Climate, Climate Variability and Impacts in the Mediterranean Area: An Overview
83
The overall goal of the experiment was to determine the interactions between
soil, vegetation, and atmosphere at a scale of approximately 10 4 km 2 • Within this
area at three representative experimental sites - one dry farming, one with mixed dry
farming and irrigated fields, and one with mainly matorral vegetation - fixed
instrumented stations were installed. In each ofthese areas was a nucleus of heavily
instrumented masts surrounded by some additional stations up to a few kilometre
distant to investigate spatial inhomogeneities. With portable equipment and remote
sensing measurements from aircraft and satellites the areas in between these densely
instrumented sites were bridged over and a synoptic view of the whole area was
generated. Due to a number of instrument intercomparisons that have been made
during EFEDA, the error range in the determination of energy budget components
(for which no absolute standard exists) could be quantified.
The detailed experimental data of the surface energy budget and water transfer
within the soils and through the plants into the atmosphere lead to an improvement
and adaption for the semi-arid conditions of models that can now be used with much
more confidence. For this purpose also an extensive intercomparison of soilvegetation-atmosphere transfer (SV AT) schemes was conducted. The structure of the
atmospheric boundary layer that is responsible for the escape into the free
troposphere of the water vapour evaporated at the surface was studied with the dense
radiosonde network that could be established in the area, sodar, and flux
measurements from aircraft that provided detailed information on fluxes and water
vapour as well as aerosol distributions. The availability of these aeronomical data
allowed to initiate and to test mesoscale models which simulated the atmospheric
circulation system in the area and the effect of the land-sea circulation that develops
at the Mediterranean coast (Bolle, 1998). The evaluation of satellite data gained
immensely from the possibility to validate the inference of primary quantities such
as reflectance, temperature and vegetation indices by intercomparisons with ground
measurements. In addition, more complex evaluation schemes such as needed to
derive surface energy fluxes from remote sensing data could be tested and applied
for the whole area. Based upon these experiences completely new satellite data
processing and correction schemes have been developed during EFEDA.
To embed the hydro-meteorological process studies into the general ecological
situation of the area, intensive studies of the hydro-geology of the area, of the
structure and the degree of degradation of the soils, of vegetation parameters
including the CO2-exchange, and of the land use as well as its recent changes have
been carried out.
The EFEDA project lead to
a general improvement of experimental and model techniques to study complex
land-surface processes,
2 a thorough understanding of the importance of and interactions between the
land-surface processes during a drying period and thus for aridification which
is one precurser of desertification, and
3 the conclusion that the sustainable development of the investigated area is in a
very critical phase, if
a) the water resources are not recharged (e.g. due to climatic change
83
The overall goal of the experiment was to determine the interactions between
soil, vegetation, and atmosphere at a scale of approximately 10 4 km 2 • Within this
area at three representative experimental sites - one dry farming, one with mixed dry
farming and irrigated fields, and one with mainly matorral vegetation - fixed
instrumented stations were installed. In each ofthese areas was a nucleus of heavily
instrumented masts surrounded by some additional stations up to a few kilometre
distant to investigate spatial inhomogeneities. With portable equipment and remote
sensing measurements from aircraft and satellites the areas in between these densely
instrumented sites were bridged over and a synoptic view of the whole area was
generated. Due to a number of instrument intercomparisons that have been made
during EFEDA, the error range in the determination of energy budget components
(for which no absolute standard exists) could be quantified.
The detailed experimental data of the surface energy budget and water transfer
within the soils and through the plants into the atmosphere lead to an improvement
and adaption for the semi-arid conditions of models that can now be used with much
more confidence. For this purpose also an extensive intercomparison of soilvegetation-atmosphere transfer (SV AT) schemes was conducted. The structure of the
atmospheric boundary layer that is responsible for the escape into the free
troposphere of the water vapour evaporated at the surface was studied with the dense
radiosonde network that could be established in the area, sodar, and flux
measurements from aircraft that provided detailed information on fluxes and water
vapour as well as aerosol distributions. The availability of these aeronomical data
allowed to initiate and to test mesoscale models which simulated the atmospheric
circulation system in the area and the effect of the land-sea circulation that develops
at the Mediterranean coast (Bolle, 1998). The evaluation of satellite data gained
immensely from the possibility to validate the inference of primary quantities such
as reflectance, temperature and vegetation indices by intercomparisons with ground
measurements. In addition, more complex evaluation schemes such as needed to
derive surface energy fluxes from remote sensing data could be tested and applied
for the whole area. Based upon these experiences completely new satellite data
processing and correction schemes have been developed during EFEDA.
To embed the hydro-meteorological process studies into the general ecological
situation of the area, intensive studies of the hydro-geology of the area, of the
structure and the degree of degradation of the soils, of vegetation parameters
including the CO2-exchange, and of the land use as well as its recent changes have
been carried out.
The EFEDA project lead to
a general improvement of experimental and model techniques to study complex
land-surface processes,
2 a thorough understanding of the importance of and interactions between the
land-surface processes during a drying period and thus for aridification which
is one precurser of desertification, and
3 the conclusion that the sustainable development of the investigated area is in a
very critical phase, if
a) the water resources are not recharged (e.g. due to climatic change