Sovereign public debt crisis in Europe. A network analysis

• Dynamical networks of government debt as a percentage of GDP; quarterly, 2000–2014.
• Cophenetic correlation to analyse persistency of hierarchical trees during the financial crisis.
• High synchronicity and connectivity and low number of communities at the time of the crisis.
• Less diversification and more centralized network arrangements.
• New network organization after the financial crisis arranged by public debt levels.

In this paper we analyse the evolving network structure of the quarterly public debt-to-GDP ratio from 2000 to 2014. By applying tools and concepts coming from complex systems we study the effects of the global financial crisis over public debt network connections and communities. Two main results arise from this analysis: firstly, countries public debts tend to synchronize their evolution, increasing global connectivity in the network and dramatically decreasing the number of communities. Secondly, a disruption in previous structure is observed at the time of the shock, emerging a more centralized and less diversify network topological organization which might be more prone to suffer contagion effects. This last fact is evidenced by an increasing tendency in countries of similar level of public debt to be connected between them, which we have quantified by the network assortativity.