Aridity Conditions in the Iberian Peninsula During the XX Century

Aridity is one of the key elements characterizing the climate of a region, having a severe impact on water management, availability and human activities. Aiming at assessing aridity conditions in the Iberian Peninsula during the XX century, the spatial distribution of the De Martonne aridity index and Pinna Combinative index are analysed between 1901?2012 and three sub-periods: 1901?1940, 1941?1980 and 1980?2012. Gridded precipitation totals and air temperature datasets are used on a monthly basis. Results show that the southernmost of Iberia is particularly vulnerable to water stress and hence to desertification processes. In particular, both aridity indices revealed an increase and northward extension of the semi-arid regime in the Iberian Peninsula between 1901 and 2012. This increase is noteworthy for the period 1981 to 2012. More than 50% of the north and western territory have experienced humid to very humid conditions, while the other regions underwent semi-dry to dry settings. Results also reveal that climate was subjected to spatial and temporal variabilities with an overall statistically significant (at a 95% confidence level) trend towards to more severe aridity conditions in the south-easternmost and central regions with the exception of a small portion of the northwestern Iberia. The remaining territory of the Iberian Peninsula does not reveal statistically significant trends. High spatial correlations were also depicted between the De Martonne aridity index and the Pinna Combinative index.