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.
Highlights
Cempaka Tropical Cyclone (TC) that reached its mature stage on 27 November 2017 in Indian Oceania raised the rainfall in southern part of Java Island significantly [1,2]
We found that the random forest (RF) and thresholding value (TV) methods could be used to map inundation in the karst region
The narrow range of radar backscatter values between standing water and the steeply sloped areas often found in the Gunung Sewu karst landscape in the form of conical hills makes the results of flood inundation detection using the RF and TV methods are not entirely accurate with a tendency to overestimation (Fig. 10)[45,46]
Summary
Cempaka Tropical Cyclone (TC) that reached its mature stage on 27 November 2017 in Indian Oceania raised the rainfall in southern part of Java Island significantly [1,2]. The District of Gunungkidul, Wonogiri, and Pacitan were the most affected region of that cyclone with average daily rainfall of 286-383 mm/day between 27 to 29 November 2017 which caused flooding in the area of Gunung Sewu karst landscape [3,4,5]. The mapping of flood inundation is prevalent in the context of future disasters effect prevention [7]. The result of flood inundation mapping has much benefit to raise public awareness and to improve the assessment for future disaster condition [8,9]. Aerial photogrammetry and optical satellite imagery have been well known as acquisition methods for flood inundation mapping [10,11,12,13]. Aerial photogrammetry is expensive and discontinued, optical satellite imagery is often hampered by the cloud [14,15,16]
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