Region: Sahara-Sahel-Arabia-Minor Asia
Name of the data files : surface_Sahara_Sahel_Arabia_MinorAsia_1x1deg_V01.dat
Spatial resolution : 1°x1°
Domain : 13°N-36°N; 17°W-77°E
References : Marticorena et al., 1997; Callot et al., 2000
PI of the data set : Béatrice Marticorena (email@example.com)
Description of the files
The «surface_xx.dat» file includes one to five types of surface features (SF) in each grid cell.
For each grid cell the parameters are:
(X,Y; referred by the left high corner of the box)
For each of the 5 SF are given:
sol(i): soil label for SF i
p(i): fraction of the cell for SF i
z0s(i): smooth roughness length for SF i
Z01(i): total roughness length for SF i
Z02(i): second roughness length for SF i
D(i): the distance between two roughness elements for SF i
E(i): erodible fraction of the surface for SF i
The «solspe_xx.dat» file contains the parameters of the soil size distribution of the different soils (3*(Dmed; σ; p), the ratio of vertical to horizontal flux and the residual soil moisture W0i.
As described in Marticorena et al. (1997) and Callot et al. (2000), all parameters are derived from a geomorphologic approach leading to the mapping of the soil types and of the mean height and cover rate of roughness elements. The basic information used for the mapping is topographic maps and their level of accuracy varies a lot as a function of the location.
For the Central and Western Sahara, the French National Geographic Institute (I.G.N.) maps at various scales (1:200 000, 1:500 000, 1:1 000 000) have been mainly used. Made by photointerpretation, their quality is usually quite good even when they have been made at the beginning of the sixties. These maps offer a good representation of the topography and the dunes areas. But they give no detail on surface features, which are indicated only on some maps of the Southern Sahara (particularly in Mauritania).
For Libya and Egypt, we mainly used the 1:200 000 and some 1:500 000 Russian maps (Map of the world, made ~1980). Their topography is correct, but being almost monochrome, they are difficult to read. They sometimes give data on the nature of the land, which are only indicated by texts as ′hard rocks′, ′sand sheet′, etc., with no accuracy on their geographical limits.
For regions where no other information was available (e.g. the Sudan, Afghanistan, Pakistan), the 1:250 000American maps (J.O.G.) issued by the Army Map Service of the US Army (1957-1958), have been used in regions. Their quality is highly variable. Some of them, being made without any photo-interpretation, are almost unusable. They also sometimes give indications on the nature of the land, but they are as lacking in details as the Russian maps.
Additional information was found in the following references available at the French National Geographic Institute (I.G.N.):
«Climatic Atlas of Asia» prepared by the Voeikov Main Geographical Observatory, Leningrad, USSR, WMO-UNESCO, Goscomgidromet USSR, UNEP, 1981.
«Atlas géologique du Monde au 1/10 000 000», Commission de la carte géologique du monde, UNESCO, Paris, 1976.
«Geological Map of Asia and the far East», second edition (revised)1976; 1/5 000 000 ; prepared under the sponsorship of the United Nations Economic Commission for Asia and the far East (ECAFE); printed by Kokudo Mpping Co., Ltd. Tokyo, Japan.
«Geologic map of the Arab World»; 1987; published by the Arab Organisation for Mineral Resources, Rabat, Morocco; under the direction of the Secretary General; H.E. Ahmed Alaoui M. Hamdi.
«Geologic Map of the Kingdom of Libya»; 1/2 000 000; compiled by Louis C. Conant and Gus H. Goudarzi; under the joint sponsorship of the kingdom of Libya (Ministry of National Economy) and the Agency for International Development, US Department of State; 1963, prepared by the Geological Survey, 1959-1962.
For the Sahel, the mapping was mainly based on the maps from the French National Geographic Institute (I.G.N.) maps at various scales (1/200 000, 1/500 000, 1/1 000 000). In these regions, indications on vegetation types lead to no detail on surface features. We thus defined typical values of roughness length for the following vegetation type (Herbaceous step, Tiger Bush, Bush land savanna, Woody savanna, dry forest, dense forest).
The roughness values are very high, since they correspond to a fully developed vegetation and has been applied to the whole surface where the maps indication the possible presence of this vegetation type. In addition the most recent maps have been made in the sixties, so the vegetation cover appears as quite over estimated when compared to present maps of vegetation indexes.