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1.
The paper compares ethnic change and diversity across two recent decades using common group and area definitions. Ethnic minority groups are shown to be growing rapidly at 41 per cent between 1981 and 1991 and 39 per cent between 1991 and 2001. Some groups have grown swiftly (Black Africans, Bangladeshis), while others have seen moderate expansion (Indians, Other Asians). The White population has hardly grown and the White British population has probably declined. Black and Ethnic Minority (BEM) populations remain concentrated in metropolitan areas in 2001 as in 1991 and 1981. Whereas between 1981 and 1991, BEM groups were concentrating into metropolitan areas, between 1991 and 2001 deconcentration began for most groups. The London region stands out as highly dominant, housing more than 50 per cent of BEM populations as a whole in 1991 and 2001. However, between 1991 and 2001, BEM groups grew outside their core areas. The consequence of BEM population growth and spread has been a dramatic increase in ethnic diversity in all regions. 相似文献
2.
Robert M Vanderbeck 《Area》2008,40(3):393-400
A small but growing number of voices have begun to raise questions about the current direction of children's geographies as a subfield and its status within the wider discipline. This article intervenes in these emerging discussions to examine the status of debate itself within children's geographies. I argue that children's geographies over the past decade has operated primarily in a consensus-based mode, with a number of potential tensions and differences between practitioners masked as a result. I develop the example of notions of children's competent social agency, a core theoretical assumption that is rarely interrogated in much depth. In closing, I pose questions regarding several contemporary political issues concerning children's agency about which geographers have had surprisingly little to say. I suggest that explicitly addressing some of these vexing issues would contribute to a richer state of debate within children's geographies. 相似文献
3.
Semi-arid ecosystems are privileged sites to address the effects of plant interactions on community structure and dynamics because environmental conditions are demanding and may change quickly, altering in significant ways the balance between positive and negative effects among neighboring plants. Plant interaction processes have been well documented in the semi-arid region of Southeast Spain over the last 15 years. In this article we review the growing body of research on plant–plant interactions available from this area, highlighting its importance in increasing our knowledge on this field of study. This review has been organized in five sections, i) facilitation mechanisms; ii) the nurse effect; iii) the balance of interactions and environmental, ontogenic, temporal, and spatial gradients; iv) the effects of facilitation on biodiversity; and, v) facilitation and ecosystem functioning. Mechanisms of facilitation in these systems are relatively well known, but not completely explored. In these environments competition, mainly for water, is intense between neighbors and switches in intensity from belowground to aboveground as productivity increases. By contrast, facilitation may decrease quickly with increasing productivity, although the balance between facilitation and competition is not fully understood, and is further complicated because shifts can also be driven by factors such as life history or physiology of interacting species. Positive interactions are critical for maintaining biodiversity in some ecosystems in SE Spain, but their role as a driver of ecosystem functioning is less clear. Research on plant–plant interactions in this region has been highly influential and has contributed to our overall understanding of plant community dynamics. Despite the important progress achieved during the last 15 years, there is still substantial scope for exploring the effects of plant interactions at the ecosystem level, and their role as modulators of disturbances such as the current global environmental change. 相似文献
4.
Spatial pattern and decadal change of agro-meteorological disasters in the main wheat production area of China during 1991-2009 总被引：2，自引：0，他引：2
Agro-meteorological disasters (AMD) have become more frequent with climate warming. In this study, the temporal and spatial changes in the occurrence frequency of major meteorological disasters on wheat production were firstly explored by analyzing the observed records at national agro-meteorological stations (AMS) of China from 1991 to 2009. Furthermore, impact of climate change on AMD was discussed by comparing the warmer decade (2000-2009) with another decade (1991-2000). It was found that drought was the most frequent disaster during the last two decades, with a highest proportion of 79%. And the frequency of AMD increased significantly with climate change. Specifically, the main disasters occurred more frequently in the reproductive period than in the vegetative period. Besides, the spatial changes in the AMD frequency were characterized by region-specific. For example, the wheat cultivation areas located on the Loess Plateau and the middle-lower reaches of the Yellow River suffered mainly from drought. All these results were strongly linked to climate change in China. Therefore, sound adaptation options should be taken based on the latest changes of AMD under global warming to reduce agricultural damages. 相似文献
5.
