The Kingdom of Thailand, located in south-east Asia, covers an area of 513 120 km2 between latitudes 5° 45´ and 20° 30´ N and longitudes 97° 30´ and 105° 45´ E. It is bounded by Myanmar on the north and west, by Laos on the north-east, by Cambodia and the Gulf of Thailand (Siam) on the south-east, by Malaysia on the south and by the Andaman Sea and Myanmar on the south-west.
The main geographic regions are:
- The Northern region consisting of a series of parallel and longitudinal fold mountains extending through peninsular Thailand into Malaysia. The average height of the peaks is 1 600 m with some above 2 000 m. Between these ridges lie relatively flat basins in which flow the four major tributaries of the Chao Phraya, Thailand´s main river-the Mae Ping, Mae Wang, Mae Yom and Mae Man. The alluvial soils of these basins are fertile. The region has a mild dry climate;
- The North-eastern region with the Khorat plateau is separated from the Central plateau by the Don Phraya mountains. The elevation of the plateau varies between 130 and 200 m. The mountains in the west are between 800 and 1 300 m and the southern edge of the plateau averages about 400 m with peaks up to 700 m.
The plateau gently slopes eastwards towards the Mekong River but fairly abruptly northward towards the Mae Nam Mun. Most of the plateau is sandstone, which is the parent material of the sandy soils. Some alluvial areas are scattered along the courses of the two major rivers, the Mae Nam Mun and Mae Nam Chi and their tributaries, and they constitute the major agricultural areas;
- The Central plain region is the largest and can be subdivided into three physiographic subregions:
- The south-eastern subregion is much dissected by southerly flowing rivers and flanked in the east by hills. The alluvial streams are utilised for rice cultivation, the higher and well-drained grounds for plantations and orchards;
- The northern rolling plains subregion where the northern rivers flow together into the Chao Phraya. This area is, in general, fertile;
- The Chao Phraya delta subregion is generally flat and usually flooded in the wet season. It is the largest and most fertile lowland area of the country, almost completely under cultivation except for the mangroves, and is composed of silt brought down by the rivers. Bangkok is situated in this delta;
- The Southern region is peninsular Thailand and is composed of mountains, in the west, up to 1 000 - 1 500 m, and flat land. Streams flow eastward toward the Gulf of Thailand and have often built up deltas suitable for wet rice cultivation.
Thailand has a monsoonal climate with a wet season (90 percent of the annual rainfall) from April to September during the south-western monsoon and a dry season from October to May with dry continental northerly winds.
During the dry season, Thailand is also influenced by the southern Asiatic cyclonic storm belt that brings irregular amounts of additional rain. Annual rainfall is highest in the southern and western parts of the peninsular region and in the south-eastern region (from 2 000 to more 3 000 mm). It is lowest (less than 1 000 mm) on the central plain that, in fact, lies in the rain shadow of the western mountains.
The north-eastern region has an average rainfall from just more than 1 000 mm in the west to more than 2 000 mm in the north-east. Temperature variations are small in the southern and south-eastern regions, around an average of 28° C. Temperatures in Bangkok vary between 16° C in December and 35° C in April. Winter temperature in the north can fall to approximately 10° C or lower.
The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.