water Article Water Resources Allocation Systems under Irrigation Expansion and Climate Change Scenario in Awash River Basin of Ethiopia Mohammed Gedefaw 1,2, * , Wang Hao 2 , Yan Denghua 2, *, Tianling Qin 2 , Kun Wang 2 , Abel Girma 1,2 , Dorjsuren Batsuren 1,3 and Asaminew Abiyu 1 1 College of Environmental Science & Engineering, Donghua University, Shanghai 200336, China; abelethiop@yahoo.com (A.G.); batsuren@seas.num.edu.mn (D.B.); asaminew@yahoo.com (A.A.) 2 State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resource and Hydropower Research, Beijing 100038, China; wanghao@iwhr.com (W.H.); tianling406@163.com (T.Q.); pingguo88wangkun@163.com (K.W.) 3 Department of Environment and Forest Engineering, School of Engineering and Applied Sciences, National University of Mongolia, Ulaanbaatar 210646, Mongolia * Correspondence: mohammedgedefaw@gmail.com (M.G.); yandh@iwhr.com (Y.D.) Received: 11 July 2019; Accepted: 17 September 2019; Published: 20 September 2019   Abstract: Rational allocation of water resources is very essential to cope with water scarcity. The optimal allocation of limited water resources is required for various purposes to achieve sustainable development. The Awash River Basin is currently faced with a scarcity of water due to increasing demands, urbanization, irrigation expansion, and variability of climates. The excessive abstraction of water resources in the basin without proper assessing of the available water resources contributed to water scarcity. This paper aimed to develop a water evaluation and planning (WEAP) model to allocate the water supplies to demanding sectors based on an economic parameter to maximize the economic benefits. The water demands, water shortages, and supply alternatives were analyzed under different scenarios. Three scenarios were developed, namely reference (1981–2016), medium-term development (2017–2030), and long-term development (2031–2050) future scenarios with the baseline period (1980). The results of this study showed that the total quantity of water needed to meet the irrigation demands of all the stations was 306.96 MCM from 1980 to 2016. Seasonally, March, April, May, and June require the maximum irrigation water demand. However, July, August, and September require minimum demand for water because of the rainy season. The seasonal unmet demand is observed in all months, which ranged from 6 × 10 6 m 3 to 35.9 × 10 6 m 3 in August and May respectively. The trend of streamflow in Melka Kuntre was a statistically significant increasing trend after 2008 (Z = 5.33) whereas the trends in other gauge stations showed a relatively decreasing trend. The results also showed that future water consumption would greatly increase in the Awash River Basin. The prevention of future water shortages requires the implementation of water-saving measures and the use of new water supply technologies. The findings of this study will serve as a reference for water resources managers and policy and decision makers. Keywords: water allocation; WEAP model; scenario; climate change; Awash River Basin 1. Introduction The increasing demand of water resources in the world is the main problem for the sustainable utilization of water resources [1]. Water scarcity is mainly caused by over-exploitation of water resources, population growth, pollution, and increasing demand for economic development [2,3]. The ever-increasing population and economic development put more stress on the hydrological cycle Water 2019, 11, 1966; doi:10.3390/w11101966 www.mdpi.com/journal/water