Complex sentence: After a gradual reduction of population during the nineties, Miranda has gained inhabitants year after year thanks partly to arrivals from neighboring Alava in search of cheap housing, but also to the increase in the immigrant population (10.8% of the total).
Split into simpler sentences: After a gradual reduction of population during the nineties, Miranda has gained inhabitants each year due in part to arrivals from neighboring Alava in search of cheap housing. There has also been an increase in the immigrant population (10.8% of the total).