ABSTRACT
Arid, semi-arid and subhumid regions are called water limited environments and occupy about half of the global land area (Parsons and Abrahams 1994). Changes in water availability can have serious repercussions on the sustainability of these sensitive environments. The pressure on water and other natural resources is increasing in these areas as demands for water for human uses are growing rapidly (e.g., Newman et al. 2006). For instance, in the dryland Mediterranean regions, large increases in population, development of irrigated agriculture and rise of living standards have drastically increased the water use and in many basins future needs are hard to satisfy as many aquifers are already overexploited and surface water resources are endangered (Cudennec et al. 2007). Southern Africa faces similar challenges (e.g., van der Zaag 2005). The expected regional climate change (Christensen et al. 2007) poses yet another dangerous alteration of the hydrological regimes in these regions. This will also cause change in the water demand pattern, with an expected two-thirds of the world facing an increase in irrigation demand (Döll 2002).
