Makarieva Anastassia M, Nefiodov Andrei V, Nobre Antonio Donato, Baudena Mara, Bardi Ugo, Sheil Douglas, Saleska Scott R, Molina Ruben D, Rammig Anja
Institute for Advanced Study, Technical University of Munich, Garching, Germany.
Theoretical Physics Division, Petersburg Nuclear Physics Institute, St. Petersburg, Russia.
Glob Chang Biol. 2023 May;29(9):2536-2556. doi: 10.1111/gcb.16644. Epub 2023 Mar 10.
The terrestrial water cycle links the soil and atmosphere moisture reservoirs through four fluxes: precipitation, evaporation, runoff, and atmospheric moisture convergence (net import of water vapor to balance runoff). Each of these processes is essential for sustaining human and ecosystem well-being. Predicting how the water cycle responds to changes in vegetation cover remains a challenge. Recently, changes in plant transpiration across the Amazon basin were shown to be associated disproportionately with changes in rainfall, suggesting that even small declines in transpiration (e.g., from deforestation) would lead to much larger declines in rainfall. Here, constraining these findings by the law of mass conservation, we show that in a sufficiently wet atmosphere, forest transpiration can control atmospheric moisture convergence such that increased transpiration enhances atmospheric moisture import and results in water yield. Conversely, in a sufficiently dry atmosphere increased transpiration reduces atmospheric moisture convergence and water yield. This previously unrecognized dichotomy can explain the otherwise mixed observations of how water yield responds to re-greening, as we illustrate with examples from China's Loess Plateau. Our analysis indicates that any additional precipitation recycling due to additional vegetation increases precipitation but decreases local water yield and steady-state runoff. Therefore, in the drier regions/periods and early stages of ecological restoration, the role of vegetation can be confined to precipitation recycling, while once a wetter stage is achieved, additional vegetation enhances atmospheric moisture convergence and water yield. Recent analyses indicate that the latter regime dominates the global response of the terrestrial water cycle to re-greening. Evaluating the transition between regimes, and recognizing the potential of vegetation for enhancing moisture convergence, are crucial for characterizing the consequences of deforestation as well as for motivating and guiding ecological restoration.
降水、蒸发、径流和大气水分汇聚（水汽的净输入以平衡径流）。这些过程中的每一个对于维持人类和生态系统的福祉都至关重要。预测水循环如何响应植被覆盖的变化仍然是一项挑战。最近，亚马逊流域植物蒸腾作用的变化被证明与降雨变化不成比例地相关，这表明即使蒸腾作用有小幅下降（例如，由于森林砍伐）也会导致降雨量大幅下降。在这里，根据质量守恒定律对这些发现进行约束，我们表明在足够湿润的大气中，森林蒸腾作用可以控制大气水分汇聚，从而增加的蒸腾作用会增强大气水分输入并导致产水量增加。相反，在足够干燥的大气中，增加的蒸腾作用会减少大气水分汇聚和产水量。这种先前未被认识到的二分法可以解释关于产水量如何响应再绿化的其他混合观测结果，正如我们以中国黄土高原的例子所说明的那样。我们的分析表明，由于额外植被导致的任何额外降水再循环都会增加降水量，但会减少当地产水量和稳态径流。因此，在较干燥的地区/时期和生态恢复的早期阶段，植被的作用可能仅限于降水再循环，而一旦达到较湿润的阶段，额外的植被会增强大气水分汇聚和产水量。最近的分析表明，后一种情况主导了陆地水循环对再绿化的全球响应。评估不同情况之间的转变，并认识到植被增强水分汇聚的潜力，对于描述森林砍伐的后果以及推动和指导生态恢复至关重要。
