Simulation of current and future water demands using the WEAP model in the Annaba province, Northeastern Algeria: a case study

Water is an essential resource crucial for human survival and pivotal in facilitating the socioeconomic development of a country (Babel et al. 2005). It serves as the foundation for numerous economic activities and has far-reaching implications for human well-being and economic growth (Berredjem & Hani 2017). The combination of population growth, urbanization, industrialization, and the expansion of irrigated agriculture, tourism, and navigation has led to a rapid escalation of demands and pressures on water resources (Mensah et al. 2022). Additionally, socioeconomic changes, including population growth and improved living standards, are projected to further strain water resources, resulting in higher water demand (Psomas et al. 2017).

The Mediterranean region stands out as a global ‘hot spot’ with regard to climate variability and change, exerting significant impacts on water resources, agriculture, and ecosystems (Rochdane et al. 2012). Northeast Algeria, including the Annaba province, is not immune to the effects of climate change (Boukli hacene & Chabane sari 2011). The anticipated impacts of climate change on the region indicate a negative effect, with an increase in the frequency and intensity of hydrologic extremes (Psomas et al. 2017). Digital models have already projected a decrease in precipitation and an increase in temperature in Northeast Algeria before 2020 (Daifallah et al. 2017). This recognition underscores the pressing need for enhanced water resource management to address the mounting conflicts arising from competing demands on water. Consequently, researchers are actively focused on developing tools and techniques to confront this challenge (Richter et al. 2011).

In alignment with the research objectives, this study employs the Water Evaluation And Planning (WEAP) software to assess the current and future water demands in the Annaba province, addressing the major difficulties and challenges associated with water shortage or scarcity. To achieve this, a scenario-based approach is utilized, enabling the exploration of a wide range of possibilities. Despite the challenge of obtaining accurate data, the adaptability of the WEAP tool to different datasets and environmental conditions allows for the effective modeling of the study area (Asghar et al. 2019).

Various studies have utilized WEAP for water supply and demand estimation globally. For instance, Khan & Kundai (2022) focused on the Langat catchment in Malaysia, analyzing water supply and demand with WEAP but without considering climate change impacts. Rajosoa et al. (2022) evaluated climate change effects on groundwater storage in the Medjerda River Basin, identifying impacts from climate change and socioeconomic development between 2045 and 2050 using Representative Concentration Pathways RCP 2.6 and RCP 6.0. Birhanu et al. (2021) assessed natural and human-induced pressures on surface and groundwater supply sources in the upper Awash sub-basin, Ethiopia, considering scenarios of population growth, leakage, expansion of supply systems, and climate change up to 2030. Ley et al. (2022) examined increasing reservoir storage and implementing silvopasture in Southeast Brazil, analyzing streamflow impacts with two regional climate change projections (RCP 2.6 and RCP 8.5). Aoun-Sebaiti et al. (2013) simulated water supply and demand in the Seybouse Valley (East Algeria) and presented four alternative water supply scenarios. Additionally, Ebrahimi & Shourian (2022) employed a simulation–optimization approach using WEAP to optimize water allocation in a reservoir-river system based on quantity and quality criteria, coupling a reservoir and river basin simulation model with a particle swarm optimization algorithm.

The goal of this study is to contribute significantly to the field of water resource assessment and planning. By leveraging the capabilities of the WEAP software and considering the unique circumstances of the region, we seek to overcome the obstacles posed by water scarcity and pave the way for improved water resource management in the Annaba province.

The study area is Annaba Province in northeastern Algeria (36°53′59″N, 7°46′00″E) (Figure 1). The projected population for 2021 is 664,850, according to the last census of the RGPH in 2008. The climate is typical Mediterranean, with an annual rainfall of 700 mm and peak rainfall in December and January (90–120 mm). Weather data (precipitation and temperature) were obtained from local meteorological station. The mean annual infiltration is 162 mm, and the area-specific runoff is 79 mm/year. Annaba's modern agricultural practices include crops such as cereals, vegetables, fruits, and fishing, covering approximately 43,850 ha, according to the survey conducted with Annaba's agriculture services. Only 13.27% of the area is irrigated, with 72% being fed by groundwater and the remaining portion supplied by the Cheffia dam. The city's highly concentrated industries include steel, chemical fertilizers, tomato processing, metal processing, dairy, and more (Achouri et al. 2017).

