Singapore Water Budget: The Past, the Present, and the Future

Abstract

Urbanization and climate change profoundly impact hydrological processes and the associated water budget, challenging sustainable water management. In this study, we use a distributed mechanistic ecohydrological model adapted for urban environments to quantify changes in the hydrological budget components in response to urbanization, as well as projected future climate conditions and additional land cover changes. The city of Singapore is selected as the study site, given the high complexity of its water management system that integrates elements highly relevant to similar tropical urban settings, where the presented framework can be applicable. Results reveal that, compared to a pristine landscape in Singapore, urbanization has increased sensible heat flux by ∼5% and decreased latent heat flux by ∼11%. This is accompanied by a ∼32% reduction in total transpiration and a ∼16% increase in runoff. Climate change scenarios with higher temperature and elevated atmospheric CO ₂ levels show minimal impact on total evapotranspiration; therefore, runoff is very much dependent on the potential changes in future precipitation. Notably, the response of vegetation is shown to be relevant for long‐term urban hydrology, with higher CO ₂ concentrations projected in the future significantly reducing the simulated stomatal conductance, which results in decreased transpiration rates broadly compensated by increased evaporation. By quantifying how urbanization and climate change can jointly impact hydrological budget components, this study demonstrates the significance of urban ecohydrology for a proper assessment of water resources, which is highly relevant to Water Sensitive Urban Design, in Singapore as well other cities.