Temporal analysis of aridity in the Dehesa agroecosystems of the Iberian Peninsula (1981-2022)

This study analyses the temporal trends (1981-2022) of two widely used aridity indices: the De Martonne index (IDM) and the FAO aridity index (IF) in the main grassland agroforestry areas (Dehesa) of the Iberian Peninsula, in the context of current climate change. It is essential to understand aridity and its trends in order to assess the sustainability of these agricultural systems, especially in a global warming scenario. The annual IDM and IF have been determined in the Dehesa areas of the southwest of the Iberian Peninsula (Spain and Portugal). The mean IDM in these areas was 20.2 (corresponding to a Mediterranean-type climate), ranging from 16.0 in Badajoz with a semi-arid climate to 28.0 in Lisbon with a humid climate. The coefficient of variation ranged from 21% in Salamanca to 34% in Córdoba, indicating significant variations in the data. The mean IF was 0.44, corresponding to a semi-arid climate, ranging from 0.31 in Salamanca, also classified as semi-arid, to 0.75 in Lisbon, characterised by a humid sub-humid climate. The coefficient of variation ranged from 23% in Salamanca to 37% in Córdoba, reflecting substantial variations in the data. The findings of this study have enabled the identification of two distinct trends: a decrease in the indices in the Spanish regions and an increase in the indices in the Portuguese regions. These results imply that changes in management are necessary, particularly in regions where the indices demonstrate a decrease, given the increasing aridity, which directly affects the productivity of the dehesa agroecosystems by reducing water availability.