Water resource management has had an inevitable link to economic development and human activities throughout history. Every continent has experienced water scarcity, and global water use has increased two times faster than the population increase in the last century [1
]. Water scarcity, especially in arid and semiarid regions, highlights the importance of water resource management worldwide. Mekonnen andand Hoekstra (2016) [2
] reported that 0.50 billion people faced severe water scarcity for the entire year from 1996 to 2005, while 3.97 billion people face severe water scarcity for at least one month each year. Approximately 80% of the population in Central Asia is experiencing difficulty associated with water stress, and approximately 50% of the population suffers from water shortages [3
]. Studies report an increase in drought severity in Afghanistan and its neighboring countries in Central Asia [4
]. Water resource management during severe drought, water scarcity, and shortages is essential to reduce the vulnerability of local people.
Afghanistan, with an arid to semiarid climate, receives most precipitation in the form of snow during winter and a smaller amount in spring as rainfall [8
]. According to Mahmoodi (2008) [9
], the total annual potential discharge in the five major basins of Afghanistan exceeds
. The Afghanistan economy strongly depends on the agricultural sector, and according to reports of the Afghanistan National Statistics and Information Authority, the agricultural sector contributed 18.6% of the country’s total gross domestic product (GDP) in 2018 [11
]. Despite the GDP, approximately 80% of the population lives in rural areas, and their livelihood is strongly related to agricultural activities [9
]. The country owns
of arable land, and in 1980,
were under cultivation [9
]. Several decades of war and severe drought have reduced arable land to the current value of
. Therefore, proper water resource management in Afghanistan can lead to economic development and the improvement of residential living standards.
The meltwater from glaciers and the snowpack in the high mountains of Afghanistan generates high amounts of surface water flow in the country. Officially, the country is divided into five major river basins; four of the river basins are transboundary basins flowing to neighboring countries except the northern basin, which uses all the water inside the basin. The Northern River basin has the smallest annual flow contribution, with only 2% of the total, while it covers 12.26% of the total country area, with 9.51% of the country’s population settled in the basin [12
]. The water resources in this river basin are the lowest among the four basins, while land coverage and the population are considerably higher. The high population and limited water resources make the area vulnerable to water scarcity and drought. Therefore, proper management practices and policy considerations are essential for the water resources in northern Afghanistan.
As described by Wheater et al. (2007) [14
], a model is a simplified depiction of a real-world system consisting of a series of contemporary equations or a logical set of operations within a computer program. Hydrological models are important tools for water resource management and its impact on the environment. The models can be used for depicting the input-output properties in an existing basin (e.g., expanding the data array for flood design in water resource assessment, water resource management, or operational flood prediction), estimating runoff for ungauged catchments, predicting impacts of changes in the basin (e.g., land use change or climate change), coupling the hydrology with geochemistry (e.g., nutrients and acid rain), or coupling the hydrology and meteorology (e.g., a global climate model) [14
]. A suitable model can predict results close to reality with the fewest parameters and lowest model complexity [15
]. Hydrological models can be classified as (1) empirical models, (2) conceptual models, and (3) physical-based models [14
The Soil and Water Assessment Tool (SWAT) [16
] is a physical-based model that is widely used for predicting water and sediment circulation, agricultural production and chemical yield, climate change impact on water resources, and policy testing. The SWAT model output can also be used to solve real-world problems. The following examples outline the worldwide SWAT applications. In Guiamel and Lee, (2020a) [17
], the SWAT output was used to calculate the potential hydropower capacity in the Mindanao River Basin, Philippines. The SWAT was applied for 7 days of low flow each year with a 10-year return period (7Q10) to analyze drought in the Muskingum watershed of eastern Ohio, USA, by Shrestha et al. (2017) [18
]. In Maghsood et al. (2019) [19
], SWAT was utilized to study the flood frequency in the Talar River basin, northern Iran, considering the impact of climate change with the Coupled Model Intercomparison Project phase 5 (CMIP5) general circulation model (GCM) dataset. In Xie and Cui, (2011) [20
], SWAT was used to study paddy rice field irrigation and crop yield management in Zhanghe, China.
