Ethiopia is constantly affected by shortage of water for rain-fed agriculture, mainly because of lack of proper water resources utilization and management practices. For efficient use of available surface water resources with balanced attention to maximize economic, social, and environmental benefits, it is necessary to have effective integrated water resources assessments and planning. Beles river basin is one of the most potential river basins in Ethiopia which is the main tributary for Blue Nile River Basin and accounting 14,200 km 2 . The objectives of this study was to assess the available surface water resources in the Beles River basin, using a surface water balance model simulation by HEC-HMS hydrological modeling system by estimating surface runoff and simulating hydrological processes due to distributed land use, soil, climatological and hydro-metrological condition in the entire river basin. DEM of four tiles (170/52, 170/53, 171/52 and 171/53 path/row) was downloaded from ASTER Global DEM (GDEM) then rectified, corrected and Geo-referenced to the UTM (WSG-1984 UTM-37N) projection system of the study area. Then GIS layers that were used as input data for the flow simulation were prepared using Arc GIS 9.3 and used in the HEC-HMS 3.5 calibration of the Beles River sub basin using daily precipitation and flow data river basin with aid of integrating remote sensing and GIS application tools using HEC-HMS. Therefore; surface water balance simulation using HEC-HMS model with the help of using remote sensing & GIS for integrated water resources management may be a better option to fill this gap in the river basin.10 Hence, the overall objective of this study is to assess surface hydrological dynamics and evaluate distribution and the available water resource using water balance model which can support planning and decision making process to improve water productivity for sustainable agricultural production in the entire river basin. The specific objectives are:I. To estimate surface runoff and evapo-transpiration distribution for sustainable water resource utilization in the entire river basin;II. To simulate hydrological processes using land use, soil, climatological and hydro metrological input parameters and generate data in Beles river basin and III. To estimate variations due to distributed land use, soil, climatological and hydro-metrological condition in the entire river basin. Materials and methods Description of the study areaThe Beles basin is situated on the Plateau of the north-western highlands and its one of the major tributary of Blue Nile. Its geographic location between from 10°56'00" to 12° 00'00" N latitude and 35°15'00" to 37°00'00" E longitude ( Figure 1) and total area of the basin is about 14,200 Km 2 . The topography of the area is mostly flat with altitudes between 458 m and 2729 m above sea level. The Beles basin is one of the most important basins in Ethiopia. It is one of the major sub-basins of upper Blue Nile basin. The recorded mean annual rainfall ranges from 700 mm t...

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This study was aimed to compare estimation methods of crop water requirement and irrigation scheduling for major crops using different models and compare the significance of models for adoption in different situations of the Metekel zone. Crop water requirement and irrigation scheduling of maize in selected districts of Metekel zone were estimated using CropWat model based on soil, crop and meteorological data, and AquaCrop based on soil, crop and meteorological data including Co 2 , groundwater, field management, and fertility status. Model performance was evaluated using Normalized Root mean square errors (NRMSE), model by Nash-Sutcliffe efficiency (NSE), Prediction error (Pe), and Model efficiency (MF). It is observed that the maximum reference evapotranspiration in the study area was found to be 7.1 mm/day in Guba and the minimum reference evapotranspiration was 2.9 mm/day in Bullen district. In all cases, the maximum ETo in all districts was fund to in March and the lowest in August. The maximum ETc of maize was found to be 702.4mm in Guba district and the minimum ETc was found to be 572.6mm in Bullen district using CropWat but the effective rainfall (Pe) for maize was determined as 185mm respectively in Wembera district. However, using the AquaCrop model the maximum ETc of 565 mm was recorded in Guba but 425 mm was recorded as a minimum in the Wembera district for irrigated maize in the study area. The study revealed that the irrigation scheduling with a fixed interval criterion for maize 10 days with 12 irrigation events has been determined. Moreover, furrow irrigation with 60% irrigation application efficiency was adjusted during irrigation water applications for all districts. The performance of the irrigation schedule and crop response was evaluated by the analysis results in the simulation using different models. It has been observed that there were a strong relationship and a significant relation between the simulated and observed values for validation. Hence, Normalized Root mean square errors (NRMSE), model by Nash-Sutcliffe efficiency (NSE), Prediction error (Pe), and Model efficiency (MF) showed that the AquaCrop model well simulated in all parameters considered. AquaCrop model is the most suitable soil-water-crop-environment management model, so future studies should suggest a focus on addressing deficit irrigation strategy with different field management conditions to improve agricultural water productivity under irrigated agriculture for the study area for major crops.

The objective of the study was to compare AquaCrop Model with CropWat Model to estimate crop water requirement and irrigation scheduling of maize in the Metekel Zone. It also tries to compare the efficiency of Models for adoption in different situations in the study area. Crop water requirement and irrigation scheduling of maize in the study area were estimated using the CropWat Model based on soil, crop, and meteorological data. However, AquaCrop Model wasbased on soil, crop, and meteorological data including Co2, groundwater, field management, and fertility management condition. From the study, it was observed that the maximum reference evapotranspiration in the study area was found to be 7.1 mm/day in Guba and the minimum reference evapotranspiration was 2.9 mm/day in the Bullen district. The maximum ETo in all districts was found to in March and the lowest in August. The maximum ETc of maize was foundto be 702.4mm in the Guba district and the minimum ETc was found to be 572.6mm in Bullen district using CropWat but the effective rainfall for maize was determined as 185mm in the Wembera district. However, using the AquaCrop Model the maximum ETc of 565 mm was recorded in Guba but 425 mm was recorded as a minimum in the Wembera district for irrigated maize in the study area. From the study, it was observed that irrigation scheduling with a fixedinterval of 10 days with 12 irrigation events performed best. Moreover, the result revealed that there was a strong relationship and a significant relation between the simulated and observed values for validation. The model performance indicators showed that AquaCrop Model was well simulated in all parameters considered. Therefore, AquaCrop Model was found to be the most suitable soil-water-crop-environment management Model. So future studies should focus onaddressing deficit irrigation strategy with different field management conditions to improve agricultural water productivity under irrigated agriculture for the study area for major crops.