Estimation of Current Water Use over the Complex Topography of the Nile Basin Headwaters: The Case of Ghba Subbasin, Ethiopia

Quantifying the available and useable water is critical work in any water resource study and design project. However, it is challenging to provide a robust and accurate estimation of water use and distribution for better water resource management and planning. is study aims to estimate the water use by dierent sectors, including water supply and irrigation sectors, by adopting estimated demand and supply water quantity. e current total population of the subbasin has been estimated to be 1.21 million. us, in the subbasin, current water use is estimated as follows: domestic and nondomestic water use in the rural area is 3.5Mm/ year and 0.174Mm/year, respectively. e domestic water use of the towns is 12.77Mm/year. e industrial water use of the urban areas is 21.2Mm/year, whereas the commercial, public, and institutional water use are 1.87Mm/year. e real loss for all the water supply uses is 7.8Mm/year. us, the total current water supply uses are about 47.225Mm/year. From the existing irrigation schemes, about 10,254.8 ha areas are irrigated by both smallholders and dierent investors, growing vegetables, cereals, and fruit trees. e annual irrigation water requirements of these schemes are computed to be 151.55Mm. Livestock water demand of the subbasin was assessed and estimated based on the population and consumption rates of the species. Currently, the subbasin has a total livestock population of 1,527,835, and the water demand of which is estimated at 5.3Mm per annum. Hence, the total current water use estimate of the subbasin is 204.1Mm.


Introduction
e rapid growth of the population is causing an alarming demand increase in freshwater resources (e.g., lakes, rivers) of the world [1][2][3]. Continuously people who are living in di erent states or even within the same boundary are creating con icts over water that they withdraw from common sources, often and even decades pass by, but such water disputes are not resolved [4,5]. Water use is often metered in all other sectors except in the agricultural sector. In this paper, we examined a case study of current water use estimates in the Ghba subbasin using geographical information system (GIS) and collected data. Several studies, e.g., [6][7][8], have applied the same techniques for the estimation of agricultural water use using GIS and collected data.
Before the assessment, the study brie y reviewed FDRE Constitution [9], Water Resources Management Policy [10], Water Resources Management Proclamation [10], Water Resources Management Regulations [10], Nile Basin Initiative Reports [11], Central Statistical Agency Reports forecasted the population of Ethiopia from 2014 to 2017 [12], and another related strategic document of water resource management policy (WRMP) prepared and ratified by the Ministry of Water and Energy. e subject of water allocation planning and its sustainable use is directly addressed in the objective of WRMP of the country, which states: ". . . to enhance and promote all national efforts towards the efficient, equitable and optimum utilization of the available water resources of the country for significant socioeconomic development on a sustainable basis" [10].
Currently, in the study area, many investors and local farmers are using different sizes of pumps upstream of the river for irrigation purposes.
is water abstraction is done without knowing their current water use, which sometimes creates a violent water conflict.
us, the economic water scarcity in the subbasin is threatening the livelihoods of smallholder farmers, investment activities, and unique biodiversity resources.
is situation has made the need for wise water management, which includes demand planning and water allocation plans, more urgent than ever. erefore, the motto of this manuscript is to initiate and create a platform to assess the current water use with simple and more reliable techniques while dealing with the study and design of any irrigation and water supply projects. e study presented in this paper is designed mainly for the civil engineers engaged in the study and design of water supply and irrigation projects. Also, it helps policymakers to understand how the water resource system in a specific subbasin/catchment is behaving. erefore, the main objectives of this study are to estimate the water uses for water supply (domestic, nondomestic, Commercial, Public, and Institutional Water Uses), irrigated agriculture (all water supplied for irrigation farms and horticultural production, as well as water used to irrigate public and private plots), and the livestock water uses including the smallholders and investment enterprises.

