共查询到20条相似文献,搜索用时 31 毫秒
1.
Tae-woong Kim Hosung Ahn Gunhui Chung Chulsang Yoo 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(6):705-717
This paper presents a stochastic model to generate daily rainfall occurrences at multiple gauging stations in south Florida.
The model developed in this study is a space–time model that takes into account the spatial as well as temporal dependences
of daily rainfall occurrence based on a chain-dependent process. In the model, a Markovian method was used to represent the
temporal dependence of daily rainfall occurrence and a direct acyclic graph (DAG) method was introduced to encode the spatial
dependence of daily rainfall occurrences among gauging stations. The DAG method provides an optimal sequence of generation
by maximizing the spatial dependence index of daily rainfall occurrences over the region. The proposed space–time model shows
more promising performance in generating rainfall occurrences in time and space than the conventional Markov type model. The
space–time model well represents the temporal as well as the spatial dependence of daily rainfall occurrences, which can reduce
the complexity in the generation of daily rainfall amounts. 相似文献
2.
E. Porcu P. Gregori J. Mateu 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(6):683-693
There is a great demand for statistical modeling of phenomena that evolve in both space and time, and thus, there is a growing
literature on correlation function models for spatio-temporal processes. In particular, various properties of these correlation
functions have been studied only for the merely spatial or temporal case, fact that constitutes a strong motivation for our
work. The goal of this paper is to inspect some properties, obtained with respect to partial differentiation and integration,
of stationary spatio-temporal correlation functions for which anisotropy is obtained through isotropy between components as
in Fernández-Casal et al. (Stat Comput 13(2):127–136, 2003). We show that through partial differentiation and integration it is possible to obtain permissible spatio-temporal correlation
functions in the space–time domain. Other new results regard specific classes of space–time correlations introduced in recent
literature. A curious result arises by differentiating scale mixtures of Euclid’s hat.
Work partially funded by grant MTM2004-06231 from the Spanish Ministery of Science and Education. 相似文献
3.
Jaymie R. Meliker Geoffrey M. Jacquez 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(5):625-634
Our research group recently developed Q-statistics for evaluating space–time clustering in case–control studies with residential histories. This technique relies
on time-dependent nearest-neighbor relationships to examine clustering at any moment in the life-course of the residential
histories of cases relative to that of controls. In addition, in place of the widely used null hypothesis of spatial randomness,
each individual’s probability of being a case is based instead on his/her risk factors and covariates. In this paper, we extend
this approach to illustrate how alternative temporal orientations (e.g., years prior to diagnosis/recruitment, participant’s
age, and calendar year) influence a spatial clustering pattern. These temporal orientations are valuable for shedding light
on the duration of time between clustering and subsequent disease development (known as the empirical induction period), and
for revealing age-specific susceptibility windows and calendar year-specific effects. An ongoing population-based bladder
cancer case–control study is used to demonstrate this approach. Data collection is currently incomplete and therefore no inferences
should be drawn; we analyze these data to demonstrate these novel methods. Maps of space–time clustering of bladder cancer
cases are presented using different temporal orientations while accounting for covariates and known risk factors. This systematic
approach for evaluating space–time clustering has the potential to generate novel hypotheses about environmental risk factors
and provides insights into empirical induction periods, age-specific susceptibility, and calendar year-specific effects. 相似文献
4.
Many hydrological and agricultural studies require simulations of weather variables reflecting observed spatial and temporal dependence at multiple point locations. This paper assesses three multi-site daily rainfall generators for their ability to model different spatio-temporal rainfall attributes over the study area. The approaches considered consist of a multi-site modified Markov model (MMM), a reordering method for reconstructing space–time variability, and a nonparametric k-nearest neighbour (KNN) model. Our results indicate that all the approaches reproduce adequately the observed spatio-temporal pattern of the multi-site daily rainfall. However, different techniques used to signify longer time scale observed temporal and spatial dependences in the simulated sequences, reproduce these characteristics with varying successes. While each approach comes with its own advantages and disadvantages, the MMM has an overall advantage in offering a mechanism for modelling varying orders of serial dependence at each point location, while still maintaining the observed spatial dependence with sufficient accuracy. The reordering method is simple and intuitive and produces good results. However, it is primarily driven by the reshuffling of the simulated values across realisations and therefore may not be suited in applications where data length is limited or in situations where the simulation process is governed by exogenous conditioning variables. For example, in downscaling studies where KNN and MMM can be used with confidence. 相似文献
5.
