Spatial flood risk mapping in east Java, Indonesia, using analytic hierarchy process — natural breaks classification

East Java is one of the provinces in Indonesia that is often hit by floods. Recorded about 170 data flood disaster since 2011 to 2015 that hit the 31 districts and cities in East Java. The government's efforts in dealing with flood disaster require a decision support system in determining the areas to be targeted in the flood disaster mitigation process. National Disaster Management Agency, called BNPB, has issued guidance documents in conducting disaster risk mapping in Indonesia based on threat, vulnerability and capacity level. Index method is used to calculate the risk value based on a threshold nominal value of the certain range, even though some of the criterias involve preference values. This research proposes a new hybrid analytic hierarchy process (AHP) — natural break classification strategy to calculate flood risk index to solve the combination of nominal and preferences values of criterias that produce Spatial Decision Support System (SDSS). AHP method is used to calculate priority value of assessment according to hazard, vulnerability and capacity indexes. The priority value that is obtained from AHP method is classified by natural break into three level of flood risk consist of low, medium and high Flood risk mapping with AHP method — natural break obtain an effective classification than the index method.