地球科学进展  2018 , 33 (10): 995-1004 https://doi.org/10.11867/j.issn.1001-8166.2018.10.0995.

综述与评述

全球变化背景下半干旱区陆气机制研究综述

管晓丹, 石瑞, 孔祥宁, 刘婧晨, 甘泽文, 马洁茹, 罗雯, 曹陈宇

兰州大学大气科学学院,半干旱气候变化教育部重点实验室,甘肃 兰州 730000

An Overview of Researches on Land-Atmosphere Interaction over Semi-Arid Region Under Global Changes

Guan Xiaodan, Shi Rui, Kong Xiangning, Liu Jingchen, Gan Zewen, Ma Jieru, Luo Wen, Cao Chenyu

Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000,China

中图分类号:  P463.1

文献标识码:  A

文章编号:  1001-8166(2018)10-0995-10

收稿日期: 2018-04-2

修回日期:  2018-09-2

网络出版日期:  2018-10-10

版权声明:  2018 地球科学进展 编辑部 

基金资助:  国家自然科学基金优秀青年科学基金项目“全球变化背景下半干旱陆气机制研究”(编号:41722502)国家自然科学基金面上项目“增温停滞对我国干湿变化的影响”(编号:41575006)资助.

作者简介:

First author:Guan Xiaodan(1983-),female,Tonghua County,Jilin Province,Professor. Research areas include climate in semi-arid region.E-mail:guanxd@lzu.edu.cn

作者简介:管晓丹(1983-),女,吉林通化人,教授,主要从事半干旱区气候研究.E-mail:guanxd@lzu.edu.cn

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摘要

半干旱区作为全球陆地的重要组成部分,在全球气候变化过程中发挥着不可忽视的作用。现代气候变化过程中,半干旱区受局地人类活动影响显著,表现出百年尺度的面积扩张及年代际的干湿周期变化。归纳近年来国内外全球半干旱区气候变化的研究成果,对以往半干旱区主要陆面观测计划进行回顾,重点分类总结陆气相互作用在半干旱气候变化过程中发挥的作用;包括半干旱区陆气相互作用中的能量循环、水循环和碳循环等变化特征,以及模式对半干旱区陆气特征的历史模拟和未来预测。随着半干旱区干旱化的加剧,未来的局地陆气相互作用将出现新的变化特征,需要进一步加强对半干旱区陆气相互作用机制的认识,从多方向推进半干旱区陆气相互作用对区域气候影响的研究。

关键词: 半干旱区 ; 陆气相互作用 ; 气候变化 ; 模式模拟

Abstract

The semi-arid region, as a key part of global land, plays an important role in climate change. In the process of modern climate change, the semi-arid region is significantly affected by local human activities, showing remarkable expansion and obvious decadal variations. In this paper, we summarized the studies of the land-atmosphere interaction in the semi-arid regions in recent years, and major land surface observation plans. We put emphasis on energy balance, water cycle, carbon cycle in land-atmosphere interaction of climate change, and their performance in historical simulation and future prediction. The prediction results illustrate that new character of land-atmosphere interaction will appear as the drying of drylands in the future. Therefore, it is necessary to deepen the understanding of land-atmosphere interaction and move forward energetically on research in regional climate from different aspects.

Keywords: Semi-arid region ; Land-atmosphere interaction ; Climate change ; Model simulation

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管晓丹, 石瑞, 孔祥宁, 刘婧晨, 甘泽文, 马洁茹, 罗雯, 曹陈宇. 全球变化背景下半干旱区陆气机制研究综述[J]. 地球科学进展, 2018, 33(10): 995-1004 https://doi.org/10.11867/j.issn.1001-8166.2018.10.0995.

Guan Xiaodan, Shi Rui, Kong Xiangning, Liu Jingchen, Gan Zewen, Ma Jieru, Luo Wen, Cao Chenyu. An Overview of Researches on Land-Atmosphere Interaction over Semi-Arid Region Under Global Changes[J]. Advances in Earth Science, 2018, 33(10): 995-1004 https://doi.org/10.11867/j.issn.1001-8166.2018.10.0995.

1 引 言

半干旱区是全球陆地的重要组成部分,占全球陆地总面积的15%,承载了世界上超过14.4%的人口[1],对全球气候变化有着重要影响。联合国环境规划署基于降水和蒸发对干湿状况的影响,将年降水量和年潜在蒸发量(Potential Evapotranspiration,PET)的比值定义为干燥度指数(Articulation Index, AI),用来反映干湿变化。定义0.2≤AI<0.5的区域为半干旱区,主要分布在美国西部、南美洲西海岸、亚洲中部和东部、澳大利亚除中部沙漠以外的大部分地区[2]。这些地区降水稀少、水资源缺乏、生态环境脆弱,对气候变化的响应十分敏感[2]。在半干旱区的气候变化过程中,陆气机制通过控制陆地与大气间的能量和物质交换,对气候变化造成显著影响[3]。对全球气候变化背景下半干旱区陆气机制的研究,不仅是前沿科学问题,更与当地的经济发展联系密切[4]

自18世纪50年代工业革命以来,由于大气中温室气体排放浓度的增加,全球气候系统出现持续增暖现象。1880—2012年,全球地表平均温度升高了约0.85 ℃[5],并以半干旱区增温最为显著,对全球陆地增温贡献达44.46%[6];不同半干旱区的增温贡献差异显著,贡献最大的区域主要分布在北半球中高纬地区,且亚洲半干旱区的贡献明显高于北美和欧洲半干旱区(图1)。随着温度的升高,全球半干旱区呈现出不同的干湿变化特征,其中东半球整体呈变干趋势而西半球整体呈变湿趋势[7]。造成东西半球干湿变化不同的原因在于PET在东亚增加,但在北美减少,而降水的变化与PET相反,最终导致AI在东亚减少(更加干旱),在北美增加(更加湿润)[1]。此外,Cai等[8]指出自20世纪70年代后期开始,南半球半干旱区,如智利南海岸、南非和南澳大利亚,在南半球秋季也表现出变干趋势,尤其在4~5月变干最为显著。

图1   不同气候区气温趋势对全球气温趋势的贡献[6]

Fig.1   The regional contribution of land-surface linear air temperature trend to global as function of climatological mean precipitation[6]

半干旱区的持续变干导致全球干旱区面积的大幅扩张[9],这种干旱扩张主要集中在非洲大陆和欧亚大陆,并以非洲大陆的程度最为剧烈[10]。Huang等[1]比较了不同时期半干旱区的面积,量化了东亚、中亚、北非、北美、非洲南部、中西亚、东澳大利亚和南美8个不同气候类型区的转化(图2)。结果表明,除北美地区的半干旱区表现出向半湿润、湿润区过渡外,东亚、中亚和北非的半干旱区均表现为显著的湿润、半湿润区向半干旱区过渡,即东亚、中亚和北非都出现了半干旱区面积扩张。其中,东亚半干旱区的扩张最为明显,对全球半干旱区扩张贡献了约50 %。马柱国等[11]进一步指出近50年来中国的干旱半干旱界线向东或向南扩展了150~300 km,干旱扩张主要出现在我国黄河中下游地区、黑龙江省和甘肃省[12]

图2   8个半干旱区气候类型的转变[1]

Fig.2   The transitions over the eight semi-arid regions[1]

长期干旱化趋势与气候变化的年代际振荡有密切的关系。研究表明,不同海盆海表温度(Sea Surface Temperature,SST)的年代际信号会造成大气环流异常,并通过遥相关影响不同地区的气候[4],导致全球增温速率加快或减缓。在过去的100多年中,由于太平洋年代际振荡(Pacific Decadal Oscillation,PDO)、北大西洋涛动(North Atlantic Oscillation,NAO)、北大西洋年代际振荡(the Atlantic Multidecadal Oscillation,AMO)等振荡指数正负相位的变化,全球曾出现2次增温减缓时期,分别是1940—1975年及从20世纪末开始的十几年时间[13]。Guan等[14]针对近期发生的增温减缓事件,将温度分离为动力温度和辐射温度,指出受气候内部变率的影响,动力温度由增温转变为降温,抵消了辐射强迫的增温作用,导致了加速增温到增温减缓的转变。增温趋势的减缓使得北半球中高纬度地区的长期干旱趋势得到了一定的缓解,尤其是欧亚与北美地区[15](图3)。