The Afghanistan water and irrigation infrastructure almost collapsed during the four decades of war and conflict. In addition, the water consumed by residents and industries for irrigation and water supply purposes is rapidly increasing. The rapid increase in the water consumption requires more accurate and scientific studies before any actions can be undertaken. In the last few years, few studies have been conducted to address hydrological modelling and water-related issues in Afghanistan. In Aawar and Khare, (2020) [21
], a watershed model of the Kabul subbasin was developed using the SWAT model from 2003 to 2010, and model calibration and validation were conducted at a single gauging station. In Hajihosseini et al. (2016) [22
], the SWAT model was utilized in the Helmand River basin from 1969 to 1979, and the model output was used to assess the 1973 treaty of the transboundary water of the Helmand River in southern Afghanistan. The Salma Dam located on the Harirod River is a newly constructed multipurpose dam in western Afghanistan. The SWAT model was used to estimate the surface runoff and sediment downstream from the Salma Dam [23
]. The snowmelt runoff model (SRM) was used to estimate the daily river discharge in the Salang River basin and upper Kabul River basin by utilizing the MODIS 7-day snow cover product and metrological data from 2009 to 2011 [24
]. Few studies have been conducted in the Afghanistan and no studies using the hydrological in the northern Afghanistan has been conducted to date. On the other hand, previous studies performed calibrations using single station discharge data for the calibration and validation of models while the current study used multiple stations, from upstream to downstream, for model verification in the study region. The result of the current study will be used for irrigation water management and as a solution for the current challenges.
The main objective for this study is to develop the hydrological model of the BRB for the sustainable water resource management practices in irrigation water management. The results of current study will be used for the evaluation of current irrigation water shortages and challenges, as well as for testing the possible policies and solutions for the proper distribution of water resources in future studies. In this study, a watershed model of the Balkhab River basin (BRB) in northern Afghanistan was developed using the SWAT, and model calibration was performed using multiple site calibration. In the mountainous watershed with arid and semiarid climates, lateral flows and springs are the main sources of surface water during the non-rainynon-rainy season. In this study, the authors used analysis of the historical discharge data at the different stations to address the issue of 190 spring discharges to the streamflow where no record of their discharge is available. In this study, the hydrological process of surface runoff within the study area was simulated using SWAT. The results of the current study can provide the core component for future work on irrigation practices and water resource management in watersheds by testing different possible scenarios. The results can also be used for studies on the impact of climate change on the water resources in northern Afghanistan.
In the current study, the SWAT model successfully reconstructed the monthly discharges at the four stations along the BRB. The model statistics showed a satisfactory to very good result with respect to the coefficient of determination (R2) and PBIAS, while the evaluation showed an unsatisfactory to very good result based on the NSE value. The hydrologic regime in mountains with arid and semiarid climates can change seasonally, and BRB surface runoff is dominated by three different sources of water during the year. The hydrological regime is dominated by an increase in precipitation in the late autumn and winter seasons. The surface runoff during the spring and early summer seasons is strongly affected by snowmelt. During May especially, a spring peak will appear due to rapid snowmelt in addition to the contribution of rainfall to the snow melting process. In late summer and early autumn, the river discharge is dominated by groundwater flow through the springs where the water infiltrates upstream and joins the river in the flat lands downstream. In such cases, SWAT is highly capable of capturing hydrological processes that vary temporarily and spatially. However, SWAT model calibration is challenging in mountainous catchments with low annual precipitation. In mountainous catchments, the conditions can change spatially and temporarily, and calibration for accurate parameters is necessary to apply the model, which can represent the actual site conditions.
Hydrologic models are valuable for water resource management and water-related practices in Afghanistan and other data-scarce countries. The results of this study can be useful in decision-making processes for short- and long-term water resource planning and management in the BRB. Studies can expand further to investigate the effects and the role of irrigation practices under different scenarios, not only in the BRB, but also in Afghanistan.