Exploring the hydrological impact of increasing urbanisation on a tropical river catchment of the metropolitan Jakarta, Indonesia

Abstract

Tropical river catchments face water resource challenges, as populations and urban footprints grow exponentially. It is acknowledged that deforestation of upstream watersheds and urbanisation pressure generally lead to an intensification of extreme flow events, such as floods and droughts, but processes such as groundwater recharge and evapotranspiration are also affected, leading to a broader impact on water balance. In this respect, the Ciliwung River basin – flowing through Jakarta, the capital city of Indonesia – represents an exemplary case of a tropical river catchment experiencing alteration of the hydrological regime as a consequence of highly impacting land use changes following rapid urbanisation. The city of Jakarta situated downstream has experienced catastrophic floods at an increasing frequency (1996, 2002, 2007, 2013), and continued urbanisation in the middle and upper stream may further alter the catchment response, leading to increased flood risk and lower groundwater recharge of the urban aquifer, which is the source of drinking water for a large part of the population. This study explores the effects associated with the rapid and drastic land use changes in the region on the hydrological response of the river, by showing how modern simulations tools can provide insights about the effect of land use policies. To this end, a distributed analysis of the hydrological regime for different scenarios of urbanisation is performed. Watershed response to the realisation of these scenarios is simulated by means of a distributed hydrological model, which allows for a physically and spatially explicit simulation of the major basin processes across the entire basin. Specifically, we used the model to test two hypothetical but plausible future land cover scenarios that correspond to an uncontrolled urban expansion, and to a scenario with strong constraints on urban expansion, combined with afforestation in the upper catchment. Results suggest that the uncontrolled urban expansion leads to a noticeable increase of flood events during the rainy season, and a decrease of base flow in the dry season. The changes in the hydrological budget components are also discussed in view of implications on water resources availability and rehabilitation of the urban river corridor.