Synchronisation of Extreme Precipitation and Sea Surface Temperature Events in the Northern Hemisphere: A Complex Network Approach

Synchronisation, the tendency of climatic events to occur simultaneously, can arise from small-scale and large-scale atmospheric dynamics. Climate variables can be synchronised across broad spatial and temporal scales, manifesting as regional, continental and global teleconnection patterns. In the study, we analysed spatiotemporal patterns of inland extreme precipitation events (EPEs) and extreme sea surface temperature events (ESSTEs) in the Northern Hemisphere (0°N–60°N) to better understand their connection. Using gridded monthly gauge- and interpolation-based datasets for precipitation and sea surface temperature from 1930 through 2020, we detected extreme events based on the 95th percentile threshold. We then quantified the synchronisation between extreme events using the event synchronisation (ES) method and compared our findings to a null model distribution to ensure that the identified links were non-random. Subsequently, we constructed EPE and ESSTE complex networks and calculated key network metrics including degree centrality (Formula presented.), mean geographic distance (MGD) and clustering coefficient (Formula presented.). Our results showed that the EPEs and ESSTEs exhibited non-monotonic trends over the past nine decades, with significant increasing trends after 1980. Key EPE network hubs were detected in Mexico, the African Sahel and parts of Asia, while ESSTE hubs appeared in the Atlantic Ocean near the UK and US borders, the Pacific Ocean close to East Asia and the Mediterranean and Red Seas. Analyses of MGD and (Formula presented.) revealed that the EPE network had larger MGDs and more intense local clustering in continental areas (Sahel and East Asia), indicating that EPEs experience teleconnections within these locations even though they also experience strong local associations. The findings of our EPE network contrast with those of our ESSTE network, which had lower MGD values and close clustering within specific ocean basins, as expected due to localised ocean–atmosphere coupling. Our findings suggest that the drivers for extreme climate events are complex and can lead to strong local and global connections.