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人类活动与气候变化影响下全球荒漠化风险研究

Global Desertification Vulnerability Impacted by Human Activity and Climate Change

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【Author in Chinese】 张国龙

【Supervisor】 黄建平

【Author's Information】 兰州大学, 大气科学·大气物理学与大气环境, 2020, 博士

【Abstract in Chinese】 根据联合国荒漠化防治公约的定义,荒漠化是指受人类活动和气候变化影响下干旱半干旱区土地退化的现象。荒漠化不仅严重威胁全球生态环境安全,而且对人类经济社会有着重大影响。确定植被生长状态的演变特征,明确气候变化下植被对温度和降水等气象要素敏感度的变化,有利于加深对全球生态系统的理解,对采取生态修复措施和制定应对气候变化的政策以及防治荒漠化的扩张有着重要的意义。构建考虑人类活动和气候变化的全球尺度的荒漠化脆弱性指数有助于在全球尺度直观了解荒漠化风险程度,有助于决策者制定荒漠化防治政策,而且还有利于敏感区域的荒漠化治理。但是目前还没有一个同时考虑气候变化和人类活动的适用于全球尺度的荒漠化脆弱性指数。本论文在年际尺度和季节尺度分析全球植被叶面积指数(LAI)时空变化特征的基础上,分析了气象要素对植被LAI的影响以及全球变暖下植被LAI对其敏感度变化。进一步利用人类活动强度指数及气候环境指数构建了适用于全球尺度的荒漠化脆弱性指数(GDVI),并且基于概率密度分布进行了等级划分,评估了当前全球荒漠化风险分布,最后利用第五次模式比较计划输出结果和社会经济模型数据预测了未来不同情景下的全球荒漠化风险演变特征,最终得到以下结论:1.根据卫星监测的结果显示,自1982年全球植被绿化程度呈增加趋势,LAI增加具有明显的季节差异性,春秋季增长趋势大于夏季,生长季的延长导致高纬度地区LAI显著增加。从全球分区来看,对全球LAI变化趋势贡献最为显著的是南亚、东亚、欧洲和南美地区。除东亚外,其他三地绿化面积在其区域占主导。湿润区依然是全球LAI增加的主要区域,但是干旱半干旱区LAI相对增加趋势最显著,干旱半干旱区降水是导致植被LAI增加的主要因素。人类活动在全球绿化的过程中起着重要的作用。2.在全球变暖的背景下,不同季节LAI占全年LAI的比例呈现明显区域变化特征。春季中亚、欧洲、中国东部、澳大利亚以及南美洲南部季节占比呈现明显上升趋势。夏季中国东部、印度、中亚、欧洲、和非洲大部季节占比呈现明显下降趋势。秋季非洲中部、美国地区、印度和中国东北地区季节占比明显增加。不同气候分区LAI对温度和降水的敏感性不尽相同,干旱半干旱区LAI和温度呈负相关,与降水呈正相关;湿润区LAI和温度呈正相关,与降水呈负相关。在全球变暖的背景下,在干旱半干旱区LAI对温度敏感性增加,对降水的敏感性降低;湿润区与干旱半干旱区相反,LAI对温度的敏感性降低,但对降水的敏感性增加。3.构建了考虑气候变化和人类活动的全球荒漠化脆弱性指数,按照概率密度函数将其风险等级划分为低、中、高和非常高四个等级。与前人结果相比,分级结果较为合理可靠。当前荒漠高风险区主要集中在生态脆弱区,比如沙漠边缘以及极端干旱区,以及人类活动强的区域,比如中国东部和印度地区。从目前经济发展程度来看,荒漠化高风险区域主要集中在不发达地区,这将影响到该地的可持续发展。从全球分区看中亚和非洲北部整体荒漠化风险很高,需要采取积极的措施防止荒漠化扩张。虽然东亚地区整体以中等荒漠化风险为主,但是由于该区域高和非常高荒漠化风险等级面积占比较大,所以要警惕其生态环境的进一步恶化。4.第五次模式评估结果显示,未来全球温度明显上升,干燥度指数明显减小。RCP4.5情景下,人类活动峰值出现在21世纪40年代左右,随后开始下降;但是RCP8.5情景下,人类活动强度随着时间不断增强。RCP4.5情景下,全球荒漠化风险有所增加,从空间分布来看,增加区域主要集中在欧洲、西亚、中国北方地区、萨赫勒边缘以及墨西哥地区。但是青藏高原和印度地区荒漠化风险有所降低,印度地区人类活动强度降低为主要因素。RCP8.5情景下,到本世纪末全球中等到非常高的荒漠化风险面积占比将增加23%,全球荒漠化风险显著增加,主要增加的区域在中国北方地区、印度、墨西哥以及非洲地区。进一步分析各地的主导因子,发现澳大利亚地区荒漠化风险是由于气候变化的因素主导以外,其他地区的荒漠化风险是由于气候变化和人类活动共同导致,为了防止未来荒漠化进一步扩展,需要降低人类对环境的直接干扰程度,也应该采取相应适应气候变化的政策。

