Climate aridity (the long-term balance between water availability through precipitation and the atmospheric evaporative demand) has a fundamental role in determining water availability and the geographic distribution of ecosystems and agricultural regions, and plays a crucial role in shaping ecological transitions under current climate change. We computed the Aridity Index, computed as the ratio of precipitation to reference evapotranspiration, over Spain for the period 1961-2020. Here we present spatially detailed climatologies of the Aridity Index, at the annual and the monthly scales, and an assessment of changes between the normal periods 1961-1990 and 1991-2020. The results show a transition towards reduced values of the Aridity Index (i.e., towards drier conditions) at the annual scale, which was more intense in the Canary Islands (where 16.3% of the territory transitioned towards more arid climate categories) than in mainland Spain and the Balearic Islands (11.6%). At the monthly level, the most striking changes over mainland Spain occurred in June, with 39.7% of the territory transitioning towards more arid categories, while transitions towards more humid conditions have only been relevant in March (23.5%) and October (13.0%) and did not compensate for the aridification trend when the whole year is considered. In the Canary Islands, the strongest changes occurred in May (22.6%) and September (19.4%), although drying trends were found almost in all months except the summer.