This seems awfully high, and this number is notoriously hard to determine -- you don't really know a cohort's divorce rate until they're all dead, and meanwhile they're all mixed up with other cohorts. Looking at the original source, these appear to be the ratio of divorces in a given year divided by marriages that same year. That kind of statistic is roundly criticized as unscientific, although it seems like it would be meaningful in the long run.
This kind of measurement will generally overstate the likelihood of divorce, because marriage rates are mostly falling, as are divorce rates. So the raw divorce rate now, from older, more plentiful, marriages, is being compared with the current marriage rate, which is lower and which will translate into a lower divorce rate later on.
Population growth or decline does not affect this, IF what is being compared is raw per capita divorce rates versus marriage rates. However, Eurostat, the source of these numbers, defines "Divorces per 100 marriages" as "the ratio between the number of divorces (independently of the duration) and the number of marriages in a given year." So if they are being careful with their terms, that means absolute numbers, not rates.
(For the study's stats on duration of marriages before divorce, and children in divorces, see European Divorce Monitor.)
Portugal: 69
Denmark: 56
Spain: 56
Finland: 55.4
France: 55
Belgium: 52.7
Netherlands: 51.2
Italy: 48.7
Norway: 42
UK: 41.7
Germany: 40.8
Hungary: 37.7
Austria: 35.5
Poland: 32.8
Greece: 22.2