【Abstract】 According to the United Nations Convention to Combat Desertification(UNCCD),desertification is the impoverishment of arid,semi-arid,and some sub-humid ecosystems due to the combined impact of human activities and climate change.Desertification not only threats the global ecological security,but also affects the economic and social development.Study the growth status of vegetation and the impact of climate change to the vegetation dynamics,which is in favor of taking action to protect and promote restoration of the ecosystems and making policy to combat climate change and desertification.The assessment of global scale desertification vulnerability to climate change and human activities is an important step to help decision makers to formulate the best strategies for land rehabilitation and the fight against global desertification in sensitive areas.However,there is no global desertification vulnerability map that considers both climate change and human activities.In this study,we first analyzed the spatial-temporal character of global leaf area index(LAI)and the impact of temperature and precipitation to vegetation dynamics.Farther,we assessed global desertification vulnerability using a global desertification vulnerability index(GDVI),which was defined by human activities and climate change indicators,to obtain a global overview of desertification vulnerability.Finally,we projected future global desertification vulnerability by the end of this century under different scenarios,the conclusion as follows:1.At global scale,the LAI increased from 1982 to 2014.The increasing trend of LAI in the spring and autumn is further lager than that in the summer,which indicated that the extension of growth length may be the dominant factor in the increasing annual LAI in the northern hemisphere.The regions with the most significant contributions to the global LAI change trend are South Asia,East Asia,Europe and South America.Although humid region dominated the increasing tendency of global LAI,the increase of relative LAI is significant in the drylands.Precipitation is the key factor influencing vegetation growth in the drylands,however,the human activities is an important contribution to global greening.2.The contribution of seasonal trend to annual LAI change shown obviously spatial heterogeneity.The fraction of spring LAI to annual LAI increased in the Central Asia,Europe,East China,Australia and Southern South America.The fraction of Summer LAI to annual LAI decreased in the East China,India,Central Asia,Africa.The fraction of Autumn LAI to annual LAI increased in the Central Africa,America,India and Northeast China.In the humid region,the vegetation growth was constrained by temperature,radiation,rather than precipitation.The sensitive of LAI to precipitation decreased in the recent decades in the drylands,and enhanced in the humid area,that indicated vegetation differently responded to global warming at regional scale.However,The sensitive of LAI to air temperature decreased in the recent decades in the drylands,and enhanced in the humid area.3.The global desertification vulnerability index were constructed by combining climate change and human activities and were used to provide another perspective on desertification vulnerability on a global scale.Using the probability density function of the GDVI,we classified desertification vulnerability into four classes: very high,high,medium,and low.Comparing with the previous studies,GDVI is reasonable and reliable.The results of the analysis indicated that areas around deserts and barren land have a higher risk of desertification.The high level of desertification risk is mainly in the western part of the United States,the Sahel,Central Asia,and northern China,where vegetation is sparse and the climate is dry.The desertification risk is moderate to severe in the Indian subcontinent and North China Plain due to intense human activity.The area coverage of high desertification risk in developing countries is larger than that in developed countries,which may have an effect on local sustainable development.Generally speaking,the desertification is high in the Central Asia and Northern Africa,so we need to take positive action to suppress the expansion of desertification.Although risk of desertification in East Asia is moderate,the area coverage of high and very high desertification risk level is high,we should be alert to the further deterioration of its ecological environment.4.The global mean AI values will decrease in the future projection,while the temperature will increase under both the RCP4.5 and RCP8.5.Under the RCP4.5,the HAI will reach a maximum around 2040 and then decline.The risk of desertification according to the GDVI will increase over Europe,western Asia,northern China,the edge of the Sahel,and Mexico.However,the global mean HAI increases monotonously under the RCP8.5,indicating that human activity would increase in the future.RCP8.5 projected that the area of moderate to very high desertification risk will increase by 23% by the end of this century.Under the RCP8.5,HAI increases significantly,the climate becomes drier,and the surface air temperature increases,resulting in a dramatic increase in desertification risk over northern China,India,Mexico,and Africa.In Australia,climate change is the main contributor to the increased risk of desertification.As the area coverage of high risk desertification expands in the future,poor people in drylands areas will experience more natural disasters,and a global plan of action is therefore needed to reduce the risk of desertification.

  • 【Contributor】 兰州大学
  • 【Year of Internet Publish】202101
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