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, Uttaranchal, 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.
Chitwan National Park is the first national park in Nepal. Formerly called Royal Chitwan National Park it was established in 1973 and granted the status of a World Heritage Site in 1984. It covers an area of 932 km2 (360 sq mi) and is located in the subtropical Inner Terai lowlands of south-central Nepal in the Chitwan District. In altitude it ranges from about 100 metres (330 ft) in the river valleys to 815 metres (2,674 ft) in the Churia Hills.
In the north and west of the protected area the Narayani-Rapti river system forms a natural boundary to human settlements. Adjacent to the east of Chitwan National Park is Parsa Wildlife Reserve, contiguous in the south is the Indian Tiger Reserve Valmiki National Park. The coherent protected area of 2,075 km2 (801 sq mi) represents the Tiger Conservation Unit (TCU) Chitwan-Parsa-Valmiki, which covers a 3,549 km2 (1,370 sq mi) huge block of alluvial grasslands and subtropical moist deciduous forests.