Agro-meteorological disasters(AMD) have become more frequent with climate warming. In this study, the temporal and spatial changes in the occurrence frequency of major meteorological disasters on wheat production were firstly explored by analyzing the observed records at national agro-meteorological stations(AMS) of China from 1991 to 2009. Furthermore, impact of climate change on AMD was discussed by comparing the warmer decade(2000–2009) with another decade(1991–2000). It was found that drought was the most frequent disaster during the last two decades, with a highest proportion of 79%. And the frequency of AMD increased significantly with climate change. Specifically, the main disasters occurred more frequently in the reproductive period than in the vegetative period. Besides, the spatial changes in the AMD frequency were characterized by region-specific. For example, the wheat cultivation areas located on the Loess Plateau and the middle-lower reaches of the Yellow River suffered mainly from drought. All these results were strongly linked to climate change in China. Therefore, sound adaptation options should be taken based on the latest changes of AMD under global warming to reduce agricultural damages. 相似文献
6.
中国典型季风海洋性冰川区"冰川-径流"系统的全球变化敏感性研究 总被引：10，自引：0，他引：10
分析多种数据和资料,再现海螺沟冰川过去100年来的冰川进退过程,分析发现,冰川末端变化阶段在滞后期的基础上,与北半球和中国气温变化的阶段相对应。运用水量-物质平衡法恢复海螺沟冰川45年来的物质平衡变化情况,通过相关性检验发现,物质平衡变化与北半球和中国同期(1960~2004年)气温变化表现出显著负相关。20世纪80年代全球加速变暖,海螺沟冰川冰舌段消融速率为7.86 m/a,冰川河径流量年际和季节变化表明流量主要贡献者是冰雪融水。分析表明,全球变暖是冰川后退、持续亏损及径流量增加的主要原因。 相似文献
7.
气候变化对东北地区玉米生产的影响 总被引：15，自引：2，他引：13
利用气象观测数据、玉米产量及面积资料,分析了东北地区气候变化事实及对玉米生产的影响。研究表明:1971年以来,东北地区≥10℃积温增加了262.8℃,≥10℃积温带(以2700℃为例)平原区向北推进了约200～300km左右,向东扩展50～150km。1991年开始玉米生长季(4～9月)降水量持续减少,年平均水分亏缺量达391.5mm,湿润区缩小,有变干趋势。初霜日推后7～9天,无霜期延长了14～21天,霜冻灾害几率降低。20世纪90年代后,玉米延迟型冷害进入低发期。随着热量资源的增加,玉米可种植区范围不断扩大,种植北界北移东扩,玉米适播起始时间提前。玉米总产、播种面积增加趋势分别为967万t/10a、72万hm2/10a。未来40年东北地区玉米产量以减产为主,与过去30年(1961～1990年)相比平均减产9.5%左右。调整玉米种植布局和品种搭配,依靠水利工程和推广旱作农业技术,选种耐旱、抗病、抗逆性强的玉米品种,是实现东北玉米生产可持续发展的主要措施。 相似文献
8.
青藏高原地气温差变化分析 总被引：6，自引：1，他引：5
利用青藏高原及其临近区域的99个气象站1960~2000年地表温度和气温资料, 利用主成分分析和功率谱分析方法, 分析了青藏高原地气温差的空间分布及时间演变特征。结果表明：青藏高原地气温差6月份最大,12月份最小。青藏高原冷、暖季和年均的地气温差空间分布前三个载荷向量场大致可表现三种分布型：西北-东南反向变化型、地形海拔反映型、冻土分布反映型;载荷所对应的时间演变型：单调上升、单调下降型、基本平稳型和具有极小值的下凹抛物线型。高原地气温差的周期振荡在不同区域的显著性不同,普遍出现的是2年左右的周期。依据温差冷季第三主分量载荷的空间分布型,可将高原划分为两大区,即多年冻土影响气温区和季节冻土影响气温区。 相似文献
9.
