The Terai is a belt of marshy grasslands, savannas, and forests located south of the outer foothills of the Himalaya, the Siwalik Hills, and north of the Indo-Gangetic Plain of the Ganges, Brahmaputra and their tributaries. The Terai belongs to the Terai-Duar savanna and grasslands ecoregion. In northern India, the Terai spreads eastward from the Yamuna River across Himachal Pradesh, Haryana, Uttarakhand, Uttar Pradesh and Bihar. Corresponding parts of West Bengal, Bangladesh, Bhutan and Assam east to the Brahmaputra River are called Dooars. The lowland plains of the Terai lie at an altitude of between 67 and 300 m (220 and 980 ft). North of the Terai rises the Bhabhar, a narrow but continuous belt of forest about 8–12 km (5.0–7.5 mi) wide.
In Hindi, the region is called तराई tarāī meaning foot-hill. In Nepali, the region is called तराइ tarāi meaning the low-lying land, plain, especially the low-lying land at the foot of the Himālayas, south to the border with India. Nepalis may also call it Madhes (Nepali: मधेस), particularly when noting its ethnic compositions similar to adjacent India and unlike the ethnic makeup of the "hills" (Nepali: पहाड, pahārd). The region's name in Urdu is ترائي tarāʼī meaning lands lying at the foot of a watershed or on the banks of a river low ground flooded with water, valley, basin, marshy ground, marsh, swamp; meadow.
The Terai is crossed by the large perennial Himalayan rivers Yamuna, Ganges, Sarda, Karnali, Narayani and Kosi that have each built alluvial fans covering thousands of km2 below their exits from the hills. Medium rivers such as the Rapti rise in the Mahabharat Range. The geological structure of the region consists of old and new alluvium, both of which constitute as alluvial deposits mainly of sand, clay, silt, gravels and coarse fragments. The new alluvium is renewed every year by fresh deposit brought down by active streams, which engage themselves in fluvial action. Old alluvium is found rather away from river courses, especially on uplands of the plain where silting is a rare phenomenon.
The Terai region has a large number of small and usually seasonal rivers, most of which originate in the Siwalik Hills. The soil in the Terai is alluvial and fine to medium textured. Forest cover in the Terai and hill areas has decreased at an annual rate of 1.3% between 1978 and 1979, and 2.3% between 1990 and 1991.
As the Terai is increasingly deforested, drained and brought under cultivation, the connection with wetness fades in contemporary usage. Terai becomes a geographic, not a hydrographic term, for districts in the plains near or bordering the Siwaliks. A permeable mixture of gravel, boulders, and sand enables the water table to sink 5–37 m (16–121 ft) deep. The Terai zone is composed of less permeable layers of clay and fine sediments, bringing groundwater to the surface in springs and wetlands.
The reduction in slope as rivers exit the hills and then transition from the sloping Bhabhar to the nearly level Terai causes current to slow and the heavy sediment load to fall out of suspension. This deposition process creates multiple channels with shallow beds, enabling massive floods as monsoon-swollen rivers overflow their low banks and shift channels. The 2008 Bihar flood was only an example of recurrent catastrophes in the Terai.
|Biratnagar, 26°N, 87°E|
|Climate chart (explanation)|
|Chandigarh, 31°N, 77°E|
|Climate chart (explanation)|
- Moving inland and away from monsoon sources in the Bay of Bengal, climate becomes more continental with greater summer-winter difference.
- In the far western Terai, which is five degrees latitude further north, the coldest months average 3 °C (37 °F) cooler.
- Total rainfall markedly diminishes from east to west. The monsoon arrives later, is much less intense and ends sooner. Winters are wetter in the west.
Terai in Nepal 
In Nepal, Terai is differentiated into "Outer" and "Inner" Terai.
Outer Terai or Madhes begins at the southern edge of the Siwalik Hills. In ordinary usage the Terai extends to the border with India, even if drier, cleared agricultural land well south of the marshes may be included. The Outer Terai of far-western Nepal consists of Kanchanpur, Kailali, Bardiya and Banke districts. These were once called the Naya Muluk and lay on the periphery of the Awadh dynasty. After Nepal lost the Anglo–Nepalese War (1814–16) these districts were annexed by the British in the Sugauli Treaty and returned in 1860 as reward for Nepal's military aid in the Indian Rebellion of 1857.
