How do trees impact cloud formation across Africa: the role of their spatial distribution

Vegetation plays a crucial role in regulating climate and sustaining the hydrological cycle. Preserving and expanding tree cover is potentially vital for mitigating climate change, as both the amount and spatial distribution of trees influence surface and atmospheric processes. While the direct effects of vegetation on surface properties are relatively well-studied, the indirect biophysical impacts of trees on cloud formation—particularly from trees outside forested areas—remain less explored, with the role of tree spatial patterns often overlooked. In this study, we used a space-for-time approach, high-resolution tree cover maps, and geostationary satellite data to investigate how tree cover, including its extent and spatial configuration, affects daytime and nighttime cloud formation across Africa. Our findings reveal distinct regional and temporal patterns: during the day, increased tree cover enhances cloud cover over tropical rainforests and arid steppes but reduces it over tropical savannahs. At night, a stronger negative relationship between tree cover and cloud formation emerges during the dry season, particularly in high-elevation areas of southern Africa. Mechanistically, these patterns are closely tied to sensible heat fluxes in water-abundant regions and to moisture availability in water-limited areas during the day, while nighttime cloud effects are linked to tree-induced variations in land surface temperature, likely through enhanced condensation on cooler surfaces. Incorporating tree cover heterogeneity alongside average tree cover offers further insights: in tropical savannahs, cloud formation is enhanced by 55.2% when heterogeneity is considered, compared to using tree cover alone, while in arid steppes, this increase is 12.4%. Conversely, in tropical rainforests, increased heterogeneity amplifies the negative impact of reduced tree cover on cloud formation. These findings underscore the importance of not only the extent but also the spatial arrangement of trees in afforestation and deforestation efforts. This data-driven analysis enhances the understanding of vegetation-cloud interactions, which remain uncertain and underrepresented in Earth system models, and provides valuable insights for planning and implementing future tree restoration projects in Africa.