Barumun River

Barumun River is a Sumatran river that begins in Siraisan, Padang Lawas Regency in the southeastern North Sumatra, Indonesia, about 1,200 km northwest of the capital Jakarta.

Hydrology
The river flows northward through North Padang Lawas, South and Labuhan Batu Regency before reaching Sumatra's east coast with its estuary in Malacca Strait.

The largest city on the Barumun is Kotapinang, in South Labuhan Batu Regency, with a population of 68,943 people in mid 2023. While the largest city in the Barumun River basin is Rantau Prapat (in Labuhan Batu Regency), which is located on the Bilah tributary with a population of 177,912 people in mid 2023. It is the largest river in Sumatra with a length of about 440 km.

Tributaries include the Bilah, Kanan, Batang Pane, Sihapas and Aek Sangkilon. All tributaries of Barumun River are sourced from mountainous areas along Barisan Mountains.

Geography
The river flows in the northern area of Sumatra with predominantly tropical rainforest climate (designated as Af in the Köppen-Geiger climate classification). The annual average temperature in the area is 23 °C. The warmest month is May, when the average temperature is around 25 °C, and the coldest is January, at 22 °C. The average annual rainfall is 2801 mm. The wettest month is November, with an average of 381 mm rainfall, and the driest is March, with 126 mm rainfall.