Based on life and food production, water is an essential resource on Earth. As a result, it is important to pay attention to water resources, to meet all humanitarian needs for drinking water and secure the requirements for agriculture and industrial needs (Machiwal et al. 2018). Surface water is supposed to be more vulnerable to groundwater, since it is directly exposed to human activities, thus it can be easily polluted (Kumar et al. 2022). However, even though groundwater is protected by the layers of the Earth, the last few decades, the quality and quantity of groundwater are at high risk. In specific, many human activities, such as intensive agriculture, rapid urbanization, overexploitation, burgeoning population, improvident use of chemical fertilizers and pesticides, as well as abusive farming practices have contributed to the qualitative deterioration of groundwater (Green et al. 2011; Saidi et al. 2011; Kumar et al. 2018; Kirlas et al. 2022a). Specifically, the extensive use of chemical fertilizers and pesticides leads to the qualitative degradation of groundwater resources and to the immense problem of nitrate pollution of aquifers. Nitrate pollution has severe effects on public health and the ecosystems; hence, the prevention of groundwater pollution is very essential for an efficient groundwater management, as well as for the sustainability of the natural resources and the economic development (Li et al. 2017; Kumar et al. 2018).
In general, the need for water resources in Iraq is growing, due to population growth and economic development, however this need is being partially offset by a decline in this essential resource due to increased investment and exploitation of water resources in Iraq's neighbors (Al-Ansari 2013). Iraq is the fifth-most exposed country in the world to climate change's effects, including water scarcity and food insecurity. Nowadays, the country is experiencing the effects of climate change at an alarming rate, and a top advisor at the ministry of water resources in Iraq warned in April that the country's water reserves had decreased by 50% since last year as a result of drought, a lack of rainfall, and falling water levels (Mawlood 2019). Moreover, in Iraq, Tigris and Euphrates are the main surface water resources; groundwater is only second in importance in terms of use. Consequently, groundwater information is still in the development (progress) stage, and therefore there is no precise estimate of the amount of groundwater that is available for use. Nonetheless, there are estimates based on investigations that have been completed in Iraq, which cover three distinct regions instead of the entire country: the mountainous region, the desert region, and the feet of the mountains.
Furthermore, more than 90% of the population in the area receives water via groundwater abstraction from this basin, and additional residents outside the study basin also receive potable water from it. Notably, rapid urbanization, industry expansion, and agricultural activity growth have been the primary occurrences in recent years that everyone has noticed. Examples of this development in the region include the construction of the Safra and Azad rice food production, and numerous yogurt factories, such as Erbil and Mersin, as well as many ice cream factories. Whilst the overexploitation of the aquifers and the sporadic decrease of yearly precipitation have both worsened the decline of the groundwater supply, delivering water of high quality and sufficient quantity for those sectors has substantially increased (Ali and Hamamin 2012). According to a statement from the ministry of Agriculture and Water Resources in Kurdistan Region Government (KRG), due to overexploitation, groundwater levels have dropped by 500 meters during the last 20 years. As a result, this abrupt decline in groundwater level has led to substantial groundwater quality and quantity deterioration in the area. Thence, there is an insistent need for a groundwater governance framework that could endorse policymakers in decision-making, aiming to protect groundwater resources from further degradation.
In many cases, groundwater monitoring is expensive and a meticulous task to represent pollution satisfactorily on a large scale. For this reason, researchers have developed various methodologies, which are more economic and easier to apply and do not require a lot of data and complex computations (Kumar et al. 2015; Canora et al. 2022; Kirlas et al. 2022a). The most important groundwater vulnerability assessment methods are DRASTIC (Aller et al. 1987), GOD (Foster 1987), AVI (Van Stempvoort et al. 1993), SINTACS (Civita 1994) and SI (Ribeiro 2000). Amongst them, DRASTIC is the most popular and widely used empirical rank/score based index method for vulnerability evaluation, developed by Aller et al. (1987) for the U.S Environmental Protection Agency (Boufekane et al. 2021; Rezig et al. 2022). This method is based on seven hydrogeological parameters, namely depth to water table (D), net recharge (R), aquifer media (A), soil media (S), topography (T), impact of the vadose zone (I) and hydraulic conductivity (C) (Metwally et al. 2022). Nevertheless, despite its popularity, DRASTIC method has some limitations, and it has been criticized for its subjectivity and uncertainty in the evaluation of its parameters’ ratings and weights (Goyal et al. 2021). To overcome this problem, many researchers started modifying the method to improve its efficiency and accuracy for a specific aquifer (Fannakh and Farsang 2022). Such modifications include the optimization of the ratings and weights of DRASTIC parameters by using Analytic Hierarchy Process (AHP), Fuzzy AHP, Analytic Network Process (ANP), multiple linear regression and sensitivity analysis (Sener and Davraz 2012; Garewal et al. 2015; Jhariya et al. 2019; Lakshminarayanan et al. 2021; Kirlas et al. 2022b). Besides, other researchers proposed the incorporation of extra factors, such as land use and irrigation type (Brindha and Elango 2015; Sarkar and Pal 2021; Sresto et al. 2021). This study is the first endeavor to evaluate the groundwater vulnerability in Kani Qirzhala aquifer, Central Erbil basin, North Iraq, using the DRASTIC method. Moreover, the results of the method can help policymakers and planners in their decision-making efforts to preserve the aquifer system from future groundwater deterioration. The accuracy of the DRASTIC model was validated using reported nitrate concentration (NO3−) in groundwater.