中国东部季风区植被物候季节变化对气候响应的大尺度特征:多年平均结果

利用1982～1993年NOAA/NASA Pathfinder AVHRR陆地数据集中的规一化植被指数(NDVI)数据集,对中国东部植被季节生长的阶段性进行了划分.在此基础上,对植被季节生长对气候响应的多年平均状况进行了分析,发现在多年平均意义上,(1)中国东部植被生长在各生长阶段都同步响应于温度的季节变化;(2)在多数时段,中国东部植被生长与降水的季节变化存在显著相关关系,植被生长滞后于降水变化,滞后时间为20～30天.通过本文的研究,在中国东部季风区,有关植被季节生长对气候响应大尺度特征的多年平均状况的定性认识得到定量化的表达,为改进陆面过程描述、提高对中国东部区域气候的长期模拟能力提供了一定的依据.     

中国植被覆盖季节变化和空间分布对气候的响应--多年平均结果

文中利用 1982～ 1993年的 12a平均归一化植被指数数据 ,并结合同期的温度、降水数据 ,运用经验正交函数分解的方法 (EOF)分析了中国植被覆盖变化的时空特征及其与温度、降水气候因子的定量关系 ,发现在多年平均意义上 ,在中国大尺度研究区域 ,归一化植被指数所表现出的植被变化时空特征具有 :(1)植被的空间分布与降水空间分布更吻合 ,植被季节生长变化与温度的季节变化特征更近似 ;(2 )植被与温度在季节生长变化上存在e指数关系 ;与降水存在幂指数关系 ;(3)植被季节生长与温度存在同期相关 ;与降水存在滞后相关 ,滞后时间两旬     

2000年以来中国区域植被变化及其对气候变化的响应

气候是植被变化的主要驱动因子,研究全球增暖背景下中国区域植被变化及其对气候的响应对于国家开展重大生态恢复评估和未来植被保护政策制定具有重要意义。利用2000-2016年MODIS植被指数(Normalized Difference Vegetation Index,NDVI)数据集,运用统计分析方法,从平均态、线性趋势、时间序列、相关性等方面系统分析了2000年以来中国区域植被变化及其对气候变化的响应。结果表明:中国区域NDVI在平均态上呈现从东南向西北递减的空间分布,受降水生长季的影响,东部地区植被指数明显较大;我国大部分地区NDVI呈现增加的趋势,其中湿润半湿润地区NDVI增长幅度为0.037·(10a)^-1,而在干旱半干旱地区变化较小[0.013·(10a)^-1]。NDVI的变化与气候驱动因素的相关性存在一定的区域差异,其中:NDVI与气温变化在东南沿海、东北东部以及青藏高原北部等地区呈现出显著正相关,而在青藏高原南部等地区呈现微弱的负相关;除青藏高原、塔里木盆地和东北北部等地区外,NDVI与降水量在全国大多数地区呈正相关。从全国平均来看,温度和降水变化对NDVI的贡献分别为7.5%和9.1%,其中温度对NDVI变化的贡献主要体现在湿润半湿润地区(9.3%),而降水的贡献则在干旱半干旱地区(12.2%)。植被变化对气候要素驱动的响应也呈现出明显的区域差异性,在我国东南沿海、云贵高原东部、四川盆地等南方地区以及黄河中下游、东北东部等部分地区,NDVI变化对气温的敏感性最强;而在中国北方干旱半干旱大部分地区,NDVI变化则是对降水驱动具有很显著的响应特征。总体而言,气温是驱动南方地区植被变化的主导因子,而降水则调控着北方地区植被生长变化。     

ENSO与中国东部地区夏季降水相关性年代际变化特征

利用国家气候中心提供的中国160站1951～2000年逐月降水资料,Hadley中心提供的1951～2000年逐月全球海表层温度资料,采用线性相关分析和滑动相关分析方法,探讨了ENSO与中国东部地区夏季降水的年际关系及二者年际关系的年代际变化特征。结果表明,夏季Nino3区海温与中国东部夏季降水年际关系同期相关显著,且二者的年际关系存在明显的年代际变化,年际相关型分3个阶段：,第1阶段(1972年前)为“东西型”,第2阶段(1973～1983年)为“南北型”,第3阶段(1984年后)也为“南北型”。     

