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Evaluating the flood and drought hazards provides vital information for sustainable water resources management, particularly in semi-arid, water-deficit environments. Most prior studies were limited in exploring the flood and drought hazards, which are important for early warning systems and preparedness. This study characterized the hydrological extreme hazards on the Gereb-Geba reservoir, namely the Suluh, Genfel, and Agula rivers. Flood frequency analysis was performed using the fitted flood frequency distribution in MATLAB. The 2D hydrodynamic model HEC-RAS was implemented to produce a flood-inundation map. Meteorological, agricultural, and hydrological droughts were analyzed using the Standardized Precipitation Index (SPI), Vegetation Condition Index (VCI), and Streamflow Drought Index (SDI), respectively. Using the Generalized Extreme Value (GEV), the estimated flood magnitude showed an increasing tendency in all the rivers across all the return periods (2-, 5-, 10-, 20-, 50-, and 100-years). The reservoir inundated an area of 12.8 km 2 at an elevation of 1830 m.a.s.l. with a water depth of 80 m at the outlet. Suluh experienced more severe to extreme hydrological drought episodes than the Agula and Genfel rivers. Severe to extreme meteorological droughts were also observed in the respective catchments. Moreover, severe agricultural drought prevalence was also detected across all the river catchments. This study provides vital and comprehensive flood and drought information for water resources planning, management, and development.

Large-scale oceanic effects of El Niño Southern Oscillation and Indian Ocean Dipole on local rainfall and streamflow variability at the catchment scale have not been well studied. This study assesses the effects of El Niño Southern Oscillation and Indian Ocean Dipole on rainfall and streamflow variability in Geba catchment Tigray Ethiopia. Modified Mann–Kendall and Pettit’s tests were used to generally understand the overall trends and expected abrupt changes in rainfall and streamflow. We also applied correlation, explained variance, and multiple regression methods to evaluate the linkages, performance, and strengths between the sea surface temperatures and station rainfall and streamflow records. The rainfall trend of the study site did not change significantly. However, the streamflow showed a significant change with the mixed increase or decrease trends. The abrupt changes in rainfall and streamflow are strongly linked with El Niño Southern Oscillation and La Niña episode events. Rainfall in the rainy season (July, August, and September) enhanced due to La Niña events and suppressed with El Niño episodes. The stream flow of the study catchment gets declined during strong El Niño years (e.g., 1982, 1983, 1987, 1997, and 2015) while also reach its peak during the strong La Niña years (1988, 1999, 2000, 2008, and 2011). Our finding ratified that 39% of rainfall and 38% of streamflow variabilities in the Geba catchment are explained by the combined effects of El Niño Southern Oscillation and Indian Ocean Dipole signals.

In arid areas prone to desertification and soil erosion, the effectiveness of radical bench terracing in reducing drought risk is dependent on its correct implementation. However, the relationship between proper terracing implementation and the landscape capacity of holding soil moisture is still not understood. Moreover, spatial patterns of Soil Water Content (SWC) within the same terraced hillslope are weakly studied. The present paper analyses SWC variations in four newly implemented terraced sites in Tigray Region, Ethiopia. In all sites, terraced areas show SWC significantly higher than non-terraced ones, with the lower part of the terraced hillslope more humid than the others. A Multiple Linear Regression (MLR) analysis highlighted significant dependency of SWC from the date of analysis, the position in the terraced slope, and its significant positive correlation with the percent of Water Stable Aggregates (WSA) analyzed at the study sites. Since high soil disturbance induces low soil aggregates stability, this result shows how low soil disturbance can significantly increase SWC of radical terraces. Overall, the results of the present paper testify the good performances of bench terraces in Northern Ethiopia in terms of soil water conservation, and can represent a benchmark study informing future terracing implementation in some arid and semi-arid agricultural areas of the world.