近40年阿拉善高原大风天气时空分布特征 总被引：9，自引：3，他引：9
以l96l-2000年阿拉善高原10个气象站气象记录为主要数据源,运用气候统计学方法,对阿拉善高原40年大风天气的时空变化特征及其区域差异,结合地形地貌和大尺度天气系统变化,导致大风天气自然环境进行了分析。分析结果表明:大风天气高值区位于阿拉善高原的西部,从年内分布看,研究区年内大风天气集中于4~7月,占全年大风天气的54.3%,3月和8月次之,占全年的18.0%。从年际变化看,阿拉善大风天气年际变化的共同特点是:20世纪60年代大风天气是逐渐上升的,70年代或80年代达到峰值,90年代逐步下降,90年代为40年来的最小值。阿拉善高原大风天气受全球气候变化、大尺度天气系统及局地地形和下垫面性质的影响,沙尘天气多发期与反厄尔尼诺事件和干冷气候期相对应。 相似文献
10.
The difference between ground soil and air temperature (Ts-Ta) was studied by using the data of ground and air temperature of 99 stations over the Qinghai–Xizang (Tibet) Plateau from 1960 to 2000,and its spatial distribution and time changing tendency have been diagnosed by principal component analysis and power spectral analysis methods. The results show that the values of (Ts-Ta) are the maximum in June and the minimum in December. The first three loading eigenvectors, which reflect the main spatially anomalous structure of (Ts-Ta) over the Qinghai–Xizang Plateau, contain the contrary changing pattern between the north-western and the southeastern regions, the pattern response of the sea level elevation and the geography, and the pattern response of the distribution of the permafrost. There are four patterns of time evolution including the patterns of monotonous increasing or decreasing trends, the basic stability pattern and the parabola pattern with the minimum value. (Ts-Ta) has a periodic variation about 2 years. According to the spatial distribution of the third loading eigenvectors of (Ts-Ta) over the Qinghai–Xizang Plateau in cold season, the permafrost re-sponse region and the seasonal frozen ground response region are identified. 相似文献
11.
青藏高原地气温差变化及空间分布 总被引：2，自引：0，他引：2
The difference between ground soil and air temperature （Ts-Ta） was studied by using the data of ground and air temperature of 99 stations over the Qinghai-Xizang （Tibet） Plateau from 1960 to 2000,and its spatial distribution and time changing tendency have been diagnosed by principal component analysis and power spectral analysis methods. The results show that the values of （Ts-Ta） are the maximum in June and the minimum in December. The first three loading eigenvectors, which reflect the main spatially anomalous structure of （Ts-Ta） over the Qinghai-Xizang Plateau, contain the contrary changing pattern between the northwestern and the southeastern regions, the pattern response of the sea level elevation and the geography, and the pattern response of the distribution of the permafrost. There are four patterns of time evolution including the patterns of monotonous increasing or decreasing trends, the basic stability pattern and the parabola pattern with the minimum value. （Ts-Ta） has a periodic variation about 2 years. According to the spatial distribution of the third loading eigenvectors of （Ts-Ta） over the Qinghai-Xizang Plateau in cold season, the permafrost response region and the seasonal frozen ground response region are identified. 相似文献
12.
A scientific evaluation of the broad reciprocal influences between urbanization and the eco-environment in the Tibetan Plateau region is of great significance for increasing the speed and quality of urbanization as well as restoring and improving the eco-environment.Based on a thorough look at the progress made by research on interactions between ur-banization and the eco-environment in the Tibetan Plateau region,this article attempts to construct a complete analytical model of the reciprocal influences that can achieve the whole process of analyzing evaluation indexes,quantifying coupling coordination,identifying cou-pling types,exploring decoupling paths,and predicting future trends.Using multi-scale analysis of the Tibetan Plateau and its provinces and prefecture-level units as a means of comparison,we attempt to clarify differences at different scales,identify problem areas and propose targeted improvement measures.The result shows that the urbanization evaluation indexes for the Tibetan Plateau at different scales rise in stages and that the urbanization index for Qinghai is higher than for Tibet;the changes in the eco-environment index of the two regions are also different,with a downward trend in Qinghai and a trend toward stability in Tibet,and with stratification in the eco-environment indexes of prefecture-level units;the de-gree of coupling coordination between urbanization and the eco-environment at different scales in the Tibetan Plateau region is increasing overall,with the type of coordination changing from uncoordinated deterioration to borderline uncoordinated deterioration,and ultimately changing into scarcely coordinated development,which basically puts the region into the logging urbanization category;and the urbanization and eco-environment indexes display a dynamic trend of alternating between strong decoupling and weak decoupling,in-dicating that there is a negative reciprocal influence between urbanization and eco-environment at different scales and that the phenomenon of passive urbanization is prominent.We predict that in the next 10 years,the system coupling coordination of prefec-ture-level units in the Tibetan Plateau region will steadily increase,but there will be significant discrepancies in the growth rates of different regions. 相似文献
13.
