Development of an Extreme Rainfall-Based Hazard Index for the Air Bengkulu Watershed, Indonesia
DOI:
https://doi.org/10.21512/emacsjournal.v8i2.16557Keywords:
Analytical Hierarchy Process, Extreme Rainfall, Rainfall Hazard Index, WatershedAbstract
Extreme rainfall is one of the main hydrometeorological factors that drive flood-related hazards in tropical watersheds. However, individual rainfall indicators may not sufficiently capture the combined spatial characteristics of extreme precipitation. The objective of this research is to develop a Rainfall Hazard Index (RHI) for the Air Bengkulu Watershed, Indonesia, based on multiple indices of extreme rainfall. Daily rainfall data of four stations for the period 2007-2025 are analyzed to compute Maximum 1-Day Rainfall (Rx1day), Maximum Consecutive 5-Day Rainfall (Rx5day), Very Wet Days precipitation (R95p) and Rainfall Trend (RT). Rainfall trends were assessed by Mann–Kendall test and Sen’s slope estimator. Inverse Distance Weighted (IDW) interpolation was applied to generate spatial distributions. The indicators were combined with Analytical Hierarchy Process (AHP) weighting to construct the RHI. The RHI was classified into five hazard categories by Jenks Natural Breaks. The AHP results gave the highest weight to Rx5day (0.471) followed by R95p (0.284), Rx1day (0.172) and RT (0.073) with a Consistency Ratio of 0.0185. The hazard class of extremely high rainfall covered 60.73% of the watershed, mainly in the upstream areas. A preliminary comparison with historical flood records from the Regional Disaster Management Agency (BPBD) and direct field observations revealed a match at 11 of 15 locations (73.3%). These findings show RHI as a first stage spatial screening tool for rainfall-related hazards that can be used in watershed management and spatial prioritization rather than full flood prediction.
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