Overview
The Kosi (also written Koshi) Zone was one of Nepal's fourteen former administrative zones, located in the eastern part of the country. Its largest city and administrative centre was Biratnagar, a regional hub for trade and industry. The zone combined lowland plains, mid-hill districts and higher northern terrain, forming an area with varied climates and communities. For a concise reference to the historical administrative framework see zones of Nepal.
Geography and rivers
Topographically the zone ranged from the flat Terai belt in the south to the rugged hills in the north. Three major rivers dominate the landscape and economy: the Arun and Tamor rivers and the Sapta Koshi system, which is formed by the convergence of several tributaries. These waterways shape irrigation, hydropower potential and seasonal flood patterns. Further information about the principal rivers can be found at river sources. The region experiences subtropical conditions in the plains, with cooler, temperate climates at higher elevations.
Districts and main settlements
Kosi Zone comprised six districts, which together contained both urban centres and rural communities. The districts were:
- Bhojpur
- Dhankuta
- Morang
- Sankhuwasabha
- Sunsari
- Terhathum
Among urban locations, Biratnagar was the largest city and administrative capital. Other important towns included Dharan, Dhankuta, Itahari and Inaruwa. For official district lists and administrative notes see district overview and municipal references such as Biratnagar information.
Economy, transport and resources
Economically the zone combined agriculture, industry and services. The Terai plains supported rice, jute, sugarcane and other crops while urban centres hosted textile and processing industries. Biratnagar became known for its factories and cross-border trade with neighbouring India. Transport links included regional roads, rail and airports that connected towns to national routes, and river valleys that have been considered for hydropower projects. Flood control structures and irrigation works are important to local agriculture and settlement safety.
History, administration and contemporary status
The zone system was part of Nepal's administrative arrangement until the federal restructuring introduced in the 2015 constitution. Under that reform zones were superseded by provinces; the territory that made up the former Kosi Zone now lies within the boundaries of Province No. 1 (the new provincial system coordinates local and regional governance). Historical and administrative accounts place Kosi within eastern Nepal's long-standing patterns of trade, migration and cultural exchange.
Culture and notable facts
The zone was culturally diverse, inhabited by many ethnic groups and languages including Nepali, Maithili and indigenous hill languages such as Limbu and Rai. Festivals, agricultural cycles and cross-border commerce have shaped local life. The Sapta Koshi river system has a long influence on settlement patterns and flood history; its seasonal behaviour has been a central concern for planners and communities alike.