Variability of the aridity index and related drought parameters in Greece using climatological data over the last century (1900–1997)

The temporal variability of the aridity index (AI) in Greece is examined over an almost century period (1900–1997) and for a number of meteorological stations according to data availability. The analysis is carried out for three distinct climatic periods: 1900–1929, 1930–1960 and 1961–1997. In addition to the use of AI, other drought related parameters based on Thornthwaite's water budget approach are adopted to provide more insights into the variability of AI. Results show a relatively slow but steadily progressive establishment of drier conditions in most areas. During the early climatic period most of the totally 25 examined areas in the Greek peninsula are classified as ‘Humid’ with a few exceptions for the ‘Sub-Humid’ class and for the ‘Semi-Arid’ class'. Within the second examined period, a shift from the ‘Sub-humid’ class towards the ‘Semi-Arid’ class appeared mostly in the Aegean Sea Cyclades Islands. The most significant shift was found to appear during the third period with changes from the ‘Humid’ class to the ‘Sub-humid’ class in parts of the continental Greece, in Eastern Crete and in mountainous areas. In some areas (e.g. Attica basin) AI values tend to approach the threshold value for shift from the ‘Semi-Arid’ class to the ‘Arid’ class whereas for a number of areas located in the western coastal region, the AI class ‘Humid’ remains unchanged during all three periods. •A relatively slow but steadily progressive establishment of drier conditions in most areas occurs•A shift from ‘Sub-humid’ towards ‘Semi-Arid’ class appeared in the Aegean Sea Cyclades during 1930–1960•The most significant shift (‘Humid’ to ‘Sub-humid’) was found to appear during 1961–1997•Some continental areas tend to approach the threshold index value for shift from ‘Semi-Arid’ to ‘Arid’•Some areas in the western coastal region maintain the Humid class unchanged during all climatic periods