图3   干燥度指数(a)与降水(实线)和潜在蒸发量(虚线)(b)的年代际变化[15]

Fig.3   Decadal variability of AI(a), precipitation (solid line) and PET (dotted line)(b)[15]

2 半干旱区主要陆面观测计划

除大尺度大气环流对半干旱气候的影响,陆—气相互作用在半干旱地区气候变化过程中也发挥了重要作用。因此,从20世纪80年代起,在世界气候研究计划(World Climate Research Programme,WCRP)和国际地圈生物圈计划(International Geosphere-Biosphere Programme,IGBP)的协调组织下,世界各国开展了50多个大型陆面过程实验[3],其中与半干旱区相关的有10个左右,如在西班牙东南部进行的欧洲植被、大气和陆面之间的气候和水文相互作用的国家计划——受沙漠化威胁地区的外场实验(ECHIVAL Field Experiment in a Desertification-threatened Area,EFEDA);在美国堪萨斯中部进行的第一次国际卫星地表气候计划外场观测(International Satellite Land Surface Climatology Project Field Experiment,ISLSCP FIFE);在尼日尔西部进行的西非荒漠草原水文和大气预实验(Hydrologic Atmospheric Pilot Experiment in the Sahel,HAPEX Sahel)等[16]

我国也先后展开了若干个大型综合观测实验,如1994年进行的青藏高原科学实验(Tibetan Plateau Experiment,TIPEX),该实验围绕青藏高原地气相互作用开展了研究,发展了相关的区域陆面过程模式,并对利用卫星资料推算陆面参数的方法进行了检验;中日合作的中—日黑河陆气相互作用外场观测试验(Atmosphere-Land Surface Processes Experiment at Heihe River Basin Western China,HEIFE)则以水分和热量交换为中心,研究了干旱气候的形成和变化的陆面物理过程,为建立和改进半干旱地带水分和能量收支的参数化方案提供了观测依据;1997—2001年进行的内蒙古半干旱草原土壤—植被—大气相互作用研究计划(Inner Mongolia Semi-Arid Grassland Soil-Vegetation-Atmosphere Interaction,IMGRASS)[17],通过分析土地利用与土地覆盖的变化,为确定退化草原的能量水分输送过程并确定局地陆面过程特征参数提供了有效资料[3]。此外,还有甘肃敦煌荒漠戈壁进行的西北干旱区陆—气相互作用野外观测试验(Land-Atmosphere Interaction Experiment in Arid Region of Northwest China,NWC-ALIEX)等[18]

然而野外观测试验的持续时间都比较短暂,不能满足半干旱区气候变化研究的需求。因此,近年来我国又在半干旱区建立了一批长期观测站,以提供长时间的观测资料。例如在我国生存环境演变和北方干旱化趋势预测项目(国家科技重大专项项目和国家重点基础发展研究计划项目)的支持下,2002年吉林通榆针对典型半干旱农田和草地下垫面建立了通榆观测实验站[9],刘辉志等[19]基于该站的近地面层微气象及能量通量观测资料,研究发现了半干旱区农田和退化草地下垫面近地层能量收支具有相似的特征。2005年,兰州大学在典型黄土高原下垫面建立了半干旱气候与环境观测站(Semi-Arid Climate and Environmental Observatory of Lanzhou University,SACOL),并进行了一系列陆气物理过程、陆气间能量、水分和物质交换过程、沙尘、黑碳气溶胶等长期定点的对比观测[20],指出黄土高原半干旱区近地层湍流能量与地表含水量显著相关[21]

2012年批准立项的国家重大科学研究计划项目“全球典型干旱半干旱区气候变化及其影响”,通过大气、水文、生态等多学科的交叉研究,揭示了干旱半干旱区气候变化规律及其对全球变暖的响应机制,提出国际领先的干旱半干旱区气候变化机理,并科学预测了干旱半干旱区气候变化趋势[2]。此外,我国还将启动第二次青藏高原综合科学考察研究与第三次青藏高原大气科学试验第二阶段。由IGBP发起实施的陆地生态系统与大气过程综合研究(Integrated Land Ecosystem-Atmosphere Processes Study,iLEAPS)第二阶段也将进一步探究不同时空尺度的陆气界面生物、化学、物理过程的相互作用,并针对人类支配的环境提出了可持续发展的管理方案。这些国际和国内的试验和项目将可验证的区域资料与全球资料相连接,建立了较好的陆面过程模式和参数化方案,并为模式的构造和评价提供了依据,有效推进了半干旱区陆气机制的研究发展。

3 半干旱区陆气机制

已有的研究指出,陆气相互作用可以通过行星边界层的湍流通量控制陆地与大气间的能量平衡、水循环以及碳循环[12],进而影响近地层的温度与降水,在半干旱区的气候变化中起到了不可忽视的作用。

3.1 水循环

当不考虑相邻土壤体积间侧面的水分交换时,某一土壤层中水平衡满足公式(1)[22]:

dSdt=P-E-Rs-Rg,(1)

式中:dS/dt表示给定土壤层中水含量的变化,P为降水,E为蒸散,Rs为地表径流,Rg为排水。其中蒸散包括地表的蒸发、植物的蒸腾、拦截蓄水的蒸发、积雪的升华以及表面水的蒸发。降水会造成土壤湿度的增加,蒸散、地表径流以及排水会导致土壤湿度的减少,同时土壤湿度也对降水和蒸散有着反馈作用。

土壤湿度(θ)与蒸发率(EF=λE/Rn)的关系如图4所示。在土壤湿度限制区域,干旱区(θ<θWILT)的土壤湿度较小,蒸发可以忽略;而在过渡区(θWILT<θ<θCRIT),蒸发率随土壤湿度的增加而增加;在能量限制区(θ>θCRIT),土壤湿度很大,蒸发率受辐射能量的限制[22]。因此,在半干旱区,蒸发率的变化由土壤湿度主导。而全球土壤湿度下降最显著的地区正处于干湿过渡区[23];这种关系也在植被覆盖率较低的地区中得以证实[24]

图4   土壤湿度定义与相应的蒸散机制[22]

Fig.4   Definition of soil moisture regimes and corresponding evapotranspiration regimes[22]

土壤湿度与降水之间的反馈是一个复杂的过程,降水会直接造成土壤湿度的增加[23],而土壤湿度又会反作用于降水,对降水产生直接影响与间接影响。一方面,土壤湿度的增加会促进蒸散,提供降水所需的水汽含量[25]。另一方面,土壤湿度还会通过改变地表有效能量在感热和潜热通量间的再分配,影响边界层温湿廓线,进而改变边界层高度、湿静力能和抬升凝结高度等,最后对降水产生影响[26]。Hohenegger等[27]发现较低的土壤湿度会产生更高的热量,更有利于对流的形成;在半干旱区,陆地表面的蒸散对降水的贡献往往高于65%[28]。前期土壤湿度的异常分布对降水变化有较显著的影响,这种影响主要作用于模式中土壤湿度的初始化方案,影响了模式模拟降水的能力[29]

3.2 能量平衡

地表能量平衡满足公式(2):

Rn=G+λE+SH,(2)

式中:Rn为地表净辐射,G为地表向下传导的热量,λE为潜热通量,SH为感热通量[30]

