**4. Conclusion**

During any river basin master planning, considering extreme hydrological events, such as floods and drought, are the important issues for sustainable water resource development. Otherwise, simply focusing on the investigation and assessment of the available natural resources in a specific river basin and utilization of the resource will never bring development. Particular attention is to be given to drought-affected areas and conjunctive use of ground and surface water is encouraged. Aridity is the general characteristic of an arid climate and represents a (relatively) permanent condition, while drought is temporary. In an arid climate, drought can still occur when local conditions are even drier than normal. But 90% of the reviewed studies in Ethiopia were conducted on arid and semiarid areas of the region. Generally, hydrological drought study lacked in the country. Therefore, in the future, it is important to focus on hydrological drought monitoring and forecasting to achieve the sustainable utilization of available water resources in Ethiopia.