1982~1999年中国地区叶面积指数变化及其与气候变化的关系

利用1982～1999年AVHRR Pathfinder卫星遥感观测的植被叶面积指数（leaf area index,LAI）资料和中国730个气象台站的温度、降水观测资料,研究了中国不同地区（东北地区、华北地区、长江流域、华南地区和西南地区）LAI的季节、生长季和年变化,及其与气候变化（温度、降水）的关系。结果表明,在中国大部分地区,年平均LAI和生长季平均LAI均是增加的。由于区域和季节气候的差异,LAI变化趋势具有明显的空间和季节非均一性。从区域平均的角度来看,不同地区年和生长季平均LAI都有增加趋势,并且在华南地区增加最快。因而,在全球变化背景下,华南地区可能是潜在的碳汇。在季节尺度上,各地区区域平均LAI基本上都是增加的,并且都在春季增加最快。温度变化是LAI变化的主要原因。但是人类活动如农业活动、城市化等对华北平原、长江三角洲和珠江三角洲等地区LAI变化的作用不容忽视。     

青藏高原不同时间尺度植被变化特征及其与气候因子的关系分析

利用1982-2006年GIMMS NDVI数据,以多种统计方法为基础,探讨了青藏高原(下称高原)不同时间尺度(年际、季节及月)植被变化的时空特征及其与气候因子的关系。结果表明:高原整体年平均NDVI变化呈波动上升趋势,其中夏季趋势最大,达0.004(10a)-1。不同覆盖度像元变化对总体植被变化的贡献不同,低植被覆盖像元变化对各季节总体植被变化贡献均较大,其中冬季最大;中等植被覆盖像元变化的贡献主要在秋季;高植被覆盖像元的贡献则夏季最明显。青藏高原植被变化存在显著的空间差异,其中夏季呈增加和减少趋势的面积均最大,分别达30.51%、10.52%,增加的区域主要位于高原东部,减少的区域主要在高原中部的藏北高原。进一步分析高原植被和气候因子的相关性表明,中等植被覆盖区植被与气候因子的相关性最高,其次是高植被覆盖区,低植被覆盖区的相关性则最低。在年际和季节尺度上,植被生长主要与温度和降水的累积效应有关,其中在植被生长较好的季节和区域更明显。而在月尺度上,中低植被覆盖区植被生长受短期降水事件影响较大,高植被覆盖区则仍是温度的累积效应占主导。     

关于东亚夏季风变化及其成因的最近研究进展

东亚夏季风变化是中国、日本和韩国的重要研究课题。回顾了关于东亚季风(尤其是东亚夏季风)的季节内变化、年际和年代际变化及其这些变化成因的最近研究进展,特别是系统地回顾了厄尔尼诺、南方涛动(ENSO)循环、西太平洋暖池、青藏高原和陆面过程对东亚夏季风的季节内变化、年际和年代际变化的作用。     

1981-2008年中国陆地植被NPP对气候变化响应的敏感性试验

在验证CENTURY模型对中国陆地植被净初级生产力(Net Primary Productivity,NPP)模拟能力的基础上,利用该模型探讨了1981-2008年中国陆地植被NPP的年际变异和变化趋势对CO₂浓度、温度和降水变化的响应。结果表明,中国陆地植被NPP对不同气候因子的响应程度存在明显不同。其中,CO₂浓度变化对植被NPP年际变异的影响不显著,但能够引起中国大部分地区植被NPP趋势系数增大;温度对中国中高纬度地区植被NPP的年际变化影响显著,但就全国范围而言,植被NPP年际变异对温度变化的响应程度总体低于对降水变化的响应程度;降水变化是对中国植被NPP变化趋势起主导作用的气候因子。此外,综合考虑温度和降水变化的影响发现,植被NPP变化趋势的响应特征类似于降水单独变化时植被NPP变化趋势的响应特征。     

