It is a typical ill-conditioned problem to invert GPS-measured loading deformations for terrestrial water storage (TWS) changes. While previous studies commonly applied the 2nd-order Tikhonov regularization, we demonstrate the truncated singular value decomposition (TSVD) regularization can also be applied to solve the inversion problem. Given the fact that a regularized estimate is always biased, it is valuable to obtain estimates with different methods for better assessing the uncertainty in the solution. We also show the general cross validation (GCV) can be applied to select the truncation term for the TSVD regularization, producing a solution that minimizes predictive mean-square errors. Analyzing decade-long GPS position time series over Taiwan, we apply the TSVD regularization to estimate mean annual TWS variations for Taiwan. Our results show that the TSVD estimates can sufficiently fit the GPS-measured annual displacements, resulting in randomly distributed displacement residuals with a zero mean and small standard deviation (around 0.1 cm). On the island-wide scale, the GPS-inferred annual TWS variation is consistent with the general seasonal cycle of precipitations. However, on smaller spatial scales, we observe significant differences between the TWS changes estimated by GPS and simulated by GLDAS land surface models in terms of spatiotemporal pattern and magnitude. Based on the results, we discuss some challenges in the characterization of TWS variations using GPS observations over Taiwan.

Active tectonics in the Arabian Shield region has substantially influenced the drainage system and geomorphic expressions. The Nabitah Fault Zone (NFZ), located in the southern portion of the Arabian Nubian Shield, is an intra-arc suture that traces the boundary between two young Neoproterozoic intra-oceanic arc terranes: the Tathlith–Malahah terrane and the Al Qarah terrane. In this study, an active tectonic model was assessed and developed to evaluate the level and distributions of the tectonic activity related to the NFZ in Saudi Arabia. To achieve that, a digital elevation model-derived drainage system and a series of geomorphic indices were used, including mountain front sinuosity, valley floor width-to-valley height ratio, basin shape, hypsometric integral, and basin asymmetry. The average value of each geomorphic index was calculated and assigned. The results extracted were integrated to obtain the Tectonic Activity index (TA). Three classes were defined in this study to indicate the tectonic activity degree: low tectonic activity (class 3; TA > 2.5), moderate tectonic activity (class 2; 1.75 < TA ≤ 2.5), and high tectonic activity (class 1; 0 < TA < 1.75). Based on the results, this paper deduced that the highly deformed regions associated with active tectonics can be recognized and evaluated using this effective integration technique. Therefore, this can be applied to other significant fault zones elsewhere, particularly those whose tectonic activity has not yet been evaluated.

The southern Red Sea coastal zone of Jizan Province in Saudi Arabia is increasingly exposed to seismic hazards, soil erosion, flash flooding, and tectonically shaped landscape instability, raising challenges for sustainable development. This paper integrates high-resolution 12.5 m ALOS PALSAR digital elevation model data, morphometric analyses, geomorphic interpretations, and the Revised Universal Soil Loss Equation (RUSLE) model to assess soil erosion vulnerability and relative tectonic activity along 24 sub-basins. A total of 22 morphometric parameters were investigated, analyzed, and integrated into a weighted compound ranking key for prioritizing erosion-prone sub-basins. Geomorphic interpretation was assessed using the hypsometric integral, valley-floor width-to-height ratio, and basin shape, which were processed in the Relative Tectonic Activity (RTA) model. The results recognize sub-basins 8, 7, 22, 18, 23, 13, 3, and 9 as the highest-priority zones for soil conservation, while hypsometric integral values (0.04–0.48) reveal mature landscapes with geomorphic reactivation. High spatial correlation among morphometric prioritization, RTA interpretation, and the RUSLE model reveals that drainage characteristics, relief, lithology, and tectonic signatures indicate a significant spatial association with the soil erosion framework. The proposed model presents a reliable baseline key for sub-basin prioritization and climate-resilient mega-structure planning in data-poor settings, directly supporting SDG 9 and SDG 13.

Flash floods represent an extreme hydro-geomorphological hazard in the arid and semi-arid regions in northwestern Saudi Arabia, presenting major risks to significantly expanding urban regions, infrastructure, and sustainable development projects of Saudi Vision 2030. The present study assesses the flood susceptibility of the Wadi Al-Disha catchment (4212.81 km²) using a high-resolution 12.5 m spatial resolution ALOS-PALSAR digital elevation model (DEM). A dual-model approach, combining the scale-dependent Morphometric Ranking Method and the scale-independent El-Shamy approach, was applied over district 18 sub-catchments to investigate, analyze, and calculate 15 hydro-morphometric effective parameters. The Ranking Method model assigned sub-catchment SC-18 to the high-flood susceptibility zone, SC-4 as a low-flood susceptibility unit, and the rest of the 15 sub-catchments as moderate risk, with SC-9, the largest sub-catchment, scoring highest among the moderate rank, just below the high-susceptibility rank threshold. On the other hand, the El-Shamy Approach model defined SC-3 and SC-8 as high-flood susceptibility classes, while the remaining 16 sub-catchments reflect moderate-flood susceptibility classes. This proposed assessment is a physically-based susceptibility evaluation extracted from terrain morphometry; it does not consider socio-economic exposure or hydrological (rainfall–runoff) information, which we identify explicitly as scope boundaries below. Comparative validation with a regional study states that a bifurcation ratio indicates that tectonic rifting impacts bifurcation parameter values ($Rb>4.0$), forcing the El-Shamy Approach model to underestimate susceptibility in structurally complex, high-relief landscapes. To underestimate the impact of these flood susceptibilities and secure sustainable infrastructure in the very close Prince Mohammed bin Salman Royal Reserve, the study suggests designing targeted dams in rapid-velocity headwaters and creating an early warning system on the plateaus upstream.

Flash flood events are among the most critical hydrological hazards in arid and semi-arid regions, posing extreme threats to critical infrastructure, human safety, and sustainable development plans. This paper evaluates the flash flood susceptibility of the Al’Ataya catchment, a key watershed on the southern Red Sea coast, using an integrated geospatial analysis approach. To assess and quantify the flood hazard, we investigated 15 morphometric parameters for 24 particular sub-catchments within a sixth-order drainage system. Two complementary methods, the Morphometric Ranking Method and El-Shamy’s approach, were utilized to classify the catchment into different flood susceptibility levels. Results from the Ranking Method identified seven sub-catchments (SC-2, SC-3, SC-6, SC-7, SC-8, SC-9, and SC-19) as having high flood hazard levels, mainly driven by large watershed areas, steep slopes, and high relief ratios. In contrast, El-Shamy’s approach resulted in a different evaluation, identifying sub-catchments in Zone B (SC-23, SC-16, SC-17, SC-15, SC-6, SC-20) as high hazard sub-catchments due to the particular relationship between the bifurcation ratio parameter and the drainage density and stream frequency parameters. The integration of the two methods suggests that the susceptibility factor is controlled by the combined influence of a low drainage density and steep mountainous terrain draining toward the coastal zone. These results provide a spatial model for flood mitigation and early warning systems, supporting Saudi Vision 2030 through improvement to the development of southern urban centers such as Al’Ataya and Sabya.