How are the upper Mekong and lower Mekong different?

The Mekong River is divided into two distinct sections based on its physical geography and descent from the Yunnan highlands.1

The Upper Mekong

The upper Mekong spans 1,215 miles (1,955 km) through a long, narrow valley in southwestern China. Rising in the Plateau of Tibet, the river cuts deeply into a rugged, remote, and sparsely populated landscape. Temperatures in this upper basin are generally lower than in the south and exhibit more significant seasonal variation due to the higher altitude.123

The Lower Mekong

The lower Mekong, which begins below the Myanmar-Laos border, stretches 1,485 miles (2,390 km). This section is characterized by more gentle terrain, including the Khorat Plateau and wide alluvial plains. The climate here is uniformly warm year-round, and the river's flow is heavily influenced by seasonal monsoon rains. This region supports diverse landforms, such as the Annamese Cordillera and a vast delta in southern Vietnam, and serves as a vital resource for agriculture and fishing across Cambodia, Laos, Thailand, and Vietnam.123