Abstract
Land Use Land-Cover Change (LULCC), such as deforestation, affects the climate system and land-atmosphere interactions. Using simulations carried out within the LUCID (Land Use and Climate, IDentification of robust Impacts) project framework, we first quantify the role of historical land-cover change induced by human activities on surface climate in West Africa. Focusing on two contrasted African regions, we find that climate responses of land-use changes are small but they are still statistically significant. In Western Sahel, a statistically significant near-surface atmospheric cooling and a decrease in water recycling are simulated in summer in response to LULCC. Over the Guinean zone, models simulate a significant decrease in precipitation and water recycling in autumn in response to LULCC. This signal is comparable in magnitude with the effect induced by the increase in greenhouse gases. Simulated climate changes due to historical LULCC could however be underestimated because: (i) the prescribed LULCC can be underestimated in those regions; (ii) the climate models underestimate the coupling strength between West African surface climate and leaf area index (LAI) and (iii) the lack of interactive LAI in some models. Finally, our study reveals indirect atmospheric processes triggered by LULCC. Over the Western Sahel, models reveal that a significant decrease in solar reflection tend to cool down the surface and thus counteract the atmospheric feedback. Conversely, over the Guinea zone, models reveal that the indirect atmospheric processes and turbulent heat fluxes dominate the climatic responses over the direct effects of LULCC.
Highlights
Humans have radically modified the land cover distribution to the gains of urbanization and agriculture activities
These land-surface models (LSMs) have different interpretation of land use classes resulting from: (i) the way Land Use induced Land Cover Change (LULCC) information is represented in models; (ii) the strategy used by each modeling group to implement LULCC in their background land cover; and (iii) the usage of different sources of information to describe present-day or potential vegetation by the modeling groups
This study disentangles result differences among models, for two contrasted African regions, and it investigates the sensitivity of climate models to LULCC intensity, bringing more physical elements to explain simulated biophysical changes
Summary
Humans have radically modified the land cover distribution to the gains of urbanization and agriculture activities. LULCC has a direct effect on biophysical properties of land surfaces. LULCC in particular is related to the reduction of forest fractions and of natural savannah, to the gains of settings crops and pastures, and this trend was observed on a global scale during the last few decades [10,11,12,13]. If this current trend continues, the cultivated surface could increase by 20% during the 50 years [14]
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