Description of the Study Ssubbasin.
e Ghba subbasin is positioned in northern Ethiopia and covers from 38°38' to 39°48' Eastern longitudes and 13°14' to 14°16' northern latitudes ( Figure 1). e total area of the Ghba subbasin is about 5125 km 2 and comprises the Tigray regional state's capital city Mekelle. It forms the headwaters of the Upper Tekeze River basin, one of the major tributaries of the Nile River [13]. e landscape is characterized by highlands and hills in the north and north-eastern and highlands in the central part of the catchment [14]. e central highlands are divided by numerous rivers that flow towards the southwestern part of the subbasin and joins the main Tekeze River at Chemey [15]. e altitude varies from 3,300 meter above seas level (m.a.s.l.) at Mugulat Mountains near Adigrat town to 930 m.a.s.l. At the subbasin outlet [16]. e mean elevation of the catchment is 2144 m, with a standard deviation of 361 m indicating that the topography is very rugged [15].
Water demand datasets of water supply, irrigated agriculture, and livestock are required for the estimation of current water use analyses. ese numerical analyses directly depend on the quality and length of the time series data [17]. erefore, sufficient exertion was given to verify the accuracy of the dataset. ese datasets and methods are summarized in the following sections, and the overall method of current water use estimation is structured in Figure 2.
e Ghba subbasin is known for its high socioeconomic development in the Tigray National Regional state [21]. e size of the population in the subbasin is increasing so alarmingly because of emerging new cities and the expansion of industries, livestock, and modern irrigated agriculture [22]. e population water intake is taking a significant share of the water resources that are either from the river, runoff, deep well, and/or shallow well. erefore, computing their demand under current and future condition is vital to estimate the overall water supply sector water requirements [17].
Generally, there is uncertainty about the actual domestic water use dataset collected from the Woreda and regional stakeholders of the subbasin area [23]. us, to reduce the level of data uncertainty, water consumption of the urban and rural settlements was estimated based on per capita water uses recommended by GTP-II [24,25] and population size and indexed by the water supply coverage rate reported by the region [26]. According to the GTP-II plan, rural settlements in Ethiopia will enjoy 25 litters of per capita domestic water consumption by 2020 [27].
us, this minimum threshold value is adopted and factorized with the reported water supply coverage of the areas to estimate the actual domestic water consumption. Similarly, as per the GTP-II, e.g., [27,28] water supply service level standard, it is required to provide safe water in urban areas in accordance with the category of towns set in line with the population size (Table 1).
During the field assessment, large numbers of industries of all categories were identified in the subbasin. However, data on the actual water consumption rates of all the identified industries still had some uncertainties [29]. To reduce the level of uncertainties, good data values were adopted and factorized with the capacity of the industry, e.g., [24,30]. e water uses of facilities, such as schools, hospitals, hotels, and small commercial enterprises, and also public service water use centers were assesed. is depends on the extent and development of the institutional and commercial base and varies with the domestic water use [31,32]. As this water use data could not be available, the values are also estimated as a function of the domestic water use.

Advances in Civil Engineering
Long-term data from selected meteorology stations representing the climatic conditions of identified major agroecology of the Ghba subbasin was collected from the Ethiopian national metrological services agency [33] and compiled to get the long-term annual, monthly average data of rainfall, temperature, wind speed, sunshine hours, and relative humidity. e agricultural water demand assessment of the subbasin has considered major agroecological zone distribution that has a direct influence on the variability of irrigation water utilization and crop water requirements. Out of the identified 32 subagroecological zones of the country [34], two of them are found in this subbasin ( Figure 1), and about 15 meteorology stations of different classes are being located in the subbasin, and its periphery used as the climate data source for water requirement analysis after screening 11 stations in the basin were considered for further analyses considering the data quality, length, and agroecology conditions. e two major and subagroecology of the subbasin as reported by MOA [34] are Tepid to cool submoist mid-highlands (SM2), Hot to warm submoist lowlands (SM1), Tepid to cool submoist plains and mountains and plateau (MS2-5), and Hot to warm submoist river gorges (MS1-4), respectively ( Figure 1).
Here, the estimation of ETo was the first step to calculate the crop water requirement based on temperature, humidity, wind speed, and sunshine hours of the respective area [35,36]. e monthly ETo data was used for the computation and establishment of monthly crop evapotranspiration (ETc) [37].
e Penman-Monteith method [38], which is the most common and recommendable method, was used in estimating ET 0 and is adopted in the demand analysis (Table 2). e overall estimation method of irrigation water requirement estimate is characterized in Figure 3. e monthly water requirements of the recommended crops were then computed after fixing the evapotranspiration of the target area and identifying the crop coefficients of the existing irrigated crops [39,40]. Appropriate crop coefficient (Kc) values for each growth stage were selected and applied [41,42]. Accordingly, an overall average of 40% irrigation efficiency was used for all current irrigated areas after averaging the different efficiency used in the Woredas [26]. e annual crop water consumption of surface and other high-tech irrigation schemes operating in the subbasin was assessed by gathering data from respective irrigation users' offices, investors, and our measurement data for the selected projects from 2019 up to 2020. en, the gross irrigation use and the requirement were estimated based on the computed net irrigation requirements and irrigation efficiency depending on the purpose of the computation [43,44].