热带对流季内振荡强度异常特征及其与海表温度的关系

利用外逸长波辐射 (outgoing longwave radiation, OLR) 资料分析了热带对流季内振荡 (ISO) 强度的季节变化及年际异常特征, 重点研究其与海表温度的关系。结果表明:最强的OLR季内振荡主要位于高海表温度 (SST) 区, 即热带印度洋和热带西太平洋区域, 终年存在, 冬、春季最强, 振荡中心偏于夏半球。OLR季内振荡强度年际异常显著区域是热带中东太平洋区域、西北太平洋区域和西南太平洋区域, 它与SST年际异常存在局地正相关关系, 伴随环流的辐合辐散, 并与ENSO事件关系密切。另外, El Ni?o事件发生之前, 热带印度洋和热带西太平区域OLR季内振荡增强, 其中心随事件的发展逐渐东移, 事件发生后这两个区域ISO减弱, 这与OLR季内振荡强度年际异常显著的区域具有内在连贯性。海表温度是决定OLR季内振荡强度季节变化、年际异常的一个关键因子。     

一个海陆气耦合模式中大气-植被的年际变化及其相互作用

含有动态植被过程的陆面模式Atmosphere-Vegetation Interaction Model(AVIM)与中国科学院大气物理研究所大气科学与地球流体力学数值模拟国家重点实验室(IAP/LASG)的9层大气环流模式AGCM 及20层的海洋环流模式(OGCM)耦合,建立了一个全球模式(GoALS-AVIM)并进行100年的模拟积分.后40年的结果分析表明,该耦合模式能够合理地模拟大气及陆地生态系统显著的年际变化.用奇异值分解(SVD)分析了东亚地区植被生长和气候变化的相互关系,发现在东业区域的植被净初级生产力(NPP)强弱的变化对血着大气环流的变化,特别是NPP分别与850 hPa的风场和500 hPa的高度场表现出很强的时空一致性.在东亚地区,由于植被类型的不同,导致NPP年际变化与降水、表面气温、短波辐射的年际变化的相关性不同,它们的年际变化与相关物理量场的年际变化表现出很强的植物种类的区别.     

中国季风区植被净初级生产力对东亚夏季风的响应机理研究

东亚夏季风可显著影响中国季风区气候变化,但是季风区植被净初级生产力(NPP)对夏季风气候变化的响应机理尚不明确。利用大气—植被相互作用模型(AVIM2)模拟了中国季风区植被NPP,分析了其与夏季风指数的相关关系,探讨了其对夏季风变化的响应机理。研究发现,我国南、北方植被对夏季风强度变化的响应方式和机理并不相同。强夏季风年北方植被NPP增加,而南方植被NPP减少。东亚夏季风对中国华北平原植被生长季NPP的作用主要是通过影响该地降水量实现的;京、津、冀地区植被NPP受东亚夏季风带来的气温和降水量变化的叠加影响,因而成为北方对夏季风变化最敏感的区域。东亚夏季风对我国南方江苏、安徽、湖南、湖北、江西植被NPP的作用是通过影响太阳辐射实现的,强夏季风导致太阳辐射减弱,从而使各省植被NPP减少。南方沿海的浙江和福建,强季风年带来的弱太阳辐射和低温是该地植被NPP减少的原因。广东、台湾植被NPP则主要受强夏季风带来的低温影响。     

