Discrete wavelet‐based trend identification in hydrologic time series     

Yan‐Fang Sang  Zhonggen Wang  Changming Liu 《水文研究》2013,27(14):2021-2031

Trend identification is a substantial issue in hydrologic series analysis, but it is also a difficult task in practice due to the confusing concept of trend and disadvantages of methods. In this article, an improved definition of trend was given as follows: ‘a trend is the deterministic component in the analysed data and corresponds to the biggest temporal scale on the condition of giving the concerned temporal scale’. It emphasizes the intrinsic and deterministic properties of trend, can clearly distinguish trend from periodicities and points out the prerequisite of the concerned temporal scale only by giving which the trend has its specific meaning. Correspondingly, the discrete wavelet‐based method for trend identification was improved. Differing from those methods used presently, the improved method is to identify trend by comparing the energy difference between hydrologic data and noise, and it can simultaneously separate periodicities and noise. Furthermore, the improved method can quantitatively estimate the statistical significance of the identified trend by using proper confidence interval. Analyses of both synthetic and observed series indicated the identical power of the improved method as the Mann–Kendall test in assessing the statistical significance of the trend in hydrologic data, and by using the former, the identified trend can adaptively reflect the nonlinear and nonstationary variability of hydrologic data. Besides, the results also showed the influences of three key factors (wavelet choice, decomposition level choice and noise content) on discrete wavelet‐based trend identification; hence, they should be carefully considered in practice. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Variation and pattern in the responses of mammal faunas to Late Pleistocene climatic change in southeastern South Australia     

Amy C. Macken  Gavin J. Prideaux  Elizabeth H. Reed 《第四纪科学杂志》2012,27(4):415-424

We examined mammal occurrence and variability through the Late Pleistocene vertebrate fossil deposit of Grant Hall in Victoria Fossil Cave, Naracoorte, South Australia. To determine long‐term patterns of change, we compared the composition and relative abundance trends of the assemblage with a nearby Middle Pleistocene deposit in Cathedral Cave. Total species richness did not change through the Grant Hall sequence, dated from 93 ± 8 to 70 ± 5 ka. However, species relative abundances varied between ecologically divergent species, and in some cases between species that demonstrate similar environmental preferences. For some species this variation is comparable to that recorded in Cathedral Cave. Of those showing similar trends between the two deposits, the forest inhabitant, Pseudomys fumeus, recorded an 8.6% decline through Grant Hall, coincident with a 9.7% increase in the dry heath/mallee dweller Pseudomys apodemoides. These patterns indicate that climatic transition from relatively warm, moist to cooler, drier conditions impacted some species in similar ways through climatic cycles of the past. However, the majority of the fauna demonstrated complex responses that are individual and variable through time. Statistical tests of species trends from the Grant Hall assemblage caution that large fossil samples are required to validate patterns observed. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Assessment of future runoff trends under multiple climate change scenarios in the Willamette River Basin,Oregon, USA     

Il‐Won Jung  Heejun Chang 《水文研究》2011,25(2):258-277

We investigated trends in future seasonal runoff components in the Willamette River Basin (WRB) of Oregon for the twenty‐first century. Statistically downscaled climate projections by Climate Impacts Group (CIG), eight different global climate model (GCM) simulations with two different greenhouse gas (GHG) emission scenarios, (A1B and B1), were used as inputs for the US Geological Survey's Precipitation Runoff Modelling System. Ensemble mean results show negative trends in spring (March, April and May) and summer (June, July and August) runoff and positive trends in fall (September, October and November) and winter (December, January and February) runoff for 2000–2099. This is a result of temperature controls on the snowpack and declining summer and increasing winter precipitation. With temperature increases throughout the basin, snow water equivalent (SWE) is projected to decline consistently for all seasons. The decreases in the centre of timing and 7‐day low flows and increases in the top 5% flow are caused by the earlier snowmelt in spring, decreases in summer runoff and increases in fall and winter runoff, respectively. Winter runoff changes are more pronounced in higher elevations than in low elevations in winter. Seasonal runoff trends are associated with the complex interactions of climatic and topographic variables. While SWE is the most important explanatory variable for spring and winter runoff trends, precipitation has the strongest influence on fall runoff. Spatial error regression models that incorporate spatial dependence better explain the variations of runoff trends than ordinary least‐squares (OLS) multiple regression models. Our results show that long‐term trends of water balance components in the WRB could be highly affected by anthropogenic climate change, but the direction and magnitude of such changes are highly dependent on the interactions between climate change and land surface hydrology. This suggests a need for spatially explicit adaptive water resource management within the WRB under climate change. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Estimation and Long-term Trend Analysis of Surface Solar Radiation in Antarctica: A Case Study of Zhongshan Station     

