Aerosols, atmospheric transmissivity and hydrological modelling of climatic change over Africa south of the equator
✍ Scribed by Tyson, Peter; Gasse, Françoise; Bergonzini, Laurent; D'Abreton, Peter
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 427 KB
- Volume
- 17
- Category
- Article
- ISSN
- 0899-8418
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✦ Synopsis
Given the uncertainties associated with GCM modelling of aerosol effects on regional precipitation, a simple model is used to make a preliminary assessment of the in¯uence of aerosols on rainfall in the Lake Tanganyika region of tropical southern Africa. No attempt will be made to consider the effects of changing carbon dioxide and moisture contents of the atmosphere that might have occurred at the same time. Atmospheric transport and recirculation of air and aerosols are considered and shown to occur on a large scale. Size distributions, residence times and concentrations of aerosols are examined and air volume and aerosol mass transports are estimated. South African data from stations on the interior plateau are used to approximate present-day seasonal and interannual variations in transmissivity due to changing aerosol loading in the atmosphere.
A lake-catchment hydrological model is used to determine rainfall over Lake Tanganyika and its environs and from this a sensitivity analysis of rainfall receipt to aerosol-induced changes in atmospheric transmissivity is carried out. It is shown that a decrease in transmissivity commensurate with the present-day interannual range of variability of 10 per cent produces, in the absence of other changes, about a 15 per cent diminution in rainfall. The analysis is extended to show that in the past, during the sixteenth-century Little Ice Age, the transmissivity induced rainfall decrease could have been about 25 per cent and that at 18 000 years BP it would have been more. Aerosol loading is shown to have important consequences for the occurrence of droughts through its modi®cation of the surface radiation balance.