應用極端流量及水溫評估氣候變遷對櫻花鈎吻鮭棲地之衝擊

Abstract

近年來，極端天氣對全球所造成之影響為眾所矚目的焦點。由於水資源在臺灣地區的生態、經濟、政策等層面皆扮演極為重要的角色，因此極端天氣對河川生態可能造成的影響也是一大研究方向。臺灣過去與氣候變遷相關之研究成果多著重於平均狀態對河川生態的影響，較少探討極端天氣之影響，然極端事件對生態之衝擊可能更致命。河川的流量與水溫都是影響河川生態之重要因子，尤其對臺灣櫻花鈎吻鮭這種對棲地環境變化相當敏感的魚類而言，河川流量及水溫的變動對於牠們的棲地皆有著舉足輕重之影響，藉由分析這些因子，將可反映氣候變遷下棲地之脆弱度。 本研究以臺灣櫻花鈎吻鮭棲地─七家灣溪為研究區域，根據不同溫室氣體排放情境所推估之未來氣候資料來設定氣候變遷情境，模擬未來在氣候變遷影響下河川連續七日之流量和水溫變動情形，以探討氣候變遷對流量極端化之影響，除此之外，亦將未來水溫資料結合可靠度的概念以描述七家灣溪之脆弱度及回復力，探討氣候變遷影響下極端天氣造成之流量極端化與水溫升高對臺灣櫻花鈎吻鮭生存環境所帶來的衝擊。 由本研究結果顯示，未來七家灣溪連續七日流量在氣候變遷影響之下，高流量增加，低流量減少，流量變化趨於極端化。根據水溫模擬結果來看冬季時水溫將受到較大的衝擊，且未來高溫事件之頻率與最大延時皆增加，高溫事件之強度與基期相比亦有增加趨勢。無論就高溫事件之發生頻率、延時或強度來看皆說明未來棲地將受到不小的衝擊。極端事件可能造成臺灣櫻花鈎吻鮭生存環境之一大衝擊，進而使魚群生存受到威脅。

In recent years, the impacts of climate change have been the focus of world attention. As a result that water resource palys an important role in ecological, economic, and policy levels in Taiwan, the possible impact of extreme weather on river ecology is also a major research issue. Climate change may cause more climate variability and more frequent extreme hydrological events. In the past, lots of studies which related to climate change emphasis the impact of the average state of the river ecosystem, but less to the extreme weather in Taiwan. However, extreme events impacting on the ecological may be more deadly. Streamflow and water temperature play important roles in river ecosystem, which influences not only aquatic biodiversity but also the area of habitat. Especially for the Formosan Landlocked Salmon which is sensitive to habitat environment, they may be significantly influenced by greater variation of streamflow and higher water temperature due to climate change. As a result, it will be able to reflect the vulnerability of the habitat by evaluating extreme streamflow and water temperature under climate change. The habit of Formosan Landlocked Salmon, ChiChiaWan creek, is the main study area. A set of ecohydrological indicators is used to estimate the vulnerability of Formosan Landlocked Salmon’s habitat under climate change. The future climate scenarios are derived from several GCMs. Then, a hydrological model is used to simulate the extreme consecutive 7-day streamflow under different climatic conditions and a water temperature model is used to further simulate the extreme water temperature. In addition, this study combined water temperature data with the concept of vulnerability and reslilence that water temperature may exceed the threshold temperature of survival, and explored the impact on the habitat which caused by extreme streamflow and water temperature under the influence of extreme weather. According to the results of this study, streamflows will become much more extremalization with the increasing consecutive 7-day high flow and decreasing consecutive 7-day low flow under different climate scenarios. The results also show water temperature may exceed the threshold temperature of survival under some GCMs’ scenarios especially in winter. The frequency of high temperature event and maximum duration are increased, while the intensity of high-temperature events also trends to increase compared with the base period. No matter the frequency, duration, or strength of high temperature events, the results show that extreme weather may cause great impact and thus threaten the habitat of Formosan Landlocked Salmon.