Our approach relies on modeling the supply and water distribution system in Annaba Province using WEAP software following the methodology as outlined by Birhanu et al. (2021). The WEAP model (https://weap21.org) is well-known for two key features. First, it uses an inclusive method to simulate water systems. Second, it is consistent with policies (Sieber & Purkey 2015). The utilization of the WEAP model is widespread in the assessment of water resource distribution. It accomplishes this by connecting between water supply and demand through the supply and demand balance principle. WEAP examines issues related to water resource allocation for integrated water resource management. This is achieved by applying linear programming at every time interval (Yates et al. 2005). The scenario is run for the period of 2021–2070. Three regular scenario modeling approaches are taken into account in WEAP: the model baseline year, the establishment from the Current Account generates a reference scenario to simulate the likely developments without interventions; and ‘what-if’ scenarios allow for the evaluation of the impacts of changes to the reference scenario (Mensah et al. 2022). This allows us to assess the impact of many internal factors. In our study, the model was set up to simulate five scenarios: (i) Scenario 1: reference scenario, (ii) Scenario 2: climate change. (iii) Scenario 3: seawater desalination plant (DP), (iv) Scenario 4: reduction of leakage in the supply system, water reuse, and recycling (RLR), and (v) Scenario 5: Managed Aquifer Recharge (MAR). The next step is to compare them with the reference scenario that includes unmet water demand. The results are analyzed to compare each scenario's performance with the reference scenario in terms of meeting the unmet water demand.

This research aims to explore alternative future development scenarios for Annaba province by building on the reference scenario projections. This involves implementing several scenarios of alternative water futures, which refer to hypothetical scenarios that explore how water resources in a particular area might be managed or used differently in the future. These scenarios typically involve changes to existing policies, technologies, or management practices, and can help decision-makers understand the potential benefits and trade-offs associated with different approaches to water management. Examining alternative water futures allows researchers and policymakers to identify strategies that can help ensure a sustainable water supply in the face of changing conditions, such as population growth and climate change. These scenarios incorporate a wide range of possible measures that alter ‘business-as-usual’ projections, including climate change scenarios and actions to improve management of the existing system or develop new local water sources (Raskin et al. 2009).

The impacts of climate change on water supplies and demand in Annaba include the following:

• Increased demand for irrigation: As temperatures rise, the need for irrigation to maintain crops and other plants will increase, putting additional pressure on water resources.

• Decreased freshwater availability: Climate change is projected to lead to a decline in freshwater availability, with a potential decrease of 15% for every 2 °C of warming (Rajosoa et al. 2022).

• Impacts on water-dependent industries: The decline in freshwater availability will impact industries that rely on water, including agriculture, industry, and energy production.

To mitigate these impacts, there may be a need for more efficient use of water resources, as well as investment in new technologies and infrastructure to help ensure a sustainable water supply in the face of a changing climate.

We create the seawater desalination scenario by building upon the reference scenario, which is based on historical trends and assumes the planning of a seawater DP with 150,000 m³/day generating capacity starting in 2025. To assess the potential impact of this plant on the water supply situation in Annaba, we model the scenario using the WEAP software, which allows us to simulate the behavior of the water system under different conditions and management options.

A DP is a facility that removes salt and other minerals from seawater or brackish water to produce fresh water suitable for human consumption or irrigation. The process of desalination typically involves three steps: pretreatment, desalination, and posttreatment.

Desalination plants can be an effective solution for areas facing water scarcity, but they also have some drawbacks, such as high energy consumption, high costs, and potential environmental impacts. Careful planning and evaluation of alternative options is important before building a DP. (Shannon et al. 2008).

The average water loss due to leakage from old distribution water networks and transmission lines is estimated to be approximately 40% in Annaba according to companies of drinking water (ADE). This considerable amount of water is lost even before it reaches demand sites. This scenario is created from which two measures were tested. First, to promote water reuse in Annaba up to 40%, and second, to minimize water leakage in Annaba by half to 20%, the following steps can be taken:

• Implementing water conservation and efficiency measures (e.g. low-flow fixtures, water reuse systems).

• Regular maintenance of pipes and plumbing systems to identify and repair leaks.

• Installation of advanced metering systems to monitor water usage and detect leaks.

• Implementation of a water loss management program to identify and address losses.

MAR is a technique used to enhance the availability and quality of groundwater by artificially recharging the aquifer system using treated wastewater. The process involves the injection of treated wastewater into the aquifer, where it is stored and undergoes natural purification processes before it can be extracted for use. This approach can be particularly useful in arid and semi-arid regions, where water resources are limited and groundwater depletion is a significant concern.

The WWTP of Annaba was built in the 2010s, the plant serves a population of over 400,000 people and treats an average of 75,000 m³ of wastewater per day, according to the survey conducted with Annaba's sanitation services.

Annaba currently faces a severe water shortage (Chouchane et al. 2014), with a demand for water reaching 30 million cubic meters (Mm³) in 2021. As a result, the water supply to different parts of the city is intermittent, with varying access times throughout the day. A continuous supply does not exist (Anzab et al. 2016). In response to the uneven distribution of available surface water sources, a significant portion of the water supply is being sourced from El Tarf province in the east (Djabri et al. 2003), where water is more abundant and readily accessible. The water is transferred through two main pipelines from three surface water reservoirs:

• Cheffia reservoir has a capacity of 171 Mm³ and is located in the municipality of Cheffia, about 60 km east of Annaba.

• Mexa reservoir has a capacity of 45 Mm³ and is located in the municipality of Mexa, about 30 km east of Annaba.

