Dryland areas are regarded as highly sensitive to climatic changes. A positive relationship between average
annual rainfall, and environmental factors (water availability, species diversity, etc.), is often assumed for areas
with an average annual rainfall of 100-300 mm. However, the global climatological models fail to address an
important issue. The above assumption disregards the fact that a climate change in some dry-land areas is not
limited to climatic factors. It is often accompanied by a pronounced variability in surface properties, such as the
deposition of loess in a wet climatic phase, and of sand during a dry climatic phase. Needless to say, the spatial
variability of the new surface properties may have variable effects on water resources and related
environmental variables. In addition, the climatic models, based on average annual rainfall, disregard the rainfall
characteristics at the rain-shower level, which greatly influence the degree to which rainwater will percolate, or
will be transformed into runoff, thereby significantly affecting the spatial redistribution of water resources. In
other words, a climate change in dryland areas would be expected to have differential hydrological effects in a
sandy area, a rocky area, or in a loess covered area. Differential spatial hydrological effects would be also
expected within each of the areas listed above. The present manuscript deals with the complex relationships
between average annual rainfall, and environmental variables in sandy areas, at three research sites, along a
rainfall gradient of 90-450 mm, in the south eastern Mediterranean area, Israel. Data obtained clearly show that
average annual rainfall is not a good indicator of water resources, and ecosystem structure, in each of the sites;
and the controlling factors vary from one site to another.
Ceramic finds from the Byzantine fort of Gradina on the island of Žirje
