Predicting Future Flooding Trends Under Different Sea Level Rise and Precipitation Scenarios in Some Coastal Communities in Ghana

Abstract

Coastal areas in Ghana are critical to the nation’s socio-economic fabric but face growing threats from erosion and flooding due to a mix of climatic and anthropogenic factors. Accurate and high-resolution scientific data are essential to manage these challenges sustainably. Previous studies have often relied on low-resolution imagery, compromising the precision required for effective decision-making and engineering responses. This study leverages a combination of high-resolution data from Unmanned Aerial Vehicles (UAVs), satellite imagery, and medium-resolution Digital Elevation Models (DEMs), along with hydrological modelling using the Malstroem (Bluespots) model, to explore the complex dynamics of coastal vulnerability across Ghana's central and eastern coasts. Employing aerial surveys with a DJI Phantom 4 drone and high-resolution satellite imagery, this study quantified short- and mid-term shoreline changes from January 2021 to December 2023 and 1974 to 2023 respectively. In the Mumford community, modest erosion rates stand in stark contrast to a worrying trend where 53.33% of the coastline is fast eroding, exacerbated by human activities such as sand mining and infrastructural development, particularly at the new fish landing site. The Atiteti community faces even more severe challenges, with 93.33% of its coastline retreating due to natural and human factors. These observations underscore the urgent need for tailored coastal management strategies to address the specific conditions in each region. Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR) analyses and bathtub model projections based on Shared Socioeconomic Pathways (SSPs) reveal significant flood risks. Under the high-emission scenario SSP 5-8.5, the projections indicate that up to 47% of Atiteti will be submerged by 2100. This integration of models with actual subsidence measurements shows how geological and human-induced subsidence exacerbate vulnerability to sea level rise (SLR) and relative sea level rise (RSLR). Furthermore, the Malstroem model simulations revealed critical vulnerabilities due to varying rainfall scenarios. In Mumford, flooding risks are exacerbated at lower rainfall levels (100 mm), showing an increase of 55,000 m2 of flooded areas by 2040 due to subsidence, rising to over 60,000 m2 at 150 mm of rainfall by 2060. Atiteti exhibits a continuous increase in flooded areas with no plateau even at 1 in 25-year flood simulations at high rainfall intensities (300 mm), suggesting a broader spread due to its flatter terrain and less effective drainage. Simulations using the Malstroem model uncovered critical vulnerabilities, particularly in Atiteti, where flattening terrain and ongoing subsidence significantly increased flood risks. This study provides a comprehensive assessment of current vulnerabilities and recommends the development of localized early warning systems or decision tools that can help alert communities in advance and aid planners in managing these coastal challenges more effectively. The findings highlight the pressing need for robust data-driven policies and adaptive strategies to bolster the resilience of these crucial areas against looming environmental threats.