Browsing by Author "You, Qinglong"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Increased sensitivity of greening to afforestation in China over the recent 20 years
    (Elsevier, 2023-08) Jin, Zheng; You, Qinglong; Zuo, Zhiyan; Li, Mingcai; Sun, Guodong; Pepin, Nick; Wang, Lixin; Earth and Environmental Sciences, School of Science
    ) to evaluate this effect. Comparing satellite-based land cover observations of 2003–2012 with 2010–2019, SGA in China increased by 1.03, 0.49, 3.3, and 2.46 (10−2 m2 m−2 %−1) for evergreen needleleaf, deciduous broadleaf, evergreen broadleaf, and mixed forests, respectively. This indicates greening (increasing LAI) becomes more sensitive to afforestation (increasing tree cover fraction), particularly in evergreen broadleaf forests. To explore possible eco-hydrothermal factors contributing to the observed SGA increase, a diagnostic framework synergizing atmospheric supply (precipitation and potential evaporation) and biological use (vegetation transpiration) of water and energy was constructed. The results suggest that an eased water-energy constraint mostly facilitates the observed SGA increase.
  • Thumbnail Image
    Item
    Weakening amplification of grassland greening to transpiration fraction of evapotranspiration over the Tibetan Plateau during 2001-2020
    (Elsevier, 2023-10) Jin, Zheng; You, Qinglong; Zuo, Zhiyan; Li, Mingcai; Sun, Guodong; Pepin, Nick; Wang, Lixin; Earth and Environmental Sciences, School of Science
    Evapotranspiration plays a key role in regulating the water cycle in terrestrial ecosystems. Transpiration fraction to evapotranspiration (TF) characterizes the role of vegetation function in evapotranspiration and is a pivot feature for the interactions between soil, ecosystem, and the atmosphere. Generally, the amount of vegetation has the most direct impact to TF, but the sensitivity of TF to vegetation change is not known, which could be a metric to evaluate the role of greening in land-atmosphere water transportation. To address this key knowledge gap, we used remote sensing observations of leaf area index (LAI) as a proxy for vegetation amount and derived the sensitivity of TF to LAI (θ = ∂TF/∂LAI)) for the grasslands over the Tibetan Plateau (TP). Results showed there is a substantial decline of θ over the TP during 2001–2020, decreasing from over 4% m−2 m2 to below 1.5% m−2 m2. To analyze the drivers of θ, we introduced a diagnosis framework for soil-atmosphere hydraulic stress shifts based on trends in soil moisture and atmospheric vapor pressure deficit. Results implicated the θ decline over the TP is likely not induced by the dry-wet balance shifts by soil and atmosphere, nor by the vegetation's stomal conductance. Instead, we speculate that the θ decline is induced by a marginal damping effect in case the TF rise is approaching to grassland's limit over the TP. Our finding appeals future studies on terrestrial evapotranspiration to consider the role of vegetation in controlling transpiration and emphasize that greening may not lead to higher TF.