Regional modelling of future African climate north of 15°S including greenhouse warming and land degradation |
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Authors: | Heiko Paeth Hans-Peter Thamm |
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Institution: | (1) Geographical Institute, University of Würzburg, Am Hubland, 97074 Würzburg, Germany;(2) Geographical Institute, University of Bonn, Bonn, Germany |
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Abstract: | Previous studies have highlighted the crucial role of land degradation in tropical African climate. This effect urgently has
to be taken into account when predicting future African climate under enhanced greenhouse conditions. Here, we present time
slice experiments of African climate until 2025, using a high-resolution regional climate model. A supposable scenario of
future land use changes, involving vegetation loss and soil degradation, is prescribed simultaneously with increasing greenhouse-gas
concentrations in order to detect, where the different forcings counterbalance or reinforce each other. This proceeding allows
us to define the regions of highest vulnerability with respect to future freshwater availability and food security in tropical
and subtropical Africa and may provide a decision basis for political measures. The model simulates a considerable reduction
in precipitation amount until 2025 over most of tropical Africa, amounting to partly more than 500 mm (20–40% of the annual
sum), particularly in the Congo Basin and the Sahel Zone. The change is strongest in boreal summer and basically reflects
the pattern of maximum vegetation cover during the seasonal cycle. The related change in the surface energy fluxes induces
a substantial near-surface warming by up to 7°C. According to the modified temperature gradients over tropical Africa, the
summer monsoon circulation intensifies and transports more humid air masses into the southern part of West Africa. This humidifying
effect is overcompensated by a remarkable decrease in surface evaporation, leading to the overall drying tendency over most
of Africa. Extreme daily rainfall events become stronger in autumn but less intense in spring. Summer and autumn appear to
be characterized by more severe heat waves over Subsaharan West Africa. In addition, the Tropical Easterly Jet is weakening,
leading to enhanced drought conditions in the Sahel Zone. All these results suggest that the local impact of land degradation
and reduction of vegetation cover may be more important in tropical Africa than the global radiative heating, at least until
2025. This implies that vegetation protection measures at a national scale may directly lead to a mitigation of the expected
negative implications of future climate change in tropical Africa. |
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