气候变化背景下,极端气候事件对生态系统的影响更甚于气候平均态的变化,对极端气候事件的影响评估及机理研究有更为重要的现实意义。研究以极端降水为例,选择我国旱涝频繁的长江中下游地区为研究对象,基于生态系统过程模型的动态模拟,选择与极端降水显著相关的生态系统功能特征量,根据IPCC脆弱性的定义,以生态系统功能特征量偏离多年平均状况的程度及其变化趋势分别定义系统对极端降水的敏感性和适应性,从而评估其脆弱性。研究表明,长江中下游地区生态系统多年平均脆弱度为轻度脆弱,轻度脆弱及以下地区占区域总面积的大半,约65%,脆弱度较高的区域占20%,主要分布在长江中下游的西北部。极端降水会增加长江中下游区域生态系统的脆弱度,多表现为不脆弱转变为轻度脆弱,中度脆弱及以上的生态系统所占比例变化不大。干旱和洪涝对区域内生态系统脆弱度的分布格局影响不大,但干旱的影响程度高于洪涝。不论是干旱还是洪涝,区域内生态系统的脆弱度在灾害过后的下一个生长季能基本恢复,没有连年灾害的情况下,长江中下游区域的旱涝灾害对生态系统的影响不会持续到下一年度。
The hazards of extreme weather events are likely greater than the change of climatic mean variables under the background of climate change. The assessment on impacts and vulnerability of ecosystem to extreme events is important and realistic. The process-based model (CEVSA) was used to simulate the responses of ecosystem to extreme precipitation in the upper and middle Yangtze Valley because of its frequency of drought and flood. The net primary productivity (NPP) in summer which has high correlation with precipitation anomalies was analyzed as an indicator of ecosystem to extreme precipitation. The variability of NPP and its changing tendency were defined as the sensitivity and adaptive capacity of ecosystem to extreme precipitation, respectively, and the vulnerability of ecosystem to extreme precipitation was calculated based on them. The results suggested that most of the ecosystem was gently vulnerable and took 65% of the upper and middle Yangtze Valley during 1961-1990, and the higher vulnerable ecosystem took about 20%, mainly distributed in the northwestern part. Extreme precipitation would increase the vulnerability of ecosystem, whatever drought or flood. The main change of vulnerability was shifted from nonvulnerable state to gently vulnerable state during the extreme precipitation years. The higher vulnerable ecosystem was mainly located in the northern part of the upper and middle Yangtze Valley, and its percent was hardly changed under different extreme precipitation. Compared with the impacts of drought and flood, the vulnerability in drought years was higher than in flood years, and even it was the same in the next year of extreme precipitation. However, the ecosystem vulnerability in most part of the valley could get back to the level of multi-year mean state in the next years of extreme precipitation.
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