the terai region

The Terai or Madhesh region begins at the Indian border and includes the northermost part of the flat, intensively farmed Gangetic Plain called the Outer Terai. This is culturally an extension of northern India with Hindi, Awadhi, Bhojpuri and Maithili spoken more than Nepali, however it was annexed to Nepal by conquest and by treaty with the British.

Rivers including the large Koshi, Narayani (called the Gandak in India), and Karnali meander across the Terai after breaking through the ranges to the north. These and smaller rivers rising south of the main Himalaya are prone to flooding during the summer monsoon.

The Outer Terai ends at the first range of foothills called the Siwaliks. This range has a forested alluvial belt along its base, marshy with springs fed by groundwater percolating down from higher elevations. Before the use of DDT the alluvial zone was dangerously infested with malaria. Nepal’s rulers used it as a defensive frontier called the char kose jhadi (twelve kilometer forest).

Beyond the alluvial belt, the Siwaliks rise as high as 1,000 meters, steepest on their southern flanks because of faults. This range is composed of poorly consolidated, coarse sediments that quickly absorb rainfall. This is unsuited to agriculture so there is very little population. However in several places north of the Siwaliks there are dun valleys or the Inner Terai. Among these are Surkhet, Dang and Deukhuri in western Nepal and the Rapti Valley (Chitwan) in central Nepal. These valleys were also malarial and lightly populated until DDT was used to suppress mosquitos, but they had significant agricultural potential that was exploited to some degree by the Tharu ethnic group who were resistant to malaria. After DDT was used to suppress malaria in the 1950s, farmers from the hills began settling in these valleys to the detriment of the Tharus.

The Terai ends and the Hills begin at a higher range of foothills called the Mahabharat Range.