22
H.-1. Bolle
consistent with summer monsoon rains penetrating much deeper northward into the
Sahara than nowadays. It is estimated (Lamb, 1982), that at this time there was 200400 mm annual precipitation in the now hyperdry regions ofthe Sahara. The current
"Azorean" high was at that time probably close to the Biscay, north-west of Spain
(Lamb, 1977). The Saharan drying period started about that time, though until about
5000 B.P. there are relics in the Sahara indicating that still enough water was
present to sustain life. This era coincided with a remarkable change in the
composi tion of forests in other parts of the world and advances of the alpine glaciers.
Between 5.5 and 5 or 4.8 ka B.P. there has been a short (few centuries) lasting cold
period that ended the warm period with its storm belt at high latitudes and had
remarkable impact on the vegetation, which did never completely recover from this
"Piora Oscillation". From that time on the high pressure belt moved back into its
current position of about 30132°N, and the positions of the Azorean high and the
Icelandic low determine to a large extent the weather situation in Europe.
From 7 ka to 5 ka B.P. oak, hazel and birch slowly gave way to hornbeam, fir
and beech. A decline of vegetation development was noted around 6 ka B.P., except
for maple, accompanied by an increase of herbaceous taxa. This could have been
caused by increased rain but also during this time the anthropogenic intervention,
clearances and grazing, became evident, probably first in Greece. Small villages
were established in lowlands near the coasts.
4.2 ka B.P. climate changed abruptly, it occurred the Mesopotanean drought
(Otterman and Starr, 1995). Dryness increased in general but with imbedded wetter
periods. Intensive agro-pastoral activities developed. Olive trees were widely grown
which contributed to the protection of vulnerable land but coastal pine forest were
cut for ship construction. First traces of desertification appeared and propagated
towards extensive erosion on hilly land and salinisation of irrigated land. Deciduous
woodland was successively replaced by garrigue. In Turkey, which is one of the
palaeolithic and neolithic settlement areas, first clearance started around lake
Beysehir 3 - 4 ka B.P. and continued up to the present time (Atalay, 2001). Around
3.2 ka B.P. the population decreased severely until about 2.5 ka B.P. when Greek
colonies were established at the northern and southern coasts of the Mediterranean.
The population moved from low lying settlements at rivers to higher fortified
locations and concentrated more in centres.
3.4 From the Roman Period to the Little Ice Age
Reorganization of land use took place by the Phoenicians and Romans. The Roman
domination started about 2.1 ka B.P. when also marginal land was cultivated and the
environment modified by drainage systems, river damming and aqueducts.
Associated with agricultural expansion and further deforestation around 2 ka B.P.
the vegetation changed as documented in palynological records and reconstructed
from historical sources (Reale and Dirmeyer, 2000).
These large scale changes ofland use may have contributed to long term climate
change in this area. To test this hypothesis a coupled land-atmosphere climate model
H.-1. Bolle
consistent with summer monsoon rains penetrating much deeper northward into the
Sahara than nowadays. It is estimated (Lamb, 1982), that at this time there was 200400 mm annual precipitation in the now hyperdry regions ofthe Sahara. The current
"Azorean" high was at that time probably close to the Biscay, north-west of Spain
(Lamb, 1977). The Saharan drying period started about that time, though until about
5000 B.P. there are relics in the Sahara indicating that still enough water was
present to sustain life. This era coincided with a remarkable change in the
composi tion of forests in other parts of the world and advances of the alpine glaciers.
Between 5.5 and 5 or 4.8 ka B.P. there has been a short (few centuries) lasting cold
period that ended the warm period with its storm belt at high latitudes and had
remarkable impact on the vegetation, which did never completely recover from this
"Piora Oscillation". From that time on the high pressure belt moved back into its
current position of about 30132°N, and the positions of the Azorean high and the
Icelandic low determine to a large extent the weather situation in Europe.
From 7 ka to 5 ka B.P. oak, hazel and birch slowly gave way to hornbeam, fir
and beech. A decline of vegetation development was noted around 6 ka B.P., except
for maple, accompanied by an increase of herbaceous taxa. This could have been
caused by increased rain but also during this time the anthropogenic intervention,
clearances and grazing, became evident, probably first in Greece. Small villages
were established in lowlands near the coasts.
4.2 ka B.P. climate changed abruptly, it occurred the Mesopotanean drought
(Otterman and Starr, 1995). Dryness increased in general but with imbedded wetter
periods. Intensive agro-pastoral activities developed. Olive trees were widely grown
which contributed to the protection of vulnerable land but coastal pine forest were
cut for ship construction. First traces of desertification appeared and propagated
towards extensive erosion on hilly land and salinisation of irrigated land. Deciduous
woodland was successively replaced by garrigue. In Turkey, which is one of the
palaeolithic and neolithic settlement areas, first clearance started around lake
Beysehir 3 - 4 ka B.P. and continued up to the present time (Atalay, 2001). Around
3.2 ka B.P. the population decreased severely until about 2.5 ka B.P. when Greek
colonies were established at the northern and southern coasts of the Mediterranean.
The population moved from low lying settlements at rivers to higher fortified
locations and concentrated more in centres.
3.4 From the Roman Period to the Little Ice Age
Reorganization of land use took place by the Phoenicians and Romans. The Roman
domination started about 2.1 ka B.P. when also marginal land was cultivated and the
environment modified by drainage systems, river damming and aqueducts.
Associated with agricultural expansion and further deforestation around 2 ka B.P.
the vegetation changed as documented in palynological records and reconstructed
from historical sources (Reale and Dirmeyer, 2000).
These large scale changes ofland use may have contributed to long term climate
change in this area. To test this hypothesis a coupled land-atmosphere climate model