Monitoring land degradation in southern Tunisia: A test of LANDSAT imagery and digital data

The possible use of LANDSAT imagery and digital data for monitoring desertification indicators in Tunisia was studied. Field data were sampled in Tunisia for estimation of mapping accuracy in maps generated through interpretation of LANDSAT false color composites and processing of LANDSAT computer compatible tapes respectively. Temporal change studies were carried out through geometric registration of computer classified windows from 1972 to classified data from 1979. Indications on land degradation were noted in some areas. No important differences, concerning results, between the interpretation approach and the computer processing approach were found

The use of LANDSAT-1 imagery for water quality studies in southern Scandinavia

The possibilities of using LANDSAT-1 images for environmental studies, with special references to water quality studies, were investigated by selecting test areas in southern Scandinavia. The MSS images of different bands are compared under the magnification of an Interpretoscope and densitometric analyses are performed in a Schnell-photometer. The possibility of tracing pollution plumes is studied in the Oresund outside Copenhagen. The effect of different sewers and the circulation of the polluted water is analyzed in various situations. The variation in reflectivity of a great number of lakes in South and Middle Sweden is studied by means of densitometric analyses and significant regional differences are found. The correlation with in situ measurements of water quality (turbidity and secchi disc transparency) of the sampled lakes (made by the National Swedish Environment Protection Board) is fairly good

Biosphere feedback on regional climate in tropical north Africa

The impact of land-surface degradation over the Sahel area on seasonal variations of atmospheric and hydrological components over tropical north Africa are investigated in a general-circulation model numerical experiment, together with the mechanisms involved. The model was integrated for four years with and without vegetation change over the Sahel region with different initial atmospheric conditions. The results demonstrate that the degradation of the land surface can have a significant impact on the Sahelian regional climate. It increases the surface air temperature and reduces the precipitation, runoff and soil moisture over the Sahel region during the July-August-September (JAS) season. The impact is not only limited to the specified desertification area and the JAS season but is found also to the south of this area and extends into the October-November-December season. The changes in the annual rainfall cycle and the JAS mean surface temperature over the Sahel area are consistent with the observed climate anomalies of the past 40 years. The changes in rainfall to the south of the Sahel including eastern Africa are also in line with the observed anomalies. The reduction in total diabatic heating rate and relative increase in subsidence motion in the upper troposphere are consistent with the rainfall anomalies. The variations in convective heating rate, which were caused by changes in latent-heat flux from the land surface and moisture flux convergence in the atmosphere, are the dominating factors in this process. The radiative cooling is a secondary effect. The influence of the initial conditions on the simulation of the soil water balance is also analysed