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801.
802.
In this paper, a Wind Direction Change Index (WI), which can describe four-dimensional spatiotemporal changes of the atmospheric circulation objectively and quantitatively, is defined to study its evolution and seasonal variation. The first four modes can be obtained by EOF expansion of the zonally averaged WI. The first mode reveals the basic spatial distribution of the annually averaged WI. The second mode reflects the quasi-harmonic parts of the WI deviations. Tropical, subtropical and extratropical monsoon areas can be clearly reflected by this mode. The third mode reflects the non-harmonic parts of the WI deviations. It shows the so-called February reverse in stratospheric atmosphere as well as the asymmetric seasonal changes from spring to fall and from fall to spring due to both the land-sea distribution contrast between the Northern and Southern Hemispheres and the nonlinear effect of atmospheric and ocean fluids. The fourth mode reveals the northward advancing of the global reversed wind fields from spring to summer and their southward withdrawal from summer to autumn. 相似文献
803.
Spatiotemporal variations of Chinese Loess Plateau vegetation cover during 1981–2006 have been investigated using GIMMS and
SPOT VGT NDVI data and the cause of vegetation cover changes has been analyzed, considering the climate changes and human
activities. Vegetation cover changes on the Loess Plateau have experienced four stages as follows: (1) vegetation cover showed
a continued increasing phase during 1981–1989; (2) vegetation cover changes came into a relative steady phase with small fluctuations
during 1990–1998; (3) vegetation cover declined rapidly during 1999–2001; and (4) vegetation cover increased rapidly during
2002–2006. The vegetation cover changes of the Loess Plateau show a notable spatial difference. The vegetation cover has obviously
increased in the Inner Mongolia and Ningxia plain along the Yellow River and the ecological rehabilitated region of Ordos
Plateau, however the vegetation cover evidently decreased in the hilly and gully areas of Loess Plateau, Liupan Mountains
region and the northern hillside of Qinling Mountains. The response of NDVI to climate changes varied with different vegetation
types. NDVI of sandy land vegetation, grassland and cultivated land show a significant increasing trend, but forest shows
a decreasing trend. The results obtained in this study show that the spatiotemporal variations of vegetation cover are the
outcome of climate changes and human activities. Temperature is a control factor of the seasonal change of vegetation growth.
The increased temperature makes soil drier and unfavors vegetation growth in summer, but it favors vegetation growth in spring
and autumn because of a longer growing period. There is a significant correlation between vegetation cover and precipitation
and thus, the change in precipitation is an important factor for vegetation variation. The improved agricultural production
has resulted in an increase of NDVI in the farmland, and the implementation of large-scale vegetation construction has led
to some beneficial effect in ecology.
Supported by the National Natural Science Foundation of China (Grant No. 40671019) and the Knowledge Innovation Project of
the Institute of Geographical Sciences and Natural Resources Research of Chinese Academy of Sciences 相似文献
804.
The study on the interrelation between sea-level changes and biodiversity with its evolution has great significance for understanding
the impact of global changes on organic evolution and exploring the inherent laws of life-environment coevolution in geological
history. In this paper, the stratigraphic distribution of fusulinacean fauna in the Carboniferous-Permian boundary section
at Xikou, Zhen’an County, Shaanxi Province, is analyzed quantitatively, and the relationship between the species diversity
of fusulinaceans and relative sea-level changes is discussed. As a whole, the species numbers of fusulinacean fauna experience
a rapid increase and an obvious decline in Xikou, Zhen’an County, from the Late Carboniferous to the Early Permian. There
is a significant increase in species diversity around the Carboniferous-Permian boundary, which is one of the biggest bio-events
of the fusulinacean fauna, and represents the radiation of Pseudoschwagerininae subfamily in the studied area. Integrated
fusulinacean species diversity into sequence stratigraphic framework, detailed study suggests that the species diversity of
the fusulinaceans is closely related to its relative stratigraphic location, and is essentially controlled by the sea-level
changes, especially by the high-frequency sea-level changes. Generally, the species diversity of fusulinaceans is low, and
the number of first and last appearance datum is small in the lower unit of high-frequency depositional cycle formed during
the quick rise of the sea level; whereas the species diversity of fusulinaceans is high, and the number of first and last
appearance datum is large in the upper unit of high-frequency cycle formed during the slow fall of the sea level. Within the
third-order depositional sequence, the species diversity of the fusulinaceans at the first flooding surfaces and the maximum
flooding surfaces is low, and it increases upward. The fusulinacean species diversity is low within the transgressive systems
track, and it is high within the highstand systems track. The second-order rise and fall in sea level coincide with the bloom
and decline of high order taxa of fusulinaceans. 相似文献
805.
