Last Friday we published a chart highlighting the precipitous falls in population going on in some of Eastern Europe’s biggest cities. The obvious question is: where did they all go?

Today’s chart provides a possible answer. When economic crises hits, rich and cosmopolitan cities find themselves flooded with job seekers. Look at the figures for London, Brussels and Berlin, all of which number among the continent’s most cosmopolitan cities:

Annual growth in working age population (%). Source: CityMetric Intelligence. 

The spike in the figures that happens in 2011-12 is largely down to immigration. Figures for Brussels and Berlin show that both cities saw an influx of migrants in 2011-12 – largely young, largely from those parts of Europe that were suffering most from the Eurozone crisis. Comparable figures for London aren’t available – but the UK as a whole recorded its highest net migration ever in the year ending March 2011.

Berlin, in particular, actively welcomed this wave of arrivals. A headline in Der Spiegel magazine read, “All Will Profit from New Wave of Immigrants”, while the German labour minister, Ursula von der Leyen , told the Frankfurter Allgemeine Zeitung newspaper:

“All sides will profit hugely from the influx because the new wave of immigrants is younger and better educated than the average population.”

The graph suggests an explanation for why the German authorities should be more welcoming to new arrivals than some others we could name: Berlin’s working age population had recently been falling. In fact, the population of what used to be East Germany, a region with Berlin at its heart, has been falling steadily since the wall came down in 1989; it’s expected to drop by another third by 2060. Birth rates are low and young people are moving away, leaving the city at risk of an ageing population.

It remains to be seen whether, as the economic situation improves, migrants will leave these cities to return home. Berlin, for one, must be hoping they’ll stay.