气候变化对农业的影响是全球关注的热点问题之一,青藏高原对气候变化尤其敏感,但气候变化对青藏高原农业产量的定量影响缺乏系统研究。为定量评估气候变化对西藏谷物单产的影响,本文使用气象数据与年鉴统计数据,选取了固定效应模型、差分模型和线性去趋势模型3类统计模型,分析了1993—2017年间气候变化（最低气温、降水量、生长度日和太阳辐射）对西藏县（区）级、市级和自治区3个尺度的谷物单产的影响。结果表明：西藏整体对于温度（最低气温和生长度日）的敏感性大于降水量和太阳辐射。各项气候因子对西藏谷物单产的整体影响为正影响,但不同区域对气候因子的敏感程度和显著性不同。除了生长度日对于拉萨为负影响以外,最低气温、降水量和太阳辐射对于所有市均为正影响。气候趋势对于西藏整体谷物单产的影响为正影响,不同模型计算结果集中在1.5%~4.8%区间内。3类模型中固定效应模型稳定性最好,线性去趋势模型好于差分模型,差分模型在引入气候因子间的交互项后模型稳定性降低。本文有助于西藏实施更加有空间针对性的农业适应气候变化措施,以应对气候造成的青藏高原农业生态系统变化。 相似文献
14.
15.
In semi-arid systems, competition among plants has limited effects on performance compared to facilitative interactions and abiotic factors. However, the balance between competition and facilitation can change over the course of plant development. Determining when each interaction is important for plant productivity allows us to identify factors limiting plant growth. In this field study, neighbor removal mid-way through the growing season did not result in a size change for any species (Clarkia purpurea, Plantago erecta, and Micropus californicus) in the first year. In the second year, two species had greater biomass when neighbors were removed very early in the growing season, indicating a competitive effect. The third species neither benefited nor suffered from neighbor removal. In some years, P. erecta and M. californicus may be negatively affected by competition at early growth stages and are later unable to capitalize on newly-available resources after removals of competitors. This study shows that early-stage competition can drive biomass production in some annual plants, even in semi-arid systems. 相似文献
16.
1990年以来中国小麦农业气象灾害时空变化特征 总被引：4，自引：0，他引：4
利用1991-2009 年中国农业气象站点记录的灾害及物候资料,首先对小麦各类气象灾害发生的频次及所在生长发育期进行了时空特征分析;然后通过对比较暖10 年（2000-2009）与其前10（1990-1999）年两个时期的灾害时空变化特点,探讨气候变化对灾害发生的影响。结果表明：干旱是小麦发生频率最高的灾害类型,其发生频率高达79.21%,冰雹、干热风、大风、连阴雨等灾害类型也在小麦生产过程中有较多发生。气候变化背景下,小麦典型气象灾害发生频次有所增加,并且主要发生在生殖生长期。空间上,灾害类型增加较为明显的有：山东半岛的干热风、西北地区东部的干旱、暴雨及冰雹。分析表明：不同灾害种类的发生及变化的空间分布与中国气候变化特征有很强的关系。 相似文献
17.
Semi-arid areas are often considered to be environmentally and economically marginal, a situation which has been exacerbated by economic change, shifts in agricultural production and land use, and changing state policy. These themes are explored with reference to a semi-arid landscape, namely the Karoo, which covers some 40% of the geographic space of South Africa and is used primarily for extensive livestock farming. Despite long-term decline in agricultural output, the traditional mainstay of the region, and weakening small town economies, the Karoo's population and the economies of its largest service centres are growing. There are, real socio-economic needs and development backlogs, and the situation has been exacerbated by recent political marginalisation. In this study, the small towns of the region are focal points of investigation and provide a lens to investigate the changing demographic and economic dynamics of the Karoo. Most of the region's population lives in these centres which are service, collection, and distribution points for what traditionally has been an agriculture-based regional economy. This paper explores the concept of marginalisation with specific reference to historical, economic, and demographic change. 相似文献
18.