Agronomy Data.
Crop coefficient and length of growing period (LGP) are the required inputs to estimate the irrigation water requirement of proposed crops. To calculate the water requirement of the individual crop, appropriate crop coefficients Kc have been used, which represent the relationship between the reference crop water requirement and evapotranspiration ETo, this being x Kc � ET crop.
Accordingly, the crop coefficients were referred from different research works of literature and adopted with a monthly weighted value of them for each crop and their growth stages.
In the case of crop LGP, the required data were collected from the field for dominant crop varieties and also referred to different agronomy guidelines [45]. In the following Table 3, the crop coefficient and length of the growing period for each of the considered crops are presented. Hence, according to many researchers, e.g., [46][47][48], the equations recommended by FAO [45] to compute current irrigation requirements are summarized from equation (1)  where  Table 4 summarizes the current water supply capacity data for the Ghba subbasin collected from different water utility offices. Mainly the    Advances in Civil Engineering 5 sources are groundwater (GW) followed by surface water (SW). Table 5 data of existing irrigation areas in hectarage (ha) were collected from all stakeholders who are working on the development of irrigation infrastructure in the sun basin.

Results and Discussion
us, the urban categories in accordance with the population size and proposed service levels collected from the Woredas and the current water supply coverage are mapped in Figure 4. Figure 4 contains two pieces of information; category means according to the policy of the country based on the consumption rates, towns are categorized under categories 1, 2, 3, 4, and 5. us, the map tells which city is categorized where.
e second information is about the coverage of water supply in the study area and is described in percentages range. Hence, there are different methods of mapping; our choice of mapping was by district level, i.e., mixing of those areas in the range of the expressed percentage.

Nondomestic and Industrial Water Use Estimate.
us, as the major industries located in the subbasin have recorded water consumption data, other water uses were also estimated indirectly based on the data from similar industrial water use. Apparently, for planning purposes, a reliable Industrial Water Demand indicator was assessed and found to be more than 100% of Domestic Water Demand in large and medium towns and 20% to 60% of Domestic Water Demand in small towns [49]. is current industrial water use estimate is summarized in Table 6. ese water uses are categorized here as nondomestic and include all water consumption other than domestic in the case of rural areas. e nondomestic water uses for the rural areas were also estimated based on the domestic water use, which is assessed to be 5% [50,51]. Accordingly, current commercial, public, and institutional water use of both urban and rural areas in the subbasin are summarized in Table 7.
e loss of water from the existing water supply schemes is included in the estimation of the total water use. In principle, the magnitude of the loss of water depends on different factors that include age and length of distribution pipe, operating pressure, number of connections, and maintenance services given to the system. As the actual value of loss could not be quantified, often it is reported as a percent of the total demand, and its value varies from 5 to 30% [51].
In the current study, real water loss percentages that varied from 10 to 30% were adopted according to our data measurements, and water utility offices with the size of population and time as proposed by current assessment and previous studies [52,53] are used for estimation of current water loss. Apparently, real water loss estimated for the rural and urban settlements of the Ghba subbasin is summarized in Table 8.   Woreda. Continuous consultation and assessment were made with the Woreda offices and Tigray Water Resource Bureau during the field survey. us, the total irrigated area for the production year 2021 was mapped in GIS ( Figure 5) from the GPS database and verified via Google Earth and physical measurements, and then estimated at around 10,254.8 ha. From the previous assessments and inventory conducted on the irrigated area size mainly by Tigray Water Resource Bureau (TWRB) in 2015 and 2016, the total irrigated areas were 8,725.98 ha and 9,0170.76 ha, respectively. ere has been an increment in the irrigated area since the inventory, but the data from Woredas somehow looked exaggerated as compared to the major finding of this study and also when compared to the then TWRB inventory assuming increment due to additional areas developed, though not able to get the specific/actual additional areas since then. Common rainfed agriculture in the basin includes Teff, wheat, barley, maize, sorghum, and pulses. However, irrigated agriculture at the household level and agricultural investment have also increased significantly in recent years [15,54]. During the mapping process, those areas less than or equal to 10 hectares were summed up. Furthermore, the  Advances in Civil Engineering total number, average, minimum, and maximum size of the subbasin population and the percentage distribution of each Woreda population are also mapped in Figure 5. e mean daily ETo for all the different AEZs in the study area ranges from 4.08 mm to 5.33 mm. e irrigation water demand was estimated for three separate irrigation cycles; the first-round irrigation starts from October to the end of January, the second round of irrigation from early February to the end of May, and supplemental irrigation from June to the end of September. e current estimated irrigation water demand is summarized in Table 9. Accordingly, the current annual irrigation water demand is found to be 151.51 Mm 3. e demand reaches its peak in December (30.87 Mm 3 ) and January (31.11 Mm 3 ), while the lowest demand is in June (1.13 Mm 3 ), also summarized in Figure 6. us, the average water demand per ha is 14,778.44 m 3 . In estimating the current gross irrigation water demand, the analysis considered the weighted average irrigation efficiency of the current irrigation system data, which is estimated at 40%. Details of existing water consumption on monthly bases are summarized in Figure 6. And also, Figure 7 summarizes the analytical annual output GIS map of ETo, and both current NIWR and GIWR per hectare, or the duty for irrigation water requirement per hectare spatial distribution of the subbasin computed from monthly ETo and agroecological zoning of the subbasin.

