Drainage

The general slope of the land in Laos is downhill from east to west, and all the major rivers--the Tha, Beng, Ou, Ngum, Kading, Bangfai, Banghiang, and Kong--are tributaries of the Mekong. The Mekong flows generally southeast and south along and through western Laos and forms its boundary with Myanmar and most of the border with Thailand. The course of the river itself is severely constricted by gorges in northern Laos, but, by the time it reaches Vientiane, its valley broadens and exposes wide areas to flooding when the river breaches its banks, as it did in August 1960. A few rivers in eastern Laos flow eastward through gaps in the Annamese Cordillera to reach the Gulf of Tonkin; the most important of these is the Ma River, which rises in Xiangkhoang province.

Soils

Soils in the floodplains are formed from alluvium deposited by rivers and are either sandy or sandy clay with light colors or sandy with gray or yellow colors; chemically, these are neutral to slightly acidic. Upland soils derived from crystalline, granitic, schistose, or sandstone parent rocks generally are more acidic and much less fertile. Southern Laos contains areas of laterite (leached and iron-bearing) soils, as well as basaltic soils on the Bolovens Plateau.

Climate

Laos has the typical tropical monsoon climate of the region, though the mountains provide some variations in temperature. During the rainy season (May to October), the winds of the southwest monsoon deposit an average rainfall of between 50 and 90 inches (1,300 and 2,300 millimeters), with totals reaching 160 inches on the Bolovens Plateau. The dry season (November to April) is dominated by the northeast monsoon. Minimum temperatures average between 60º and 70º F (16º and 21º C) in the cool months of December through February, increasing to highs of more than 90º F (32º C) in March and April, just before the start of the rains. In the wet season the average temperature is 80º F (27º C).

Plant and animal life

Laos has tropical rain forests of broad-leaved evergreens in the north and monsoon forests of mixed evergreens and deciduous trees in the south. In the monsoon forest areas the ground is covered with tall, coarse grass called tranh; the trees are mostly second growth, with an abundance of bamboo, scrub, and wild banana. The forests support a rich wildlife, including elephants, gaurs (wild oxen), deer, bears, tigers and leopards, monkeys, and a large variety of birds.

Settlement patterns

Laos is predominantly rural and agricultural. The numerous isolated valley communities preserve a variety of different traditions and dialects. Villages usually are located close to rivers and roads that give the people access to itinerant traders as well as to each other. Most villages are laid out around a main street or open area, farmlands being adjacent to the residential areas. Every village, if it can, has a Buddhist temple and supports at least one monk. The temple compound usually includes a public building that serves as a school and a meeting hall. Village leadership is usually divided, the headman having authority in secular matters and the monk in religious.

The hill peoples usually are organized on tribal lines and live in smaller groupings. They are hunters and gatherers of forest products, as well as farmers, but their practice of shifting cultivation prevents them from establishing permanent villages. Hill peoples living close to the lowland areas tend to acquire the languages and cultures of their neighbors and to engage in limited trade with them; those living at higher elevations remain unacculturated.

Urban life in Laos is limited mainly to the capital, Vientiane, the former royal capital, Louangphrabang, and four or five other large towns. With the exception of Louangphrabang, all are located in the floodplain area near the Mekong River. Their populations are predominantly Lao, with smaller groups of Chinese, Vietnamese, and Indians. Compared with the cities of Thailand, Malaysia, or Vietnam, those of Laos are small and provincial.