臺灣中部常綠闊葉林之水與能量收支季節性差異

Seasonal variations of water and energy budget of evergreen broad-leaved forest in central Taiwan

邱文昱(Wen-Yu Chiou) ； 李明旭(Ming-Hsu Li) ； 陳觀印(Kuan-Yin Chen) ； 陳沛芫(Pei-Yuan Chen)

《農業工程學報》 67卷4期 (2021/12) Pp. 64-77

https://doi.org/10.29974/JTAE.202112_67(4).0004

摘要

森林生態系之水文與能量收支深受大氣條件與地表狀態影響，於乾濕季節下會有不同特徵。本研究使用2010～2020年間蓮華池水文氣象站之微氣象與通量觀測數據，依據月降水量多寡，區分成乾季（10～3月）與濕季（4～9月）各6個月二種類型，在濕季的潛熱通量與淨輻射均較乾季為高，可感熱於乾濕季間差異不大，在水文收支如土壤含水量、蒸發散量與河川流量均呈現濕季高與乾季低的特徵。接著利用標準化降水指數（Standardized Precipitation Index, SPI），計算三個月累積降水的SPI時間序列（即SPI3），再將各年的乾濕季依據其SPI3中位數，分為偏濕濕季（SPI3 ＞ 1）、正常濕季（0 ＜ SPI3 ＜ 1）、正常乾季（-1 ＜ SPI3 ＜ 0）或偏乾乾季（SPI3 ＜ -1）等四種類型，偏濕濕季比正常濕季有較大的潛熱通量與較小的可感熱，原因為偏濕濕季之降水日數與降水量較正常濕季為多，使淨輻射較小；而偏乾乾季與正常乾季之潛熱通量卻差異不顯著，但偏乾乾季有較高之淨輻射與可感熱通量，原因為偏乾乾季之降水日數與降水量較正常乾季為少。在水文量部分，偏濕濕季有最高之土壤含水量與河川流量，偏乾乾季則為最低。過去十年間蓮華池並未發生嚴重乾旱，常綠闊葉林於輕度至中度乾旱期間仍能由土壤水分支撐蒸發散作用。長期且持續的水文與能量觀測有助於我們了解森林生態系的季節變動特徵，特別是極端事件的影響，幫助我們對於森林經營管理提出更好的策略。

關鍵字

標準化降水指數 ； 水與能量收支 ； 常綠闊葉林 ； 季節性變異

並列摘要

Water and energy budget in forest ecosystem are deeply affected by changes in meteorological conditions and surface characteristics, which lead to distinct behaviors in dry and wet seasons. Meteorological and energy fluxes data observed at the Lianhuachi (LHC) Research Center in central Taiwan during 2010 to 2020 were analyzed in this study. Based on rainfall amount, dry (i.e., Oct.~Mar.) and wet (i.e., Apr.~Sept.) seasons were identified to have 6 months in each season. Latent heat flux (LE) and net radiation (Rn) in wet seasons are larger than those in dry seasons, while differences in sensible heat flux (H) between dry and wet seasons are insignificant. Soil moisture, evapotranspiration, and streamflow of wet seasons are also larger than those in dry seasons. In order to understand effects of different dryness and wetness on energy and water budget, the Standardized Precipitation Index (SPI) was applied to further identify dryer (i.e., SPI3 ＜ -1), dry (i.e., -1 ＜ SPI3 ＜ 0), wet (i.e., 0 ＜ SPI3 ＜ 1), and wetter (i.e., SPI3 ＞ 1) seasons in different years based on the median of SPI3 calculated by 3 months accumulated precipitation in each season. The wetter season has larger LE and smaller H than the wet season due to more rainfall and rainy days which lead to small Rn. Although differences in LE between dryer and dry seasons are insignificant, larger H and Rn are observed in the dryer season than those in dry seasons due to less rainfall and rainy days in dryer seasons. The wetter seasons have the largest soil moisture and streamflow, which are the lowest in the dryer seasons, among 4 types of wet/dry seasons. Since the LHC did not suffer extreme drought with long duration during past 10 years, the evergreen broad-leaved forest is still able to sustain functions of evapotranspiration by uptaking deeper soil moisture under moderate drought condition. Long-term and continuous observation of water and energy contributed to understanding the characteristics of seasonal variation, especially the impacts of extreme wet and dry events to the forest ecosystem, and supporting to propose sound strategies of forest management.

並列關鍵字

Standardized precipitation index ； Water and energy budget ； Evergreen broad-leaved forest ； Seasonal variations

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