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41.
黄河流域天然径流量突变性与周期性特征 总被引:22,自引:1,他引:22
突变性和周期性是水文时间序列的两个重要特征。黄河流域面积广阔,各区域水文水资源系统演变规律各不相同,它们的突变和周期变化及其形成的物理机制遍异,因此系统分析各区域水资源突变性和周期性特征及其影响机制具有重要意义。把黄河流域划分为15个区域,计算出各区域1951—1998年的年天然径流量系列。利用Mann-Kendall非参数检验方法检测黄河流域各区域年天然径流量的突变年份,结果表明各区域的突变年份不完全一致,主要在1953—1955年、1979—1983年、1991—1993年等发生了突变,这些突变与北半球气候突变具有一致性,且由于下垫面改变、人类活动等影响而复杂化。利用Morlet小波分析各区域年天然径流量的变化周期,发现主要存在3~4a、7~9a、11a的周期,形成这些周期的物理因子有太阳黑子、海—气相互作用和下垫面因素等。通过分析黄河流域主要产流区不同时段小波系数变化,发现20世纪80年代之后年径流量主要以短周期变化。 相似文献
42.
43.
青藏高原的水塔功能 总被引:5,自引:0,他引:5
青藏高原是维持我国乃至东亚地区生态系统的重要水塔。高原平均海拔在4000m以上,与周边地区形成了巨大的地势差。高原东南部不仅具有丰富的降水,而且在3500m以上以冰川雪被形态储存了巨大的水资源,因此,高原具有重要的水塔功能。基于高原潜在输出总水量和不同海拔区域水体所具有的势能两个方面,建立了高原水塔功能的模型,从而利用GIS方法,通过对我国1∶400万系列图和相关资料的统计分析,计算出高原不同高度带贮存的大气降水、冰川储水量、湖泊水量以及工农业用水量。计算结果表明,青藏高原冰川湖泊的淡水储量达39921×108m3,其中冰川储水量为39228×108m3,可利用湖泊储水量为693×108m3,平均每年由降水获得的水资源量为8495×108m3,高原工农业用水量为129×108m3。因此,高原的输出水量即出境河川径流量为6870×108m3。高原储水主要分布在海拔3000~5000m间,与高原周围相比,平均势差在2000~4000m间,最大的势差达5500m。水体具有巨大的势能,在势能的作用下,自然向周边区域输送汇集,维持着周边地区的生态过程和社会经济活动,因此,青藏高原的水塔功能对于周边地区的生态系统和社会经济系统是极其重要的。 相似文献
44.
中国兴凯湖北岸平原晚全新世花粉记录及泥炭沼泽形成 总被引:7,自引:1,他引:7
通过兴凯湖北岸平原泥炭剖面高分辩率花粉分析研究,对晚全新世花粉划分4个组合带。XKH-4组合时期(1857~1746aB.P.)为沼泽发育前期,这一时期花粉浓度小,陆生草本植物占优势,气候干冷。XKH-3组合时期(1746~1287aB.P.)为沼泽发育早期,这一时期花粉浓度较大,且水生植物花粉含量为剖面最高,喜温落叶阔叶植物大发展时期,气候温和湿润。XKH-2组合时期(1287~602aB.P.)为沼泽发育中期,这一时期花粉浓度最小,但以陆生草本植物为主,木本植物为辅,水生植物急剧减少,针叶植物出现两次高峰,气候向冷干方向发展。XKH-1组合时期(602aB.P.至今)为沼泽发育盛期,这一时期花粉浓度最大,陆生草本植物大发展时期,气候波动较大。 相似文献
45.
46.
国外国土开发整治与规划的经验及启示 总被引:3,自引:1,他引:3
本文简要回顾了20世纪以来国外国土开发整治与规划的过程,总结了国外在国土规划方面取得的经验:即国土规划的权威性、系统性、针对性、可操作性、实效性和参与性等特点。在此基础上,结合我国国情,针对当前面临的形势,提出发展和完善我国国土规划的基本思路:重视国土规划;将国土规划纳入规范化、法制化的轨道;强化国土规划的系统调控和管理等。 相似文献
47.
