the river flows in the northwest area of java with a predominantly tropical monsoon climate. the annual average temperature in the area is 24 °c. the warmest month is may, when the average temperature is around 26 °c, and the coldest is january, at 22 °c. the average annual rainfall is 2646 mm. the wettest month is january, with an average of 668 mm rainfall, and the driest month is september, with 14 mm rainfall.