Trends of sea-level rise effects on estuaries and estimates of future saline intrusion

Abstract

One of the effects associated with climate change is sea-level rise (SLR). Initial IPCC reports predicted that sea levels would rise by 60 cm by 2100. However, the most recent IPCC report (AR6) already considers, due to our failure to control greenhouse gas emissions, that this increase should reach 1 m or even 2 m by 2100. Satellite altimetry studies have also shown that this effect is uneven across the globe. Thus, some regions will experience the SLR effects first. On the local scale, transitional environments such as estuaries will be the first to experience such effects (e.g., flooding, saline intrusion and erosion). Studies that deal with the prediction of such effects in estuaries are diffuse in the literature and represent a precious source of information for decision-makers. Thus, the aim of this study was to carry out a synthesis of the predictions made about the effects of SLR on estuarine systems. A systematic literature review was performed. From the recovered studies, a qualitative synthesis of the global distribution and the predicted SLR effects on estuaries was carried out. The quantitative synthesis for saline intrusion was performed using data from SLR and river discharge. Additionally, a case study was proposed with the application of the multiple regression model to predict saline intrusion in a real estuary. The results showed that most of the studies were carried out in the northern hemisphere and, in areas identified as vulnerable to SLR, which are potentially already experiencing some SLR effects. Most of them dealt with saline intrusion in the estuary using predictive hydrodynamic numerical models. The results of the quantitative synthesis showed that these studies predict a direct relationship between saline intrusion and SLR and the inverse with the river discharge. Results also reveal that discharge reduction due to future drought scenarios could be a very important factor for the saline intrusion increase. Ecological studies used a predictive approach and laboratory experiments and mainly dealt with the flooding and salinity increase effects. The incorporation of hydrodynamic models to ecological models and simulations that assess the effects of human interventions to mitigate the SLR impacts on estuaries are recommended. In this study we review the main environmental impacts associated with climate change in estuaries and discuss limitations and the use of tools that can be applied in building estuary governance and management strategies.