The purpose of this research is to assess the future flood risk in rapidly urbanizing cities under climate change. A flood inundation model and a flood damage costs model were employed to project the future flood risk. We employed the combinations of eight global climate models (GCMs) and three representative concentration pathways (RCPs) for precipitation to represent the climate change. Land-use change and land subsidence information were employed to represent the urban development effects. The expected annual damage costs (EADC) were also calculated to explain the severity of the flood risk. In addition, a global approach was used to estimate the asset values by comparing the common parameters (e.g. gross domestic production (GDP) or population). As a result, the combination of climate change and urban development amplified the mean future flood risk by 322% to 402% in 2050, with a 95% confidence interval. The results also show a large uncertainty of the future flood risk due to the future scenarios. These findings will assist policymakers in determining the investment for future flood prevention and mitigation. KEYWORDS damage cost; flood inundation model; land-use change; land subsidence; climate change

Jakarta is the capital of Indonesia and is considered one of the most vulnerable cities to climate-related disasters, including flooding, sea-level rise, and storm surges. Therefore, the development of a flood-forecasting system for Jakarta is crucial. However, the accurate prediction of flooding in Jakarta is challenging because of the short flood concentration time in highly urbanized basins and the shortage of rainfall data in poorly gauged areas. The aim of this study is to simulate recent flood inundation using global satellite mapping of precipitation (GSMaP) products. The GSMaP products (NRT and Gauge V7) were evaluated and compared with hourly observation data from five ground stations in the Ciliwung River Basin. In addition, a rainfall-runoff and flood inundation model was applied to the target basin. The results of the analysis showed that the GSMaP Gauge data were more accurate than the GSMaP NRT data. However, the GSMaP Gauge cannot be used to provide real-time rainfall data and is, therefore, inadequate for real-time flood forecasting. We conclude that the GSMaP Gauge is suitable for replicating past flood events, but it is challenging to use the GSMaP NRT for real-time flood forecasting in Jakarta.

Floods are considered to be one of the major natural disasters in Indonesia. Jakarta in Indonesia has experienced many floods in the past, such as those in 1996, 2002, 2007 and 2013. In this paper, land subsidence problems contributing to flooding in Jakarta were described and historical and future land subsidence situations in Jakarta were reconstructed and projected using a simple linear extrapolation method. Also, those land subsidence impacts were analyzed by using a flood inundation model. As a result of analysis, it was found that the land subsidence in Jakarta contributed by 17.6% to increase of the total flood inundation volume from 1983 to 2013. Also, it was estimated that the land subsidence situations for the future period of 2050 would increase the flood inundation volume by 10.3% compared to those of 2013. However, impacts from land use/cover changes on the flood inundation were found to be much greater than those from land subsidence in Jakarta. It should be noted that the land subsidence affects flooding from the coast when high waves and surges occur but those effects were not considered in this paper.

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Abstract:Jakarta is facing several issues related to flooding, including land subsidence in the coastal area and rapid land-use/ cover changes in the upstream area. In this study, we analyzed the effects of future changes in land use and land subsidence using a rainfall-runoff and flood inundation model. The future land-use scenarios were projected based on the SLEUTH model, and land subsidence was projected based on an extrapolation of the current state in Jakarta.Based on this analysis, land-use changes and land subsidence contributed to an increase in flood inundation volume of 36.8% from 2013 to 2050. Moreover, the effects of land-use changes on flood inundation in Jakarta were much greater than those of land subsidence. The government's current target to stop land subsidence by 2020 would cause a 7.7% decrease in the flood inundation volume by 2050. Furthermore, controlling and regulating land-use/cover changes by 2020 would cause a 10.9% decrease in the flood inundation volume by 2050. From these results, we conclude that a flood mitigation plan should be made not only for land subsidence, but also for land-use changes.