Assessing the influence of watershed characteristics on flood vulnerability in Nyirakigugu cell of Jenda sector, Nyabihu district in Western Province of Rwanda

Introduction Flooding is one of the most widespread climates‑related disasters, and Rwanda’s northwestern volcanic highlands are highly vulnerable due to steep terrain, clay soils, and rising rainfall. Methods This study aimed to assessed seven watershed characteristics: elevation, slope, drainage density, stream proximity, rainfall, land‑use/land‑cover (LULC), and soil hydrologic groups; and integrated them into a Flood Vulnerability Index (FVI) using Analytic Hierarchy Process–Multi‑Criteria Decision Analysis (AHP‑MCDA) in ArcGIS Pro 3.6. Spatial datasets included a 10‑m DEM, METEO Rwanda rainfall, and Ministry of Agriculture soil records. Parameters were reclassified on a 1–5 scale using Jenks natural breaks and national guidelines. AHP weights were elevation 28.5%, slope 19.6%, drainage density and stream distance 14.8% each, rainfall 11.2%, LULC 6.5%, and soil 4.6% with a Consistency Ratio of CR = 0.034, confirming acceptable matrix consistency. Results and discussion Results show Nyirakigugu Cell (408.8 ha) is highly exposed: 63.4% lies below 2,400 m, 45.7% has gentle slopes ≤16%, and 23.6% is within 20 m of streams. Rainfall rose by ~25% between 2001 and 2021. Land‑use change revealed a threefold expansion of Nyirakigugu Lake (8.6 to 25.3 ha), 99% loss of tree plantations, and growth of built‑up and cropland. The composite FVI shows 21.3% of the cell is very highly vulnerable and 24.1% highly vulnerable, concentrated in southeastern valleys and lake margins, while only 11.3% is very low vulnerability in uplands. Conclsion These findings provide spatial evidence to guide land‑use planning, riparian buffer enforcement, reforestation, and climate adaptation in Nyabihu District and similar highland catchments in sub‑Saharan Africa.