氣候變遷對棲蘭雲霧森林地表通量特性的影響

Changes of Surface Flux Characteristics in Chi-Lan Montane Cloud Forest under Climate Change

楊子瑩(Tzu-Ying Yang) ； 羅敏輝(Min-Hui Lo) ； 鄭兆尊(Chao-Tzuen Cheng)

《大氣科學》 49卷2期 (2021/12) Pp. 111-152

https://doi.org/10.53106/025400022021124902001

摘要

雲霧森林是經常性受到雲霧籠罩所影響的森林生態系。雲霧對於當地有調節水分與能量的作用，是維持該生態系平衡的重要因子。過去研究指出，大量樹冠水在早晨受太陽加熱蒸發，造成潛熱通量的峰值提前而有利於當地雲霧生成。但在氣候變遷下，降水、溫度、濕度及二氧化碳濃度的改變可能影響樹冠水的累積，進而改變地表通量和雲霧生成。本研究利用NCAR地表過程模式，搭配棲蘭雲霧森林及蓮華池森林的大氣觀測資料，以及TCCIP模式的未來氣候推估資料，討論氣候變遷影響雲霧森林樹冠水及地表通量的機制。結果顯示未來增強的降水強度將不利於樹冠水累積，但大氣增溫造成的水氣量增加卻有助於夜間露水凝結，使氣候變遷下平均的樹冠水量增加。二氧化碳濃度的增加對樹冠水量沒有明顯影響，但會提升光合作用效率並造成氣孔縮小而使蒸散量降低。暖化下增加的樹冠水，提升了雲霧森林在早晨的潛熱通量，但全天平均的潛熱通量則因降水截留的減少而下降，然而其中氣溫提升所造成的潛熱通量增加仍扮演緩解降水強度變強對雲霧森林衝擊的角色。植被透過蒸散作用調節其表面溫度，是暖化下有利夜間露水凝結的重要因素，而在二氧化碳提升下所增加的光合作用速率亦能調節當地二氧化碳濃度的變化，顯示雲霧森林中植被在氣候變遷下的重要性。雲霧森林中的地表通量在氣候變遷下的改變也會同時透過陸地與大氣間的交互作用而影響到當地的大氣穩定度與邊界層發展等，因此未來將利用大氣與陸地耦合模式並考慮雲霧與山谷風環流在雲霧森林中的關係，進一步討論未來氣候變遷下雲霧森林內的水與能量循環的變化。

關鍵字

氣候變遷 ； 暖化 ； 雲霧森林 ； 樹冠水 ； 蒸發 ； 潛熱通量

並列摘要

Cloud-fog forest is known as a forest ecosystem governed by frequent fog immersion. Fog plays a vital role in maintaining the ecosystem's equilibrium in montane cloud forests, where a large amount of canopy water evaporates in the morning, being a critical factor for fog formation. Recent studies found that precipitation, temperature, humidity changes, and elevated CO_2 concentration under climate change may affect the canopy water amount and surface fluxes in cloud forests, but the mechanisms remain unclear. We explore the changes in surface flux characteristics in the Chi-Lan montane cloud forest under climate change by using the NCAR Community Land Model, in-situ observation from Chi-Lan cloud forest and Lien-Hua-Chih forest, and future climate scenarios from TCCIP modelling outputs. Results show that the future intensified rainfall is unfavorable for canopy water accumulation, while more water vapor under future warming leads to more nighttime condensation on leaves. Elevated CO_2 concentration does not greatly impact canopy water amount, but the photosynthesis efficiency is enhanced and the transpiration is suppressed under higher CO_2 concentration. The combining results show overall increased canopy water under various climate changes. It promotes strong canopy evaporation when sun rises, but the total daytime evaporation still decreases due to the decreased intercepted rainfall. The response of canopy water and surface fluxes under rising temperature mitigates the impact of higher precipitation intensity on cloud forests. The regulating factor of vegetation temperature plays a critical role in the increasing canopy water under a warming climate. The increased photosynthesis under elevated CO_2 weakens the local change of CO_2 concentration, implying the importance of vegetation in forests under climate change. The atmosphere can interact with the land surface through the adjusted surface fluxes under climate change. Therefore, future work may require coupled land and atmosphere model simulations and considering changes of fog and local circulations in the future scenario to explore the impact of climate change on cloud forests.

並列關鍵字

climate change ； warming ； cloud forest ； canopy water ； canopy evaporation ； latent heat flux