8
H.-J. Bolle
topography and an improved representation of the land-surface processes in the
models. These models have to simulate interacting processes from the scale of the
general circulation down to regional and even local processes at or near the Earth
surface. Without going into modelling details an overview of the interactions
between the various scales involved is presented in the following section. Land
surfaces are coupled to the atmospheric climate system by the exchange of energy,
momentum, and fluxes of substances. These processes are dealt with in the next two
sections under very specific points of view. Firstly, the exchange of carbon in its
volatile compounds is considered, because the global carbon cycle is offundamental
importance for the estimation ofthe future evolution of the greenhouse effect. Some
of these volatile compounds as well as particles raised from the surface furthermore
interact with atmospheric chemistry and radiative energy transfer and therefor are
of equal importance for the climate system at least in a regional sense. A central
question for the Mediterranean area is, whether a trend is superimposed to the
presently observed climate variability or whether "simply" an increase of the
amplitude of the variability is experienced. The water cycle is discussed in the light
of data analysis and model predictions. Conclusions are summarized in the final
section.
2 Characteristics of the Mediterranean Environment
2.1 Climatological Mean Values
The Mediterranean type of climate is found mainly at the west coasts of the
continents between 30' and 45' latitude in the European/ African/Levantine
Mediterranean basin, South Africa, Chile, Mexico, USA, and South Australia. It is
characterized by winter rains and summer droughts with a strong soil water deficit
in summer. It is a temperate rainy, humid meso-thermal climate with dry subtropical
warm to hot summers. The average temperature of the hottest month can be >22
c
C.
The strong difference between the wet winters and the dry summers is caused by the
seasonal alternation of the dominance of cyclonic storms in winter and subtropical
high pressure cells over the adjacent ocean in summer with subsiding maritime
tropical air causing dry conditions in summer. The Mediterranean climate in most
regions is confined to narrow coastal belts. Only in the European/African/Near East
area, because of the Mediterranean Sea, it covers about 10 Mkm 2 reaching from
Portugal to south of the Caspian Sea with a core area that stretches over 46 degrees
longitude and covers about 6 Mkm 2 . Of this area 2.496 * 10 6 km 2 belong to the
Mediterranean sea surface. If the Black and Marmara Seas are counted as well, the
sea surface covers 3.1 * 10 6 km 2 •
Within the belt of Mediterranean climate exists a strong gradient of the
meteorological parameters. As an example, in Monterey, California (3605' N), the
annual monthly temperatures range between lO'C and 16.TC, the precipitation
H.-J. Bolle
topography and an improved representation of the land-surface processes in the
models. These models have to simulate interacting processes from the scale of the
general circulation down to regional and even local processes at or near the Earth
surface. Without going into modelling details an overview of the interactions
between the various scales involved is presented in the following section. Land
surfaces are coupled to the atmospheric climate system by the exchange of energy,
momentum, and fluxes of substances. These processes are dealt with in the next two
sections under very specific points of view. Firstly, the exchange of carbon in its
volatile compounds is considered, because the global carbon cycle is offundamental
importance for the estimation ofthe future evolution of the greenhouse effect. Some
of these volatile compounds as well as particles raised from the surface furthermore
interact with atmospheric chemistry and radiative energy transfer and therefor are
of equal importance for the climate system at least in a regional sense. A central
question for the Mediterranean area is, whether a trend is superimposed to the
presently observed climate variability or whether "simply" an increase of the
amplitude of the variability is experienced. The water cycle is discussed in the light
of data analysis and model predictions. Conclusions are summarized in the final
section.
2 Characteristics of the Mediterranean Environment
2.1 Climatological Mean Values
The Mediterranean type of climate is found mainly at the west coasts of the
continents between 30' and 45' latitude in the European/ African/Levantine
Mediterranean basin, South Africa, Chile, Mexico, USA, and South Australia. It is
characterized by winter rains and summer droughts with a strong soil water deficit
in summer. It is a temperate rainy, humid meso-thermal climate with dry subtropical
warm to hot summers. The average temperature of the hottest month can be >22
c
C.
The strong difference between the wet winters and the dry summers is caused by the
seasonal alternation of the dominance of cyclonic storms in winter and subtropical
high pressure cells over the adjacent ocean in summer with subsiding maritime
tropical air causing dry conditions in summer. The Mediterranean climate in most
regions is confined to narrow coastal belts. Only in the European/African/Near East
area, because of the Mediterranean Sea, it covers about 10 Mkm 2 reaching from
Portugal to south of the Caspian Sea with a core area that stretches over 46 degrees
longitude and covers about 6 Mkm 2 . Of this area 2.496 * 10 6 km 2 belong to the
Mediterranean sea surface. If the Black and Marmara Seas are counted as well, the
sea surface covers 3.1 * 10 6 km 2 •
Within the belt of Mediterranean climate exists a strong gradient of the
meteorological parameters. As an example, in Monterey, California (3605' N), the
annual monthly temperatures range between lO'C and 16.TC, the precipitation