The river flows in the northern area of Sumatra with predominantly tropical rainforest climate (designated as Af in the Köppen-Geiger climate classification).[3] The annual average temperature in the area is 21 °C. The warmest month is March, when the average temperature is around 26 °C, and the coldest is October, at 20 °C.[4] The average annual rainfall is 3,730 mm. October is the wettest month with an average of 491 mm rainfall, and March is the driest, with 136 mm rain on average.[5]