One History, Many Futures: Exploring Climate‐Driven Changes in Estuarine Water Temperature and Salinity (Sado Estuary Case Study)

Abstract

Although the future is uncertain, global projections point to a destabilization of estuarine ecosystems as a response to climate change, with important implications for coastal habitats and communities. However, the vulnerability of these systems to climate change varies regionally. Thus, it is crucial to fully understand the challenges that coastal populations and ecosystems will face. In this paper, Sado Estuary in Portugal was considered as a case study to predict future conditions of water temperature and salinity in a seasonality and trends assessment, using Delft3D model. We first evaluated the capacity of the model to reproduce past conditions, which helped to improve the understanding of changes over the last decades by overcoming the limitations of restricted in situ observational data. Then, future conditions were assessed under SSP2‐4.5 and SSP5‐8.5 scenarios through to 2100. Results showed that Delft3D is very well suited to reproduce water properties in well‐mixed estuaries such as the Sado, even showing a better performance than the satellite in retrieving the seasonality of the water temperature. The future is of warming conditions for the estuary (average of 0.109°C/decade and 0.275°C/decade, under SSP2‐4.5 and SSP5‐8.5, respectively), in line with the predicted global warming. The two different scenarios present opposite trends for salinity, mainly driven by differences in future conditions of river flow. This highlights the importance of climate forcing and environmental drivers in shaping future estuarine conditions and the applicability of the approach to comparable mesotidal, well‐mixed systems.