Coastal vulnerability analysis of the north coast of Central Java province

The Central Java Province, responsible for managing the North Coast of Central Java, faces severe challenges threatening coastal communities and urban areas. Several measures and plans have been applied to solve these problems and will undoubtedly change the coastal vulnerability index along the coast. Furthermore, it is necessary to perform an assessment that takes into account these plans in the future. In 2019, the OKP project for Integrated Coastal Zone Management for the North Coast of Central Java was established to support stakeholders' capacity building in managing the north coast sustainably. As part of the project, this research had developed a coastal vulnerability analysis to be used as a reference in decision making for Integrated Coastal Zone Management for the North Coast of Central Java. In the first phase, this research adopted the RisckKIT toolkit. One of the tools is the Coastal Risk Assessment Framework (CRAF) to locate increased coastal risk areas (hotspots). The CRAF methodology was developed and have been applied in several coastal zone locations in Europe under the EU FP7 project, and several projects worldwide have also adopted this methodology. The first phase analysis was performed at the sub-district level, considering the data's availability. In this phase, the exposures index was calculated from the geometric mean of the social vulnerability index, land use index, transport system index and utilities index. The hazard index was calculated by taking into account the land subsidence, flooding and erosion. The hazard index of flooding was calculated using the hazard index of river flooding and the hazard index of coastal flooding. The hazard index of coastal flooding was calculated by using a simple bathtub model. The hazard index of erosion was calculated by using the DSAS toolbox in ArcGIS. Furthermore, eight combinations of hazards and exposures have been developed as scenarios for the present and future. The results of the first phase on the north coast of Central Java shows that at a Regency level, Brebes, Pekalongan and Semarang emerged as hotspots. The second phase focuses on the risk analysis on the Pekalongan Municipality as the selected hotspot with the future land use (spatial plan) as disaster risk reduction measures. The hazard assessment on flooding was performed with SFINCS model to see the inundation extent to determine the risk. The risk assessment was done by adopting the global flood depth damage functions. The risk assessment results showed that for the future extreme scenario, the area with the risk of flooding would decrease from 51.43% in the present to 44.57% in the future when the spatial plan is implemented correctly and will decrease to 32.15% if the land subsidence is stopped. The model simulation also showed that the current tidal inundation system would not be effective in future worst-case scenarios. From the results of both phases, it can be concluded that the coastal area in the north coast of Central Java is vulnerable to risk, and a good spatial plan and controlling the land subsidence can also limit the increase of the risk in the future