地表可利用能量以3种方式消耗释放:加热大气的感热通量、加热土壤的土壤热通量和蒸发水分的潜热通量。而能量分配方式的区域差异是造成气候空间差异的根本原因[31]。曾剑等[31]指出感热通量与气候干燥程度正相关,而潜热通量与气候干燥程度负相关。最干点的地表能量分配由感热通量主导,而在最湿点,感热和潜热通量贡献相当[32]。这主要是由于干旱地区降水少,地表植被稀疏,土壤干燥,对太阳辐射的吸收较小,反射较强。如果在热平衡方程中仅考虑感热和潜热的变化,则能量交换以感热为主,而潜热的作用较小[33]

土壤湿度通过改变蒸散调节感热潜热占比,进而影响半干旱区能量平衡,因此其对于潜热通量的影响与蒸散相同,都是在过渡区表现出最显著的变化。土壤湿度的下降会抑制潜热通量,导致感热通量增加、气温升高。而升高的温度会带来更高的蒸发需求,从而使土壤湿度进一步下降。这个过程会持续进行,直到土壤全部干燥,此时陆气能量交换中潜热通量不再存在,温度急剧上升。这种正反馈作用造成了干湿过渡区的土壤显著变干[23](图5)。此外,较低的土壤湿度对炎热天数百分比、热浪持续时间的正异常都有显著的影响[34]

图5   不同气候区年均气温和土壤湿度的趋势[23]

Fig.5   The linear trends of annual mean temperature and soil moisture as a function of climatological mean precipitation[23]

3.3 碳循环

陆地生态系统是全球碳循环的重要组成部分,在全球碳收支中占主导地位。而土壤作为连接大气圈、水圈、生物圈及岩石圈的纽带,其碳循环研究是分析陆地生态系统碳循环的重要前提[35]。干旱半干旱区土壤有机碳储量巨大,约占全球土壤有机碳的27%[36],对全球碳储存、缓解大气CO2浓度升高过程起到了重要作用,在区域及全球碳循环过程中的贡献日益显著。干旱区的土壤碳主要分布在表面,对聚居于其上的生物体活动十分敏感[36]。当植物输入到土壤中的碳超过分解的碳时,将使CO2对气候变化产生负反馈;当储存在地下的碳由于升温加速释放到大气中时,将产生正反馈[37]。而全球碳汇的异常主要是受南半球半干旱区植被的增长所影响,半干旱区生物群落中碳库的更新率对全球碳循环年际变化的影响日益增大[38]。从夏季到早春,半干旱区森林通过光合作用在干湿过渡区维持大量的碳固定[39]。其中,热带稀树草原的固碳能力十分显著,通过保护热带稀树草原可以有效增加固碳场所[40]

温度上升会显著增强土壤的碳排放,降低土壤净CO2吸收[36]。因此,随着全球变暖,半干旱区储存的有机碳将不断减少,释放出更多C O2[12]。同时,土壤温度和水分也会影响半干旱区土壤呼吸。在适宜的温度范围内,土壤温度与土壤呼吸强度存在正相关关系,但当温度过高时,固碳能力和初级生产力逐渐下降。而土壤水分的增加则会提高系统的固碳能力、初级生产力及呼吸作用[41]。此外,半干旱区生态系统碳交换的季节性变化还与降水变化高度相关,在干旱的生态系统或干湿交替的生态系统中比较干旱的季节,降水可能会强烈地激发土壤呼吸[42]。一个可能的原因是降水激活了土壤微生物的活性,增加了微生物的种群数量,进而增强了其分解活动;另一个可能的原因是降雨增加了根系的呼吸[43],加强了土壤呼吸作用。

4 模式对半干旱区陆气特征的模拟

除了观测外,模式在陆面过程发展的进程中,也发挥了重要作用。陆面模式发展大体经历了水循环、能量循环和碳循环等阶段。其中,第一代与第二代陆面模式围绕水循环与能量分配等基本的物理过程,建立了陆面过程的基本框架,并利用观测资料,提出了不同的参数化方案,有效推动了陆面模式的发展。而随着计算能力的加强以及植被在陆面过程中作用研究的进步,第三代陆面模式在第二代的基础上进一步考虑了植被的生物化学作用,将光合作用和碳循环引入到了陆面模式,可以更加真实地反映土壤、地表、大气、生物圈相互作用[44]。新一代模型的提出不仅更加真实地反映了陆面过程的特征,更提升了耦合模式中气候系统的模拟精度。

4.1 模式对历史半干旱区陆气特征的模拟

随着对半干旱区研究的深入,气候模式已经成为研究半干旱区陆气相互作用并预测未来气候变化不可替代的工具。WCRP组织实施的耦合模式比较计划(Coupled Models Intercomparison Project, CMIP)为模式模拟提供了重要的研究平台。然而CMIP5模式模拟的集合平均温度在半干旱区的重复实验中出现了较大的偏差,没有模拟出半干旱区的强化增温现象[45],而且低估了温度的变化趋势[46]。同时,CMIP5模式低估降水的变化趋势,高估降水的范围,这导致全球降水被高估,尤其是在半干旱区[47](图6)。降水模拟的不确定性可能是由于区域变化趋势受内部气候变率主导,而CMIP5多模式总体平均消除了自然变率,仅模拟出了外部气候强迫的影响[46]

图6   不同区域观测与模拟的潜在蒸散、降水、干燥度指数、气温距平[47]

Fig.6   Temporal variations in regionally averaged precipitation, PET, AI, and SAT in hyper-arid, arid, semi-arid,and dry subhumid regions from observations and the CMIP5 MME[47]

在CMIP5的大部分模式中,PET都与降水呈负相关,模式总体平均虽然能再现干旱区的PET趋势,但在空间分布上仍与实际情况有较大出入[47],大部分模式模拟的半干旱区P/PET都与实际情况存在一定差异[48]。1948—2005年,观测的AI下降了0.050,全球66%的区域呈变干趋势,而模拟的AI仅下降了0.012,是观测的1/4,全球仅59%的区域发生了变干,半干旱区的扩张被大大低估[45],这是由于当整体PET下降时,降水的减少会导致区域变干[46],而模式对降水存在高估现象[47]

4.2 模式对未来半干旱区陆气特征的模拟

虽然模式对半干旱区陆气特征的模拟存在一定误差,但是模式模拟仍然是预测未来气候变化最重要的工具之一。模式结果表明,在高排放情景(Rcp8.5)下,2100年全球陆地平均温度将增加3~10 ℃,且北半球中高纬地区的增加趋势较热带和南半球更剧烈。随着温度的增加,降水和PET的特征也发生了改变[9]。降水将在北半球中高纬地区和东亚南部、非洲热带增加,呈现出“湿变湿,干变干”的特征[49]。同时,南北2个半球的变干都呈现出明显的春—秋不对称,尤其是北半球秋季的变干程度明显低于其他季节[50]。而PET则表现为增加趋势,同时呈现明显的横穿大陆的空间分布[48]。中等排放情景(Rcp4.5)和低等排放情境(Rcp2.7)下的变化特征与Rcp8.5下相似,但程度较为平缓[46]

降水和PET的改变进一步导致了全球气候类型的重新分布[9]。在21世纪前半叶,Rcp8.5和Rcp4.5下都出现了显著的干旱扩张,而在21世纪后半叶,Rcp8.5下干旱扩张的趋势更加显著,但Rcp4.5下变化不大[49]。在Rcp8.5下,半干旱区主要的扩张出现在地中海南岸、非洲南部、美国南部和北部。到2100年,Rcp8.5和Rcp4.5下全球将分别有46.3%和31.4%的陆地气候类型出现转变[49],其中半干旱区将表现出最显著的干旱扩张,分别扩张23%和11%,占全球陆地面积的20.3%和19.0%[45]。此外,即使是在中低等排放情境下,模式中全球农业干旱的发生频率和范围都将继续增长[46]。除东亚地区,生长季的干旱现象都将持续增加[51]

