Why are water levels of the Mekong at a 100-year low?

WAT NONG BUA YAI, a Buddhist temple in Lopburi province in central Thailand, has been under water ever since the nearby Pasak Chonlasit dam was built 20 years ago. This week, with water levels at record lows, the temple re-emerged drawing thousands of curious visitors. Such scenes are becoming ever more common as the region experiences its worst drought in a decade. Nowhere is this more evident than along the banks of the Mekong river, whose waters have dropped to their lowest levels in more than 100 years.

This is bad news. Originating in the Himalayas, and running from the Tibetan Plateau through Myanmar, Laos, Thailand, Cambodia and Vietnam, the 4,350km (2,700-mile) waterway is a source of food and water for some 60m people. After the Amazon, it is the most biologically diverse river in the world. And yet today, in some places, it is barely flowing. In Vientiane, the capital of Laos, the water level has fallen to 3.2 metres, according to the Mekong River Commission. This is more than 4.5 metres below its normal level at this time of year (see chart). At the end of July, it fell 6 metres below its long-term average.

At least two factors are to blame. First is a lack of rain. The annual monsoon, which typically arrives in June, was late and weaker than usual. The El Niño effect led to drier conditions throughout South-East Asia; sustained rainfall started appearing only late last month. The result is a drought in the wet season. The Thai government has responded by asking farmers to stop planting more rice. The Royal Thai Air Force has deployed cloud-seeding planes. Yet along much of the Mekong’s shores in Thailand and Laos, the river known as the “mother of waters” has refused to give much life.

Hydroelectric dams have also reduced the river’s flow of freshwater. China has built 10 dams on the upper portion of the river. Another 11 are under construction along the lower stretch; 120 are being planned on the river’s tributaries. Once the building is complete, scientists reckon that the flow of nutrient-rich sediment to the South China Sea will drop by more than 90%. Operators of the Xayaburi dam, the first dam to be built on the lower Mekong in Laos, say the structure has nothing to do with the shortage of water downstream. But Thai authorities allege that since the $3.8bn dam began storing water on July 9th, water levels have dropped by almost 1.8 metres.

Battles over the Mekong’s receding waters are becoming political. This month Mike Pompeo, America’s secretary of state, put the blame squarely on China’s dam-building programme. But America’s influence on the matter is marginal. Geography, not history, defines power along the Mekong. Myanmar, Laos, and Cambodia are firmly in China’s orbit; Thailand is increasingly so. Vietnam, America’s ally, may be forced to look elsewhere for its rice and fish.