This study aimed to assess the spatiotemporal sensitivity of the net irrigation water requirement (NIWR) to changes in climate, for sixteen crops widely cultivated in four irrigation projects located in arid and semi-arid regions of Iraq. Using LARS-WG and five GCMs, the minimum and maximum temperature and precipitation were projected for three periods from 2021–2080 with 20-year steps (P1, P2, and P3) under representative concentration pathways (RCPs) 2.6, 4.5, and 8.5. Weather data available for a reference period from 1990–2019 in four representatives’ meteorological stations were used. The climate variables and other required data were inserted into the CROPWAT 8 NIWR tool. Findings revealed that the increase in the NIWR for the considered crops due to climate change falls in the range 0.1–42.4%, 1.8–44.5%, 1.2–25.1%, and 0.7–14.7% for the North Jazeera Irrigation Project (NJIP), Kirkuk Irrigation Project (KRIP), Upper Khalis Irrigation Project (UKIP), and Dalmaj Irri-gation Project (DLIP), respectively. Barley is more susceptible to changes in climate, whereas maize, potato, soybean, and millet are found to withstand changes in climate better than others. The novel outcomes of this study support optimal spatiotemporal allocation of irrigation water requirement and the sustainable management of water resources in a changing climate in arid and semi-arid regions.

An assessment of the total hydrologic response of arid and semi-arid river basins to various scenarios of climate change by considering evapotranspiration, streamflow, and snowmelt is essential for sustainable management of water resources. The Diyala River Basin in Iraq has been chosen as a typical case study of dozens of river basins in arid and semi-arid regions. Here, the Long Ashton Research Station-Weather Generator (LARS-WG), the Soil and Water Assessment Tool (SWAT), and the SWAT Calibration and Uncertainty Program (CUP) were used to evaluate the total response by considering three Representative Concentration Pathways (RCPs); RCPs 2.6, 4.5, and 8.5 over three periods, 2021–2040, 2041–2061, and 2061–2080. The results indicate that by the year 2080, the basin will experience a temperature increase by 6.6, 10.1, and 16.6% for RCP 2.6, RCP 4.5, and RCP 8.5, respectively. The corresponding reduction in precipitation will be 3.2, 6.4, and 8.7%, resulting in 38.8, 47.9, and 52.8% fall in streamflow for RCPs 2.6, 4.5, and 8.5, respectively. Due to the increase in temperature, an earlier and less contribution of snowmelt is expected in the projected streamflow. Our findings provide a useful reference and a guide to decision makers for developing adaption plans to sustainably manage water resources in the Diyala River Basin and other similar basins in arid and semi-arid regions.

Climate change and population growth play crucial roles in the planning of future water resources management strategies. In this paper, a balancing between projected water resources and water demands in the Iraqi Part of the Tigris River Basin (TRB) was evaluated till the year 2080 based on RCPs 2.6, 4.5 and 8.5 and population growth. This paper examined a sustainable adaptation plan of water resources in the TRB considering three scenarios; (S1) as no change in the current strategy, (S2) as improved irrigation efficiency and (S3) as improved irrigation and municipal water use efficiency. The results showed a decline in streamflow will occur in the range from 5 to 18.4% under RCP 2.6 and RCP 8.5, respectively. The minimum increase in water demand is expected for RCP 2.6 (maximum increase for RCP 8.5) by 51.8 (208.2), 9.9 (42) and 1.2 (7)% for the municipal–industrial, irrigation and environmental water demands, respectively, compared with the RP. The main finding indicated that S1 is the worst scenario, with water stress in four provinces, especially on the warmest RCP. Whereas, under S2 and S3 conditions, water stress can be eliminated. Increasing ambition towards adaptation becomes obligatory for developing sustainable water sources, supporting water food securities and increasing resilience towards climate change.

This study aimed to identify the hydrologic characteristics and investigate the effect of hydrological flow changes for the Adhaim tributary by updating the information of watershed hydrology and examined the possibility of changing the spillway dam from being ungated to a controlled gated spillway to reduce the impact of water releases on the Tigris River and Baghdad City during the flood season. In addition, an attempt is made to store as much water as possible to benefit the summer growing season by supplying water to irrigation projects downstream of Adhaim Dam. The results indicated that if the gates were installed at the level of 135 m above sea level, flood waves with a probability of 1/100 can be controlled and safely flow to the Tigris River at ~200 m3/s. The gates would also increase the capacity of the Adhaim reservoir. Different options for controlling the gated spillway are suggested, and the designers can choose one of them.

In the past few years, the adverse effects of climate change on the water resources of Iraq become significant. The observation indicated an increase in the frequency and intensity of extreme climate events. Scientific pieces of evidence showed that water resources in Iraq declined and more decrease is expected in the future due to reduced precipitation and evaporation rate rise. Water demands have also increased as a consequence of these effects. Climate change and population growth impose adaptation plans in all consumed sectors, these plans involve the balancing of water resources and water demands to prevent water stress and support sustainability. The adaptation strategy involved improving irrigation system efficiency, water use pricing, water meter installation, enhancing urban water network, institutional and legal changes and efficient water management plans that could support water and food securities increase resilience and reduce vulnerability. The adaptation plans should be implemented in ascending manners on the time horizon to eliminate adaptation barriers, as the negative impact of climate change increases with time. Modern adaptation options are beneficial to implement smart agriculture, crop genetic engineering, micro-irrigation and drought-resistant crops.