5 结语与展望

随着近百年全球温度的不断升高,半干旱区呈现出显著的强化增温,并通过增温—变干的正反馈过程使近年来的变干趋势不断增强,湿润半湿润区不断转化成半干旱区,半干旱区面积持续扩张,全球干旱化程度日益严重。而在增温减缓期间,中高纬度地区的干燥度指数和土壤湿度都出现了变干减缓的现象,半干旱区陆—气间的水循环与能量交换呈现出年代际变化特征。虽然半干旱区陆气机制的研究已经取得了一系列的成果,但是随着气候背景的改变和人类活动影响方式的变化,半干旱区陆气机制的研究仍存在很多亟待解决的问题:例如长期观测数据的缺失仍然是阻碍半干旱区陆气机制研究的主要问题之一。大部分半干旱区分布在发展中国家,对科学研究的投入相对有限,站点数据密度稀疏。近年来,我国提出了“一带一路”倡议,提倡沿线国家发展共赢,不仅对沿路国家的经济文化发展提供了机遇,更是为半干旱区的科学发展和合作提供了更多的机会;此外,模式结果在半干旱区温度、湿度等模拟中仍普遍存在较大偏差,为了得到更精确的预测结果,除了修正大尺度背景场的影响外,还需要进一步发展陆面非均匀参数化方案,构建不同时间和空间尺度模式,提高模式模拟能力;最后,目前关于半干旱区生态系统碳循环的研究及氧循环还存在许多不确定性,如碳的“源汇效应”及氧消耗对植被不同时间尺度的影响等[52],这些问题需要对不同时空不同生物群落进行详细的野外试验和更细致的动态生态模式模拟,并进一步建立更加完善的综合分析系统。

The authors have declared that no competing interests exist.


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[J]. Advances in Atmospheric Sciences, 2015, 32(6):870-876.

DOI      URL      [本文引用: 2]      摘要

This study examines the expansion of drylands and regional climate change in northern China by analyzing the variations in aridity index (AI), surface air temperature (SAT), precipitation and potential evapotranspiration (PET) from 1948 to 2008. It is found that the drylands of northern China have expanded remarkably in the last 61 years. The area of drylands of the last 15 years (1994–2008) is 0.65×10 6 km 2 (12%) larger than that in the period 1948–62. The boundary of drylands has extended eastward over Northeast China by about 2° of longitude and by about 1° of latitude to the south along the middle-to-lower reaches of the Yellow River. A zonal band of expansion of semi-arid regions has occurred, stretching from western Heilongjiang Province to southern Gansu Province, while shifts to the east of semi-arid regions in dry subhumid regions have also occurred. Results show that the aridity trend of drylands in northern China is highly correlated with the long-term trend of precipitation and PET, and the expansion of semi-arid regions plays a dominant role in the areal extent of drylands, which is nearly 10 times larger than that in arid and subhumid regions.
[13] Huang J, Xie Y, Guan X, et al.

The dynamics of the warming hiatus over the Northern Hemisphere

[J]. Climate Dynamics, 2017, 48(1/2):429-446. DOI:10.1007/s00382-016-3085-8.

URL      [本文引用: 1]      摘要

A warming hiatus is a period of relatively little change in global mean surface air temperatures (SAT). Many studies have attributed the current warming hiatus to internal climate variability (ICV). But there is less work on discussion of the dynamics about how these ICV modes influence cooling over land in the Northern Hemisphere (NH). Here we demonstrate the warming hiatus was more significant over the continental NH. We explored the dynamics of the warming hiatus from a global perspective and investigated the mechanisms of the reversing from accelerated warming to hiatus, and how ICV modes influence SAT change throughout the NH land. It was found that these ICV modes and Arctic amplification can excite a decadal modulated oscillation (DMO), which enhances or suppresses the long-term trend on decadal to multi-decadal timescales. When the DMO is in an upward (warming) phase, it contributes to an accelerated warming trend, as in last 20 years of twentieth-century. It appears that there is a downward swing in the DMO occurring at present, which has balanced or reduced the radiative forced warming and resulted in the recent global warming hiatus. The DMO modulates the SAT, in particular, the SAT of boreal cold months, through changes in the asymmetric meridional and zonal thermal forcing (MTF and ZTF). The MTF represents the meridional temperature gradients between the mid- and high-latitudes, and the ZTF represents the asymmetry in temperatures between the extratropical large-scale warm and cold zones in the zonal direction. Via the different performance of combined MTF and ZTF, we found that the DMO's modulation effect on SAT was strongest when both weaker (stronger) MTF and stronger (weaker) ZTF occurred simultaneously. And the current hiatus is a result of a downward DMO combined with a weaker MTF and stronger ZTF, which stimulate both a weaker polar vortex and westerly winds, along with the amplified planetary waves, thereby facilitating southward invasion of cold Arctic-air and promoting the blocking formation. The results conclude that the DMO can not only be used to interpret the current warming hiatus, it also suggests that global warming will accelerate again when it swings upward.
[14] Guan X, Huang J, Guo R, et al.

Role of radiatively forced temperature changes in enhanced semi-arid warming in the cold season over east Asia

[J]. Atmospheric Chemistry and Physics, 2015, 15(23):13 777-13 786.

DOI      URL      [本文引用: 1]     

[15] Guan X, Huang J, Guo R.

Changes in aridity in response to the global warming hiatus

[J]. Journal of Meteorological Research, 2017, 31(1):117-125.

DOI      URL      [本文引用: 3]      摘要

The global warming slowdown or warming hiatus, began around the year 2000 and has persisted for nearly 15 years. Most studies have focused on the interpretation of the hiatus in temperature. In this study, changes in a global aridity index (AI) were analyzed by using a newly developed dynamical adjustment method that can successfully identify and separate dynamically induced and radiatively forced aridity changes in the raw data. The AI and Palmer Drought Severity Index produced a wetting zone over the mid-to-high latitudes of the Northern Hemisphere in recent decades. The dynamical adjustment analysis suggested that this wetting zone occurred in response to the global warming hiatus. The dynamically induced AI (DAI) played a major role in the AI changes during the hiatus period, and its relationships with the North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), and Atlantic Multi-decadal Oscillation (AMO) also indicated that different phases of the NAO, PDO, and AMO contributed to different performances of the DAI over the Northern Hemisphere. Although the aridity wetting over the mid-to-high latitudes may relieve long-term drying in certain regions, the hiatus is temporary, and so is the relief. Accelerated global warming will return when the NAO, PDO, and AMO revert to their opposite phases in the future, and the wetting zone is likely to disappear.
[16] Luo Yong, Wang Shaowu, Dang Hongyan, et al.

Recent advances in climate models and model intercomparison projects

[J]. Advances in Earth Science, 2002, 17(3):372-373.

Magsci      [本文引用: 1]     

[罗勇, 王绍武, 党鸿雁, .

近20年来气候模式的发展与模式比较计划

[J]. 地球科学进展, 2002, 17(3):372-373.]

DOI      URL      Magsci      [本文引用: 1]      摘要

<p>20世纪80年代以来,全球气候观测系统的不断完善、国际大型外场观测试验的成功实施以及高性能计算机的飞速发展,为气候模式的迅猛发展提供了基础和条件。近20年来气候模式的复杂程度和模拟能力得到了显著的提高,目前已成为研究全球和区域气候的形成及变异、气候系统各圈层之间的相互作用以及全球变化等的有力工具。对气候模式(包括大气环流模式、陆面过程模式、海洋环流模式以及区域气候模式)的主要发展进行综合评述,并简要介绍了目前世界上一些主要的模式比较研究计划。</p>
[17] Chen Haishan, Sun Zhaobo.

Review of land-atmosphere interaction and land surface model studies

[J]. Journal of Nanjing Institute of Meteorology, 2002, 25(2):277-288.

[本文引用: 1]     

[陈海山, 孙照渤.

陆气相互作用及陆面模式的研究进展

[J]. 南京气象学院学报, 2002, 25(2):277-288.]

