Exploring the hydrologic impact of increasing urbanization in a tropical river catchment in the megacity of Jakarta, Indonesia

Abstract:

The impacts on hydrologic dynamics of land-use changes are examined in a Southeast Asian watershed. The watershed—Indonesia’s Ciliwung River basin—is characterized by a variety of conditions, from pristine tropical forests to the dense urban fabric of Jakarta. The region faces several challenges in terms of water resources, as its population and urban footprint grow exponentially. The Ciliwung River basin represents an exemplary case with positive trends in the occurrence of flooding events, and with three catastrophic floods hitting the city in 2002, 2007 and 2013.
We explore the effects of land-use changes on the hydrologic response of the Ciliwung River basin providing a distributed analysis of the hydrological regime for different scenarios of urbanization. The hydrological dynamics is simulated with the distributed model TOPKAPI-ETH, which allows for an explicit simulation of the major basin processes. Hourly model simulations are first tested for the period 2003-2008, when the most reliable meteorological and flow ground data are available. Subsequently, we compare the hydrologic regime across present and past land-use patterns, the latter as obtained by historical information. Finally, we use the model to test two future land-use scenarios (2030) which were prepared for a related study of regional planning. The worst-case scenario explores aggressive urban expansion, while the best-case scenario represents a strong constraint on urban expansion, combined with afforestation in the upper catchment.
Results suggest that the projected urban expansion leads to an (intuitive) increase in the peak event runoff during the rainy season. Within this scenario downstream discharge increases by up to 20%. Slightly lower baseflow in the dry season is predicted in the order of a reduction of 5% on average in the months of June and July. A detailed overview of possible changes in the hydrological budget components is finally provided.