Lower Mekong Basin highly vulnerable to climate change - study

Bangkok - Climate change will bring higher temperatures and longer wet seasons to the Lower Mekong Basin, affecting the cultivation of rice and other crops the majority of its 65 million inhabitants rely on for food and income, experts say.

“It is one of the most vulnerable watersheds in the world to the threat of global climate change,” Paul Hartman, director of the Mekong Adaptation and Resilience to Climate Change Project (Mekong ARCC), told Thomson Reuters Foundation.

The Mekong, flowing from the Tibetan plateau to the South China Sea through China, Myanmar, Thailand, Cambodia, Vietnam and Laos, is the world’s 12th largest river.

More than four out of five people living in the fertile lower basin, which covers Cambodia, Laos, Vietnam and Thailand, are rural and highly dependent on the river. Experts say fish and other aquatic animals provide between 40 and 80 percent of animal protein in local diets.

An average global temperature increase of 2 degrees Celsius is seen by scientists as a threshold to dangerous changes in the Earth's climate. Yet according to a preliminary report by the Mekong ARCC, released in March, the Lower Mekong Basin could see average temperatures rise between 3 and 5 degrees by the end of the century, with some pockets predicted to experience much larger increases.

This could affect commercial crops such as coffee and rubber, as well as food staples such as rice, the basin’s most important crop, and cassava.

“A decrease in average rice yields of just a few percent per hectare would have dramatic impact on (Lower Mekong Basin) food security and food production,” said the draft report, which is currently being peer-reviewed.

Winners and losers

The key message is that the basin’s climate is shifting, said Hartman, who hopes the study will help countries prepare better.

“The better you can plan and prepare, and develop these processes for governments, communities and businesses, the better off you'll be in the long run,” he added.

“Across the basin, the study forecasts a 1.5 to 4 degree shift in average maximum daily temperature. And you're looking at an increase of more than 5 percent in peak daily rainfall across the entire basin,” Hartman said.

The central highlands of Vietnam, an important coffee-growing region, and Cambodia’s eastern plains will see the largest temperature rises across the basin, according to the study. Annual precipitation is projected to increase between 3 and 14 percent across the basin.

Optimal growing conditions for robusta coffee varieties, rubber and cassava will shift from lower altitudes to higher altitudes centered on northern Thailand and northern Laos, Hartman said.

Changes in precipitation, temperature and drought conditions are also expected to affect the growing cycles of crops, leading to falling yields in some areas and increases in others.

For instance, rain-fed rice and irrigated rice on the lowlands will likely yield less in some areas due to temperatures above 35 degrees during the growing stage, while northeast Thailand can expect a higher yield of rain-fed rice due to increased rainfall.

“There are some winners and there're some losers. How you adapt to climate change impacts will further determine where you'll come out in the end,” Hartman said.

Development adds to concerns

Hartman said the next step for the Mekong ARCC, which is funded by the U.S. Agency for International Development (USAID), is to use information from the study at a handful of priority sites across the basin to help local communities strengthen their capacity to adapt to climate change.

It is also working with the Washington-based World Resources Institute to calculate economic impacts based on the study’s projections.

Development activities in the Mekong - from renewable energy to population growth and forest exploitation - are expected to exacerbate the impacts of climate change.

“Things like hydropower dams will affect fisheries to a greater extent than climate change. But when you combine these two things, then the effect gets magnified,” Hartman said.

Plans to build a series of mega dams on the Mekong have been especially controversial, with activists charging they pose serious threats to food security and income for hundreds of thousands of people.

International Rivers said on Wednesday the Don Sahong Dam in Laos would be “an environmental calamity”. It would “irreversibly” block the only fish migration channel in the area, harming species, fish catches and the livelihoods of people in the region, the U.S.-based organisation said.