Analysis of beginning, end, and length of the rainy season along a Mediterranean-arid climate transect for geomorphic purposes

Geomorphic processes are controlled by rainfall, particularly in Mediterranean semi-arid and the arid regions. From a geomorphological aspect the characteristics of rainstorms and dry spells in these regions should be analysed as they might explain these processes. As a part of such analysis the beginning, end, and length of the rainy season should be determined. Eleven stations along a climatic transect extending from Judean Mountains with a Mediterranean climate to the Dead Sea arid region in Israel were studied. The beginning, end, and length of the rainy season, based on rainfall data for 30 years, are presented for daily rainfall and for accumulated rainfall within a rain spell (ARWS), and for different thresholds that might be used for different geomorphic processes. The results show that: (1) a close linear relationship exists between the beginning and end dates, as well as the rainy season's length, and the various rainfall thresholds; (2) as rainfall threshold increases the rainy season begins later, ends earlier, and consequently it is shorter in length; (3) likewise, as aridity increases the rainy season begins later, ends earlier, and it is shorter in length; and (4) the differences increase as the threshold increases. The regression line slopes emphasized a distinction between the two climatic regions, the Mediterranean and the arid region.