Zhaoliang ZENG  Zemin WANG  Minghu DING  Xiangdong ZHENG  Xiaoyu SUN  Wei ZHU  Kongju ZHU  Jiachun AN  Lin ZANG  Jianping GUO  Baojun ZHANG 《大气科学进展》2021,38(9):1497-1509

Long-term,ground-based daily global solar radiation (DGSR) at Zhongshan Station in Antarctica can quantitatively reveal the basic characteristics of Earth’s surface radiation balance and validate satellite data for the Antarctic region.The fixed station was established in 1989,and conventional radiation observations started much later in 2008.In this study,a random forest (RF) model for estimating DGSR is developed using ground meteorological observation data,and a highprecision,long-term DGSR dataset is constructed.Then,the trend of DGSR from 1990 to 2019 at Zhongshan Station,Antarctica is analyzed.The RF model,which performs better than other models,shows a desirable performance of DGSR hindcast estimation with an R~2 of 0.984,root-mean-square error of 1.377 MJ m~(-2),and mean absolute error of 0.828 MJ m~(-2).The trend of DGSR annual anomalies increases during 1990–2004 and then begins to decrease after 2004.Note that the maximum value of annual anomalies occurs during approximately 2004/05 and is mainly related to the days with precipitation (especially those related to good weather during the polar day period) at this station.In addition to clouds and water vapor,bad weather conditions (such as snowfall,which can result in low visibility and then decreased sunshine duration and solar radiation) are the other major factors affecting solar radiation at this station.The high-precision,longterm estimated DGSR dataset enables further study and understanding of the role of Antarctica in global climate change and the interactions between snow,ice,and atmosphere.  相似文献   

长江口涨、落潮槽底沙输移趋势探讨   总被引：5，自引：0，他引：5  

刘高峰  沈焕庭  王永红  吴加学 《海洋通报》2003,22(4):1-7

选择长江口南港南小泓和南港主槽作为典型涨、落潮槽为研究对象，以2001年9月所采底沙的颗粒分析资料为根据，并结合实测水文、泥沙资料进行水动力分析，运用Gao-Collins粒径趋势分析模型分析了底沙输移趋势，结果表明：南小泓的底沙主要是来自口门附近，由于涨潮流强于落潮流而使底沙向上游输移，即SE—NW方向，而南港主槽的底沙主要来自上游，由于落潮流强于涨潮流而使泥沙向下游输移，即NW—SE方向。  相似文献   

辽东湾北部海域营养状况与趋势评价   总被引：3，自引：0，他引：3  

田金  宋伦  王年斌  周遵春  薛克  吴金浩 《海洋通报》2007,26(6):113-118

根据 1999-2006 年 6-8 月的调查数据,分析辽东湾北部海域的营养水平及变化趋势,以了解辽东湾北部海域营养水平的分布特点及污染状况.由 E 值和 CN/CP 值的总体评价结果来看,辽河口、双台子河口和大凌河口海域的富营养化程度较高,属于磷中等限制潜在性富营养区,而锦州湾海域污染相对较轻,属于中度营养区;在时空分布上,辽东湾北部海域 1999 年与 2006 年污染较为严重,中间年份污染相对较轻.针对辽东湾的具体环境用 CN/CP 值的评价模式更能揭示出营养盐限制对富营养化的影响.  相似文献   