East of Banke the Nepalese outer Terai is interrupted where the international border swings north and follows the edge of the Siwaliks adjacent to Deukhuri Valley. Here the Outer Terai is entirely in Uttar Pradesh's Shravasti and Balrampur districts. East of Deukhuri the international border extends south again and Nepal has three more Outer Terai districts Kapilvastu, Rupandehi and Nawalparasi.
In Chitwan district east of Nawalparasi the international border again follows the southernmost Siwaliks, placing the outer Terai in Bihar's West Champaran district. Then the international border extends south and the Nepalese Outer Terai is continuous across eleven districts to the country's eastern border. These additional districts are: Parsa, Bara, Rautahat, Sarlahi, Mahottari, Dhanusa, Siraha, Saptari, Sunsari, Morang and Jhapa.
The 2001 national census counted 10.3 million population (45% of the national total) in the outer Terai districts.
Inner Terai 
Inner Terai (Nepali: भित्री तराई, Bhitrī Tarāī) is also called ''Bhitrī Madhes (Nepali: भित्री मधेस). It consists of seven elongated valleys (Nepali: उपत्यका, upatyakā) lying within the Siwalik Hills or between them and the 1,500-2,700 metre Mahabharat Range further north. In India these valleys would be called Dūn (Hindi: दून), for example Dehradun. Most of these valleys extend east-west or SSE-WNW parallel to enclosing ranges. They are five to ten kilometers wide (north-south) and up to a hundred kilometers long (east-west).
Nepal's Inner Terai valleys are (from west to east):
- Jogbudhā (Nepali: जोगबुढा) in Dadeldhura district north of outer Terai Kanchanpur district; a relatively small and undeveloped valley near the western border with India.
- Surkhet (Nepali: सुर्खेत) in Surkhet district, located north of outer Terai Kailali and Bardiya districts.
- Deukhurī (Nepali: देउखुरी), in Dang and eastern Banke districts. The international border follows the Duduwa Siwaliks south of this valley.
- Dāng (Nepali: दाङ)Valley parallels Deukhuri but north of it, also in Dang and Banke districts.
- Nawalparasi (Nepali: नवलपरासी) Nawalpur region of Nawalparasi district which stretch from Daaune Devi hill to Gaidakot to the Border of Chitwan District.
- Chitwan (Nepali: चितवन) occupies Chitwan and Makwanpur districts. Chitwan district borders Bihar, India's West Champaran district to the south while Makwānpur lies north of Nepal's Parsa district.
- Marin Kholā (Nepali: मरिन खोला) is a small valley in Sindhuli district north of outer Terai Sarlahi, Mahottari and Dhanusa districts.
- Udayapur (Nepali: उदयपुर) is in Udayapur district north of Siraha and Saptari.
The 2001 national census counted 2.3 million population (10% of the national total) in these seven Inner Terai districts (counting Banke district as Outer Terai). Adding 45% in the outer Terai gives 55% of Nepal's population living in its Terai districts.
The Terai was heavily forested with Sal before heavy logging began in the 19th century, particularly for use as railroad sleepers. Foresters of the British Raj were of the opinion that in ancient times the Terai was cleared and cultivated. After Buddhism went into decline, the area was largely abandoned, and quickly re-vegetated with shrubs and trees, but took much longer — centuries perhaps — for Sal forest to return.
Inner Terai valleys historically were agriculturally productive but extremely malarial. Some parts were left forested by official decree during the Rana dynasty as a defensive perimeter called Char Kose Jhadi, meaning four kos forest; one kos equals about 3 km (1.9 mi). A British observer noted, "Plainsmen and paharis generally die if they sleep in the Terai before November 1 or after June 1." British travelers to Kathmandu went as fast as possible from the border at Raxaul in order to reach the hills before nightfall.
Ethnic groups 
Tharu people have been living in the Terai for many centuries, and reputedly had an innate resistance to malaria. Following the malaria eradication program using DDT in the 1960s, a large and heterogeneous non-Tharu population settled in the region.
Pahari farmers from the mid-hills moved to the plains in search of arable land including Bahun, Chhetri and Newar. Tharus constitute the traditional population in the western Terai. The eastern part has been occupied by castes and ethnic groups that migrated from India — the Madhesi people, a term that sometimes also includes the Tharu people. High caste migrants from the hills have purchased, or otherwise got hold of large landholdings. Together with traditional Tharu landlords, they constitute the upper level of the economic hierarchy, which in the rural parts of the Terai is determined to a large extent by the distribution and the value of agriculturally productive land. The poor are the landless, or near landless, Terai Dalits, including the Musahar and Chamar, as well as the traditional fishermen, the Mallaah, and some of the hill Dalits. In particular the Musahars rarely get other work than hard farm labor.
