El Nino and NAO to shape summer and autumn climate projections

The simultaneous development of the North Atlantic Oscillation (NAO) and El Nino could increase environmental risks such as droughts, heavy rainfall, floods, marine heatwaves, and mucilage in the Eastern Mediterranean Basin, including Türkiye, according to a Turkish climate expert.

Speaking to Anadolu, Director of the Istanbul University Institute of Marine Sciences and Management Cem Gazioglu said NAO, an atmospheric–ocean interaction mechanism, can play a decisive role in precipitation and temperature anomalies across Türkiye’s Marmara, Black Sea, Aegean, and Mediterranean regions.

He noted that 2026 projections indicate NAO may oscillate between a weak positive and neutral phase in the second half of the year, while an El Nino developing in the same period could generate a strong teleconnection mechanism capable of influencing NAO.

"NAO and El Nino may increase environmental risks such as droughts, heavy rainfall, floods, marine heatwaves, and mucilage in the Eastern Mediterranean Basin where Türkiye is located." he said.

He noted that sea surface temperatures along the Mediterranean, Aegean and Marmara coasts could rise significantly above long-term averages, extending the duration and intensity of marine heatwaves.

"This could create critical risks in terms of oxygen depletion, algal blooms, coastal ecosystem pressures and mucilage formation in the Sea of Marmara," he warned.

Positive and negative phases of the NAO

Pointing out that the positive phase of NAO leads to more stable, high-pressure-controlled atmospheric conditions over the Mediterranean Basin, he said this process can result in reduced precipitation, above-normal seasonal temperatures, and an increased risk of meteorological drought, especially during winter.

He added that more dynamic and unstable atmospheric conditions are observed throughout Türkiye, stating that heavy rainfall, floods, and storms can be seen more frequently, especially in the Black Sea, Marmara, and Mediterranean regions.

El Nino can feed short-duration but high-intensity rainfall

Gazioglu noted that El Nino extends ocean–atmosphere interactions originating in the tropical Pacific to global-scale systems reaching the Atlantic and Mediterranean circulation, adding that this process can affect precipitation and temperature balances in the Eastern Mediterranean.

"Strong El Nino events can lead to noticeable increases in sea surface temperatures around Türkiye. The increase in sea surface temperatures raises the atmosphere’s moisture-carrying capacity, which can contribute to short-duration but high-intensity rainfall systems," he said.

"In recent years, mucilage events observed in the Sea of Marmara, floods in the Black Sea, long heatwaves in the Mediterranean, and ecosystem changes along the Aegean coasts are among the reflections of this process. The Eastern Mediterranean Basin is one of the hotspots of climate change. An increase in atmospheric humidity may also raise the risk of sudden heavy rainfall, flooding, and surface runoff, especially around the Black Sea and Marmara regions," Gazioglu concluded.

*Writing by Yesim Yuksel