A number of streams flowing southwards traverse geography of West Champaran District. The southern portion of the tract is characterized by stretches of upland varied in places by large marshy depressions known as 'chaurs'. The Gandak or Narayani and Sikrahana are the two important rivers of this district.
Geography of West Champaran District includes a cool climate as compared to the adjoining districts of the state. The terai area comprising mainly Ramnagar, Bagaha and Narkatiaganj is considered unhealthy while all other areas have a healthy climate. Winter begins in November and lasts till February, followed by hot summer months when temperature rises to maximum 43 degree Celsius. Rains set in during the later part of June. The district receives some winter rain also. Rainfall is heavier than most of the districts and is especially heavy in the terai region.
However, West Champaran District has recently suffered large scale denudation of forests. Forests are confined to the northern tract and particularly the Sumeswar and the Dun ranges are covered with forests. Tirhut, Tribeni and Done canals are the most prominent canals operating in this district. The Dun and Sumeswar hills in the extreme north, which are the continuation of Shivalik hill range, are formed of ill compacted sandstone. There are beds of Kankar (sandstone) in parts of the district and saltpetre is found almost everywhere.