Understanding of water resources and trends of water consumptions is important to offer sustainable water resources management strategy. In this research, water resources and trends of water consumptions in Saudi Arabia were investigated. The non-renewable groundwater reserves were estimated to be 259.1–760.6billion cubic meters (BCM) with an effective annual recharge of 886million cubic meters (MCM). The total internal renewable water was estimated to be 2.4BCM/year. Approximately 1.4BCM/year of runoff is collected by 302 dams. The country produces approximately 1.06BCM desalinated water annually. The wastewater treatment plants treat approximately 0.73BCM/year of domestic wastewater from which 0.33BCM is recycled. The water demand in 2009 was 18.51BCM in which 83.5% were for agriculture. From 2004 to 2009, agricultural water demand was decreased by 2.5%/year, while the domestic and industrial water demands were increased by 2.1%/year and 2.2%/year, respectively. Between 1999 and 2008, domestic water subscribers were increased by 22.7%, while the annual domestic water consumption was increased from 1391 (609–2164) to 3818 (1687–7404) m3/subscriber. The industrial water demands were increased from 56 to 713MCM/year between 1980 and 2009. Following characterization, nonlinear equations were developed to predict the domestic, industrial and agricultural water demands. The predicted water demands were within 1–10% of the historically reported values. The findings might be useful in understanding water sources, water demands and identifying new sources for sustainable water resources management

Climate change is an important factor for sustainable water resource management in the arid and semi-arid countries. In this study, future trends of temperature and rainfall were assessed for several regions in Saudi Arabia. The linear and Mann–Kendall analyses showed an increase of temperature in all regions and decrease of rainfall in many regions. Following trend analysis, the outputs of the NCAR Community Climate System Model were obtained for three emission scenarios (high: representative concentration pathways RCP8.5; high medium: RCP6; and low: RCP2.6) for the assessment periods of 2025–2044, 2045–2064 and 2065–2084 respectively, and compared with the average values from the reference period (1986–2005). In all emission scenarios, temperature showed an increase from 1986 to 2005 in all regions. For RCP8.5, increase of temperature are in the ranges of 0.8–1.6 °C, 0.9–2.7 °C and 0.7–4.1 °C during 2025–2044, 2045–2064 and 2065–2084 respectively. However, rainfall showed variable patterns with respect to emission scenarios and assessment periods. In most regions, the RCP6 showed decrease in rainfall from the reference period while the RCP8.5 and RCP2.6 showed variable patterns. The increase of temperature and variable pattern of rainfall may increase uncertainty in developing sustainable water resource management strategies.