Hazard Assessment of Rockfalls in Mountainous Urban Areas, Western Saudi Arabia

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.