Flood Change Detection, Attribution and Management Implication in Data-Scarce Watersheds: A Case of Wabi Shebele River Basin, Ethiopia
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Date
2022-03
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Addis Ababa University
Abstract
Trends and variability of hydroclimatic extremes have received excessive attention in many hydrological modeling studies. However, many scientists are still uncertain to attribute the proportion of hydrologic variability is driven by climate change/variability and anthropogenic factors, particularly in tropical catchments. Wabi Shebele River Basin in Ethiopia experiences flooding with limited availability of the type data is used as a case study to investigate changes in flood discharges and potential driving factors affecting hydrologic response changes and management implication of understanding flood variabilities. Both statistical non-parametric tests and SWAT hydrologic model are used in flood change detection and attribution process. Among the discharge-based flood indicators, annual maximum series (AMS) and peak over threshold (POT) are used to analysis flood time series. Overview of flood discharge analysis indicates the increasing tendency of flood events throughout the basin since 2000. The seasonality analysis reveals cycles of significant extreme high river flows at five to ten-year intervals in the river basin. Precipitation extremes show an increasing trend in the western and eastern upper basin and a decreasing trend in the middle between 1980-2018. The assessment upon driving forces of floods: rainfall, drainage area, elevation, slope, sand soil, forest, and agricultural land coverage identified as the most influential variables in flood formation of the basin. The correlation analysis between extreme streamflow with precipitation and global climate indices reveals a moderate to high correlation value. The semi-distributed hydrological model (i.e., SWAT) conducted to disentangle the impact of climate change and LULC change on flood hazard showed that precipitation and agricultural land coverage led to increment in flood indices. In the middle and upper parts of the Wabi Shebele basin, streamflow increases with increases in agricultural land, and forest coverage decrease. The simulation of hydrologic response to climate change in the future (i.e., 2041-2060 and 2081-2100) showed that the river basin is likely to experience an increase in flood hazard with an increase in precipitation in the future as temperatures increase less than 2oC. Finally, the study on the implication of flood variability revealed that socio-economic damages follow a similar trend tendency to flood variabilities in the river basin. In such cases, development-based climate adaptation mechanisms and flood risk management strategies need to placed. In transboundary river basins like Wabi Shebele, floods have transboundary consequences which need cooperation between riparian countries for Integrated Flood Management (IMF).
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Keywords
Flood Change Detection, Data-Scarce Watersheds, Wabi Shebele River Basin