Climate-Driven Transformations in Flood Hydrograph Characteristics in a Mountainous Catchment

Flooding in the mountainous catchments remains a major concern due to its steep terrain, intense monsoon rainfall, and rapidly changing climate. The complex hydro-geomorphic setting makes communities, agricultural systems, and critical infrastructure highly vulnerable to flood hazards in the mountainous regions. As climate change accelerates, shifts in precipitation patterns, storm intensity, and temperature regimes are expected to influence the magnitude, duration, and timing of flood events. Despite these emerging risks, the climatic controls on annual flood hydrographs and their future trajectory in the Himalayan mountains of Nepal remain insufficiently understood. A clearer understanding of how flood characteristics are evolving under a warming climate is essential for improving hydrologic design standards, strengthening flood forecasting systems, and guiding risk reduction strategies in this mountainous environment. This study investigates historical (1986–2019) and projected future (2031–2100) changes in annual maximum flood hydrograph properties across the western Nepal mountains. Key attributes, including flood peak, flood volume, flood duration, and timing of occurrence, are evaluated to characterize how flood behavior has responded, and is likely to respond, to changing climatic conditions. Additionally, shifts in flood seasonality and the sensitivity of flood peaks and volumes to variations in precipitation and temperature are examined to identify the dominant climatic drivers shaping future flood regimes. The historical analysis reveals marked interannual variability in flood characteristics, influenced by monsoon dynamics, catchment topography, and antecedent moisture conditions. Future climate projections indicate a pronounced transformation in flood behavior, with flood peaks expected to increase and flood durations to decrease, suggesting a trend toward more intense and short-lived flood events. The timing of annual maximum floods is also projected to shift later into the monsoon season, reflecting changes in seasonal rainfall distribution and catchment wetness. Sensitivity assessments demonstrate that changes in event-scale precipitation exert a stronger influence on flood peaks and volumes than temperature variations, underscoring the critical role of rainfall intensity in steep mountainous catchments. While temperature-driven effects are evident, they remain secondary compared to precipitation-driven changes. Overall, the findings highlight the need to incorporate climate-informed variations in flood hydrograph characteristics into regional water management, hydro-infrastructure planning, and disaster risk reduction frameworks. This study provides valuable insights into evolving flood hazards and supports the development of adaptive and resilient strategies for safeguarding vulnerable communities in the Nepal mountainous region.