快速城镇化进程中太湖流域下垫面的剧烈变化对流域产水量时空分布产生了深刻影响.在分析太湖流域城镇化进程及土地利用变化的基础上,采用太湖流域模型对3种典型降雨过程(1991、1999和2009年)与5种下垫面(1985、1995、2000、2005和2010年)的组合情景进行模拟,综合分析了城镇化进程中全流域和各水利分区在全年期、汛期、涨水期产水量变化的时空分布特征.结果表明:时程上,太湖流域和所有水利分区的各统计时段产水量增幅伴随城镇化进程推进均呈现增加趋势,2005年后产水量增幅进一步加大,且全年产水量增幅主要集中在汛期;空间上,东、中部城市集聚区的产水量增长率明显高于西部山丘区与太湖湖区,这主要是由于西部山丘区、太湖湖区不透水率增幅较小所致.产水量变化的时空非均匀分布特征为城镇化背景下太湖流域防洪除涝格局演变及流域-区域-城市防洪除涝协调性研究提供了重要的先验认识. 相似文献
806.
1960年以来太湖水生植被演变 总被引:4,自引:5,他引:4
太湖的富营养化污染日益严重,针对太湖水生植被的研究工作非常重要,然而全面的太湖水生植被调查已经有将近二十年未见报道.基于2014年夏季全湖水生植被调查结果,结合历史资料,比较分析1960年以来太湖水生植被演变情况.结果表明,1960年以来,共有23种水生植物从太湖消失,其中1981、1997和2014年分别消失7、4和12种.从分布区面积来看,1960年以来太湖水生植被总体呈北部湖区水生植被消失,东北部、东部及南部湖区水生植被分布区面积持续扩张的态势,1981年全湖水生植被分布区面积占8%,到2014年已经有33.82%的水面有水生植被分布.从生物量组成来看,太湖水生植被先升后降,从1960年的10×104 t,持续上升到1988年的44.72×104 t,1997年下降到36×104 t,2014年进一步下降到29.09×104 t.但挺水植被以外的水生植被,尤其是浮叶植被的生物量一直保持上升态势.总生物量的下降与东太湖挺水植被大面积消失有关,到2014年全湖挺水植被生物量比重仅占5.15%,东太湖沼泽化问题已不复存在.从群落组成变化情况来看,苦草(Vallisneria natans)群落分布区面积锐减,马来眼子菜(Potamogeton malaianus)和荇菜(Nymphoides peltatum)分布区持续扩张.目前太湖水生植被管理面临的主要问题是北部湖区水生植被恢复和东部湖区水生植被过量生长. 相似文献
807.
808.
1957-2006年塔里木河流域气候变化和人类活动对水资源和生态环境的影响 总被引:9,自引:5,他引:9
塔里木河是我国最大的内陆河,历史上是环塔里木盆地九大水系144条河流的总称,目前呈"四源一干"格局.依据1957—2006年近50a气象及水文监测资料,分析了气候变化和人类活动对塔里木河流域水资源的影响.虽然近50a来塔里木河流域山区与平原整体呈现气温升高、降水量增加特征,出山口径流量也呈增加趋势,然而在2000年前塔里木河流域生态环境急剧退化.其成因主要为:1)从20世纪50年代起到近2006年,四条源流入塔里木河水量50a减少了15.4×108m3;2)塔里木河上、中、下游耗水量比例的失调及区域水资源分配发生变化,造成塔里木河下游生态环境恶化;3)实施塔里木河综合治理后,即使进入塔里木河的下游的水量增加,中游段耗水量下降,但是上游耗水迅速增加且数量巨大,还是对塔里木河水资源综合利用、改善的下游生态环境产生负面影响. 相似文献
809.
论地质历史中区域构造沉降史与海平面变化 总被引:2,自引:1,他引:2
区域构造沉降史和海平面变化是层序地层学中起决定作用的两个主参数。运用“反剥法”。(back-stripping)建立了研究区内泥盆纪至三叠纪盆地构造沉降地球动力学曲线模型,识别出盆地演化从被动大陆边缘、成熟被动大陆边缘、周缘前陆盆地到后造山前陆盆地的演化序列。同时,运用沉积体系域、地震及碳氧同位素信息反演编制了二叠-三叠纪海平面变化轨迹曲线,研究区内海平面变化与全球海平面升降具同步效应,至晚三叠世研究区海平面变化表现为上升趋势,而全球海平面变化总体处于海平面下降阶段,这与前陆挠曲变形和造山俯冲有关。 相似文献
810.
全球气候变化和人类活动双重作用对生态环境的影响是当今研究的热点问题.本文以国家级榆林能源化工基地为研究区,以MODIS遥感数据为依据,以归一化差值植被指数NDVI为参数,研究了植被生态的时空分布规律,分析了植被生态与降水、地貌、地下水、包气带岩性等自然条件的关系,揭示了人类活动对植被生态正负两方面的影响.研究结果表明,自然条件控制着植被生态的格局,植被生态具有明显的水平分带性,由东南向西北,随着降水量的减少、蒸发量和干燥度的增加,植被状况由好变差;2000年以来区内植被状况总体呈现好转的趋势,其中71.22%的区域好转,28.43%的区域基本维持不变,0.35%的区域退化.植被生态对气候变化尤其是降水量的年际变化具有敏感的响应,煤炭和地下水资源开采等人类活动对植被生态总体上造成负面影响,退耕还林(草)、限耕禁牧政策的实施是研究区植被生态总体呈现好转趋势的根本原因. 相似文献