With a population density almost twice that of the Netherlands and a annual population growth of over 1% the island of Java in Indonesia faces inevitable land use changes in order to meet the needs of all its inhabitants. Land use change is not a new phenomenon on Java but the dynamics have shifted, presently Java faces a rapid urbanization of prime agricultural lands and a conversion of wet agriculture (sawahs) to dry agriculture. In order to quantify the possible hydrological effects of such land use change the Sacramento Soil Moisture Accounting (SAC-SMA) model was used for a medium sized catchment in Java (the upper Citarum river catchment). Land use was classified into 5 groups: forest, sawah, rain fed agriculture, built up areas and “other”. Each land use was parameterized using the physically based Sacramento parameters to represent the individual hydrological properties. The Sacramento model is run in the PCRaster GIS package, enhancing the possibility of use in ungaugedcatchments. The results predict a 10.5% increase in average monthly discharge over a year with a 13.2% increase in urban areas. Further work is needed in improving the parameterization, testing the model on other catchments and on daily rainfall/runoff data, as well as incorporating human induced water allocation measures such as irrigation to improve the results of downstream discharge modeling.