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1.
了解降水的当前特征及未来的变化趋势对理解气候变化对区域生态系统的影响具有重要的意义。科尔沁沙地是中国北方农牧交错带的典型区域,年降雨量300~500mm,对气候变化(特别是降水的变化)非常敏感。对科尔沁沙地沙漠化较为严重的奈曼旗1971—2013年的降水资料进行了分析研究。结果表明:(1)该地区多年平均降水量为338.8mm,5—9月降雨量占全年降水量的(85.32±7.71)%,5—9月降雨量、年降水量1971—2000年经历了先增加后减少的趋势,2001—2013年有缓慢增加的趋势;同时降水量的年际变异性近10年也呈增加的趋势。(2)5—9月降雨量呈先增大后减小的趋势,在7月最大,为104.2 mm,5月和9月最小(分别为32.7 mm和32.8mm),月降雨量的年际变率均大于49%;生长季内降雨主要以〈10mm的事件为主,占总降雨事件的64.41%,却仅占总降雨量的16.95%;≥30mm的降雨事件占总降雨事件的10.96%,占到总降雨量的45.93%,且对总降雨量具有决定性的影响。(3)≥5mm降雨的平均间隔为9.4d,以1~10d为主,占到69.5%,10~20d(19.5%)的次之;≥30d的发生频率最小,为3.81%,降雨间隔的年际变异性均呈增加的趋势。(4)生长季降雨日数呈减少的趋势,降雨事件降雨量的变异性与生长季降雨量的变化具有相似性,从2001年开始呈增加的趋势。该地区的降雨量年际变异性强,降雨日数的减少和降雨事件降雨量变异性的增加将提高极端干旱事件发生的频率,可能对该地区的生态系统产生严重影响,加剧该地区的沙漠化发展方向。因此,加强气候变化对生态系统影响的研究,可为合理利用土地资源及调整土地管理方式提供理论依据。 相似文献
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节理分布空间变异的地下洞室稳定性概率分析 总被引:1,自引:0,他引:1
以岩土材料力学参数空间变异性的"点估计-有限元"分析方法为基础,结合节理分析时自身存在几何模型、网格划分等特性,扩展了该方法在节理分布空间变异性分析方面的适用性,明确了具体的研究步骤与方法。以某抽水蓄能水电站为例,通过分析节理空间变异性对围岩变形与塑性区的影响,验证了扩展后该方法的准确性和合理性。对工程案例开挖揭露的1400余条节理进行概率统计,建立了节理空间变异性的有限元分析模型;采用扩展后的概率分析方法,研究了节理分布对地下洞室群围岩开挖稳定性的影响。研究结果表明:(1)对比概率分析得到的围岩变形概率分布与现场监测结果,发现剔除变形异常点后监测变形量值大部分位于得到的位移概率分布范围内,说明节理的空间变异性是导致监测变形波动的主要影响因素;(2)围岩变形概率分布的标准差能有效识别出围岩开挖变形受节理空间变异性的影响程度,对于所给出的案例依次为:机窝>边墙>顶拱;(3)围岩塑性区的概率分区能合理判断地下洞室群开挖时受节理影响较大的区域和范围,为工程施工的支护设计提供依据。 相似文献
3.
