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The current study aims to analyse the vertical structure of the ocean during upwelling events using in situ and modelled data. Additionally, the influence of climate patterns, namely the North Atlantic Oscillation (NAO) and the East Atlantic (EA) pattern, on the vertical structure and their impact on the upwelling activity are assessed for a period of 25 years (1993–2017). The study focuses on the central part of the Canary Current (25–35 ∘ N) with persistent upwelling throughout the year, with an annual cycle and the strongest events from June to September. Upwelling is determined using two different approaches: one index is calculated based on temperature differences between the coastal and the offshore area, and the other is calculated based on wind data and the resulting Ekman transport. Different datasets were chosen according to the indices. Stable coastal upwelling can be observed in the study area for the analysed time span, with differences throughout the latitudes. A deepening of the isothermal layer depth and a cooling of temperatures are observed in the vertical structure of coastal waters, representing a deeper mixing of the ocean and the rise of cooler, denser water towards the surface. During years of a positive NAO, corresponding to a strengthening of the Azores High and the Icelandic Low, stronger winds lead to an intensification of the upwelling activity, an enhanced mixing of the upper ocean, and a deeper (shallower) isothermal layer along the coast (offshore). The opposite is observed in years of negative NAO. Both effects are enhanced in years with a coupled, opposite phase of the EA pattern and are mainly visible during winter months, where the effect of both indices is the greatest. The study therefore suggests that upwelling activities are stronger in winters of positive North Atlantic Oscillation coupled with a negative East Atlantic pattern and emphasizes the importance of interactions between the climate patterns and upwelling. [ABSTRACT FROM AUTHOR]

The current study aims to analyse the vertical structure of the ocean during upwelling events using in situ and modelled data. Additionally, the influence of climate patterns, namely the North Atlantic Oscillation (NAO) and the East Atlantic (EA) pattern, on the vertical structure and their impact on the upwelling activity is assessed for a period of 25 years (1993–2017). The study focuses on the central part of the Canary Current (25–35° N) with persistent upwelling throughout the year with an annual cycle and strongest events from June to September. Upwelling is determined using three different approaches: One index is calculated based on temperature differences between the coastal and the offshore area and two based on wind data and the resulting Ekman transport. Different data sets were chosen according to the indices. Stable coastal upwelling can be observed in the study area for the analysed time span with differences throughout the latitudes and a time lag of four to five months between the wind and the temperature-based indices. A deepening of the isothermal layer depth and a cooling of temperatures is observed in the vertical structure of coastal waters representing a deeper mixing of the ocean and the rise of cooler, denser water towards the surface. During years of a positive NAO, corresponding to a strengthening of the Azores High and the Iceland Low, stronger winds lead to an intensification of the upwelling activity, an enhanced mixing of the upper ocean and a deeper (shallower) isothermal layer along the coast (offshore). The opposite is observed in years of negative NAO. Both effects are enhanced in years with a coupled, opposite phase of the EA pattern and are mainly visible during winter months where the effect of both indices is the greatest. The study therefore suggests stronger upwelling activities in winters of positive North Atlantic Oscillation coupled with a negative East Atlantic pattern and emphasizes the importance of interactions between the climate patterns and upwelling. [ABSTRACT FROM AUTHOR]

Fluctuations in groundwater level in the Ria Formosa coastal aquifers, southern Portugal, owe 80% of the variability to climate-induced oscillations. Wavelet coherences computed between hydraulic heads and the North Atlantic Oscillation (NAO) and East Atlantic (EA) atmospheric teleconnections show nonstationary and spatially varying relationships. The NAO is the most important teleconnection and the main driver of long-term variability, inducing cycle periods of 6–10 years. The NAO fingerprint is ubiquitous and it accounts for nearly 50% of the total variance of groundwater levels. The influence of EA emerges coupled to NAO and is mainly associated with oscillations in the 2–4-year band. These cycles contribute to less than 5% of the variance in groundwater levels and are more evident further from the coast, in the northern part of the system near the main recharge area. Inversely, the power of the annual cycle increases towards the shoreline. The weight of the annual cycle (related to direct recharge) is greatest in the Campina de Faro aquifer, where it is responsible for 20–50% of the variance of piezometric levels. There, signals linked to atmospheric teleconnections (related to regional recharge) are low-pass filtered and have periods >8 years. This behavior (lack of power in the 2–8-year band) emphasizes the vulnerability of coastal groundwater levels to multi-year droughts, particularly in the already stressed Quinta do Lago region, where hydraulic heads are persistently below sea level. [ABSTRACT FROM AUTHOR]

Research on climate-driven variability in the water and energy sectors is required to drive adaptative policies to climate change and boost cross-sectorial synergies. This study addresses the role of the North Atlantic Oscillation (NAO) and East Atlantic pattern (EA) on the water-energy nexus in southern Portugal (Algarve region) from the point of view of water demand, instead of the usual point of view of hydropower production. Water at surface reservoirs and aquifers and solar and wind energy potentials (SP and WP, respectively) do not share the same dominant variability scales, but their interrelationships have implications for leveraging the use of renewable energy in the water sector, particularly through water pumping efficiency gains. Water availability is dominated by interannual fluctuations (70% of the total variance), whereas SP and WP are characterized by seasonal variability scales (98% and 41% of the total variance, respectively). At interannual scales NAO is the main driver of low-frequency variability governing cycles in the 6–8 -year band, whereas fluctuations in the 2–4 -year band are mainly associated with EA. Coupling or synchronizations between opposite phases of NAO and EA correspond to extremes in water availability. Minimum water levels in the summer and during droughts, corresponding to maximum energy demand in the water sector, are clearly connected to synchronized positive NAO and negative EA phases in the preceding winter. Recent advances in the seasonal and long-term predictability of NAO and EA climate patterns can help to improve drought resilience and groundwater sustainability and have huge potential benefits for the water-energy nexus in the Algarve region. Finally, to decarbonize freshwater supply in the Algarve, policy instruments will need to account for unregulated pumping which enables conditions for groundwater depletion, encourage energy and water management integration, and explore innovative energy investments. • NAO (and EA) drive interannual variations with peak periods of 6.5 (and 3.5) -years. • Maximum energy demand in the water sector is expected for NAO+ and EA− phases. • SP is the most reliable renewable energy source for the water sector in the Algarve. • NAO+ EA− are associated with droughts raising implications for solar and wind energy. • Policies promoting solar based technologies should account for aquifer depletion. [ABSTRACT FROM AUTHOR]