The effect of forest area change in tropical islands towards baseflow and streamflow

Baseflow is a very important component in maintaining river flow. Baseflow is generated from groundwater flow. Baseflow is very important role in water conservation. Indonesia is located in a tropical climate. Based on the Koppen climate classification, Indonesia is included in the tropical rainforest climate (type Af), so that the characteristics of the climate, soil, flora and fauna are unique. About 70% of Indonesia's territory consists of water. Baseflow in the tropical island region has a unique characteristic. This research aimed to obtain the knowledge on the effect of forest area change in tropical islands towards the characteristics of baseflow and streamflow that involved RDF filter parameter calibration, baseflow contribution towards streamflow based on the Baseflow Index (BFI) and Q90 on Q50 ratio, rain contribution on the total baseflow, baseflow stream domination, and discharge stability of streamflow. This research was conducted in three sub watersheds with forest area percentage of ±18% Bango Sub watershed, ±23% Brantas Hulu Sub watershed, and ±59% Cobanrondo Sub watershed. The results showed that One Parameter Algorhitm method satisfied the application of baseflow separation. There was a positive correlation between rain and baseflow. Baseflow dominated the streamflow in the research location. The greater the forest area, the more stable the flow condition from year to year.