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301.
高温热浪直接影响人体健康和作物生长。研究全球变暖背景下我国高温热浪发生率的趋势是气候变化研究的基本问题之一,可为人们的生产生活等提供重要的科学信息。目前对于高温热浪趋势的研究大都使用最小二乘(Ordinary Least Squares,OLS)方法估计趋势,结合学生t检验判断趋势的统计显著性。本文审视了以往常用方法在研究我国高温热浪发生率的线性趋势时的适用性。首先,以2018年东北局部地区因当年高温日数异常多而形成离群值的例子展开,说明OLS方法估计趋势时对离群值非常敏感,造成虚假趋势。进一步,通过正态分布检验和自相关计算,发现1960~2018年中国至少有91.14%站点、90.06%格点的高温日数和92.18%站点、87.74%格点的热浪次数的序列不服从正态分布,而且多数存在自相关。采用一种不易受离群值影响并考虑自相关的非参数方法,本文对1960~2018年中国站点和格点、4个典型区域以及全国平均的高温日数和热浪次数的线性趋势做出了更为准确的估计。研究发现,高温日数显著增多的站点主要出现在华南和西北地区,热浪次数呈显著增多趋势的站点目前几乎仅限于华南地区和新疆的个别站点;区域平均而言,仅有华南区域和西北区域的高温日数和热浪次数是显著增多的,华北区域和东北区域趋势并不显著;全国平均的高温日数和热浪次数都是显著增多的。本文对高温热浪的趋势及其显著性估计、统计预测的方法选择上有重要参考价值。 相似文献
302.
利用1951—2018年吉林省50站逐日最高气温资料,采用气候倾向率、距平累积、灰色关联度、正态分布等方法分析了吉林省高温天气的时空分布特征、建立了吉林省高温过程综合指数、高温过程评估等级指标和气候重现期指标。结果表明:近68 a来,吉林省年平均高温日数总体呈增加趋势,气候倾向率为0.04 d/10 a。吉林省高温次数阶段性变化明显,1959—1996年为偏少时段;1951—1958年、1997—2018年为偏多阶段。吉林省高温天气主要出现在6月中旬至8月中旬,其中7月下旬最多,8月上旬次多。西部为高温的高发区,吉林省年平均高温日数呈自西向东减少特征。对高温过程进行了等级划分,并给出等级及气候重现期评估指标,对于高温过程,可采用综合指数评估指标和各分项评估指标进行评估,便于在决策业务中应用。 相似文献
303.
以榆林飞播林区的土壤微生物、土壤养分和土壤可溶性盐为研究对象,对林区土壤可溶性盐的变化规律及其与土壤养分、微生物的相关性进行研究,为水土资源可持续利用以及飞播造林功效的提高提供理论依据.研究表明,研究区土壤属硫酸盐型,土壤层分异特征不显著,土壤仍处于初级发育阶段.土壤总盐与养分的相关性不明显,适当增加K+利于真菌的存活和生物量的积累,在1 kg土壤中,每增加1 g K+,真菌数量就会增加14个左右.在土层表层,适量减少Cl-能促进土壤细菌的生长,在40 cm土层的盐分上行过程中出现表聚现象,在土壤中层,出现板结现象,在土壤底层,HCO3-和Na+质量分数的增加,有利于土壤全氮质量分数的增加,且HCO3-的影响力最强. 相似文献
304.
305.
1 INTRODUCTION Bioavailability to the biota and the biogeo-chemistry of trace metals in marine environment areaffected by their chemical speciation in the naturalsystem (Bruland et al., 1991; Van den Berg andDonat, 1992; Wells et al., 1998). Therefore, thesetwo parameters, the ligands concentrations andconditional stability constants, are important todetermine the complexing capacity. Sea surface microlayer (SML), the thin interfa-cial boundary between ocean and atmosphere, playsan imp… 相似文献
306.