George C. S. Lin 《The Professional geographer》2013,65(1):56-70
Much of the development literature and the theory of urban transition have been based on an arbitrary division of production space into city and countryside. Despite growing recognition of the need for an integrated approach to urban-rural relations, controversial issues related to the definition and measurement of the phenomenon remain unresolved. This case study of spatial transformation in China’s Pearl River Delta analyzes with greater precision the geographic extent and functional attributes of a zone of urban-rural interaction located outside and between major metropolitan centers. This zone has been the spatial focus of industrial and commercial development, although most of its population remains officially classified as “agricultural.” The peri-urban zone was initially left behind by the central cities in terms of its contribution to the regional economy. After a decade of postreform development, this zone has moved ahead of the central cities and become the region’s main destination for in-migrants and foreign investment. The growth of the zone of urban-rural interaction outside the central cities has absorbed a significant amount of the increased urban population, but it has not brought about a reduction of regional economic inequality because of the persistence of a backward economy in the periphery. Theoretical questions are raised concerning the validity of several fundamental assumptions underlying the conventional model of urban transition. 相似文献
19.
青藏高原毗邻全球大气污染物排放增长最快速的地区,受西风和南亚季风的影响,中亚、南亚等高原周边排放的污染物通过大气环流传输,进入高原并对其气候环境产生重要影响。观测事实表明：近几十年青藏高原东部和南部雪冰中黑碳含量呈显著上升趋势,这可能导致冰川加速融化和积雪持续时间缩短,最终影响青藏高原的水循环过程。前人对青藏高原黑碳的外源输送,特别是南亚大气污染物的贡献及其对高原气候、冰冻圈变化的影响,还没有较清晰和统一的认识。青藏高原污染物定点监测网络的发展及高分辨率区域气候—大气化学模式的应用,为定量评估高原污染物外源输送及气候效应提供了契机。本文在国家自然科学基金青年科学基金项目“南亚黑碳气溶胶跨境传输及其对青藏高原气候影响的数值模拟研究”的资助下,在以下三个方面取得了进展：①系统性论证了高分辨率区域气候—大气化学模式在高原的适用性,模拟了青藏高原及周边区域黑碳时空分布、传输和沉降过程;②揭示了污染物扩散的机制,评估了大气黑碳的气候及雪冰效应,并对比了自然源粉尘和人为源黑碳对青藏高原气候的影响;③定量估算了不同区域排放对高原黑碳外源输送的贡献率,其中来自南亚的黑碳对青藏高原外源输送的贡献率最高,在非季风期为61.3%,季风期为19.4%。本文揭示了外源输送黑碳对青藏高原气候的影响,为提高一带一路核心区冰冻圈与水资源的管理及预测能力,制定应对环境变化策略及国家气候外交谈判提供科学依据。 相似文献
20.
DIANA K DAVIS 《The Geographical journal》2006,172(2):88-105
Neoliberal restructuring in Morocco has been taking place for over twenty years. Beginning with a decade of structural adjustment, from the early 1980s to the early 1990s, parts of the public sector have been privatized, state services such as health care and education reduced, tariffs lowered and exports heavily promoted. In the dryland agricultural areas, a declensionist colonial environmental narrative has been appropriated to help justify and implement the neoliberal goals of land privatization and the intensification of agricultural production in the name of environmental protection. This paper contributes to areas of growing interest for geographers through an analysis of the underexplored relationship between neoliberalism and environmentalism, in the form of questionable environmental narratives, in Morocco. Land degradation in the dryland agricultural areas of Morocco is commonly blamed on overgrazing by local pastoralists despite existing documentation that suggests instead that ploughing of marginal lands and over-irrigation are the primary drivers of land degradation in the region. The deployment of this colonial environmental narrative of 'native improvidence' has facilitated an expansion of state power over collective rangelands under neoliberalism at the same time that government involvement has decreased in other sectors. The effects of neoliberalism in Morocco have been complex and thus the paper argues that current neoliberal reforms such as the Morocco–US free trade agreement need to be scrutinized carefully to prevent a further exacerbation of poverty as well as to prevent further land degradation in these areas. 相似文献