Geography

Thailand is a Southeast Asian country located at Latitude 15° 00’ N, and Longitude 100° 00’ E. Thailand is the 50^th largest country in the world with a total area of 514,000 Sq.Km. The north and the west of the country contain mountainous regions. The northeast is mainly plateau. The east occupies short mountain ranges alternating with small basins of short rivers. The eastern area is adjacent to neighboring Cambodia. The southern tip of Thailand is part of a peninsula located between the Andaman Sea and the Gulf of Thailand. Central Thailand is a large basin releasing river water into the Gulf of Thailand. Thailand has 76 provinces besides Bangkok, which is a special administrative area, the capital.

Population and land use

The total population of Thailand was around 66 Million in mid-2019 as per the Population Reference Bureau, of which 66% lives in rural areas. Thailand has the 20^th largest population and accounts for 0.90% of the total world population. The annual population growth rate is estimated at 0.97%, and the population density is about 134 inhabitants / Km². Out of the entire area, 23.84 Mha is used for agriculture.

Climate and rainfall

Located 15 degrees north of the equator, Thailand has a tropical climate. The climate is mainly hot and humid across the entire region. There are three seasons in Thailand: (i) summer or pre-monsoon season (mid-February to mid-May); (ii) rainy or southwest monsoon season (mid-May to mid-October); and, (iii) winter or northwest monsoon season (mid-October to mid-February). The temperature ranges from 19 to 38 degrees C.

The northern part of Thailand usually is dry and gets less rainfall during winter. Maximum precipitation occurs in August and September. Rainfall is abundant in the southern part except during summer. The west coast gets the highest amount of rain during September, while rains in the east coast reach its peak in November. The average rainfall in Thailand is about 1,622 mm per annum.

Food and agriculture

About 30.22% of the total population of Thailand is engaged in agriculture. Thailand has about 23.84 Mha of agricultural land. Nearly 46% of the total area under cultivation is used for growing rice. The remaining area is under permanent crops. Major crops of Thailand are rice, cassava (manioc, tapioca), rubber, corn, sugarcane, coconuts, and soybeans. Significant crops for domestic consumption are rice, maize, yams, chilies, cassava, eggplant, and beans. Major crops for export are rice, sugarcane, tobacco, rubber, coconuts, jute, and pineapples.

Water resources management

The country’s annual water requirement is around 147,749 Mm³. Agriculture requires 113,960 Mm³, which is about 75% of the total. Water reservoirs and irrigation systems account for 65,000 Mm³. The remaining 48,960 Mm³ is located outside of the irrigation zone and depend on rainwater for agriculture. Watershed areas in Thailand can be divided into 25 main watersheds and 254 small watersheds. The average annual precipitation is 1,379 mm. Total runoff is around 200,973 Mm³, which works out to 3,086 m³ per person per year. The runoff during the rainy season is 175,345 Mm³ (87.25%), and 35,628 Mm³ (12.75%) during the dry season. The total catchment capacity is 74,788 Mm³. The total internal water resources of Thailand add up to about 224.55 Km³/year. Thailand’s hydrology is highly variable due to the influence of monsoon and storm. This results in floods and droughts. The Mekong river constitutes an additional external resource for Thailand, which has been estimated as half the discharge of the river. The flow of the Mekong River at the point where it enters Lao People’s Democratic Republic is about 280 Km³/year. The contribution of Thailand to the Mekong River is an estimated 51.9 Km³/year. The estimated flow of the Mekong border river for Thailand is about 114.05 Km³/year. The Salween river on the border with Myanmar, with an estimated flow of 200 Km³/year, flows only over a relatively short distance on the border. Therefore, there is not much contribution from Thailand over the short span.

Irrigation and drainage

Thailand has a long history of irrigation development. Over the last seven centuries, weirs, canals, storage dams, conveyance systems, etc. have been constructed by the reigning monarchs. Modern irrigation development began in 1902 when King Rama V engaged a Dutch hydraulic engineer to draw up a plan for an advanced irrigation system. In 1957, the Chao Phraya barrage, the primary control structure of the project was completed. This was followed by the completion of the major storage reservoirs, Bhumibhol dam in 1964 and Sirikit dam in 1971. From then on, Thailand has constructed many large, medium and small-scale storage dams and weirs with canal systems to serve the expanded irrigated area.

Altogether, there are 682 dams across the region in which 33 are large dams; 517 dams with medium storage capacity account for a total storage of 4,799 m³, and 4,156 are categorized as small reservoirs.

River basins

Thailand can be divided into seven river basins, but it is generally divided into 25 sub-basins. The total surface water resources amount to 213.35 Km³/year. Aquifer recharge from rainfall is around 41.90 Km³/year (about 5-6% of the total precipitation). Approximately 30.70 Km³/year is estimated to return to the river system. Thailand shares three major river systems with its neighbors: the Mekong river forms the border with Lao People’s Democratic Republic in the north and east (about 18% of the total Mekong catchment area is located in Thailand). The Salween river is on the northwestern border with Myanmar. And, the Kolok river is on the southern border with Malaysia. The Kolok river, which originates in Thailand and borders between Thailand and Malaysia, is a very short river with a total length of just over 100 Km.

ICID and National Committee

The Thai National Committee on Irrigation and Drainage (THAICID) has been a founder member of ICID since its inception in 1950. The ICID past Vice Presidents from Thailand were: Late Mr. M.L. Xujati Kambhu (1964 to 1967); Late Mr. S. Raunglak (1983 to 1986) and Mr. Chaiwat Prechawit (2010-2013). The 67^th IEC Meeting and the 2^nd World Irrigation Forum were held from 6-12 November 2016 at Chiang Mai in Thailand.