Population Replacement and Migration in Two Spanish Regions during the Twentieth century

This short paper analyses population reproduction in two different regions of Spain, Castile-Leon and Madrid, during the twentieth century. Over this period, although the two regions experienced a similar demographic transition in terms of both mortality and fertility, the population of Madrid grew eight-fold (from 0.7 to 6 million) while that of Castile-Leon increased by less than 10% (from 2.3 to 2.5 million). This difference is due mainly to the effect of migration. In order to analyse this process, we used the birth replacement ratio index. This indicator provides two advantages with respect to other methods: first, it is a retrospective indicator that does not assume hypothetical scenarios about the impact of migration on population dynamics; second, it enables us to distinguish the effect of each component, specifically the impact of migration in the generational replacement process. We found that in contexts of very low fertility and very high survival rates, this migration component is the main determinant of the replacement process.