The thesis examines this question: What are the relative effects of changes in land use and climate on the quantity and variability of river flows in Indonesia in relation to land use and water use planning and management for sustainable development? The contribution of this thesis is to provide a method and tool for shedding light on this important research question. A new integrated model system INDOCLIM has been developed for policymakers and planners as a tool for examining the possible impacts of changes in land use patterns and climate on the river flows, as part of an effort to support environmentally sustainable development in a country such as Indonesia. This is a trial model that consists of three components (land use, climate and hydrology). The land use component is used to generate land use change patterns based on four policy-related scenarios: business-as-usual; ecological concern; pro-industrialisation; and pro-agriculture. These scenarios were constructed in a time-series between 2000 and 2100, with 1990 as the baseline. The land use change pattern is created by using a GIS, based on the cellular automata principal. The climate component is used to generate time dependent climate scenarios, based on the global temperature change under IPCC SRES GHG emission scenarios and downscaled GCM patterns. The land use patterns are translated into a set of hydrological parameters and, together with the climate variables, are used for calculating the monthly discharge on a cell-by-cell basis. The runoff is totalled from all cells in the basin area. The model is: very specific in purpose; user oriented; designed for sensitivity analysis to answer ‘what if’ questions; designed for a catchment scale; and transportable. The model has been implemented in the Upper Citarum river system, Bandung basin, Indonesia for a preliminary assessment. The results from the model show that: both land use change and climate change have impacts on the annual yield, monthly discharge, and changes in seasonal variations of river flows; climate change has a greater possible impact on the change of the annual yield, and on monthly discharge variations, than the land use change; the superimposed effects of land use change and climate change can exacerbate or reduce the impacts; the land use change has a more significant impact on local scale variation than the climate change. The findings suggest that land use management as part of an integrated management programme for sustainable development is very relevant. Characteristics of this integrated model and some feedbacks from potential users have been identified for further development and improvement of the model. This thesis contributes to the need for an integrated assessment for examining the possible changes in the quantity and variability of river flows as the result of changes in land use and climate. It specifically contributes by: developing the integrated system for this specific purpose; developing the methodology for transferring land use information to monthly water consumption as required by the hydrological model; and developing procedures to create land use change scenarios. Overall, the integrated model framework, as developed, tested and applied in the Bandung basin of Indonesia, is potentially transferable to other basins and countries in Southeast Asia where similar issues of climate change, land use change and water resource management are key elements of sustainable development.