Flood risk assessment for delta mega-cities: a case study of Jakarta

Jakarta has suffered major floods in 2002, 2007, and 2013. To cope with and adapt to both the current and future flood problem, the city requires quantitative assessments of flood risk. In this study, we develop a flood risk assessment model for Jakarta. The model is based on the Damagescanner model, adapted for Jakarta using local information on hazard, exposure, and vulnerability. The model was first set up using existing estimates of economic exposure of different land use classes to represent exposure and depth-damage functions (vulnerability curves) from several existing studies in south-east Asia to represent vulnerability. Using these data to simulate damage led to an overestimation by several orders of magnitude. Hence, we held a series of expert meetings and workshops with local stakeholders to develop specific estimates of economic exposure per land use class and to derive vulnerability curves specific for Jakarta. We compare the resulting simulated damages to reported damages and found them to be in good agreement, giving confidence in the use of the model for flood risk assessment. Under current conditions, we found the annual expected damage due to river flooding in Jakarta to be approximately USD 321 million per year. We also examined the sensitivity of flood risk assessments to the use of different vulnerability curves. The sensitivity is high: using the six curves described in this study to simulate risk led to a factor eight difference between the lowest and highest values. Our findings demonstrate that flood risk assessments need to pay close attention to the selection, development, and testing of vulnerability curves