Cempaka Tropical Cyclone (TC) occurred on November 27, 2017, at the Indian Ocean and induced high rainfall leading to flooding in the southern part of Java island. One of the most affected areas is the karst landscape of Gunung Sewu. This study aims to identify flood inundated areas caused by the Cempaka TC in the Gunung Sewu karst landscape through satellite imagery of Sentinel 1B. Sentinel 1B imageries were used to extract the flood inundation area through the processing of random forest (RF) and the thresholding value (TV). A significant difference in flood inundated area was obtained between RF and TV, where RF shows a result of 526.07 ha of the total inundated area while the TV shows a result of 105.46 ha. However, both methods show the same sequence for three regencies with the highest total flood inundated area (Gunungkidul, Pacitan, and Wonogiri) and show the same range of each flood inundated area (0-0.5 ha). This distribution of flood inundated area can be used by policymakers as a basis for spatial planning in Gunung Sewu karst landscape.
Sinkhole is a depression of the land surface, causing hazardous effects on the karst landscape. Land subsidence is a phenomenon of sinkhole formation due to karstification. Land subsidence associated with any of the existing evaporite-karst sinkholes Land subsidence is a gradual settling or sudden sinking of the Earth’s surface, which can be very dangerous as it relates to life on the surface and infrastructure planning. Ponjong and Semanu District, Gunungkidul Regency, are included in the Gunung Sewu Karst area, with landscapes highly influenced by the karstification process. Decision-makers need increasing attention to make assessments also mitigation on karst management. This study aims to determine the potential areas of land subsidence caused by natural factors in the karst landscape in the Ponjong and Semanu District, Gunungkidul Regency using integrated geospatial technology. For making some maps, we initially need a process from SRTM. Land Surface Temperature map, The Normalized Difference Vegetation Index (NDVI) map, slope map, and geological map are integrated into a GIS platform using the scoring and matrix then the overlay method. Descriptive spatial analysis of potential subsidence area is based on land surface temperature, vegetation factor, slope inclination, and geological formation related to altitude. The results show that approximately 80 percent of Ponjong and Semanu District places are high potential land subsidence areas. Policymakers can use this distribution of the potential regions of land subsidence as essential spatial planning in Gunungkidul Karst, especially in Ponjong and Semanu district.
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