Biological processes and environmental factors regulating the dynamics of the Norwegian Skagerrak cod populations since 1919   总被引：1，自引：1，他引：1  

Fromentin  Jean-Marc; Gjosaeter  Jakob; Bjornstad  Ottar N.; Stenseth  N. Chr. 《ICES Journal of Marine Science》2000,57(2):330-338

  相似文献   

东太平洋多金属结核分布的二维趋势面分析   总被引：1，自引：0，他引：1  

章伟艳  张富元  马维林 《海洋学研究》2001,19(1):27-34

对规则网的 469个测站的多金属结核丰度和 93个测站的 Mn、 Cu、 Co、 Ni元素进行趋势面分析 ,经 F检验 ,各变量的变异性显著 ,拟合度较低 ,表明多金属结核丰度及 Mn、Cu、Co、Ni金属元素的控制因素比较复杂。趋势面分析结果与相关分析结果一致 ,Mn、Cu、Ni元素有极相似的趋势特征 ,有两个轴向分布 ,一个为东西向轴 ,高值区在东部 ,另一个为北西向轴 ,高值区在北西部 ;结核丰度与 Co也有极相似的趋势特征 ,高值区在西部。应用逐次趋势面分析的结果将结核丰度的地质特征分解成各种简单控制因素的叠加 ,使对多金属结核的控矿因素、分布规律和物质来源的研究方法多样化  相似文献   

Distribution and abundance patterns of two parapagurid hermit crabs (Crustacea: Decapoda: Anomura) along the west and south coasts of South Africa     

AG Wright  TP Fairweather 《African Journal of Marine Science》2020,42(2):177-183

A series of over 6 000 research-trawl samples collected along the west and south coasts of South Africa between 1987 and 2014 were analysed for the presence and biomass of two parapagurid hermit crabs, Sympagurus dimorphus and Parapagurus bouvieri. The percentage of trawls that landed S. dimorphus and P. bouvieri and the mean caught biomass were higher on the west than on the south coast for both the more-abundant S. dimorphus (30.59 vs 5.81% success and 287.88 vs 31.37 kg km^–2, respectively) and for the less-abundant P. bouvieri (13.76 vs 3.58% success and 38.56 vs 16.32 kg km^–2, respectively). Very few parapagurids were caught shallower than 150 m; thereafter, the proportion of trawls containing hermit crabs increased, peaking over the depth range 201–250 m for S. dimorphus (54%) and 401–450 m for P. bouvieri (51%), and declining steadily thereafter. On the west coast, the relative caught biomass of S. dimorphus increased significantly from north to south, but there was no apparent latitudinal trend in relative biomass for P. bouvieri. Similarly, there was a significant decline in caught biomass of S. dimorphus with increasing longitude along the south coast, but no apparent trend for P. bouvieri. Although this represents by far the most comprehensive global analyses of distribution and abundance patterns for parapagurids to date, extremely little remains known about the biology and ecological relationships of these species, or indeed of other members of the group.  相似文献   

GIS与遥感支持下的南黄海辐射沙脊群现代演变趋势分析   总被引：4，自引：1，他引：4  

李海宇  王颖 《海洋科学》2002,26(9):61-65

南黄海辐射沙脊群是世界罕见的大型水下泥沙堆积体，具有独特的动力地貌组合。利用1988-1995年的LANDSATTM遥感影像，ERS1SAR影像及1979年编绘地形资料，综合应用GIS与遥感方法，对这一区域在20世纪80-90年代的变化及演变趋势作出分析，其基本演变特征与趋势表现为；沙脊群枢纽地区处于不断的增长，扩张过程；南部区域堆积与侵蚀作用较弱，沿岸潮滩向海淤进；而北部区域变化较强烈，并继续脊槽相间的模式，所取得的结果与该区域动力地貌研究结果相吻合。  相似文献