Although Eddy Covariance (EC) technique is one of the best methods for estimating the energy and mass exchanges between underlying surface and atmosphere in micrometeorology, errors and uncertainties still exist without necessary corrections. In this paper, we will focus on the effect of coordinate system on the eddy fluxes. Based on the data observed over four sites (one farmland site, one grassland site and two forest sites), the effects of three coordinate system transforming methods (Double Rotation-DR, Triple Rotation-TR and Planar Fit-PF)on the turbulent fluxes are analyzed. It shows that (i) the corrected fluxes are more or less than the uncorrected fluxes, which is related mainly to the sloping degree of surface, wind speed and wind direction; and (ii) pitch angle has a sinusoidal dependence on wind direction, especially in the regular sloping terrain; and (iii) PF method is something like the simplification of TR or DR,and there are not obvious distinctions in correction in sloping grassland and flat farmland, but PF method is not suitable for uneven and irregular forest sites. 相似文献
48.
The alpine meadow is widely distributed on the Tibetan Plateau with an area of about 1.2×106kn2. Damxung County, located in the hinterland of the Tibetan Plateau, is the place covered with this typical vegetation. An open-path eddy covariance system was set up in Damxung rangeland station to measure the carbon flux of alpine meadow from July to October,2003. The continuous carbon flux data were used to analyze the relationship between net ecosystem carbon dioxide exchange (NEE) and photosynthetically active radiation (PAR), as well as the seasonal patterns of apparent quantum yield (α) and maximum ecosystem assimilation (Pmax).Results showed that the daytime NEE fitted fairly well with the PAR in a rectangular hyperbola function, with α declining in the order of peak growth period (0.0244 μmolCO2 · μmol-1pAR) >early growth period > seed maturing period > withering period (0.0098 μmolCO2 · μmol-1pAR).The Pmax did not change greatly during the first three periods, with an average of 0.433mgCO2· m-2· s-1, i.e. 9.829 μmolCO2· m-2· s-1. However, during the withering period, Pmax was only 0.35 mgCO2 · m-2 · s-1, i.e. 7.945 μmolCO2 · m-2 · s-1. Compared with other grassland ecosystems, the α of the Tibetan Plateau alpine meadow ecosystem was much lower. 相似文献
49.
SHA Liqing ZHENG Zheng TANG Jianwei Wang Yinghong ZHANG Yiping CAO Min WANG Rui Liu Guangren WANG Yuesi SUN Yang 《中国科学D辑(英文版)》2005,48(Z1)
With the static opaque chamber and gas chromatography technique, from January 2003 to January 2004 soil respiration was investigated in a tropical seasonal rain forest in Xishuangbanna, SW China. In this study three treatments were applied, each with three replicates: A (bare soil), B (soil+litter), and C (soil+litter+seedling). The results showed that soil respiration varied seasonally, low from December 2003 to February 2004, and high from June to July 2004. The annual average values of CO2 efflux from soil respiration differed among the treatments at 1% level, with the rank of C (14642 mgCO2· m-2. h-1)>B (12807 mgCO2· m-2. h-1)>A (9532 mgCO2· m-2. h-1). Diurnal variation in soil respiration was not apparent due to little diurnal temperate change in Xishuangbanna. There was a parabola relationship between soil respiration and soil moisture at 1% level. Soil respiration rates were higher when soil moisture ranged from 35% to 45%. There was an exponential relationship between soil respiration and soil temperature (at a depth of 5cm in mineral soil) at 1% level. The calculated Q1o values in this study,ranging from 2.03 to 2.36, were very near to those of tropical soil reported. The CO2 efflux in 2003was 5.34 kgCO2· m-2. a-1 from soil plus litter plus seedling, of them 3.48 kgCO2· m-2. a-1 from soil (accounting for 62.5%), 1.19 kgCO2· m-2. a-1 from litter (22.3%) and 0.67 kgCO2·m-2. a-1 from seedling (12.5%). 相似文献
50.
High buildings or architectural complex in urban areas remarkably distort the urban surface wind fields. As the air flow approaches,local strong wind may appear around the buildings. The strong wind makes the pedestrians on sidewalks, entrances and terrace very uncomfortable and causes the pedestrian level wind environment problem. In this studies, hot-wire wind measurement, wind scouring in wind tunnel and numerical computation were carried out to evaluate the wind environment of tall buildings in the prevailing flow conditions in Beijing areas. The results obtained by three techniques were compared and mutually verified. The conclusions drawn from three approaches agree with each other. Also the advantages and limitations of each method were analyzed. It is suggested that the combination of different techniques may produce better assessment of wind environment around high buildings. 相似文献