Livestock.
e current livestock water demand for the subbasin was computed based on the population and average livestock water intake rate per head per day. As mentioned in the previous section, the number of livestock is available from stakeholders, and the average water intake rate values for each species were adopted from this study [55]. e adopted consumption unit rates are presented in Table 10.
According to the study, the total annual current livestock water requirement of the subbasin is estimated at 5.25 Mm 3 . As presented in Table 11, the highest consumption demand goes to the cattle group, which accounts for about 69% of the total livestock demand. e share of annual water requirement for sheep is 11%, donkeys 10%, goats 5%, beehives 3%, and poultry 2%.

Overall Water Use
Estimate. Finally, after estimating each current water use at the Woreda level both for rural and urban areas of different sectors, the total current water use estimate of the subbasin is 204.1 Mm 3 and is summarized in   Table 12, and the estimated current water use GIS map of the subbasin is quantified in raster calculator by IDW method shown in Figure 8. is result shows high stress or water abstraction is in the central part of the subbasin where the capital city of the Regional Government of Tigray is lying, and, of course, almost all industries exist in concentration    Figure 7: Annual ETo, current NIWR, and current GIWR.

Conclusion and Recommendation
is study estimates the current use of water both for water supply and agriculture purposes. e estimate shows that the current domestic and nondomestic water use of the rural area of the subbasin is 3.5 Mm 3 /year and 0.174 Mm 3 /year, respectively. At the same time, the domestic water use of the towns in the Ghba sSubbasin is estimated to be 12.77 Mm 3 / year. e industrial water use of the urban areas is estimated to be 21.2 Mm 3 /year, whereas the commercial, public, and institutional water use is 1.87 Mm 3 /year. e estimated real loss for all the water supply uses is 7.8 Mm 3 /year. e current irrigation water consumption of the abovementioned groups of irrigation water users was estimated independently, considering their water management efficiency and distribution. e existing irrigated land in 2019/ 20 was estimated for the first and second rounds under a full irrigation system. e first round, which extends from October to January of the cropping year of 2020/21, has an estimated irrigated land of 10,254.8 ha, while the case of the second-round irrigation period, which extends from February to the end of May, has the area coverage of 7,715.91 ha. In addition, the supplementary irrigation activities, which were mainly experienced in the highland part of the subbasin, had an estimated area coverage of 2,420.29 ha. Based on the estimated irrigated areas of different seasons, the irrigation water consumption for different cropping patterns was estimated using the Penman-Monteith method and empirical formula for ETo, crop water requirement, and irrigation water requirements. Accordingly, the estimated results for smallholders and investors irrigation water consumption in the subbasin is around 151.55 Mm 3 per annum.
Livestock husbandry is the second most important agricultural water user sector in the subbasin. As mentioned earlier, the water used for livestock production simply depends on the current livestock population and rate of consumption for each species. Accordingly, the current (2020/21) total livestock and poultry population of the subbasin is estimated to be about 923, 170, and 604,665, respectively. Accordingly, their corresponding annual water consumption is 5.3 Mm 3 .
ese methods of current water use estimation are curtail preliminary working input data that have to be incorporated in any study and design of water resource projects. us, they help to reduce the level of uncertainty of efficient water use distribution in the study area, violent water conflict, optimum utilization of water resource projects, and so on.
e method of these current water uses estimations considered in this study may not be absolute as validation of these products in different study periods and conditions could result in different estimates. Assessment and interpolation of the data collection and estimation method over complex terrains may also introduce uncertainties and therefore limits the validity of the result. However, considering the current data availability, the result of this study provides a basis for the utilization of water allocation plans for the current and future scenarios over the complex topography of the Ghba subbasin. It will be a useful reference

12
Advances in Civil Engineering for future related studies of current water use estimation techniques that will help improve water allocation plans.

Data Availability
Data are available at the Ethiopian National Meteorological Services Agency, the Ministry of Water and Energy (Ethiopia), Ethiopian Central Statistical Agency, the Tigray Water Resource Bureau, and THE Tigray Water Utility Offices.

Conflicts of Interest
e authors declare that they have no conflicts of interest.