Characteristics of hydrological extremes in Kulfo River of Southern Ethiopian Rift Valley Basin

Comparing surface water supply index and streamflow drought index for hydrological drought analysis in Ethiopia

Recently, floods and drought have become common natural hydroclimatic hazards in several countries. Consequently, the identification of an appropriate drought index is now a challenging task for researchers. It is obvious that there is not a single best drought index; rather a comparison of indices will give a relative option. The objective of this study was to compare two hydrological drought indices; the modified surface water supply index (M1SWSI) and streamflow drought index (SDI) over eight river basins, in Ethiopia. The M1SWSI and SDI value was computed from 1973 to 2014 using 34 streamflow stations, 42 rainfall gauge stations, and 3 lake-level data. The two indices results showed that the 1980s were the most severe drought years for all river basins. But for the case of Genale Dawa and Wabishebele basins, the drought severity increased from 2000 to 2014. Hydrological drought analysis using SDI has more drought occurrence frequency than M1SWSI. In all river basins from 1973 to 2014, there were a total of 18 severe drought events when using M1SWSI, but there were a total of 39 severe and 12 extreme drought events when using SDI. This implied that M1SWSI reduced the occurrence probability of severe drought by 53.85% and extreme drought by 100%. It is known that Ethiopia is stricken by extreme droughts in the last few decades. But M1SWSI doesn't detect those invidious drought events. In this study, SDI is found to be a better hydrological drought index. Therefore, policy and strategic planners, master plan developers, and decision-makers can use SDI to analyze historical and future hydrological drought trends to develop effective drought mitigation measures.

Quantifying Sustainable Land-Water-Energy-Food Nexus: The Case of Sustainable Livelihoods in an East African Rift Valley

The sustainable management of Land-Water-Energy-Food (LWEF) nexus requires an environmental characterization that allows the comparison of complex interlinkages between nexus resources and livelihoods. This complexity makes this characterization difficult coupled with limited study in quantifying sustainability of LWEF nexus and its linkage with livelihood. Therefore, the present study aimed to investigate the link between sustainable LWEF nexus and livelihoods. In order to address the objective the proposed methodology starts with a detailed identification of LWEF and livelihood indicators which depicts well-defined, shared, and holistic methods to evaluate sustainability. With this we used analytical hierarchy process and pair wise comparison matrix in combination with weighting model. The result of composite LWEF nexus index was 0.083 representing, low sustainability. Besides, this composite index implies the use and management of LWEF nexus resources in the study area is very low, as the composite index approach to 1, the use and management of nexus resources are in a good condition which characterized by sustainability. This could be linked with nexus resources consumption, use, and management. From the analysis of the weight of land, water, energy and food nexus resources, the highest weight was observed for food. The focus of on food production only shows no clear synergy on provisioning, supporting or regulating nexus resources to address livelihoods. The result further showed that LWEF nexus resources have strong correlation with livelihoods. This was evidenced by social (r > 0.8, p < 0.01), natural (r > 0.3, p < 0.05) and physical (r > 0.6, p < 0.01) livelihood indicators showed strong positive correlation with LWEF nexus resources. Based on the finding of the study, it was observed that managing nexus resources not only provide a significant contribution to achieve sustainable LWEF nexus, but also be effective for enhancing livelihood through food security. This could be attained by strong evidence based policy to ensure sustainable use of nexus resources. The results provided by this study would serve as the foundation for future study, policy formulation and implementation.

Study on the theories and methods of ecological flow guarantee rate index under different time scales

Human activities have altered the region's natural attributes to a certain extent, leading to the competition of resources. As a result of the contradiction between water use inside and outside the river, the river ecosystems are under increasing pressure. Ecological flow has been proposed to ensure the health of the river ecosystem and habitat integrity. However, there are few special studies on its guarantee rate and lack of systematic analysis. To scientifically evaluate the ecological flow guarantee rate, this study proposed an ecological flow guarantee index for long-time by frequency analysis and an ecological flow guarantee index for short-time by Satisfaction Rate. Taking four typical sections of the mainstream of the Huai River as the research objects, we evaluated the ecological flow guarantee rate at different time scales based on the runoff sequence from 1956 to 2018. It was found that over the mid-long term scale (multi-year series), the guarantee rate of each section during the non-flood period reached 87%, while the guarantee rate during the flood period was about 83%. Over a short time scale (day series within the year), taking typical years of wet, normal, dry, and withered years to calculate the guarantee rate within the year, the average ecological flow guarantee rate reached about 70%. In practice, the joint application of the mid-long term and short-term ecological flow guarantee rate can take into account both long-term planning and short-term regulation, ensuring the sustainable development of river ecosystems in all aspects.