[本文引用: 1]     

[18] Zhang Qiang, Huang Ronghui, Wang Sheng, et al.

NWC-ALIEX and its research advances

[J]. Advances in Earth Science, 2005, 20(4):427-441.

Magsci      [本文引用: 1]     

[张强, 黄荣辉, 王胜, .

西北干旱区陆—气相互作用试验(NWC-ALIEX)及其研究进展

[J]. 地球科学进展, 2005, 20(4):427-441.]

DOI      URL      Magsci      [本文引用: 1]      摘要

<p>简要阐述了国家重点基础研究发展规划项目&ldquo;我国重大气候和天气灾害形成机理和预测理论的研究&rdquo;支持的&ldquo;我国西北干旱区陆&mdash;气相互作用野外试验(NWCALIEX)&rdquo;的科学意义、试验方案和科学目标,总结了该试验在最近几年取得的部分研究进展和研究成果,概括叙述了该项目在地表辐射平衡和热量平衡、总体输送系数、陆面过程参数、湍流通量参数化和地表水分循环以及陆面过程模式的改进和陆面过程的模拟等许多方面的重要发现和一些新的认识。最后,提出并讨论了在干旱区陆面过程方面需要进一步研究和思考的一些重要科学问题。</p>
[19] Liu Huizhi, Dong Wenjie, Fu Congbin, et al.

The long-term field experiments on aridfication and the ordered human activity in semi-arid area at Tongyu, Northeast China

[J]. Climatic and Environmental Research, 2004, 9(2):378-389.

[本文引用: 1]     

[刘辉志, 董文杰, 符淙斌, .

半干旱地区吉林通榆“干旱化和有序人类活动”长期观测实验

[J]. 气候与环境研究, 2004, 9(2):378-389.]

DOI      URL      [本文引用: 1]      摘要

简单介绍了吉林通榆"干旱化和有序人类活动"长期观测实验,该实验站同时也是国际协同加强观测计划(CEOP)的地面观测站.分析了2002年10月~2003年3月(CEOP-EOP3)非生长季观测到的近地面层微气象及能量通量资料.结果表明,在非生长季,半干旱地区农田和退化草地下垫面近地面层能量收支基本一致;感热通量占主要地位,占净辐射通量的70%左右;潜热通量及地热流都很小,通常小于30 W m-2.土壤温度日变化主要集中在地表以下20 cm土壤层,20 cm以下土壤温度日变化很小,但存在明显的季节变化.在非生长季,土壤表层10 cm厚度内,草地下垫面土壤体积含水量比农田大;20 cm以下深度土壤体积含水量的日变化很小,同样存在季节变化.
[20] Huang J, Zhang W, Zuo J, et al.

An overview of the semi-arid climate and environment research observatory over the Loess Plateau

[J]. Advances in Atmospheric Sciences, 2008, 25(6): 1-16. DOI:10.1007/s00376-008-0906-7.

URL      [本文引用: 1]     

[21] Xiao Xia, Zuo Hongchao, Liu Huizhi, et al.

Observational study of the surface energy closure in the semi-arid regions of Loess Plateau in late spring

[J]. Journal of Glaciology and Geocryology, 2010, 32(1):70-77.

Magsci      [本文引用: 1]     

[肖霞, 左洪超, 刘辉志, .

春末黄土高原半干旱区地表能量闭合的观测研究

[J]. 冰川冻土, 2010, 32(1):70-77.]

URL      Magsci      [本文引用: 1]      摘要

<FONT face=Verdana>利用兰州大学半干旱气候与环境监测站的连续观测数据, 分析了该站的数据质量情况和黄土高原半干旱区的近地层湍流通量特征及地表能量平衡能量闭合状况. 结果表明:兰州大学半干旱气候与环境监测站(SACOL)湍流通量的平均时间取30 min为宜. 该站利用EdiRe获得的湍流通量较TK2和CR5000数据自动记录器输出的湍流通量结果要好. 黄土高原半干旱区近地层湍流能量与地表含水量状况明显相关,地表干燥时感热通量处于主导地位,接近于干旱区的特征;地表湿润时感热通量和潜热通量则相当,接近于湿润地区的特征. 地表能量平衡分析表明,兰州大学黄土高原半干旱环境监测站观测的地表能量闭合度高达85%,与已有的观测相比,能量闭合情况属于较好水平. </FONT>
[22] Seneviratne S I, Corti T, Davin E L, et al.

Investigating soil moisture-climate interactions in a changing climate: A review

[J]. Earth-Science Reviews, 2010, 99(3/4):125-161.

DOI      URL      [本文引用: 4]      摘要

Soil moisture is a key variable of the climate system. It constrains plant transpiration and photosynthesis in several regions of the world, with consequent impacts on the water, energy and biogeochemical cycles. Moreover it is a storage component for precipitation and radiation anomalies, inducing persistence in the climate system. Finally, it is involved in a number of feedbacks at the local, regional and global scales, and plays a major role in climate-change projections. In this review, we provide a synthesis of past research on the role of soil moisture for the climate system, based both on modelling and observational studies. We focus on soil moisture emperature and soil moisture recipitation feedbacks, and their possible modifications with climate change. We also highlight further impacts of soil moisture on climate, and the state of research regarding the validation of the relevant processes. There are promises for major advances in this research field in coming years thanks to the development of new validation datasets and multi-model initiatives. However, the availability of ground observations continues to be critical in limiting progress and should therefore strongly be fostered at the international level. Exchanges across disciplines will also be essential for bridging current knowledge gaps in this field. This is of key importance given the manifold impacts of soil moisture on climate, and their relevance for climate-change projections. A better understanding and quantification of the relevant processes would significantly help to reduce uncertainties in future-climate scenarios, in particular with regard to changes in climate variability and extreme events, as well as ecosystem and agricultural impacts.
[23] Cheng S, Guan X, Huang J, et al.

Long-term trend and variability of soil moisture over East Asia

[J]. Journal of Geophysical Research Atmospheres, 2015, 120(17):8 658-8 670.

DOI      URL      [本文引用: 5]      摘要

Abstract The variability of soil moisture over East Asia was analyzed using a long-term data set from the Global Land Data Assimilation System. Overall, a clear decreasing trend occurred over a period of 63 ears, with pronounced drying over northeast China, north China, part of Mongolia, and Russia near lake Baikal. Statistical analyses show that decreasing precipitation and global warming have different effects on the decrease in soil moisture. The qualitative analysis and quantitative contributions illustrated that soil drying is driven primarily by decreasing precipitation and is enhanced almost twofold by increasing temperatures. As soil moisture decreases, the positive feedback between soil moisture and temperature may result in future water shortages. Following the Representative Concentration Pathways 8.5 (RCP8.5) and 4.5 (RCP4.5) simulation scenarios of Coupled Model Intercomparison Project phase 5, the model-predicted soil moisture demonstrated a continuously decreasing trend during the 21st century.
[24] Bing Longfei, Su Hongbo, Shao Quanqin, et al.

Changing characteristic of land surface evapotranspiration and soil moisture in China during the past 30 years

[J]. Journal of Geo-Information Science, 2012, 14(1):1-13.

Magsci      [本文引用: 1]     

[邴龙飞, 苏红波, 邵全琴, .

近30年来中国陆地蒸散量和土壤水份变化特征分析

[J]. 地球信息科学学报, 2012, 14(1):1-13.]

