Coastline variations on a section of a coast dominated by cliffs: Past, current and future changes in the municipality of São Francisco de Itabapoana, Brazil

Abstract

According to IPCC projections, if there is no joint action between countries to curb the advance of greenhouse gas emissions, the temperature could rise by up to 4 °C, the worst-case scenario. With rising temperatures come adversities that will be and are being faced worldwide, one of which is rising sea levels. Given these level sea-level fluctuations and future projections, there is a need for research into multi-temporal coastline variations, thus providing a view of the past, present, and future of coastal zones around the globe, given that the world's growing population lives on the coast and that a repositioning of the coastline towards the continent has and will have devastating effects on populous regions. This work aims to analyze the coastline variations for the municipality of São Francisco de Itabapoana/Rio de Janeiro (Brazil). Three time periods were chosen: first, for the past 4773–4400 cal yr BP; second, for the present period between 1984 and 2022; third, to project a future scenario for the year 2100 using the sixth IPCC report on mean sea level. For the analysis of the coastline of the present, the area chosen was the entire length of the coast of the municipality of São Francisco de Itabapoana, and for the past and future projections, the area selected was the stretch from Lagoa Doce beach to the mouth of the Itabapoana river. The methodology used consisted of obtaining and processing high-resolution drone images and using Landsat satellite images (5, 7, and 8) to reconstruct and build sea levels for the three time periods chosen in this study. Based on the drone images, a digital surface model and an orthophoto were produced, which were used to reconstruct the sea level of the past when it was 2.5 m higher than the current level and to construct the future scenario (2100) with the scenario of 1.01 m higher than the current level. In the past, the results showed that the study area was flooded and that the current paleocean was active. The worst-case scenario from the IPCC's sixth report (1.01 m) was chosen for the future simulation. The result indicated that the area near the mouth, which is inhabited, will be flooded; in other words, there will be a social, environmental, and economic risk for the region. For the present time frame, the extraction of the coastline from 1984 to 2022 showed the evolution of the entire coastline of the municipality, both positive and negative, showing that the active cliff, which is on Lagoa Doce beach, is eroding continuously. The results show that in the reconstruction of the past, the paleofault was active, indicating that the ridges developed later. The current rate of change of the coastline indicated that it is generally stable in the municipality. The simulation for 2100 shows that the mouth of the Itabapoana River will suffer severe flooding, and that adaptations will be necessary for the region's population.