The river flows along the northwest area of Sumatra, which has a predominantly tropical rainforest climate (designated as Af in the Köppen-Geiger climate classification).[4] The annual average temperature in the area is 25°C. The warmest month is March, when the average temperature is around 26°C, and the coldest is January, at 23°C.[5] The average annual rainfall is 3953mm. The wettest month is November, with an average of 588mm rainfall, and the driest is June, with 175mm rainfall.[6]
