IHCantabria presents the results of a study highlighting the role of climate variability in the protection of coastal cities and ecosystems

An international study, in which researchers from the Institute of Environmental Hydraulics of the University of Cantabria(IHCantabria) have participated, reveals the global impact of long-term climate variability on coastal urban areas and ecosystems. The results have been published in the journal Environmental Research Letters.

Coastal areas – home to large concentrations of population, economic centers and critical infrastructure – are increasingly vulnerable to climatic phenomena such as windstorms, storm surges and rising sea surface temperatures (SST). These hazards not only threaten urban areas, but also essential ecosystems, such as mangroves and coral reefs, which act as natural barriers against storms and flooding. However, as the paper explains, most coastal risk assessments have overlooked the role of long-term natural climate variability in these regions.

The study entitled “Global assessment of interannual variability in coastal urban areas and ecosystems” represents a significant advance in the understanding of how natural climate patterns – such as the El Niño-Southern Oscillation (ENSO), the Arctic Oscillation (AO) and the Southern Annular Mode (SAM) – influence coastal hazards. The line of research to which the study refers is led by postdoctoral researcher Itxaso Odériz, under the supervision of IHCantabria’s Research Director, Íñigo Losada. The aim of the study was to identify how the three main climate patterns-ENSO, AO and SAM-affect coastal hazards globally, particularly in terms of seasonal averages and extreme events. In doing so, they sought to improve understanding of the interannual variability of these hazards and their consequences for both urban areas and ecosystems.

To achieve this objective, a detailed analysis of coastal hazard conditions was conducted, evaluating how extreme events vary, with a 20-year return period, under the influence of these climate modes. The study included data on seasonal fluctuations and extreme conditions in high-risk coastal zones, including areas with coral reefs, mangroves and large urban centers. The research methodology involved calculating seasonal composite anomalies to track variations in average conditions and analyzing extreme weather events associated with different phases of ENSO, AO and SAM.

The findings reveal the significant role these climate modes play in coastal hazards worldwide. For example, research shows that ENSO, particularly in its positive (El Niño) phase, intensifies winds, waves, and SSTs in several regions, including the eastern Pacific, the Caribbean, and parts of the Indo-Pacific. This increased intensity of extreme wind events affects patterns that have been identified in tropical cyclones, especially in the Pacific, a phenomenon that has been linked to El Niño conditions. Similarly, the study shows that both the AO and the SAM contribute to extreme wave and wind activity in different parts of the globe. The AO, for example, is associated with increased wind activity in Europe during the winter, while the SAM has a notable impact on swells in the coastal regions of Australia, South Africa and South America.

Effects on coral reefs

One of the fundamental aspects of the study is the effect of these climate modes on critical ecosystems such as coral reefs and mangroves. Coral reefs are highly sensitive to changes in SST, whose values increase during ENSO+ and SAM+ phases, when SST increases significantly, which can lead to thermal stress, bleaching and even mortality. Extreme wind anomalies in mangrove ecosystems can induce changes in their forest structure or tree mortality during extreme wind events.

Odériz and Losada stress that these findings have important implications for long-term coastal risk management and the development of climate adaptation strategies. Ignoring the role of interannual variability, they warn, could lead to risk reduction measures that miss their target and compromise the effectiveness of nature-based solutions (NBS), such as mangrove or coral reef restoration, which are increasingly used for coastal protection.

The study also highlights the need to integrate long-term climate variability into the design and maintenance of these BNS. Unlike rigid infrastructure, ecosystems evolve over time in response to environmental factors and their ability to continue to provide protection could be compromised if the effects of climate modes are not considered in the design phase. For example, extreme winds resulting from ENSO+ could alter mangrove structures, and higher SSTs could reduce the protective capacity of coral reefs, affecting their effectiveness in mitigating coastal hazards.

The authors suggest further research on the topic to ensure that nature-based solutions and other coastal protection strategies remain effective in a changing climate.

Access to the complete study: here.