Forests play a pivotal role in regulating climate and sustaining the hydrological cycle. The biophysical impacts of forests on clouds, however, remain unclear. Here, we use satellite data to show that forests in different regions have opposite effects on summer cloud cover. We find enhanced clouds over most temperate and boreal forests but inhibited clouds over Amazon, Central Africa, and Southeast US. The spatial variation in the sign of cloud effects is driven by sensible heating, where cloud enhancement is more likely to occur over forests with larger sensible heat, and cloud inhibition over forests with smaller sensible heat. Ongoing forest cover loss has led to cloud increase over forest loss hotspots in the Amazon (+0.78%), Indonesia (+1.19%), and Southeast US (+ 0.09%), but cloud reduction in East Siberia (-0.20%) from 2002-2018. Our data-driven assessment improves mechanistic understanding of forest-cloud interactions, which remain uncertain in Earth system models.

Bowen ratio reflects the partitioning between sensible and latent heat fluxes and plays a crucial role in land–atmosphere interaction. In this study, the spatiotemporal variations of Bowen ratio among 12 vegetation types were analyzed using observations from 203 FLUXNET sites and compared against Community Land Model (CLM) simulations. Results showed that the annual mean Bowen ratio across all sites was 1.48 ± 1.20 (mean ± SD). Sites with Bowen ratios less than 1 were found across all continents, and the ones with a higher Bowen ratio appeared in dry and warm areas. Open shrublands showed the highest Bowen ratio (3.04 ± 0.58), whereas wetlands showed the lowest (0.74 ± 0.09). In terms of seasonality, Bowen ratio generally showed lower values in local summer and higher in spring and autumn in the northern hemisphere; the opposite occurred in the southern hemisphere. The spatiotemporal variations in Bowen ratio can be explained by climatic, geographical, and biological factors, with climate factors having the greatest impact. The spatial correlation analyses suggested Bowen ratio increased under higher VPD (R = 0.45, p < 0.001) and hotter (R = 0.14, p < 0.05) conditions and decreased with higher precipitation (R = −0.34, p < 0.001), albedo (R = −0.16, p > 0.05), and leaf area index (R = −0.25, p < 0.001). Compared to FLUXNET observations, CLM well reproduced the global annual mean Bowen ratio (1.48 for CLM vs. 1.56 for FLUXNET) but showed larger differences for certain vegetation types. Our results could enhance our understanding of biotic and environmental controls on land surface energy fluxes and help improve the land surface and climate models.

Bowen ratio reflects the partitioning between sensible and latent heat fluxes and plays a crucial role in land-atmosphere interaction. In this study, the spatiotemporal variations of Bowen ratio among 12 vegetation types were analyzed using observations from 203 FLUXNET sites worldwide and compared against Community Land Model. Results showed that the annual mean Bowen ratio across all sites was 1.48 ± 1.20 (mean ± SD). Sites with Bowen ratios less than 1 (39%, 80 sites) were found across all continents, and the ones with higher Bowen ratios (>3)(7%, 14 sites) appeared in dry and warm areas.Open shrublands showed the highest Bowen ratio (3.04 ± 0.58), whereas wetlands showed the lowest (0.74 ± 0.09). In terms of seasonality, Bowen ratio showed a U-curve with lower values in local summer and higher in spring and autumn in the northern hemisphere; the opposite occurred in the southern hemisphere. The spatiotemporal variations in Bowen ratio can be explained by climatic, geographical, and biological factors, with climate factors having the greatest impact. Bowen ratio increased under higher VPD (R = 0.45) and hotter (R=0.14) conditions with more shortwave radiation (R=0.39), and decreased with higher precipitation (R=-0.34), albedo (R=-0.16), and leaf area index (R=-0.25). CLM well reproduced the global annual mean Bowen ratio, but showed larger differences for certain vegetations types such as open shrublands (-1.51), woody savannas (+0.98). Our results could enhance our understanding of biotic and environmental controls on land surface energy fluxes and help improve land surface and climate models. Hosted file manuscript_huiqinglin.docx available at https://authorea.com/users/548662/articles/603200partitioning-of-sensible-and-latent-heat-fluxes-in-different-vegetation-types-and-theirspatiotemporal-variations-based-on-203-fluxnet-sites Partitioning of sensible and latent heat fluxes in different vegetation types and their spatiotemporal variations based on 203 FLUXNET sites