Indonesia: Threats to physical urban water problems

The world population percentage placed Indonesia in fourth place of the highest populated countries in the world. The majority of Indonesians live in an urban area. Java Island is the highest populated island in Indonesia, especially in Jakarta, Semarang, and Surabaya. This study showed the flood depth in these three cities, which has become a yearly threat during the rainy season. At the same time, another problem due to water withdrawal was analyzed. Land subsidence has occurred due to simultaneous water withdrawal and overload of alluvial soil due to land-use conversion. A remote sensing data and geographical information system (GIS) took account in this analysis to achieve the aim of this study. The hydraulic model was created to produce a flood depth map, and differential interferometric synthetic aperture radar (DInSAR) technique generated a land subsidence map. This study aims to show the problem in these three cities related to water in urban areas. This study found that all study areas had a severe risk of flood and land subsidence. Semarang received more threats to flood and land subsidence comparing to the other cities.