone, causing far more annual flooding, the studies said.
Dam development upstream could stem this increased flooding downstream, but still adversely affect the natural “flow regime” of the lake, state the reports, which were conducted by the University of Technology in Helsinki, Finland, in cooperation with the Southeast Asia START Regional Center in Bangkok.
One harmful effect both dams and climate change would deliver
is an increase in the dry-season water level of the Tonle Sap. This would extend the dry-season lake area and wreak havoc on large portions of the floodplains around the lake, destroying eco-systems such as seasonally flooded forests.
Dams would release additional water during the dry season and less water during the rainy season, causing a disruption of the natural water flow, report researcher Mat-ti Kummu wrote in an e-mail.
Changes in the lake’s dry-season water levels created by dams are expected to range from 15 cm to 60 cm, which could be harmful to existing ecosystems and the people depending on them for their livelihoods, he wrote.
“It is therefore extremely important for the Tonle Sap and other floodplains in the Lower Mekong Basin to maintain the natural hy-drological regime of the Mekong River,” his research paper said.
Dam development could have an impact on water quality by, for example, trapping sediment up-stream, and thereby change fish migration routes, rice field flooding, and wetlands in the Tonle Sap Basin, the reports’ co-author Mar-ko Keskinen wrote in an e-mail.
The impact of hydrological dev-elopments will be noticeable within a decade, while a sharp increase in Mekong River water flow be-cause of climate change is likely to occur over several decades, the researchers said.
The researchers predict that if no dams are built, the Tonle Sap’s storage capacity could rise from the current 5 cubic km to 70 cubic km or more over the coming dec-ades because of climate change. Consequently, lake water levels would rise all year round and hit new highs; flooded areas would increase in size; and flooding would start earlier and last longer, they said, adding that changes would start around 2040.
Improving livelihoods is the most effective way for the population around the Tonle Sap to adapt to the changes ahead, and efforts to reduce poverty should be sped up or widened to this end, one of the reports said.
Tin Polok, national coordinator for climate change policy at the Ministry of Environment, welcomed the new study and said climate change, including its effect on the Tonle Sap, was a major challenge for Cambodia and that more research was needed to formulate good policies.
Touch Seang Tana, a senior government fisheries expert, said he had not seen the report but emphasized the need for research-ers, organizations and the government to come together to understand and solve the future problems the Mekong River and the Tonle Sap are facing.
“This is our problem at the mo-ment: our management,” he said.
“There is mismanagement; there is a need to understand the problem.”