| Abstrakt: |
Assessing flood frequency in a changing climate is crucial for evaluating and managing flood risk in river basins. Often, rivers lack sufficient observational streamflow data, particularly for annual maximum flood discharge analysis, either due to ungauged or inadequate record lengths. However, most river basins have access to rainfall data with longer records. Hydrologic modeling, a valuable tool for simulating streamflows using available rainfall data, can address the lack of longer peak discharge values necessary for reliable flood-frequency analysis. A popular hydrologic model, HEC-HMS, was employed to establish rainfall-runoff relationships and develop a flood discharge simulation tool for the Bagmati river basin in Nepal. The Bagmati river basin, encompassing 593 km² catchment area upstream of the Khokana hydrological station, includes Kathmandu valley which has faced frequent flooding in recent years. The flood discharge simulation model was calibrated and validated using daily discharge data of three largest flood events between 1995 and 2015. The performance of the flood simulation model was found satisfactory based on visual (hydrographs) and statistical (Nash-Sutcliffe Efficiency and Percentage Bias) parameters. To simulate annual maximum discharge values and assess flood frequency under climate change scenario, NHRCM precipitation data with 2-km spatial resolution was utilized. Comparing flood-frequency analysis results between current (1981–2000) and future (2080–2099), annual daily maximum discharge values for various return periods revealed a significant increase in extreme flood events in future. The increase in maximum discharge for current and future climate conditions can be reflected with the values of 1362 m³/s and 1818 m³/s, respectively. The extreme flood events are expected to be higher in future considering similar flood discharge values of 1707 m3/s and 1771 m3/s for 100-year return period in the current climate and 25-year return period in the future climate conditions respectively. This underscores the pressing need for flood managers and policy makers to focus on reducing the heightened flood risks due to climate change. |
Full text from SpringerLink