Characterizing Watersheds to Support Land-use Planning in Indonesia: A Case Study of Brantas Tropical Watershed

Abstract

This work addresses the challenge of classifying watersheds to support land use policy-making in rapidly developing, wet tropical regions, using a case study of the Brantas River Basin, Java, Indonesia. Hierarchical Clustering on Principal Components of the watershed descriptors resulted in three optimal clusters. Differentiation among these three clusters is mainly related to climatic regimes, topographic features, and land uses. Stepwise regression was used to identify the watershed descriptors that explain the spatial variability of four flow indices (95% non-exceedance percentile Q95; 5% non-exceedance percentile Q5; the slope of the flow duration curve SFDC; and the runoff coefficient RC). This gave, for these four indices in turn, R² values of 0.77, 0.76, 0.84 and 0.45. The results show that built-up areas and dryland forest are primary land-use controls on flow indices. Clustering results suggest that existing regional development trends will have major hydrological impacts, especially related to runoff generation and groundwater. The results support the view that failure to implement land-use policy – failure that is expected to increase built-up areas across the watershed and increase forest loss in the upper watershed - will jeopardize watershed hydrological functions. The findings of this research support the need for frequent and updated land-use monitoring to control urban development and conserve dryland forest, as well as land-use policies that control increases in built-up areas and that minimize forest loss.