Eco-geomorphological system response variability to the 2004–06 drought along a climatic gradient of the Littoral Betic Range (southern Spain)

One of the main characteristics of the Mediterranean climate is the high frequency of droughts which last for a year or more and the appearance of dry spells within the wet season. The Littoral Betic Range, in the South of the Iberian Peninsula, shows a significant climatic gradient from the Straits of Gibraltar (1600 mm year− 1) to the Cabo de Gata (150 mm year− 1). These differences in climatic conditions result in variations in the elements of the eco-geomorphological system at the hillslope scale. This study aimed to analyse the immediate consequences of a two-year drought period (2004–06) on several elements of the Mediterranean eco-geomorphological system on three hillslopes under different climatic conditions (sub-humid, dry Mediterranean and semi-arid). The soil water content, the pattern of vegetation and some soil properties (organic matter content, aggregate stability and permeability) were analysed before (Nov-2003) and during (Nov-2005) the drought period. The most important findings were: i) a reduction in the soil water content which reached values below the wilting point in the wet seasons, affecting negatively the water available for vegetation especially in the wettest sites; ii) a reduction in vegetation cover and the number of plants, especially on semi-arid field sites; iii) changes in the organic matter content which aggravate the loss of stability of soil aggregates, a process seen more clearly under more arid conditions; and iv) a reduction of soil permeability in all situations in the climate gradient studied, which supposes a priori an increase in erosive processes due to surface runoff. These results indicate increased vulnerability of the eco-geomorphological system because of the rainfall drought situation.