Trends in evapotranspiration, temperature and precipitation in the main grassland areas of the Iberian Peninsula (1981-2022).

The dehesa, recognised as the most extensive High Natural Value Agricultural System in Europe, is one of the main natural and economic resources of the Southwest of the Iberian Peninsula and therefore of Europe. Numerous studies indicate that an increase in temperatures (Tm) and a reduction in precipitation (P) are expected due to climate change, especially in this area. This would lead to an increase in Evapotranspiration (ETP), which represents the water requirements of plants, and a reduced rainfall.  Utilizing time series data on climatic parameters spanning the period 1981-2021, a comparative analysis was conducted on the major pasture regions of Spain and Portugal (namely, Salamanca, Cáceres, Badajoz, Beja, Lisbon, and Córdoba). The analysis employed a range of statistical tests, including one-way analysis of variance (ANOVA) and Tukey's test, as well as Dunnet's test. Additionally, trends were examined through the utilization of the Mann-Kendall test and Sen's slope estimator (Q). The results obtained demonstrated significant variations between the grassland areas for the variables analyzed. Córdoba was found to have the highest mean annual temperature and ETP, while Salamanca exhibited the lowest values for temperature, precipitation and ETP. All areas demonstrated an increase in temperature, with Lisbon, Córdoba and Badajoz exhibiting particularly significant trends. However, precipitation did not exhibit a discernible trend. These findings contribute to the climatic characterization of the grassland regions and have the potential to impact the productivity and quality of pasture and woodland. This necessitates an adaptation of management techniques (stocking rate, frequency of grazing) and cultivation, as well as a change in the distribution of suitable areas.