How do local topological changes affect the global operation and stability ofcomplex supply networks? Studying supply networks on various levels ofabstraction, we demonstrate that and how adding new links may not only promotebut also degrade stable operation of a network. Intriguingly, the resultingoverloads may emerge remotely from where such a link is added, thus resultingin nonlocal failure. We link this counter-intuitive phenomenon to Braess'paradox originally discovered in traffic networks. We use elementary networktopologies to explain its underlying mechanism for different types of supplynetworks and find that it generically occurs across these systems. As animportant consequence, upgrading supply networks such as communicationnetworks, biological supply networks or power grids requires particular carebecause even adding only single connections may destabilize normal networkoperation and induce disturbances remotely from the location of structuralchange and even global cascades of failures.
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