Physical Geography

Thailand has four major regions: northern, central, eastern, and peninsular. The northern region is the northerly bulge of land between the Salween and Mekong rivers. It consists of roughly parallel mountain ranges and intervening valleys running north-south. The mountains attain heights of 4,000 to 8,000 feet (1,200 to 2,400 m) above sea level and are for the most part densely forested. Doi Inthanon, with an elevation of 8,513 feet (2,595 m), is Thailand's highest peak. Draining the region are the Nan, Ping, Wang, and Yom rivers; their waters eventually join in central Thailand to form the Chao Phraya River.

Central Thailand is largely a hilly area cut by the flat and fertile Chao Phraya valley—the most populated part of the country. The valley is a low-lying expanse, stretching almost 200 miles (320 km) northward from the Gulf of Thailand and varying from 30 to 90 miles (48 to 145 km) in width. There are also mountainous areas, especially along the Burma border. Swamps occur along the coast.

The eastern region consists chiefly of the Khorat Plateau, a relatively level tableland with some hilly and mountainous areas. In almost all respects it is Thailand's least developed area. It is drained by the Mun and other tributaries of the Mekong, which forms much of Thailand's border with Laos.

The peninsular region, 500 miles (800 km) in length, is the long northern half of the slender Malay Peninsula, part of which Thailand shares with Burma. The peninsula's mountainous backbone is the predominant feature; however, sizable lowlands flank the coast.

Thailand lies entirely within the tropics and has warm to hot weather all year. Temperatures usually range between 60° and 90° F. (16° and 32° C.). Less variation occurs in lowland areas, especially near the coast. In the capital city of Bangkok, for example, average monthly temperatures vary only a few degrees—between 77° and 85° F. (25° and 29° C.). Frosts never occur, even in the mountains.

As in most of southeastern Asia, a monsoonal wind system prevails, causing marked rainy and dry seasons. The southwest monsoon begins in May and continues through October, during which time nearly all of the annual rainfall occurs. Some mountainous areas are drenched by as much as 130 inches (3,300 mm) of rain a year, but most of the country gets 40 to 60 inches (1,000 to 1,500 mm). High humidity during the southwest monsoon makes the weather extremely oppressive. From November through February the northeast monsoon blows from Asia's interior, bringing little rain and somewhat lower temperatures. The period from March until the onset of the southwest monsoon is the hottest time of the year.