干旱对生态系统脆弱性的影响研究——以长江中下游地区为例

将干旱作为定性事件，以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，根据IPCC有关脆弱性的概念，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生态系统对降水变化的敏感性和适应性，在生态系统的尺度上评估其对干旱的脆弱性。结果表明，长江中下游区域生态系统对降水脆弱性的空间分布有较为明显的区域差异。轻度脆弱及以下的生态系统占区域总面积的65%，主要分布在区域的中南部。重度脆弱和高度脆弱区域约占20%，主要分布在长江中下游的西北部。区域内生态系统对降水变率的平均脆弱度为轻度脆弱。干旱会显著增加研究区生态系统的脆弱性，具体表现为干旱导致原本不脆弱的生态系统脆弱度增加，而对脆弱度较高的生态系统的脆弱性影响不大。不同类型生态系统对干旱的响应稍有差异，干旱导致森林生态系统和农业生态系统的脆弱性均有所增加，但农业生态系统对干旱的脆弱性更高于森林生态系统。在研究区内，干旱对生态系统的影响会持续一段时间，但在干旱过后一年，不论是农业生态系统还是森林生态系统的脆弱性均有进一步上升，但相对多年平均水平没有显著差异

ASSESSMENT ON ECOSYSTEM VULNERABILITY TO DROUGHT——THE CASE STUDY OF THE MIDDLE AND LOWER REACHES OF THE YANGTZE RIVER

Under the background of global warming,there have been more and more extreme weather events which have also become frequent and intense.Research on extreme events and their impacts have been more focused than before,especially on the drought.The middle and lower reaches of the Yangtze River is an important agricultural production base of China,and one of regions with relatively abundant water resources,but droughts and floods are frequent.In recent years,the extreme precipitation events such as drought sharp reversal to flooding occurred occasionally in this region.In this research,drought was defined as qualitative extreme event,new approach of assessing the vulnerability of ecosystem to drought was attempted in a regional scale for a case study in the middle and lower reaches of the Yangtze River.The processes based model (CEVSA) was used to simulate the dynamic responses of ecosystem to the drought and to assess the impacts of drought.According to the definition of vulnerability from IPCC,the key ecosystem function which correlated with the rainfall was selected as the indicator,the variability of indicator and its tendency of change were defined as the sensitivity and adaptive capacity of ecosystem to the drought,respectively.NPP in summer was regarded as the receptor of the drought events in this study,to assess the vulnerability of the ecosystem to drought.Specifically,the fluctuation degree of NPP in summer was used to indicate the sensitivity of the ecosystem to drought,while the trend of NPP fluctuation was used to reflect the adaptability of the ecosystem to drought.The vulnerability of ecosystems to drought in ecosystem scales was calculated and assessed by comparing with the average status in the reference period.The results of this study suggested that the spatial distribution of ecosystem vulnerability to drought had more obvious regional differences in the middle and lower reaches of the Yangtze River.Most of the ecosystems were low vulnerable and took about 65% of middle and lower reaches of Yangtze River over the period of 1961-1990, and the higher vulnerable ecosystems took about 20%,mainly distributed in the northwest of research area.Drought can increase the vulnerability of ecosystem distinctly.The main change of vulnerability was the shift from very low vulnerable ecosystems to low vulnerable ecosystems induced by drought.The medium vulnerable ecosystems and above were mainly located in the north of middle and lower reaches of the Yangtze River,and its percent was little changed due to drought.The response of different ecosystems to drought had a little difference,the vulnerability of agricultural ecosystem and forest ecosystem had increased according to the drought,but the vulnerability of agricultural ecosystem to drought was higher than the forest ecosystem. The vulnerability of the agricultural ecosystem and the forest ecosystem would continue to rise further in subsequent years after the drought.But there was no significant difference by comparing with the baseline.It indicated that the vulnerability of the two ecosystem types could go back to the mean level of multi years in the next year of drought generally