no
CLAUDE J. GRENOT
Sahara, can be estimated only in the context of the general atmospheric
circulation."
The Plioquaternary paleoclimatology of the Sahara seems to be dominated by a series of contractions and expansions of the desertic domain
each of which are directly related to either a pluvial or an interpluvial
phase.
The succession of climatosedimentary events occurring in the western
part of the Algerian Sahara during that period is perfectly summarized
in Table I established by Conrad ( 1969).
From these ancient and moister periods, we find (a) a vestigial remainder of a vast hydrographie network (Fig. 2) (b) skeletons of animals
no longer existing in the Sahara today, but which are still found in Africa
(giraffe, elephant, rhinoceros), as well as fossil wood (Lavauden,
1927; Boureau, 1958; Louvet, 1971); (c) presence of abundant material of stone implements (paleolithic and neolithic), rock paintings, and
engravings which represent the animals mentioned above (Alimen, 1957;
Huard, 1953a,b, 1957; Lhote, 1955, 1957, 1958); (d) discovery of pollens, in neolithic strata, pertaining to species of mediterranean trees that are
now extinct in this region (Pons and Quézel, 1956; Van Campo et al.,
1965); and (e) presence of relict species of trees such as the cypress of
Duprez reported in Ajjer Tassili (Barry et al, 1970), as well as the Myrtus
nivellei, the Olea laperrini and the Pistacia atlantica (Quézel, 1965).
C. CLIMATIC FACTORS
The Sahara is of climatic origin. It is a desert because of its aridity and
not because of the nature of its soil (Lasserre, 1930; Brooks, 1932; Perret,
1935; Emberger, 1938; Dubief, 1953, 1959, 1963; UNESCO, 1958;
UNESCO-FAO, 1963; Monod, 1968, 1969; Planhol and Rognon, 1970).
This aridity is due to an insufficient amount of atmospheric precipitation
and also to an inadequate balance existing between the quantity of water
provided by rainfalls and the quantity lost through evaporation. We will
present here some unpublished météorologie data obtained at Reggan, a
hyperdesertic station of the central Sahara.
1. Rainfall
Because of the wind pattern and of its location far away from the sea,
the true Sahara is characterized by the scarcity of its rainfalls and also
by the irregularity of their yearly distribution, their volume and their intensity. There is less than 50 mm of precipitation per year. Rainfall in the
Sahara is not seasonal, and it is therefore impossible to measure it on a
CLAUDE J. GRENOT
Sahara, can be estimated only in the context of the general atmospheric
circulation."
The Plioquaternary paleoclimatology of the Sahara seems to be dominated by a series of contractions and expansions of the desertic domain
each of which are directly related to either a pluvial or an interpluvial
phase.
The succession of climatosedimentary events occurring in the western
part of the Algerian Sahara during that period is perfectly summarized
in Table I established by Conrad ( 1969).
From these ancient and moister periods, we find (a) a vestigial remainder of a vast hydrographie network (Fig. 2) (b) skeletons of animals
no longer existing in the Sahara today, but which are still found in Africa
(giraffe, elephant, rhinoceros), as well as fossil wood (Lavauden,
1927; Boureau, 1958; Louvet, 1971); (c) presence of abundant material of stone implements (paleolithic and neolithic), rock paintings, and
engravings which represent the animals mentioned above (Alimen, 1957;
Huard, 1953a,b, 1957; Lhote, 1955, 1957, 1958); (d) discovery of pollens, in neolithic strata, pertaining to species of mediterranean trees that are
now extinct in this region (Pons and Quézel, 1956; Van Campo et al.,
1965); and (e) presence of relict species of trees such as the cypress of
Duprez reported in Ajjer Tassili (Barry et al, 1970), as well as the Myrtus
nivellei, the Olea laperrini and the Pistacia atlantica (Quézel, 1965).
C. CLIMATIC FACTORS
The Sahara is of climatic origin. It is a desert because of its aridity and
not because of the nature of its soil (Lasserre, 1930; Brooks, 1932; Perret,
1935; Emberger, 1938; Dubief, 1953, 1959, 1963; UNESCO, 1958;
UNESCO-FAO, 1963; Monod, 1968, 1969; Planhol and Rognon, 1970).
This aridity is due to an insufficient amount of atmospheric precipitation
and also to an inadequate balance existing between the quantity of water
provided by rainfalls and the quantity lost through evaporation. We will
present here some unpublished météorologie data obtained at Reggan, a
hyperdesertic station of the central Sahara.
1. Rainfall
Because of the wind pattern and of its location far away from the sea,
the true Sahara is characterized by the scarcity of its rainfalls and also
by the irregularity of their yearly distribution, their volume and their intensity. There is less than 50 mm of precipitation per year. Rainfall in the
Sahara is not seasonal, and it is therefore impossible to measure it on a