DOI      URL      Magsci      [本文引用: 1]      摘要

对NOAH陆面模式模拟的近30年中国陆地蒸散量和土壤含水量,按照6大片区和5种生态系统类型进行了统计分析。讨论全国以及各大区不同生态系统类型蒸散和土壤含水量的变化,研究不同类型蒸散和土壤含水量的关系。中国陆地蒸散量总体呈增加的趋势,年内蒸散量最大的月份是7月,年末和年初蒸散量较小。而我国中南、西南、华东、东北和西北蒸散量变化趋势和全国的总趋势一致,呈增加的趋势。华北地区蒸散量近30年来总体趋势是下降的,华北蒸散量最大的年份是上世纪90年代。在所有生态系统类型中,林地蒸散最大的有东北、华东、西南和中南4区;而华北和西北草地在各类型中蒸散量所占比例最高。6大片区对比,林地蒸散水量最大的地区是西南和中南,最小的西北;草地蒸散水量最大的地区是西南,最小的是东北区;农田蒸散水量最高的是华东,最低的是西北;荒漠蒸散量最大的片区是西北;湿地蒸散最大的是东北。80年代以来,全国土壤含水量总体呈下降的趋势。从各片区的情况看,仅西北地区稍有增加,其余5区土壤含水量皆是下降的。植被覆盖度和土壤水分是影响蒸散量最重要的因子,在植被覆盖较差时,土壤水分和蒸散量相关性较好。
[25] Brubaker K L, Entekhabi D, Eagleson P S.

Estimation of continental precipitation recycling

[J]. Journal of Climate, 1993, 6(6):1 077-1 089.

DOI      URL      [本文引用: 1]     

[26] Zhang Shuwen, Liu Yuan, Cao Bangjun, et al.

Soil moisture-precitation coupling and trends in China, based on GLDAS and CMIP5 products

[J]. Climatic and Environmental Research, 2016, 21(2):188-196.

[本文引用: 1]     

[张述文, 刘源, 曹帮军, .

GLDAS和CMIP5产品的中国土壤湿度—降水耦合分析及变化趋势

[J]. 气候与环境研究, 2016, 21(2):188-196.]

DOI      URL      [本文引用: 1]      摘要

利用GLDAS同化产品和12个CMIP5模式的输出结果,从土壤湿度对降水影响的两个中间环节出发,通过分析陆面耦合指数ILH、潜热通量—抬升凝结高度耦合指数ILCL以及抬升凝结高度ZLCL间接研究中国区域土壤湿度与降水间耦合特征,并对1958~2013年及RCP4.5辐射强迫情景下50年(2006~2055年)的4个代表性区域夏季耦合强度的年代际变化特征进行分析。研究发现:1958~2013年期间,内蒙古阴山山脉附近、新疆和青海的部分地区为夏季中国土壤湿度与降水耦合的最强区域;陆面耦合指数ILH变化幅度从高到低依次出现在华北、华南、内蒙古中部和西北地区,并在20世纪70年代中到80年代中发生转折。2006~2055年的平均而言,预估内蒙古阴山山脉附近仍为耦合最强区;与历史时期(1958~2005年)比较,新疆中部和内蒙古阴山山脉附近的耦合指数ILH增大,而广西和广东地区的则减小;对于耦合指数ILH的年代际变化(2006~2055年),2026~2035年间华北最大而华南最小,西北地区变化不大,而内蒙古中部地区的耦合强度逐渐增大。
[27] Hohenegger C, Brockhaus P, Bretherton C S, et al.

The soil moisture-precipitation feedback in simulations with explicit and parameterized convection

[J]. Journal of Climate, 2009, 22(19):5 003-5 020.

DOI      URL      [本文引用: 1]     

[28] Ma Zhuguo, Fu Congbin, Xie Li, et al.

Some problems in the study on the relationship between soil moisture and climate change

[J]. Advance in Earth Sciences, 2001, 16(4):563-568.

Magsci      [本文引用: 1]     

[马柱国, 符淙斌, 谢力, .

土壤湿度和气候变化关系研究中的某些问题

[J]. 地球科学进展, 2001, 16(4):563-568.]

DOI      URL      Magsci      [本文引用: 1]      摘要

<p>从土壤湿度研究的历史出发,阐述了土壤湿度在气候变化乃至全球变化研究中的重要性;并从土壤湿度研究的科学背景出发,总结和综合评述了该研究领域所存在的两个重要科学问题及其研究现状。最后,对未来研究的方向及可能取得的进展进行了论述。</p>
[29] Guo Weidong, Ma Zhuguo, Wang Huijun.

Soil moisture-an important factor of seasonal precipitation prediction and its application

[J]. Climatic and Environmental Research, 2007, 12(1):20-28.

[本文引用: 1]     

[郭维栋, 马柱国, 王会军.

土壤湿度——一个跨季度降水预测中的重要因子及其应用探讨

[J]. 气候与环境研究, 2007, 12(1):20-28.]

DOI      URL      [本文引用: 1]      摘要

阐述了土壤湿度对短期气候变化的重要作用,结合我国的业务现状提出亟需将这一因子应用于跨季度降水预测。通过将一个土壤湿度反演模型引入IAP跨季度气候预测系统,探讨了土壤湿度应用于季节降水预测的可行性及其效果。初步的个例分析表明:前期土壤湿度的异常分布对降水变化有较显著的影响,继续改进土壤湿度反演模型可望获得更好的降水预测效果。同时,提出的基于常规气象观测进行反演以获得大范围土壤湿度分布的办法在当前业务预测中具有很强的可操作性。
[30] Burba G G, Verma S B, Kim J.

Surface energy fluxes of Phragmites Australis, in a prairie wetland

[J]. Agricultural and Forest Meteorology, 1999, 94(1):31-51.

DOI      URL      [本文引用: 1]     

[31] Zeng Jian, Zhang Qiang, Wang Sheng.

Regional differences in the characteristics of clear sky land surface processes in distinct climatic zones over Northern China

[J]. Chinese Journal of Atmospheric Sciences, 2011, 35(3):483-494.

Magsci      [本文引用: 2]     

[曾剑, 张强, 王胜.

中国北方不同气候区晴天陆面过程区域特征差异

[J]. 大气科学, 2011, 35(3):483-494.]

DOI      URL      Magsci      [本文引用: 2]      摘要

采用2008年7~9月份观测的中国干旱—半干旱区实验观测协同与集成研究资料, 将我国北方干旱—半干旱区根据气候类型和地理位置划分为西北干旱区、 黄土高原区和东北冷区三个区域, 分析了干旱—半干旱区陆面热量平衡和辐射平衡日变化的区域差异。结果显示: 不同气候区域的地表辐射和能量过程差异明显, 而这种差异主要源于大气和土壤中可利用水分的不同, 因而区域差异的分析也可归结于探讨陆面辐射和能量过程对不同强弱干旱气候的响应特征。在辐射平衡的比较方面: 晴天的总辐射在各区域呈现随纬度上升而递减的趋势; 反射辐射在东北冷区最小而在西北干旱区最大; 大气逆辐射在东北冷区最明显, 在黄土高原区最弱; 地表长波辐射在西北干旱区最强而在东北冷区最弱。在能量平衡方面: 西北干旱区的地表可利用能量的70%左右用于加热大气, 小部分消耗于蒸发和加热土壤; 黄土高原区可利用能量中用于加热大气的能量占30%, 蒸发水分的消耗能量约50%; 东北冷区接近一半的可利用能量用于蒸发, 另一半的大部分消耗于加热大气。
[32] Zhang Qiang, Zhang Liang, Huang Jing, et al.

Spatial distribution of surface energy fluxes over the Loess Plateau in China and its relationship with climate and the environment

[J]. Science in China (Series D), 2014, 57(9): 2 135-2 147.

[本文引用: 1]     

[张强, 张良, 黄菁, .

我国黄土高原地区陆面能量的空间分布规律及其与气候环境的关系

[J]. 中国科学:D辑, 2014, 44(9):2 062-2 076.]

[本文引用: 1]     

[33] Hui Xiaoying, Wang Chenghai, Zuo Hongchao, et al.

Abnormal features of sensible and latent heat fluxes in arid region of Northern China

[J]. Plateau Meteorology, 2005, 24(3):415-421.

Magsci      [本文引用: 1]     

[惠小英, 王澄海, 左洪超, .

中国北方干旱区感热及潜热的异常特征

[J]. 高原气象, 2005, 24(3):415-421.]

