Flood hazards and risk mapping using geospatial technologies in Jimma City, southwestern Ethiopia

Spatial congruency or discrepancy? Exploring the spatiotemporal dynamics of built-up expansion patterns and flood risk

Most coastal cities have been experiencing unprecedented urbanization-induced flood risk, climatic events, and haphazard anthropogenic activities, jeopardizing residents' lives and building environments. Despite mounting flood-related studies, analyzing the correlation between the spatiotemporal dynamics of Built-up Expansion patterns (BE) and flood risk remains unknown and holds divergent perspectives. In this context, the coastal city of Alexandria, Egypt, characterized by multiple urban patterns and experiencing heavy rainfall annually, was selected as a testbed. Our method defined the spatiotemporal rates of BE from 1995 to 2023, quantified flood risk spatially, and finally investigated the correlation between BE and flood risk through spatial and statistical analysis. Our results show the built-up area occupied 30.32 % of the total city area till 2023, and the infilling pattern dominated the BE growth by 45.21 % of the total built-up area, followed by leapfrogging and edge expansion by 33.25 % and 21.55 %, respectively. The unplanned-infilling pattern is predominantly highly correlated with the flood-vulnerable peaks (correlation coefficient (rk) = 0.975, p-value < 0.05) and lowers dramatically towards planned-infilling regions with flood protections. Meanwhile, a spatial mismatch exists between high-risk peaks and leapfrogging and edge expansion (rk = 0.118 and 0.662, respectively, with a p-value < 0.01), indicating that controlling the built-up amount is inadequate for mitigating flood risk. Porosity-based urban configuration and spatial distribution of built-up patches in harmony with nature-based solutions are recommended for shaping flood-resilient and effective urban planning.

Geo-hazards assessment and land suitability estimation for spatial planning using multi-criteria analysis

The fundamentals contribution of multi-hazard assessment lies in its ability to guide and identify directions for territorial development, aiming to reduce vulnerability through the implementation of appropriate measures. In the present study, Multi-Criteria Decision Making supported by Geographic Information System was utilized to solve spatial problems related to territorial sprawl. Considering this perspective, an analysis was conducted on the susceptibility of land to the occurrence of geo hazards in the Moldova catchment, situated in the northeastern region of Romania, within a transitional zone between mountains and plateaus. The analysis focused on assessing the likelihood of geo-hazards like floods, landslides, and earthquakes, utilizing the weights obtained through the implementation of the Analytical Hierarchy Process (AHP). Subsequently, the obtained results were utilized to generate a multi-hazard map, which facilitated the identification of areas that are suitable for territorial development. The results were validated in two ways: by sensitivity analysis in which two minimum and maximum scenarios were proposed concerning the result obtained and by validation using the receiver operating characteristic (ROC) curve method. The areas with high susceptibility to geo-hazards triggers are located in the southeastern part of the region, in the proximity of the hydrographic network. Flood risk is the hazard with the highest recurrence. Localities with high suitability for spatial development have a central-western distribution. According to the applied model, sites for each locality included in the study area can be identified. The high and very high suitability classes account for 54% of the total area, while the unsuitable classes represent 15% of the area. However, the vulnerability of the area and the need for the study are generated by 35% of the settlements being located in areas with high susceptibility.