The study was conducted to evaluate surge irrigation against continuous irrigation in terms of irrigation and water use efficiencies to produce onion. It was carried out at Mekelle Agricultural Research Center, Ethiopia on 70 m long and 0.6 m center-center spacing furrows of 0.26% average slope on a clay soil. The treatments consisted of factorial combination of two discharges (Q ₁ = 1 l/s and Q ₂ = 2 l/s) and three-cycle ratios (CR₁ = 1/3, CR₂ = 1/2, and C = 1 for continuous irrigation). Surge flow treatments advanced faster than the respective continuous flow treatments with surge flow treatment SF₂₁ being the fastest. The best value of application efficiency (60%) was achieved for SF₁₁ and the least (46%) for CF₂. The maximum (87%) and minimum (68%) values of distribution uniformity were obtained for cycle ratios CR₁ and C, respectively. Storage efficiency was highest (89%) for CF₂ and lowest (78%) for SF₁₂. Onion yield was significantly affected (p < 0.05) by the interaction effect, the highest (14,400 kg/ha) and the lowest (13,363 kg/ha) yields were obtained for SF₁₁ and SF₂₁, respectively. The maximum irrigation water use efficiency (2.27 kg/m³) was observed for SF₁₁ and the minimum (1.68 kg/m³) for CF₂. Surge irrigation was found to be a promising irrigation practice for onion production in the study area as it saves water, reduces irrigation period, and increases the crop yield.

Ethiopia is one of the poorest countries in the world. It is characterised by famine as a result of high population pressure, resource base degradation, and insufficient rainfall for rainfed agriculture. On the other hand, it is endowed with a huge annual water resource potential of about 110 billion m3, a potentially irrigable land of 3.6 million ha and productive manpower of about 48% of the total population. In view of these facts, the Agricultural Development-Led Industrialization (ADLI) development strategy adopted in August 1992 has set irrigation as a major pillar to increase food production and to achieve food self-sufficiency. The earthen dam irrigation development program in the regional state of Tigray is part of this initiative. The effective and sustainable utilization of the limited water resource is very crucial in arid and semi-arid areas like Tigray. The results of the study carried out at two earthen dam irrigation schemes indicated that the schemes are playing a very important role in improving the livelihood of the poor farmers. However, the research has also identified problems that may affect the sustainability and ultimately the food security effort of the regional Government. These are related to sedimentation in the reservoirs, reservoir operation schedule, water management, salinity, policy, institutional and socio-economics issues. The major lesson learnt from the study was that the success and sustainability of the irrigation schemes depend on the level of integrated approach in the development and management. The integrated approach need to take the whole irrigation scheme as one entity, including the catchment, the reservoir and dam, the command area, the beneficiaries and downstream impacts. Failure or weakness in one of the links may affect the entire system.

IntroductionThe climate of Tigray, northern Ethiopia, is mainly semi-arid and most of the region experiences erratic and inadequate rainfall that remains insufficient for crop production. Climatic change over the past decades has resulted in a temperature increase of about 0.2 ºC. This has resulted in a notable decrease in the amount of, and altered the distribution of, precipitation in Ethiopia (NMSA 2001). The distribution of mean annual rainfall over the country is characterized by large spatial variation and ranges from 2000 mm in some pockets in the south-west to less than 100 mm in the Afar lowlands in the north-east. Trend analysis of annual rainfall showed that rainfall levels remained more or less constant when averaged over the whole country while a declining trend has been observed over the northern half and south-western Ethiopia. The average annual minimum temperature has been increasing by about 0.25ºC while average maximum temperature has been increasing by about 0.1ºC every decade (NMSA 2001).Climate change may have far reaching implications for Ethiopia for various reasons. The country’s economy depends mainly on agriculture, which is very sensitive to climatic variations. A large part of the country is arid and semiarid, and is highly prone to desertification and drought. Ethiopia has a fragile highland ecosystem, which is currently under stress due to population pressure. Forest, water and biodiversity resources of the country are also climate sensitive. Vector-borne diseases such as malaria, which are closely associated with climatic variations, affect Ethiopia. The country has experienced environmental problems such as recurring droughts, high rates of deforestation, soil degradation and loss, overgrazing, etc., which may be exacerbated by climate change. Climate change is, therefore, a case for concern (NMSA 2001). Assessing vulnerability to climate change and exploring adaptation options should therefore become a critical element of the development programme of the country. Among the possible adaptations to recurrent drought is the promotion of small-scale irrigation agriculture through small household-managed water harvesting structures.