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.