Obtaining holistic solutions for wet extremes and flooding in the Awash basin, Ethiopia  

The Awash basin of Ethiopia experiences frequent climate extremes-related disasters. Climate change is contributing to frequent flooding in different parts of the basin. This study explores the drivers of extreme rainfall, the multi-causality and consequences of flooding, governance, and policy implications using a combination of interdisciplinary approaches. The multi-dimensional perspective includes analysis of hydroclimatic variables at the basin level including global drivers, flood characterization, and understanding of affected communities at different parts of the basin through examining the experiences of different water and land users. The study covered urban and rural areas, small-scale agricultural, and pastoral or agropastoral catchments. To obtain diversified perspectives consultation with various basin stakeholders was conducted. By considering the 2020 extreme wet season the study aims to contribute to future management practices that might adapt to extremes and associated floods. The results show that recent rainfall extreme during the summer of 2020 occurred in unusual parts of the basin. Compared to the 1981-2010 baseline the lower part of the basin had a rainfall anomaly of more than 50%. Moreover, antecedent rainfall conditions during April-June contributed to saturating the soils as the months before July were wetter than the base period on average by 62%. The soil moisture content conditions were wetter than average from 10 to 40% in these antecedent months. Unusual rainfall in terms of location, magnitude, and timing is the major cause of flooding in the cases of 2020.  First, the western part of the lower basin received higher rainfall than normal earlier in the season. Then, in the later part of the season, the upper basin received high rainfall that increased the amount of water in upstream rivers which contributed to the massive flooding in the lower basin. This characterizes the 2020 flood occurrences by early onset and delayed recession. The extreme rainfall collided with weak La Nina and positive Western Indian Ocean as global drivers. There are other contributing factors that exacerbate the cause and impacts of flooding on communities. This includes challenges in river morphology, flood forecasting, reservoir management, and differences between private investors and local vulnerable communities in managing extreme cases. For instance, the Awash River broke off its normal course during 2020 extreme rainfall. Uncontrolled water diversion by farmers for irrigation created new water pathways. Low quality of engineering structures e.g., dikes failed to prevent extreme floods. Land use changes, such as urbanization and deforestation increased erosion and blocked drainage ways. Lack of coordination among institutions, weak collective action and governance aspects are exacerbating factors of climate extreme impacts on vulnerable communities. A holistic approach to solving the devastating impact of climate extremes provides better understanding of the multi-causality and multi-dimensionality of water-related risks, to support implementation of adaptive management and coordination approaches in monitoring human-physical systems interactions across sectors.