Glaciers play also a major role in several parts of the world to smooth water flows in rivers across time, for which irrigation is in some cases strongly dependent on (FAO, 2011). Climate change could also have implications in terms of the interactions betw een ground and surface water compartments, as water stress on the latter could be transmitted to the former in the dry season. One can also expect an indirect effect of climate change through an increasing demand for groundwater as surface water becomes scarce and droughts more frequent and severe. Groundw ater depletion may occur in some places and be aggravated in places where depletion already exists. Agricultural w ater withdrawal, including irrigation, already represents a substantial amount of groundwater withdrawals in some countries (Figure 1.5), and a trend towards more frequent droughts may be an incentive to close the crop w'ater requirement gap with groundwater resources. Data for Greece refer to year 2004.