Areal reduction factor estimation for flood risk assesment towards sustainable disaster management in North Coastal Area of Central Java Indonesia

Sustainable flood risk assessment relies heavily on areal reduction factor (ARF). Large mistakes in the calculations of design rainfall might results in significant error in the calculation of design discharge. ARF is used to transform estimates of point rainfall to estimates of areal-averaged rainfall. Point rainfall can only represent a limited area. If used for a larger area, the actual rainfall may be much less than the observed rainfall. The North Coastal Area of Central Java is one area that has major risk of flood disaster. Therefore, it is necessary to develop ARF formula in this area to obtain more accurate design rainfall. Rainfall data from five rainfall stations in the Bodri-Kuto River Basin located in the north coastal Area of Central Java were used for calculating ARF. ARF was applied to one of the watersheds in the North Coastal Area of Central Java, namely the Tuntang watershed, to test its accuracy using the MAPE test. Based on the results of the analysis, the formulation of ARF = 18.248.A-0.499 was obtained. The results of the MAPE test for the Tuntang watershed are 8,201. The results of the accuracy test are acceptable so that the ARF formulation can be used.