Fig. 1: Four preferred heatwave propagation pathways in the Northern Hemisphere from 20°N to 70°N, detected by the complex network algorithm.

Network divergence is a directed-network metric defined as the difference between the number of outgoing edges and the number of incoming edges at that specific grid cell, with positive values (red) representing the occurrence sources of events and negative values (blue) representing sinks. The four pathways (yellow) cover North America and the Eurasian continent, with starting and ending points indicated by cyan and red, respectively. The starting node of the Western Europe (WE) path is starting from the land (since we focus on land heatwaves), although strongest positive divergence over this pathway is over the ocean.