Abstract
Rapid urbanization, accelerating land subsidence, and sea-level rise have positioned Jakarta, Indonesia, as one of the world's most flood-vulnerable megacities. While conventional engineering interventions such as sea walls and channelization have dominated urban flood defense strategies, their long-term efficacy and ecological compatibility remain heavily contested. This study evaluates the hydrological performance and socio-economic viability of Nature-Based Solutions (NbS) for flood risk mitigation across the Ciliwung River Basin in Greater Jakarta. We employed a coupled one- and two-dimensional (1D/2D) hydrodynamic model (EPA-SWMM coupled with LISFLOOD-FP) forced by projected 10-, 25-, and 50-year return period rainfall events under climate change scenarios (IPCC SSP2-4.5 and SSP5-8.5). Three NbS intervention portfolios were simulated: urban green infrastructure (bioswales, permeable pavements, and decentralized retention basins), upstream riparian reforestation, and coastal mangrove rehabilitation. In parallel, an extended Cost-Benefit Analysis (CBA) was executed across a 30-year operational horizon, factoring in avoided flood damage, carbon sequestration, and recreational co-benefits. Hydrodynamic simulations reveal that an integrated hybrid portfolio decreases peak discharge by 28.4% and diminishes urban inundation extent by up to 37.2% under a 25-year design storm. Economically, the hybrid NbS framework yields a Benefit-Cost Ratio (BCR) of 2.14 and a Net Present Value (NPV) exceeding USD 1.82 billion at a 6% discount rate, outperforming purely grey infrastructure baselines. These findings provide empirical backing for reorienting Indonesian spatial planning frameworks toward polycentric, green-grey adaptive flood governance.