Specification of thermal growing season in temperate China from 1960 to 2009

A number of studies have reported an extension of the thermal growing season in response to the warming climate during recent decades. However, the magnitude of extension depends heavily on the threshold temperature used: for a given area, a small change in the threshold temperature results in significant differences in the calculated thermal growing season. Here, we specified the threshold temperature for determining the thermal growing season of local vegetation across 326 meteorological stations in temperate China by using vegetation phenology based on satellite imagery. We examined changes in the start, end, and length of the thermal growing season from 1960 to 2009. The threshold temperatures for determining the start and end increased strongly with increasing mean annual temperature. Averaged across temperate China, the start of the thermal growing season advanced by 8.4?days and the end was delayed by 5.7?days, resulting in a 14.1-day extension from 1960 to 2009. The thermal growing season was intensively prolonged (by 0.59?day/year) since the mid-1980s owing to accelerated warming during this period. This extension was similar to that determined by a spatially fixed threshold temperature of 5?°C, but the spatial patterns differed, owing to differences in the threshold temperature and to intra-annual heterogeneity in climate warming. This study highlights the importance of specifying the temperature threshold for local vegetation when assessing the influences of climate change on thermal growing season, and provides a method for determining the threshold temperature from satellite-derived vegetation phenology.     

Investigating the relationship between growing season quality and childbearing goals

Agricultural production and household food security are hypothesized to play a critical role connecting climate change to downstream effects on women’s health, especially in communities dependent on rainfed agriculture. Seasonal variability in agriculture strains food and income resources and makes it a challenging time for households to manage a pregnancy or afford a new child. Yet, there are few direct assessments of the role locally varying agricultural quality plays on women’s health, especially reproductive health. In this paper we build on and integrate ideas from past studies focused on climate change and growing season quality in low-income countries with those on reproductive health to examine how variation in local seasonal agricultural quality relates to childbearing goals and family planning use in three countries in sub-Saharan Africa: Burkina Faso, Kenya, and Uganda. We use rich, spatially referenced data from the Performance Monitoring for Action (PMA) individual surveys with detailed information on childbearing preferences and family planning decisions. Building on recent advances in remote monitoring of seasonal agriculture, we construct multiple vegetation measures capturing different dimensions of growing season conditions across varying time frames. Results for the Kenya sample indicate that if the recent growing season is better a woman is more likely to want a child in the future. In Uganda, when the growing season conditions are better, women prefer to shorten the time until their next birth and are also more likely to discontinue using family planning. Additional analyses reveal the importance of education and birth spacing in moderating these findings. Overall, our findings suggest that, in some settings, women strategically respond to growing season conditions by adjusting fertility aspirations or family planning use. This study also highlights the importance of operationalizing agriculture in nuanced ways that align with women’s lives to better understand how women are impacted by and respond to seasonal climate conditions.     

Climate change alters growing season flux dynamics in mesic grasslands

Changing climate could affect the functioning of grassland ecosystems through variation in climate forcings and by altering the interactions of forcings with ecological processes. Both the short and long-term effects of changing forcings and ecosystem interactions are a critical part of future impacts to ecosystem ecology and hydrology. To explore these interactions and identify possible characteristics of climate change impacts to mesic grasslands, we employ a low-dimensional modeling framework to assess the IPCC A1B scenario projections for the Central Plains of the United States; forcings include increased precipitation variability, increased potential evaporation, and earlier growing season onset. These forcings are also evaluated by simulations of vegetation photosynthetic capacity to explore the seasonal characteristics of the vegetation carbon assimilation response for species at the Konza Prairie in North Central Kansas, USA. The climate change simulations show decreases in mean annual soil moisture and and carbon assimilation and increased variation in water and carbon fluxes during the growing season. Simulations of the vegetation response show increased variation at the species-level instead of at a larger class scale, with important heterogeneity in how individual species respond to climate forcings. Understanding the drivers and relationships behind these ecosystem responses is important for understanding the likely scale of climate change impacts and for exploring the mechanisms shaping growing season dynamics in grassland ecosystems.     

The Effect of Vegetation Productivity on Millet Prices in the Informal Markets of Mali, Burkina Faso and Niger

Systematic evaluation of food security throughout the Sahel has been attempted for nearly two decades. Food security analyses have used both food prices to determine the ability of the population to access food, and satellite-derived vegetation indices that measure vegetation production to establish how much food is available each year. The relationship between these two food security indicators is explored here using correspondence analysis and through the use of Markov chain models. Two sources of quantitative data were used: 8 km normalized difference vegetation index (NDVI) data from the Advanced Very High Resolution Radiometers (AVHRR) carried on the NOAA series of satellites, and monthly millet prices from 445 markets in Mali, Niger and Burkina Faso. The results show that the growing season vegetation production is related to the price of millet at the annual and the seasonal time scales. If the growing season was characterized by erratic, sparse rainfall, it resulted in higher prices, and well-distributed, abundant rainfall resulted in lower prices. The correspondence between vegetation production and millet prices is used to produce maps of millet prices for West Africa.     

