In the near future, water availability will be very important for various purposes, especially for domestic and irrigation use. Thus it becomes important to tap as much water as possible into the river basin as possible. Harvesting water is one of the essential methods used to tap water by constructing irrigation facilities such as test dams, storage ponds and dams, etc. Water preservation acts as a way of avoiding precipitation variability as an insurance strategy (Payen et al., 2012).
Decades of war and maladministration and the growing demand for water due to population growth have considered water a scarce resource in Iraq, as well as the droughts recently recalled by Iraq's developing neighbours, Iran, Syria and Turkey because of their siege. Difficult water shortages in some areas have in recent years prompted thousands of people to leave their places, this phenomenon is likely to increase with continuing droughts condition in Iraq. Alternative proposals for reducing Iraq's water shortages therefore urgently need to be enforced (Al-Abadi et al., 2017).
Owing to climate change and high population growth water demand is on the rise (Schewe et al., 2014). However, Iraq is an agriculture-based country and water demand increases in order to guarantee food security, for further agricultural production (A. M. Noori et al., 2019).
Rainfall may be the most critical concept in the water balance equation, so it is one of the challenges for engineer designers and hydrologists to interpret historic data of rainfall and hydrology in terms of potential occurrence probabilities. Annual maximum analysis over the catchment at different daily or better predictive is a fundamental method of safe and economic planning, water management and hydraulic system design (Gavit et al., 2018).
Rain Water Harvesting (RWH) is used to induce, capture, save and use local surface water for agriculture and domestic in arid and semi-arid countries (Gupta et al., 1997). The main goals for hydrological engineers include an understanding of the performance of the RWH, the catchment water output, and flood flows to plan structures for the harvest of rainwater. Structures for the RWH are designed to capture, within a specific recurrence interval, as much of the anticipated river as possible while meeting crop/ tree water requirements (Adham et al., 2016).
Rainfall data can be checked on the likelihood and frequency of receiving expected precipitation amounts for different likelihoods (Bhakar et al., 2008). Use equivalent computational techniques to predict the average daily precipitation of predicted events from available evidence (D. Kumar & Kumar, 1989). Rate rainfall analysis is a way of addressing multiple water supply concerns (A. Kumar et al., 2007). Therefore, in the preparation and development of water sources for small dams, lakes, storm drains, drainage systems and rainwater storage facilities (Dabral et al., 2009), the likelihood and duration of the occurrence of potential rainfall events should be used to minimize the risk of floods and drought cycles.
New technologies have been developed in recent times to address the shortcomings in traditional water scraping methods such as GIS, remote sensing and multi-criteria decision making that can be applied to accurately assess catchment rush production, incorporate spatial and time differences of catchment properties in resource estimation and make informed decision-making (Saxena et al., n.d.).
The soil and drainages trends must be captured in GIS remotely for the efficient localisation of the required systems, and the watersheds have distinct physiographical characteristics, such as geomorphology, structures, land use and land cover (LULC).
In recent years, geographical information systems offered a complex and effective forum to combine data from remote sensing and runoff models to optimally position WH structures, normally using spatial analysis instruments (Nykanen, 2011). Description of suitable WH-built fields is also achieved by the integration of numerous overlays and index-based multi-criteria decision analysis (MCDA) variables using GIS, that can provide GIS with a range of effective essential decision-making techniques and procedures. (Gbanie et al., 2013).
Analytical hierarchy process (AHP) between MCDM approaches commonly used in different fields of decision-making (Lai, 1995). It provides the product of complex decision-making that is versatile, low-cost and understandable. (Hajkowicz & Collins, 2007) revealed that AHP is perhaps the technique of most common use in all other methods that are available when considering the application of the MCDM technique for controling water supplies. Indeed, the global academic community has widely recognized the GIS-based AHP strategy as a strong method to analyse spatial decisions (Rahmati et al., 2015).
Accordingly, MCDM and GIS are implemented in order to enhance site suitability analysis capabilities (Abdulkareem et al., 2018). A Spatial Decision Framework is used for in-depth research with the use of GIS (Abdullahi et al., 2014). Some crucial elements of MCDM include a small range of alternatives and a clear collection of solutions, involving knowledge about the decision maker 's decisions and relying on outcomes (Chakhar & Martel, 2003). When a person addresses an MCDM, the value and weight of the non-substantial characteristics and evaluations of the alternatives must be understood. Simple additive mass, the perfect point form, analytical hierarchy (AHP) and fugitive emblem are the most widely-known MCDM models (A. M. Noori et al., 2019).
Many site-suitability studies were recorded using multicriteria assessment and analytical hierarchy process in each of (Ahmad & Verma, 2018) (Bamne et al., 2014) (Ahmad & Verma, 2016) (Ahmad et al., 2015) (Gavade et al., 2011) (Bodin & Gass, 2004) (Teknomo, 2006) (Harker & Vargas, 1987) (Salih & Al-Tarif, 2012) (Haas & Meixner, 2005) (Triantaphyllou & Mann, 1995) (Banai-Kashani, 1989). As the decision-making method, Analytic Hierarchy Process calculates the percentage value of different criteria in the determination of suitable locations.
Most rainwater is wasted by dry environmental evaporation and thus rainwater production is extremely poor. by using a GIS-based model of suitability, which included integration by Multi-Criteria Assessment (MCE) of different factors the dry spell problem will appear (Ketsela, 2009).
Using commercially accessible remote sensing instruments and GIS to identify rainwater harvesting areas in the mainland of Zanzibar (Tanzania), and Unguja Island (Munyao, 2010). Micro and macro catchments have been used to map and identify various potential impoundment sites using the multi-criteria assessment process through the integration of remote sensing data, GIS, Hydrological Modulation and Multi-criteria appraisal approach. The effect has been evaluated on agricultural development in the Pangani basin catchment area of Chome-Makanya in Tanzania (Mzirai & Tumbo., 2010). Researchers confirmed that, during the dry season, rivers were used as additional irrigation and the production of crops with rainfall-fed rain was increased by more than 120%.
The precipitation in Iraq is very seasonal and takes place in winter between Oct and May, except the north and northeast part of the country where precipitation takes place between Nov and Apr. The estimated average annual rainfall from 1200 mm to less than 100 mm in the northeast (Bazza et al., 2018).
The Iraqi ministry of water resources-through its management responsibility decided to build 9 large dams and 18 small dams, for the hydrological and related modelling studies, as well as central and field office for water quantity and quality control. The restoration of sealants, including drought and seasonal water shortages, also plays a major role in response to hydraulic disasters. Create a water management plan aimed at rehabilitating drought areas and reducing the likelihood of potential hydrological disasters (UNDP, 2013).