The hydrology of the Mediterranean is characterised by high rainfall intensities,
orographic regions, rapid changes in land use and cover and small and highly
variable recharge rates. The implications of global climate change on the
hydrology of the area are highly uncertain with respect to predictions
of precipitation and precipitation variability. In contrast, land use change
and human use of water are likely to have a profound impact on the water
cycle of the area.
Precipitation.
To understand the variability of rainfall in the region and its sensitivity
to global climate change, we need first to analyse existing data records.
Secondly we need to develop the use of new technologies such as radar and
satellite information to improve our predictive capability in regions with
sparse networks. Existing regional models could also be used to determine
the relative role of the land surface versus oceanic forcing of rainfall.
It is essential for hydrological studies that rainfall is modelled at a
scale comparable to those of hydrological catchments. Techniques to down
scale rainfall from models to hydrologically relevant scales are currently
being developed and need to be tested and maybe adapt for the Mediterranean
area. Attempts at coupling of hydrological and atmospheric mesoscale models
must be supported and further developed. Special attention needs to be
paid to topographical effects.
Land use change and hydrology.
Human induced land use change and human use of water are particularly
important in assessing the impact on water availability in the region in
long term development of agricultural and other socio-economic practices.
Considerable effort needs to be put into place to understand the basic
hydrological processes in the area which allow sustainable rates of ground
water use. These may be differ for the Northern and Southern countries.
In particular the role of vegetation, or land cover, in determining rates
of evaporation, infiltration, runoff and erosion and ground water recharge
needs to be better understood. Our current understanding of ground water
recharge rates in the area is still extremely poor. The role of fires in
the hydrological cycle is poorly understood, but is likely to be important
in terms of runoff and sediment transport and nutrient availability.
Monitoring of land use change in the area is critically important in assessing changes in the hydrological regimes.
Aspects of water quality are likely to be important, both in terms
of changes in nutrient availability for vegetation as well as pollution
by agriculture or other sources.
Paleo hydrological studies have a special role here. Especially the
North African regions has a relatively good record of paleoclimatology.
It may be desirable on this basis to install experimental catchments
with more detailed process studies to identify the basic processes determining
recharge. Ultimately the water budget of heterogeneous areas needs to be
determined to know how much water is available for recharge. Such studies
should concentrate on the major gains and losses of water in the system
such as adequate estimation of precipitation input, estimation of areas
evaporation and runoff, etc.. From the basic process knowledge we need
to be able to generalise this knowledge to other areas of the Mediterranean.
The high spatial heterogeneity of the region, in soils, vegetation and
topography makes this a non-trivial task. New experimental work should
be concentrated in areas with expected high sensitivity to changes in land
use.
Capacity building and training
Existing networks such as Friend-Amhy and Med-Hycos collate records
of streamflow. These should be used to build new networks upon. Integrated
modelling of hydrological, meteorological, ecological and oceanographic
cycles will automatically bring together scientist from the Mediterranean
area and establish a joint network aimed at understanding the "life" of
the Mediterranean.