The Terai is the most productive region in Nepal with the majority of the country's industries. Agriculture is the basis of the economy. Major crops include rice, wheat, pulses, sugarcane, jute, tobacco, and maize. In the eastern districts from Parsa to Jhapa they support agro-based industries: jute factories, sugar mills, rice mills and tobacco factories.
Cities over 50,000 population in Nepal's Terai include:
|Biratnagar||Morang||166,674||agro-industry, education, trade/transport Hub|
|Birganj||Parsa||112,484||trade/transport hub, agro and other industry|
|Dharan||Sunsari||95,332||tourism hub and destination, education, financial services|
|Bharatpur||Chitwan||89,323||agro-industry and food processing, tourism, health care, education|
|Bhim Dutta||Kanchanpur||80,839||transport hub, education, health services|
|Butwal||Rupandehi||75,384||transport hub, retailing, agro-industry, health care, education|
|Hetauda||Makwanpur||68,482||transport hub, cement factory, large and small-scale industry|
|Janakpur||Dhanusa||67,192||transport hub, agro-industry, education, health care, pilgrimage site|
|Nepalganj||Banke||57,535||transport hub, retailing, financial services, health services|
|Siddharthanagar||Rupandehi||52,569||trade/transport hub, retailing, tourist and pilgrim services|
Mahendra Highway crosses the Nepal Terai from Kankarbhitta on the eastern border in Jhapa District, Mechi Zone to Mahendranagar near the western border in Kanchanpur District, Mahakali Zone. It is the only motor road spanning the country from east to west.
Tourist attractions in the Terai include:
- Lumbini, birthplace of Lord Buddha (near Siddharthanagar)
- Bardia National Park (near Nepalganj)
- Chitwan National Park (near Bharatpur)
- Janakpur - the birthplace of Sita, wife of Rama in he Ramayana.
Terai in India 
|This section requires expansion. (April 2011)|
- Uttar Pradesh: Pilibhit
- Uttarakhand: Udham Singh Nagar district, Gonda district, Ballia, Bahraich, ...
- Johnsingh A.J.T., Ramesh K., Qureshi Q., David A., Goyal S.P., Rawat G.S., Rajapandian K., Prasad S. 2004. Conservation status of tiger and associated species in the Terai Arc Landscape, India. RR-04/001, Wildlife Institute of India, Dehradun
- Bhuju, U.R., Shakya, P.R., Basnet, T.B., Shrestha, S. (2007), Nepal Biodiversity Resource Book. Protected Areas, Ramsar Sites, and World Heritage Sites, Kathmandu: International Centre for Integrated Mountain Development; Government of Nepal, Ministry of Environment, Science and Technology; United Nations Environment Programme, Regional Office for Asia and the Pacific
- Bahri, H. (1989). "Learners' Hindi-English dictionary — Siksarthi Hindi-Angrejhi sabdakosa.". Rajapala, Delhi.
- Turner, R.L. (1931). "A Comparative and Etymological Dictionary of the Nepali Language". K. Paul, Trench, Trubner, London.
- Platts, J. T. (1884). "A dictionary of Urdu, classical Hindi, and English.". W. H. Allen & Co., London.
- Das, K.K.L., Das, K.N. (1981), "Alluvial Morphology of the North Bihar Plain – A study in applied geomorphology", in Sharma, H. S., Perspectives in geomorphology 4, New Delhi: Naurung Rai Concept Publishing Company, pp. 85–105
- Guneratne, A. (2002). Many tongues, one people: the making of Tharu identity in Nepal. Ithaca, New York: Cornell University Press.
- Terrenato, L., Shrestha, S., Dixit, K.A., Luzzatto, L., Modiano, G., Morpurgo, G., Arese, P. (1988). "Decreased malaria morbidity in the Tharu people compared to sympatric populations in Nepal". Annals of tropical medicine and parasitology 82 (1): 1–11. PMID 3041928.
- Hatlebakk, M. (2007). Economic and social structures that may explain the recent conflicts in the Terai of Nepal. Norwegian Embassy, Nepal
- Sharma, R. P. (1974). Nepal: A Detailed Geographical Account. Kathmandu: Pustak-Sansar.
Further reading 
- Chaudhary, D. 2011. Tarai/Madhesh of Nepal : an anthropological study. Ratna Pustak Bhandar, Kathmandu. ISBN 978-99933-878-2-4.