• Bougous reservoir has a capacity of 60 Mm³ and is located in the municipality of Bougous, about 45 km east of Annaba.

In 2021, distinct volumes of water were transferred from reservoirs to the city as detailed in Table 1. These reservoirs are important sources of surface water for Annaba, but they do not provide enough water to meet the city's needs, which is why water is also sourced from other areas, including groundwater sources (Aoun-Sebaiti et al. 2013).

The province of El Tarf contains the majority of the region's groundwater potential, which is primarily used for drinking water supply and industry; and to a lesser extent the neighboring provinces of Guelma and Skikda to the south and west, respectively (Aoun-Sebaiti et al. 2013). Table 2 shows the amount of groundwater mobilized transferred to Annaba (Algerian water authority).

The industrial sector in Annaba province faces the highest unmet water demand in both scenarios due to its high water intensity, economic significance, limited allocation, and water management challenges. Inadequate water supply fails to meet the substantial water requirements of industries, resulting in significant unmet demand.

However, alternative scenarios such as DP demonstrate the potential to eliminate industrial unmet water demand entirely. To achieve this, promoting water efficiency, sustainable management practices, and infrastructure upgrades are crucial. Exploring alternative sources like desalination plants, as proposed in scenario 3 (DP), can effectively eliminate unmet water demand in the industrial sector. Careful evaluation of the environmental and economic impacts of desalination is necessary to ensure sustainability, considering factors such as energy consumption, ecological harm, and potential increases in water rates.

Scenario 5 (MAR) yields a moderate outcome, reducing unmet water demand in the industrial sector to 23 Mm³ by 2070, a significant decrease of 36%. MAR plays a vital role in integrated water management, offering advantages over surface storage, such as reduced evaporation losses, pollution prevention, prevention of eutrophication, and lower costs. MAR improves groundwater quality through replenishment and natural purification. However, it can also introduce contaminants or alter water properties. To mitigate negative impacts, water quality must be managed through treatment and monitoring, and MAR can be combined with other strategies. Careful site selection and injection rate management minimize impacts on ecosystems and hydrological regimes. Despite potential impacts, MAR remains crucial for arid and semi-arid regions.

Scenario 4 (RLR) focuses on reducing water leakage and promoting water reuse in Annaba, which is projected to decrease the annual unmet water demand in the domestic sector to 24 Mm³. This scenario offers several benefits, including increased availability of water resources, reduced infrastructure requirements, and alignment with Algeria's National Water Strategy and the United Nations Sustainable Development Goals. However, implementing these measures requires careful consideration of economic costs, policy changes, and potential environmental impacts. It is crucial to assess their feasibility and long-term sustainability for the region.

The expansion of agricultural activities contributes to the increasing water demand, which can surpass the available supply. Surface and sprinkler irrigation systems are identified as the main drivers of the high unmet water demand. Seasonal variations in water availability further exacerbate the situation, leading to insufficient water resources for irrigation and subsequent unmet water demand. Additionally, competition for water resources, inefficient water management practices, and traditional farming methods also contribute to the unmet water demand in agriculture.

To address this challenge, various solutions are proposed. These include adopting efficient irrigation techniques, implementing conservation practices, adopting comprehensive water resource management strategies, utilizing advanced technologies, and investing in storage infrastructure. It is crucial to ensure fair water allocation, upgrade existing infrastructure, and promote sustainable farming practices to effectively reduce the unmet water demand in agriculture.

The study highlights the significant challenge faced by Annaba province in meeting its future water demands, reflecting the increasing demand from 98 Mm³ by 2021 to over 148 Mm³ by 2070. This challenge is driven by limited water resources, industrial sector development, population growth, and the expansion of the irrigation sector.

The industrial sector emerges as the sector with the highest unmet water demand, reaching 36 Mm³. This can be attributed to its substantial water usage, economic importance, limited allocation, and water management challenges. However, alternative scenarios, such as the DP scenario simulation, provide potential solutions to eliminate unmet water demand in the industrial sector.

Similarly, the domestic sector also faces significant unmet water demand, totaling 27 Mm³. The RLR scenario simulation targets water leakage reduction and water reuse promotion in Annaba, with the potential to decrease unmet water demand by 11% in the domestic sector.

The agriculture sector heavily relies on water resources, particularly for irrigation, resulting in significant unmet water demand. In the reference scenario, the projected unmet water demand is 19 Mm³. Expansion of agricultural activities, surface and sprinkler irrigation systems contribute to this challenge. Proposed solutions include efficient irrigation techniques, conservation practices, comprehensive water resource management, advanced technologies, and storage infrastructure to reduce unmet water demand in agriculture.

By implementing a comprehensive set of measures, the potential exists to completely eliminate unmet water demands in Annaba province. These findings underscore the significance of adopting water-efficient technologies, integrating rainwater harvesting systems, and enhancing public education and awareness regarding water conservation and reuse. Policymakers and stakeholders should proactively address the challenges arising from water scarcity to ensure a sustainable water future for Annaba province.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.