DOI      URL      Magsci      [本文引用: 1]      摘要

通过对1949-1999年逐月NCEP/NCAR感热通量和潜热通量再分析资料的分析,发现在我国北方干旱区感、潜热通量的年际变化存在着2~3个敏感区,分别位于西北和华北及内蒙一带。其中以东部的华北-内蒙区最为显著。代表上述两个地区通量的平均年际变化表明,在20世纪60年代后期,感、潜热通量存在一个突变;进入70年代以后,上述两个地区的感热通量保持在一个较高的水平上,潜热通量的变化则呈现出相反的变化。
[34] Meng L, Shen Y.

On the relationship of soil moisture and extreme temperatures in East China

[J]. Earth Interactions, 2014, 18(1):1-20.

DOI      URL      [本文引用: 1]      摘要

Soil moisture conditions affect energy partitioning between sensible and latent heat fluxes, resulting in a change in surface temperatures. In this study, the relationships between antecedent soil moisture conditions [as indicated by the 6-month standardized precipitation index (SPI)] and several temperature indices are statistically quantified using the quantile regression analysis across East China to investigate the influence of soil moisture on summer surface temperatures. These temperature indices include percentage of hot days (%HD), heat-wave duration (HWD), daily temperature range (DTR), and daily minimum temperature (Tmin). It was demonstrated that soil moisture had a significant impact on %HD and HWD at higher quantiles in all regions but the east, suggesting that drier soil moisture conditions tend to intensity summer hot extremes. It was also found that hot extremes (%HD and HWD at higher quantiles) had increased substantially from 1958 to 2010. Soil moisture also significantly affected the DTR in all regions but tended to have more impacts on the DTR in soil moisture-limited regimes than in energy-limited regimes. This study provides observational evidence of soil moisture influences on hot extremes in East China.
[35] Chen Qingqiang, Shen Chengde, Yi Weixi, et al.

Progresses in soil carbon cycle researches

[J]. Advances in Earth Science, 1998, 13(6):555-563.

Magsci      [本文引用: 1]     

[陈庆强, 沈承德, 易惟熙, .

土壤碳循环研究进展

[J]. 地球科学进展, 1998, 13(6):555-563.]

DOI      URL      Magsci      [本文引用: 1]      摘要

<p>土壤碳是陆地碳库的主要组成部分,全球土壤有机碳总量达1270 Gt。气候变化影响植物生长、植物碎屑分解速率以及土壤&mdash;大气碳通量,这对大气CO<sub>2</sub>含量有重要影响。土壤有机质模型是研究生态系统尺度土壤碳循环的唯一可用工具,目前已开发出多种。大量研究表明,<sup>14</sup>C测试是研究土壤有机碳组成及驻留时间的重要手段,土壤有机碳由一系列具不同更新时间的组分构成。土壤粒级组成、矿物特征及土体结构等内在因素制约土壤有机碳存量及状态,对于长时间尺度碳的更新具有重要意义。研究不同气候带土壤有机碳储量及动态变化特征,可为预测未来农、林生态系统变化提供理论依据。</p>
[36] Maestre F T, Escolar C, Guevara M L D, et al.

Changes in biocrust cover drive carbon cycle responses to climate change in drylands

[J]. Global Change Biology, 2013, 19(12):3 835.

DOI      URL      PMID      [本文引用: 3]      摘要

AbstractDryland ecosystems account for ca. 27% of global soil organic carbon (C) reserves, yet it is largely unknown how climate change will impact C cycling and storage in these areas. In drylands, soil C concentrates at the surface, making it particularly sensitive to the activity of organisms inhabiting the soil uppermost levels, such as communities dominated by lichens, mosses, bacteria and fungi (biocrusts). We conducted a full factorial warming and rainfall exclusion experiment at two semiarid sites in Spain to show how an average increase of air temperature of 2–302°C promoted a drastic reduction in biocrust cover (ca. 44% in 402years). Warming significantly increased soil CO2 efflux, and reduced soil net CO2 uptake, in biocrust-dominated microsites. Losses of biocrust cover with warming through time were paralleled by increases in recalcitrant C sources, such as aromatic compounds, and in the abundance of fungi relative to bacteria. The dramatic reduction in biocrust cover with warming will lessen the capacity of drylands to sequester atmospheric CO2. This decrease may act synergistically with other warming-induced effects, such as the increase in soil CO2 efflux and the changes in microbial communities to alter C cycling in drylands, and to reduce soil C stocks in the mid to long term.
[37] Davidson E A, Janssens I A.

Temperature sensitivity of soil carbon decomposition and feedbacks to climate change

[J]. Nature, 2006, 440(7 081):165.

DOI      URL      [本文引用: 1]     

[38] Poulter B, Frank D, Ciais P, et al.

Contribution of semi-arid ecosystems to interannual variability of the global carbon cycle

[J]. Nature, 2014, 509(7 502):600-603.

DOI      URL      PMID      [本文引用: 1]      摘要

The land and ocean act as a sink for fossil-fuel emissions, thereby slowing the rise of atmospheric carbon dioxide concentrations. Although the uptake of carbon by oceanic and terrestrial processes has kept pace with accelerating carbon dioxide emissions until now, atmospheric carbon dioxide concentrations exhibit a large variability on interannual timescales, considered to be driven primarily by terrestrial ecosystem processes dominated by tropical rainforests. We use a terrestrial biogeochemical model, atmospheric carbon dioxide inversion and global carbon budget accounting methods to investigate the evolution of the terrestrial carbon sink over the past 30 years, with a focus on the underlying mechanisms responsible for the exceptionally large land carbon sink reported in 2011 (ref. 2). Here we show that our three terrestrial carbon sink estimates are in good agreement and support the finding of a 2011 record land carbon sink. Surprisingly, we find that the global carbon sink anomaly was driven by growth of semi-arid vegetation in the Southern Hemisphere, with almost 60 per cent of carbon uptake attributed to Australian ecosystems, where prevalent La Ni a conditions caused up to six consecutive seasons of increased precipitation. In addition, since 1981, a six per cent expansion of vegetation cover over Australia was associated with a fourfold increase in the sensitivity of continental net carbon uptake to precipitation. Our findings suggest that the higher turnover rates of carbon pools in semi-arid biomes are an increasingly important driver of global carbon cycle inter-annual variability and that tropical rainforests may become less relevant drivers in the future. More research is needed to identify to what extent the carbon stocks accumulated during wet years are vulnerable to rapid decomposition or loss through fire in subsequent years.
[39] Rotenberg E, Yakir D.

Contribution of semi-arid forests to the climate system

[J]. Science, 2010, 327(5 964):451.

DOI      URL      [本文引用: 1]     

[40] Grace J, Jose J S, Meir P, et al.

Productivity and carbon fluxes of tropical savannas

[J]. Journal of Biogeography, 2010, 33(3):387-400.

DOI      URL      [本文引用: 1]      摘要

Aim (1) To estimate the local and global magnitude of carbon fluxes between savanna and the atmosphere, and to suggest the significance of savannas in the global carbon cycle. (2) To suggest the extent to which protection of savannas could contribute to a global carbon sequestration initiative.
[41] Wang Xinyuan, Li Yulin, Zhao Xueyong, et al.

Responses of soil respiration to different factors in semi-arid and arid areas

[J]. Acta Ecologica Sinica, 2012, 32(15):4 890-4 901.

[本文引用: 1]     

[王新源, 李玉霖, 赵学勇, .

干旱半干旱区不同环境因素对土壤呼吸影响研究进展

[J]. 生态学报, 2012, 32(15):4 890-4 901.]

