Flood vulnerability assessment of urban agglomeration under the background of urban expansion

Land use and land cover (LULC) transformations significantly impact ecosystem hydrological characteristics. This study analysed the Sakumo catchment from 1990 to 2020 to assess changes in runoff volume and nonpoint source (NPS) pollutant loads. Using remote sensing, GIS products, and the QNSPECT (QGIS Plugin for Nonpoint Source Pollution and Erosion Comparison Tool) hydrologic model, we quantified and spatially analysed rainfall-runoff and pollutant loads. Our results revealed increasing trends in runoff (110.3 mm/year) and pollutant loads (total nitrogen: 0.22 kg/year; total phosphorus: 0.34 kg/year), attributed to population growth (1, 475 ppl/km²) and urbanization-induced LULC changes (Development: 44.7%). GIS outputs identified the sources of these increments. This research addresses critical gaps in understanding Ghanaian wetlands by estimating runoff magnitudes, identifying spatial pollution sources, and assessing catchment-scale impacts on wetland functions. The study's findings align with historical water quality trends in the Sakumo Ramsar Site, and our runoff estimates demonstrate satisfactory agreement with global runoff model products. This study provides a practical approach for stakeholders in data-deficient regions to investigate hydrological and environmental changes, guiding informed decision-making.

China’s monsoon climate, characterized by hot summers and substantial rainfall, leads to significant seasonal water accumulation in river basins. This often results in short-term heavy rainfall events, causing rapid water flow into river basins and subsequent flooding. River embankments, which narrow channels, exacerbate downstream flooding and pose severe safety threats. This study explores integrated urban and riverine flood risk management strategies within the Fujiang River Basin, focusing on Mianyang City. The research addresses the growing challenges of global climate change and rapid urbanization, which have intensified flood risks. Utilizing the one-dimensional Storm Water Management Model (SWMM) and two-dimensional hydrodynamic Rainfall-Runoff-Inundation (RRI) model, the study simulates flood events and urban flooding in Mianyang City and the Fujiang River Basin. These models were validated with data from hydrological stations and satellite imagery. The study evaluates extreme flood events in Mianyang City between 2015 and 2021. The findings highlight the significant role of sponge city initiatives and low-impact development (LID) facilities in mitigating flood impacts. Despite their benefits, these measures have limitations under extreme flood conditions. This study contributes to understanding the interactions between urban and riverine systems and provides a basis for improving flood risk management and resilience in rapidly urbanizing river basins. It supports ongoing efforts to implement sponge city concepts in China, offering crucial insights into effective strategies for managing flood risks in similar geographic and climatic contexts.

Coastal wetlands are complex ecosystems that support biodiversity. They provide many benefits, including flood mitigation and sustenance for communities. The unique characteristics of wetlands make them vulnerable to natural and human-induced disturbances. Numerous factors, including industrialisation, urbanisation, and climate change, add to this phenomenon. The activities that threaten coastal wetlands in the world are relevant to coastal wetlands in Ghana. The Songor and Sakumo wetland catchments are international ecosystems endangered by land modifications and sea level rise. There are gaps in the body of knowledge that need investigation as regards underlying processes and transformation. This study assessed land use and land cover (LULC) changes between 1990 and 2020. The study used geospatial techniques and intensity analysis. LULC change results were from Landsat images (1990, 2000, 2011, and 2020). These changes were attributed to an increase in human activities. Changes in the Sakumo wetland catchment fell more into human-induced LULC categories, and vice versa for the Songor wetland catchment. The study recommends comprehensive methods of LULC change analysis. This would enhance biodiversity and allow the sustainable usage of wetland resources.