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Accueil du site → Doctorat → Royaume-Uni → 1999 → Modelling the impact of land surface degradation on the climate of tropical North Africa (BL)

University of Reading (1999)

Modelling the impact of land surface degradation on the climate of tropical North Africa (BL)

Clark, D.B.

Titre : Modelling the impact of land surface degradation on the climate of tropical North Africa (BL)

Auteur : Clark, D.B.

Université de soutenance  : University of Reading

Grade : Doctor of Philosophy (PhD) 1999

Résumé
Degradation of the land surface has been suggested as a cause of persistent drought in tropical North Africa. Historical observations of the land surface are inadequate for accurate determination of what degradation has occurred, so idealised scenarios are used. The general circulation model of the Center for Ocean-Land-Atmosphere Studies is used to assess the effect of degradation of five regions within tropical North Africa. It is found that degradation generally results in less precipitation over the degraded area, with the largest impact in the West African Sahel. This is consistent with an important rôle for land surface processes in rainfall mechanisms in the Sahel and substantial recycling of local evaporation. Degradation of eastern areas has less impact on rainfall. Degradation of an area next to the Gulf of Guinea has little impact on precipitation due to a compensating increase of moisture flux convergence. The occurrence of synoptic wave disturbances is unchanged by degradation. Integrations of another model, the Hadley Centre model HadAM3, confirm that degradation of the Sahel results in substantially reduced precipitation. Agreement between the models indicates that the results are robust and not dependent on model details. A separate sensitivity test shows that increase evaporation in the Sahel results in a large increase of precipitation, whereas other regions show less sensitivity. The simulated decrease of rainfall following degradation of the Sahel is comparable to observed decreases over recent decades, suggesting that degradation may have contributed to the observed change.

Présentation (ProQuest)

Page publiée le 10 juin 2021