DOI      URL      [本文引用: 1]      摘要

土壤呼吸是全球陆地生态系统碳循环的重要环节,也是全球气候变化的关键生态过程.阐明和探讨影响土壤呼吸的各类环境因素,对准确评估陆地生态系统碳收支具 有重要意义.干旱半干旱区是陆地生态系统的重要组成部分,研究该区域影响土壤呼吸的环境因素有助于深刻了解干旱半干旱区土壤碳循环过程.就土壤温度、土壤 水分、降水、土壤有机质等非生物因子及植被类型、地上、地下生物量、土壤凋落物等生物因子两个方面对土壤呼吸的影响进行了综述.以干旱半干旱区的研究进展 为主要论述对象,在上述因素中重点阐述了土壤温度、水分及其耦合作用下土壤呼吸的响应,并就土壤呼吸的Q10值及各影响因素间的交互作用进行归纳总结.在 此基础上,说明了土壤温度和水分是影响干旱半干旱区土壤呼吸的主要因素.为了更准确的估算干旱半干旱区土壤呼吸速率,综合分析多种因子的交互影响,提出目 前土壤呼吸研究存在的问题和今后重点关注的方向:1)不同尺度下干旱半干旱区土壤呼吸的研究;2)荒漠生态系统土壤呼吸研究;3)非生长季土壤呼吸研 究;4)多因素协同作用土壤呼吸模型建立;5)测量方法的改进与完善.
[42] Fu Y, Yu G, Wang Y, et al.

Effect of water stress on ecosystem photosynthesis and respiration of a Leymus chinensis, steppe in Inner Mongolia

[J]. Science in China (Series D), 2006, 49(Suppl.2):196-206.

[本文引用: 1]     

[43] Zhou Ping, Liu Guobin, Xue Sha.

Review of soil respiration and the impact factors on grassland ecosystem

[J]. Acta Prataculturae Sinica, 2009, 18(2):184-193.

Magsci      [本文引用: 1]     

[周萍, 刘国彬, 薛萐.

草地生态系统土壤呼吸及其影响因素研究进展

[J]. 草业学报, 2009, 18(2):184-193.]

DOI      URL      Magsci      [本文引用: 1]      摘要

<FONT face=Verdana>土壤呼吸在全球碳收支中占有重要的地位,笔者对草地生态系统土壤呼吸在陆地生态系统碳平衡中的作用、土壤呼吸的分类及其影响因素等方面进行了综述。结果表明,草地生态系统土壤呼吸在不同时间空间各组分所占比例不同,生物、非生物及人为活动等因素对草地土壤呼吸影响各异,主要从土壤温度、气候变暖、土壤湿度、降水、干旱化、土壤C/N 等非生物因素,叶面积指数、植物光合作用、植被凋落物等生物因素以及人类干扰活动等方面具体阐述这些因素变化对土壤呼吸产生的影响,并对草地土壤呼吸的Q10值及各影响因素间的交互作用进行归纳总结。提出草地生态系统土壤呼吸研究存在的问题和今后重点发展方向,并对未来草地生态系统土壤呼吸的研究工作做了进一步的展望。</FONT>
[44] Wang Wei, Zhang Ying.

Advances in research on land surface processes model

[J]. Meteorology and Disaster Reduction Research, 2010, 33(3): 1-6.

[本文引用: 1]     

[汪薇, 张瑛.

陆面过程模式的研究进展简介

[J]. 气象与减灾研究, 2010, 33(3):1-6.]

[本文引用: 1]     

[45] Huang J, Yu H, Guan X, et al.

Accelerated dryland expansion under climate change

[J]. Nature Climate Change, 2016,6:166-171. DOI:10.1038/nclimate2837.

URL      [本文引用: 3]      摘要

Drylands are home to more than 38% of the total global population and are one of the most sensitive areas to climate change and human activities. Projecting the areal change in drylands is essential for taking early action to prevent the aggravation of global desertification. However, dryland expansion has been underestimated in the Fifth Coupled Model Intercomparison Project (CMIP5) simulations considering the past 58 years (1948-2005). Here, using historical data to bias-correct CMIP5 projections, we show an increase in dryland expansion rate resulting in the drylands covering half of the global land surface by the end of this century. Dryland area, projected under representative concentration pathways (RCPs) RCP8.5 and RCP4.5, will increase by 23% and 11%, respectively, relative to 1961-1990 baseline, equalling 56% and 50%, respectively, of total land surface. Such an expansion of drylands would lead to reduced carbon sequestration and enhanced regional warming, resulting in warming trends over the present drylands that are double those over humid regions. The increasing aridity, enhanced warming and rapidly growing human population will exacerbate the risk of land degradation and desertification in the near future in the drylands of developing countries, where 78% of dryland expansion and 50% of the population growth will occur under RCP8.5.
[46] Zhao T, Dai A.

Uncertainties in historical changes and future projections of drought. Part II: Model-simulated historical and future drought changes

[J]. Climatic Change, 2017, 144:535-548. DOI:10.1007/s10584-016-1742-x.

URL      [本文引用: 5]      摘要

Abstract While most models project large increases in agricultural drought frequency and severity in the 21st century, significant uncertainties exist in these projections. Here, we compare the model-simulated changes with observation-based estimates since 1900 and examine model projections from both the Coupled Model Inter-comparison Project Phase 3 (CMIP3) and Phase 5 (CMIP5). We use the self-calibrated Palmer Drought Severity Index with the Penman-Monteith potential evapotranspiration (PET) (sc_PDSI_pm) as a measure of agricultural drought. Results show that estimated long-term changes in global and hemispheric drought areas from 1900 to 2014 are consistent with the CMIP3 and CMIP5 model-simulated response to historical greenhouse gases and other external forcing, with the short-term variations within the model spread of internal variability, despite that regional changes are still dominated by internal variability. Both the CMIP3 and CMIP5 models project continued increases (by 50 200 % in a relative sense) in the 21st century in global agricultural drought frequency and area even under low-moderate emissions scenarios, resulting from a decrease in the mean and flattening of the probability distribution functions (PDFs) of the sc_PDSI_pm. This flattening is especially pronounced over the Northern Hemisphere land, leading to increased drought frequency even over areas with increasing sc_PDSI_pm. Large differences exist in the CMIP3 and CMIP5 model-projected precipitation and drought changes over the Sahel and northern Australia due to uncertainties in simulating the African Inter-tropical convergence zone (ITCZ) and the subsidence zone over northern Australia, while the wetting trend over East Africa reflects a robust response of the Indian Ocean ITCZ seen in both the CMIP3 and CMIP5 models. While warming-induced PET increases over all latitudes and precipitation decreases over subtropical land are responsible for mean sc_PDSI_pm decreases, the exact cause of its PDF flattening needs further investigation.
[47] Ji M, Huang J, Xie Y, et al.

Comparison of dryland climate change in observations and CMIP5 simulations

[J]. Advances in Atmospheric Sciences, 2015, 32(11):1 565-1 574. DOI: 10.1007/s00376-015-4267-8.

[本文引用: 5]     

[48] Scheff J, Frierson D M W.

Terrestrial aridity and its response to greenhouse warming across CMIP5 Climate Models

[J]. Journal of Climate, 2015, 28(14):150427110053004.

[本文引用: 2]     

[49] Feng S, Hu Q, Huang W, et al.

Projected climate regime shift under future global warming from multi-model, multi-scenario CMIP5 simulations

[J]. Global and Planetary Change, 2014, 112(1):41-52.

[本文引用: 3]     

[50] Scheff J, Frierson D M W.

Robust future precipitation declines in CMIP5 largely reflect the poleward expansion of model subtropical dry zones

[J]. Geophysical Research Letters, 2012, 39(18):18 704.

[本文引用: 1]     

[51] Schlaepfer D R, Bradford J B, Lauenroth W K, et al.

Climate change reduces extent of temperate drylands and intensifies drought in deep soils

[J]. Nature Communications, 2017, 8:14 196.

[本文引用: 1]     

[52] Huang J, Huang J, Liu X, et al.

The global oxygen budget and its future projection

[J]. Science Bulletin, 2018.DOI:10.1016/j.scib.2018.07.023.

[本文引用: 1]     

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