Abstract
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.
Highlights
Forests play a pivotal role in regulating climate and sustaining the hydrological cycle
The cloud effect is measured by cloud cover fraction derived from Moderate Resolution Imaging Spectroradiometer (MODIS) and Meteosat Second Generation (MSG) satellite data, which represent the occurrence frequency of clouds over a period of time with a valid range of 0–1 (Supplementary Fig. 1)
The cloud effects estimated in our study reflect the local impact of forests on cloud cover and is, more representative of real-world smallscale forest cover change, without generating the large-scale climate feedbacks which are usually triggered in Global climate models (GCMs) experiments[3,12]
Summary
Forests play a pivotal role in regulating climate and sustaining the hydrological cycle. Global climate models (GCMs) have predicted a reduction in precipitation and a frequent decrease in cloud cover resulting from large-scale deforestation, with the greatest decrease in tropical regions[7–9] These results generally support that vegetation enhances clouds and precipitation at large-scales[10,11], especially in the tropics, these continental- or global-scale land clearing experiments implemented in models with a relatively coarse resolution are not consistent with the ongoing small-scale land activities in the real world. In contrast to cloud and precipitation reduction simulated in the GCM experiments[7,8,14], high-resolution regional climate models[15,16] and empirical analyses using satellite imagery[17,18] reported that small-scale deforestation increases rather than decreases clouds and precipitation in the Amazon due to land surface heterogeneity[19] These results revealed inhibited clouds over some forests (e.g., West Africa20) at a realistic scale which seemingly contradicts the highly hypothetical GCM results[21] and the enhanced cloud observations over forests in other regions (e.g., western Europe[22] and Central America[23]). The global pattern of forest impacts on cloud cover, especially how it is shaped by the interplay of different mechanisms, remain largely unresolved
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