Wenxiang ZHANG Shilun YANG Jun ZHU Shiliang GONG Pingxing DING 《国际泥沙研究》2007,22(3):199-207
This paper reports the results of continuous monitoring of turbidity, water depth, salinity (using an Optical Backscatter Sensor (OBS)), and current velocity (using a Current meter (SLC9-2)) in the South Passage of the Changjiang Estuary over a spring–neap period in February 2003 (dry season). The turbidity measured via OBS was closely correlated with the suspended sediment concentration (SSC), which was highly variable. Over the study period, the SSC in the middle layer ranged from 110 to 1400 mg/l. The minimum SSC occurred during a late ebb tide, and the maximum SSC occurred during a late flood tide. On average, the SSC was 1.5 times higher during flood tide than during ebb tide. Vertically within the water column, SSC increased downward, with the ratio of SSC measured near the bed to that measured at the surface ranging from 1.90 to 18.3. The temporal variability in SSC is jointly governed by tides and wind-induced waves, whereas the vertical variability in SSC is attributed to the effect of gravity and vertical water circulation. 相似文献
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基于16S rRNA高通量基因测序技术,对毛乌素沙地小叶锦鸡儿(Caragana microphylla)、柠条锦鸡儿(Caragana korshinskii)根系微域(即根系、根际土、根区土、灌丛间空白土)间的细菌群落多样性和结构差异性进行表征。本研究对各根系微域间细菌群落的Alpha多样性指数进行了单因素方差分析以及基于OTU水平的PCA分析,探究其在根系微域间Alpha和Beta多样性的层级变化,证实了有关植物根系微域生态位分化的报道,并发现锦鸡儿属植物根系微域间细菌群落的多样性和结构组成随着4个微域类型由外及内呈现出显著的层级差异性(P<0.05)。通过对优势细菌群组的结构组成分析,发现锦鸡儿属植物对特定细菌群组具有显著的向根系内筛选富集的作用(P<0.05)。这种植物通过根系微域对特定细菌群组的逐级筛选富集作用,是导致锦鸡儿属植物灌丛下不同生态位间细菌群落结构和组成发生层级变异的主要原因。 相似文献
6.
Yii Siang Hii Siti Aisyah Alias Monica Riofrio Nadia Ordoniez Hernain Moreano 《极地研究(英文版)》2013,(4):273-280
This study aims to report baseline soil nutrients, specifically the organic carbon, nitrogen and phosphorus profile, in soil samples collected from Puntta Fort William on Greenwich Island in maritime Antarctic. Samples were collected along two transect lines during the early summer of 2008. Ward's method of hierarchical agglomerative clustering was employed to group the sampling points based on their physico-chemical properties. In this context, the soil samples can be grouped into three major clus- ters: (1) Samples with intensive biological activities, (2) samples from the area recently exposed by glacial retreat and (3) samples from barren and dried areas. Nutrient contents in Punta Fort William are driven by the intensity of biological activities as well as melt water from the Qnito glacier. 相似文献
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本文用不同经度的7对中低纬台站水平磁场分量H,求得1965年随世界时(UT)变化的Sq指数(一种描述Sq电离层发电机电流强度的地磁指数).结果表明,Sq发电机电流不仅有显著的逐日变化,而且有很大的UT变化.UT变化主要表现在电流总强度的强弱和电流涡焦点纬度移动两方面,这意味着决定发电机过程的太阳潮汐风场和电离层电导率随UT而变.用求得的Sq指数重新构造出的Sq变化与观测值符合得较好,它不仅显示出Sq幅度逐日变化的特点,而且还能复现出Sq形态的某些逐日变异性. 相似文献
10.
The impacts of the seasonal and interannual SST variability in the East Asia coastal regions (EACRSST) on the East Asian summer monsoon (EASM) have been examined using a regional climate model (PδRCM9) in this paper. The simulation results show that the correlation between the EACRSST and the EASM is strengthened after the mid-1970s and also the variability of the EACRSST forcing becomes much more important to the EASM interannual variability after the mid-1970s. The impacts of the EACRSST on the summer precipitation over each sub-region in the EASM region become weak gradually from south to north, and the temporal evolution features of the summer precipitation differences over North and Northeast China agree well with those of the index of EASM (IEASM) differences.
The mechanism analyses show that different EACRSST forcings result in the differences of sensible and latent heat flux exchanges at the air-sea interface, which alter the heating rate of the atmosphere. The heating rate differences induce low level air temperature differences over East Asia, resulting in the differences of the land-sea thermal contrast (LSTC) which lead to 850 hPa geopotential height changes. When the 850 hPa geopotential height increases over the East Asian continent and decreases over the coast of East China and the adjacent oceans during the weakening period of weakens consequently. On the contrary, the EASM enhances during the strengthening period of the LSTC. 相似文献
The mechanism analyses show that different EACRSST forcings result in the differences of sensible and latent heat flux exchanges at the air-sea interface, which alter the heating rate of the atmosphere. The heating rate differences induce low level air temperature differences over East Asia, resulting in the differences of the land-sea thermal contrast (LSTC) which lead to 850 hPa geopotential height changes. When the 850 hPa geopotential height increases over the East Asian continent and decreases over the coast of East China and the adjacent oceans during the weakening period of weakens consequently. On the contrary, the EASM enhances during the strengthening period of the LSTC. 相似文献