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- Title
Divergent Responses of Summer Terrestrial Evapotranspiration to Cloud Increase in East Asia.
- Authors
Wang, Yipu; Li, Rui; Song, Binbin; Hu, Jiheng
- Abstract
Cloud impact on terrestrial evapotranspiration (ET) can be significant, while a fundamental understanding of ET response to cloud change has not been addressed in regional aspects. In this study, seven ET datasets from satellite and land surface models are used to analyze the summer ET in response to low cloud cover (LCC) over East Asia, in combination with satellite microwave and optical vegetation data, as well as ERA5 climatic and surface parameters. In general, all ET datasets present a strong negative relationship with LCC over dense vegetation (e.g., forests), which leads to the ET reduction of more than −0.5 mmday−1 under the large LCC increase, compared with the least cloudy sky conditions. Such reduction is stronger under more humid and denser forests (aridity index AI > 0.5 and enhanced vegetation index EVI > 0.6). In contrast, a positive relationship between ET and LCC presents over arid and sparse lands (AI < 0.2 and EVI < 0.2), accompanied by enhanced ET (>0.2 mmday−1). Analysis shows that under increased LCC conditions, substantial reduction in radiation availability results in the decline in both plant transpiration (ETveg) and soil evaporation (ETsoil) over humid dense vegetation, dominating the overall negative response. The increase of near‐surface relative humidity over arid sparse vegetation may indicate a stronger moisture availability, which promotes ETsoil and partly offsets the negative effect of radiation reduction. The change of vegetation water content, indicated by a satellite microwave vegetation index, is important for ETveg over arid mountainous lands with cloud cover. These findings contribute new insights to the understanding of vegetation‐atmosphere interactions. Plain Language Summary: Cloud cover presents frequently over East Asia and affects terrestrial evapotranspiration (ET) significantly. Few studies have revealed the continental ET response to cloud change and a fundamental understanding needs to be addressed. In this study, we analyze the summer ET in response to low cloud cover and find that such response is spatiotemporally heterogeneous. Under the increasing LCC conditions, ET typically presents a negative response over densely vegetated lands and a positive response over shortly vegetated and barren lands. This is related to the dynamic controls of radiation and humidity availability on plant transpiration and soil evaporation processes over heterogeneous surfaces, which are intrinsically regulated by surface vegetation cover, aridity, and cloud‐increasing conditions. The change of vegetation water content is found to be important for the change of plant transpiration over arid mountainous lands under cloud cover. The underlying mechanism is further analyzed. Key Points: ET response to clouds shows a spatiotemporal heterogeneity during summer in East AsiaET in humid forests responds negatively to clouds mainly due to radiation limitationET can be enhanced over arid barrens via cloud‐induced increase of surface humidity
- Subjects
EAST Asia; PLANT transpiration; EVAPOTRANSPIRATION; CLOUDINESS; ARID regions; HUMIDITY control; HUMIDITY; SUMMER
- Publication
Journal of Geophysical Research. Atmospheres, 2024, Vol 129, Issue 6, p1
- ISSN
2169-897X
- Publication type
Article
- DOI
10.1029/2023JD039246