中亚及中国新疆干旱区植被物候时空变化

基于1982-2006年GIMMS（Global Inventory Modeling and Mapping Studies）长序列归一化植被指数数据,采用比例阈值法反演得到中亚及新疆地区植被过去25年的物候数据集;采用M-K趋势检验和Theil Sen斜率方法,分析植物生长季开始期、停止期和生长季长度的变化趋势,并结合历史土地利用数据和DEM数据评价不同植被覆盖类型和不同高程下的植被物候变化特征。结果表明：1982-2006年,中亚及中国新疆干旱区植被生长季开始期和停止期在区域尺度上没有显著提前或者延迟,但在局部地区变化明显,且空间差异较大。各植被覆盖类型的物候动态表现不同,农用地的生长季开始期提前最明显;落叶阔叶林等木本植被类型的生长季停止期以推迟为主,但其面积比例很小,影响十分有限;除灌丛和裸地外,其他类型均表现出生长季长度延长的趋势,但整个研究区植物生长季长度变化并不明显。不同高程下植被物候变化同样存在差异,区域气候变化改变了不同高程带的环境限制因子,继而对植被物候产生影响,特别是在2000～3000 m高程带,植被生长季开始期提前、停止期推迟和生长季长度延长更加明显。     

重庆岩溶地区气候变化对植被的影响

岩溶生态系统是一种脆弱的生态系统,植被类型与盖度成为岩溶环境中最重要、最敏感的自然要素。介绍了以重庆岩溶地区为对象,利用气象和NDVI数据,采用相关分析等方法探讨了植被对气候变化的响应。结果表明:(1)在多年平均水平上,气候对重庆岩溶植被生态系统起着比降水大的作用;在植被生长的年际变化方面,气温和降水对植被生长起着大致相反的趋势。(2)年际变化方面,气温和降水对植被生态系统的生长起着大致相反的作用。一般来说,气温与NDVI之间的关系为正相关。(3)植被指数的动态变化受气候波动的影响较大,近20 a来,总体呈增加的趋势。可为岩溶生态系统恢复和重建提供科学依据。     

The resilience of annual vegetation primary production subjected to different climate change scenarios

We examined if climate change in two dry ecosystems—Mediterranean (DME) and Semiarid (SAE)—would cause substantial reduction in the production of annual vegetation. Field measurements and computer simulations were used to examine the following six climate change scenarios: (1) rainfall amount reduction; (2) increases of 10 % in annual evaporation rate and 5 % in annual temperature; (3) increase in magnitude of rainfall events, accompanied by reductions in frequency and seasonal variation; (4) postponement of the beginning of the first rainfall event of the growing season; (5) long dry spells during the growing season; and (6) early ending of the growing season. The results revealed the following outcomes. a) Reduction by 5–35 % in annual rainfall amount did not significantly affect productivity in the DME, but a large (25–35 %) decrease in rainfall would change vegetation productivity in the SAE and lead to a patchier environment. b) Similar results were observed: when temperature and evaporation rate were increased; when the magnitude of rainfall events increased but their frequency decreased; and during a long mid-season dry spell. c) In both ecosystems, changes in the temporal distribution of rainfall, especially at the beginning of the season, caused the largest reduction in productivity, accompanied by increased patchiness. d) Long-term data gathered during the last three decades indicated that both environments exhibited high resilience of productivity under rainfall variability. These results imply that the response of dry ecosystems to climate change is not characterized by a dramatic decrease in productivity. Moreover, these ecosystems are more resilient than expected, and their herbaceous productivity might undergo drastic changes only under more severe scenarios than those currently predicted in the literature.