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Global warming and anticipated increase in rainfall frequency and magnitude are linked to enhanced rockfall activity worldwide. Arid environments, which currently receive limited amount of annual rainfall, will be particularly subject to frequent and unpredictable rockfall activity that can substantially jeopardize human lives and infrastructures. The main scope of this study is to assess the rockfall hazards in Thawr Mountain and Al-Azyziah district, western Saudi Arabia, using integrated field, geological, climatological and remote sensing datasets and modeling. Our findings indicated that: (1) there are general increasing trends of average annual precipitation and temperature for the period between 2009 and 2019, (2) inspection of multi-temporal satellite images between 2003 and 2017 showed rapid urban expansion, mainly through modification of hillslopes for urban development, which is expected to pose critical consequences on slope instability, (3) field investigations attributed rockfall activity to weathered exfoliated granodiorite hillslopes with abundant tension cracks and steep slopes, (4) slope degrees reached 79° with a general slope direction toward the urbanized areas, and (5) the rockfall motion was simulated along six profiles with dynamic urban areas along the termination of each profile, which showed that several blocks along the six profiles can reach the profile termination with medium intensity rockfall activity and kinetic energy ranges between 50 and 80 kj. The reported rockfall motion can threaten lives, houses and infrastructures. Therefore, protective precautions were suggested to prevent and mitigate the impact of rockfall activity along the studied profiles and similar areas in the mountainous western Arabian Peninsula. [ABSTRACT FROM AUTHOR]

• Assessment of sustainability, origin, age, and evolution of fossil aquifers. • Test site: Mega Aquifer System (area: 2 × 106 km2) in the Arabian Peninsula. • Application of integrated (GRACE, Land Surface Models, geochemistry) methods. • Sustainable agricultural development is achievable in southwest Saudi Arabia. • Adopted integrated approach provides a replicable and cost-effective model. An integrated approach was developed to assess the sustainability, origin, age, evolution, and groundwater potential of large fossil aquifers using the Mega Aquifer System (MAS) (area: 2 × 106 km2) in the Arabian Peninsula as a test site. A two-step exercise was adopted, the sustainability of the MAS was first investigated through the analysis of GRACE data and land surface model (LSM) outputs. Then, integrated geochemical, remote sensing, and field studies were conducted to address the age, origin, hydrogeological setting, and evolution of the southern sections of the MAS (Rub Al Khali Aquifer System (RAKAS)), the area identified from the analysis of GRACE and LSMs as being the most suited for sustainable development. Analysis of GRACE and LSMs revealed: (1) the MAS central and northern sections are experiencing high groundwater extraction (6.6 km3/yr) and depletion rates (−2.8 ± 0.8 km3/yr) with minimum balancing potential through aquifer capture processes, yet sustainability could be achieved by reducing annual extraction by 2.8 km3, and (2) the MAS southern sections (Rub Al Khali Aquifer System (RAKAS)) are experiencing low groundwater depletion rates (eastern RAKAS: −1.8 ± 1.4 mm/yr) to steady-state conditions (western RAKAS: −0.73 ± 1.4 mm/yr). Geochemical, remote sensing, and field investigations over the RAKAS revealed: (1) the presence of west to east trending drainage networks and large-scale groundwater flow systems consistent with a meteoric source (precipitation over Red Sea Hills); (2) increasing 36Cl model ages along groundwater flow directions (up to 970,000 years), indicating aquifer recharge in wet Pleistocene periods; (3) progressive depletion in the O and H stable isotopic compositions of aquifers with increasing distance from the Red Sea Hills basement outcrops, indicating modest recharge during prevailing dry conditions; and (4) the presence of relatively fresh (TDS: 800–2800 mg/L) and non-radioactive (226Ra + 228Ra < 0.185 Bq/kg) water in western RAKAS. Findings suggest that sustainable agricultural development is achievable at current extraction rates in western RAKAS and provide a replicable and cost-effective model. [ABSTRACT FROM AUTHOR]