Flood Inundation Mapping of Cempaka Tropical Cyclone Effect in Gunung Sewu Karst Landscape Using Sentinel 1

Abstract

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.