The river flows in the central area of Sulawesi with predominantly tropical rainforest climate (designated as Af in the Köppen-Geiger climate classification).[4] The annual average temperature in the area is 22 °C (72 °F). The warmest month is October, when the average temperature is around 23 °C (73 °F), and the coldest is January, at 20 °C (68 °F).[5] The average annual rainfall is 2,715 millimeters (106.9 inches). The wettest month is December, with an average of 368-millimeter (14.5 in) rainfall, and the driest is September, with a 66-millimeter (2.6 in) rainfall.[6]