ANALYSIS OF FLOOD INUNDATION DISTRIBUTION BASED ON METEOROLOGICAL FACTORS AND LAND COVER USING HEC-RAS IN THE TUKAD BADUNG WATERSHED (CASE STUDY: THE BALI FLOODS OF SEPTEMBER 9–10, 2025)
Abstract
Abstract:  The September 9–10, 2025, flood in the Tukad Badung Watershed was the most severe event of the past decade, triggered by extreme rainfall that resulted in 16 fatalities and widespread inundation across several regencies and cities in Bali. This study aims to analyze meteorological conditions and land cover during the flood event and to model flood inundation using HEC-RAS software. Data used include meteorological parameters (rainfall, temperature, air pressure, wind speed and direction, and evapotranspiration) and land cover (land use land cover and soil type). Results indicate abnormal meteorological conditions at both observation stations: ARG Abiansemal recorded rainfall of 284.6 mm, temperature of 22.72°C, pressure of 1,004.34 hPa, wind speed of 3.3 m/s, wind direction from the northwest, and evapotranspiration of 0.171–0.172 mm/h; while AWS Tuban recorded rainfall of 116 mm, temperature of 23.59°C, pressure of 993.23 hPa, wind speed of 4.48 m/s, wind direction from the northwest, and evapotranspiration of 0.120–0.121 mm/h. built up area-dominated land cover and clay loam soils from upstream to downstream further intensified the flooding. HEC-RAS simulations produced inundation depths of 1–3 meters, accurately representing actual flood conditions with a hit rate of 83.33%.
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Abstrak: Banjir yang terjadi pada 9–10 September 2025 di Daerah Aliran Sungai (DAS) Tukad Badung merupakan peristiwa terparah dalam satu dekade terakhir, yang dipicu oleh curah hujan ekstrem yang mengakibatkan 16 korban jiwa dan genangan luas di beberapa kabupaten dan kota di Bali. Penelitian ini bertujuan untuk menganalisis kondisi meteorologi dan tutupan lahan selama peristiwa banjir tersebut serta memodelkan genangan banjir menggunakan perangkat lunak HEC-RAS. Data yang digunakan meliputi parameter meteorologi (curah hujan, suhu, tekanan udara, kecepatan dan arah angin, serta evapotranspirasi) dan tutupan lahan (penggunaan lahan, tutupan lahan, dan jenis tanah). Hasil penelitian menunjukkan kondisi meteorologi yang tidak normal di kedua stasiun pengamatan: ARG Abiansemal mencatat curah hujan sebesar 284,6 mm, suhu 22,72°C, tekanan 1.004,34 hPa, kecepatan angin 3,3 m/s, arah angin dari barat laut, dan evapotranspirasi sebesar 0,171–0,172 mm/jam; sedangkan AWS Tuban mencatat curah hujan sebesar 116 mm, suhu 23,59°C, tekanan 993,23 hPa, kecepatan angin 4,48 m/s, arah angin dari barat laut, dan evapotranspirasi sebesar 0,120–0,121 mm/jam. Tutupan lahan yang didominasi kawasan permukiman dan tanah lempung liat dari hulu ke hilir semakin memperparah banjir. Simulasi HEC-RAS menghasilkan kedalaman genangan 1–3 meter, yang secara akurat menggambarkan kondisi banjir sebenarnya dengan tingkat akurasi sebesar 83,33%.
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