Shuko Hamada Takeshi Ohta Tetsuya Hiyama Takashi Kuwada Atsuhiro Takahashi Trofim C. Maximov 《水文研究》2004,18(1):23-39
Seasonal changes in the water and energy exchanges over a pine forest in eastern Siberia were investigated and compared with published data from a nearby larch forest. Continuous observations (April to August 2000) were made of the eddy‐correlation sensible heat flux and latent heat flux above the canopy. The energy balance was almost closed, although the sum of the turbulent fluxes sometimes exceeded the available energy flux (Rn ? G) when the latent heat flux was large; this was related to the wind direction. We examined the seasonal variation in energy balance components at this site. The seasonal variation and magnitude of the sensible heat flux (H) was similar to that of the latent heat flux (λE), with maximum values occurring in mid‐June. Consequently, the Bowen ratio was around 1·0 on many days during the study period. On some clear days just after rainfall, λE was very large and the sum of H and λE exceeded Rn ? G. The evapotranspiration rate above the dry canopy from May to August was 2·2 mm day?1. The contributions of understory evapotranspiration (Eu) and overstory transpiration (Eo) to the evapotranspiration of the entire ecosystem (Et) were both from 25 to 50% throughout the period analysed. These results suggest that Eu plays a very important role in the water cycle at this site. From snowmelt through the tree growth season (23 April to 19 August 2000), the total incoming water, comprised of the sum of precipitation and the water equivalent of the snow at the beginning of the melt season, was 228 mm. Total evapotranspiration from the forest, including interception loss and evaporation from the soil when the canopy was wet, was 208–254 mm. The difference between the incoming and outgoing amounts in the water balance was from +20 to ?26 mm. The water and energy exchanges of the pine and larch forest differed in that λE and H increased slowly in the pine forest, whereas λE increased rapidly in the larch forest and H decreased sharply after the melting season. Consequently, the shape of the Bowen ratio curves at the two sites differed over the period analysed, as a result of the differences in the species in each forest and in soil thawing. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
307.
Based on the stochastic and phenomenological aspects of hydrological processes, a conceptually based stochastic point process (SPP) model for daily stream‐flow generation is proposed in this paper. In which, storms are defined by a stochastic point process with marked values. All the random variables defining the process are assumed to be mutually independent, which constitutes a compound Poisson point process. The direct surface runoff is regarded as occurring from storage in a cascade of surface linear reservoirs and is responsible for the short‐term variation of the daily stream flows. The baseflow component is considered as coming from subsurface/groundwater storage and is responsible for the long‐term persistence of the storm time‐series. This type of model is proposed as a more realistic model of daily stream flow than models based on pure stochastic processes. Studies on the instantaneous unit hydrograph and the mechanism of baseflow could thereby provide some parameters for this model. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
308.
Evapotranspiration was studied at a salt marsh site in the Hunter River estuary, NSW, Australia, during 1996–8. Estimates of actual evapotranspiration (Ea) were obtained for three sites using the eddy correlation method. These values were compared with results obtained with the Penman and Penman–Monteith equations, and with pan evaporation. The Penman–Monteith method was found to be most reliable in estimating daily and hourly evapotranspiration. Surface resistance values averaging 12 s m?1 were derived from the eddy correlation estimates. Recent tidal flooding and rainfall were found to decrease surface resistance and increase Ea/Ep ratios. Estimates of evapotranspiration obtained using the Penman–Monteith method were shown to be sensitive to changes in surface resistance, canopy height and the method used to estimate net radiation from incoming solar radiation. These results underline the importance of accurately estimating such parameters based on site‐specific data rather than relying on empirical equations, which are derived primarily for crops and forests. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
309.
The ground water flow path of the coastal area in the Yellow Sea, Korea, was interpreted using both the cross‐correlation analysis of hydraulic properties and the principal component analysis (PCA) of ground water chemistry. Data was obtained from observation wells in the underground liquefied petroleum gas (LPG) cavern constructed in the coastal area of Pyeongtaek. Cross‐correlation results showed that the operating pressure became more influenced on artificial factors for the variation of the groundwater level of the study area (45–66% of correlation coefficient) even though its affecting area was limited to the region with fractures or faults, and also showed that the delay time from the variation of operating pressure to the fluctuation of ground water level were relatively long periods (28–31 days). Three hydrogeochemical events (encrusted cement dissolution, host rock dissolution, and seawater intrusion), which were dominantly influenced on ground water quality, could be induced from the result of PCA. Quantitative evaluation for these events using the mixed equation with principal component scores suggest that the dissolution of encrusted cement materials was the predominant factor (39·0% of the total mixed proportion) to change the chemical composition of the seepage water during the ground water flow from the observation wells to the cavern. Integration of the statistical results also imply that ground water flow and hydrogeochemistry were predominantly affected by artificial factors such as cavern operation pressure and dissolution of encrusted cement materials, which were interdependent factors on the observation wells with high cross‐correlation coefficients and pH. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
310.