Pingping Zhang 《水文科学杂志》2013,58(1):96-110
AbstractKnowledge of the variability of soil water content (SWC) in space and time plays a key role in hydrological and climatic modelling. However, limited attention has been given to arid regions. The focus of this study was to investigate the spatio-temporal variability of surface soil (0–6 cm) water content and to identify its controlling factors in a region of the Gobi Desert (40 km2). The standard deviation of SWC decreased logarithmically as mean water content decreased, and the coefficient of variation of SWC exhibited a convex upward pattern. The spatial variability of SWC also increased with the size of the investigated area. The spatial dependence of SWC changed over time, with stronger patterns of spatial organization in drier and wetter conditions of soil wetness and stochastic patterns in moderate soil water conditions. The dominant factors regulating the variability of SWC changed from combinations of soil and topographical properties (bulk density, clay content and relative elevation) in wet conditions to combinations of soil and vegetation properties (bulk density, clay content and shrub coverage) in dry conditions. This study has important implications for the assessment of soil quality and the sustainability of land management in arid regions. 相似文献
6.
John H. Cushman Moongyu Park Monica Moroni Natalie Kleinfelter-Domelle Daniel O��Malley 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(1):1-10
When formulated properly, most geophysical transport-type process involving passive scalars or motile particles may be described
by the same space–time nonlocal field equation which consists of a classical mass balance coupled with a space–time nonlocal
convective/dispersive flux. Specific examples employed here include stretched and compressed Brownian motion, diffusion in
slit-nanopores, subdiffusive continuous-time random walks (CTRW), super diffusion in the turbulent atmosphere and dispersion
of motile and passive particles in fractal porous media. Stretched and compressed Brownian motion, which may be thought of
as Brownian motions run with nonlinear clocks, are defined as the limit processes of a special class of random walks possessing
nonstationary increments. The limit process has a mean square displacement that increases as tα+1 where α > −1 is a constant. If α = 0 the process is classical Brownian, if α < 0 we say the process is compressed Brownian while
if α > 0 it is stretched. The Fokker–Planck equations for these processes are classical ade’s with dispersion coefficient
proportional to tα. The Brownian-type walks have fixed time step, but nonstationary spatial increments that are Gaussian with power law variance.
With the CTRW, both the time increment and the spatial increment are random. The subdiffusive Fokker–Planck equation is fractional
in time for the CTRW’s considered in this article. The second moments for a Levy spatial trajectory are infinite while the
Fokker–Planck equation is an advective–dispersive equation, ade, with constant diffusion coefficient and fractional spatial
derivatives. If the Lagrangian velocity is assumed Levy rather than the position, then a similar Fokker–Planck equation is
obtained, but the diffusion coefficient is a power law in time. All these Fokker–Planck equations are special cases of the
general non-local balance law. 相似文献
7.
Amir H. Hosseini Clayton V. Deutsch Kevin W. Biggar Carl A. Mendoza 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(5):735-749
The spatial distribution of residual light non-aqueous phase liquid (LNAPL) is an important factor in reactive solute transport
modeling studies. There is great uncertainty associated with both the areal limits of LNAPL source zones and smaller scale
variability within the areal limits. A statistical approach is proposed to construct a probabilistic model for the spatial
distribution of residual NAPL and it is applied to a site characterized by ultra-violet-induced-cone-penetration testing (CPT–UVIF).
The uncertainty in areal limits is explicitly addressed by a novel distance function (DF) approach. In modeling the small-scale
variability within the areal limits, the CPT–UVIF data are used as primary source of information, while soil texture and distance
to water table are treated as secondary data. Two widely used geostatistical techniques are applied for the data integration,
namely sequential indicator simulation with locally varying means (SIS–LVM) and Bayesian updating (BU). A close match between
the calibrated uncertainty band (UB) and the target probabilities shows the performance of the proposed DF technique in characterization
of uncertainty in the areal limits. A cross-validation study also shows that the integration of the secondary data sources
substantially improves the prediction of contaminated and uncontaminated locations and that the SIS–LVM algorithm gives a
more accurate prediction of residual NAPL contamination. The proposed DF approach is useful in modeling the areal limits of
the non-stationary continuous or categorical random variables, and in providing a prior probability map for source zone sizes
to be used in Monte Carlo simulations of contaminant transport or Monte Carlo type inverse modeling studies. 相似文献
8.
Hwa-Lung Yu Alexander Kolovos George Christakos Jiu-Chiuan Chen Steve Warmerdam Boris Dev 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(5):647-572
This paper describes the spatiotemporal epistematics knowledge synthesis and graphical user interface (SEKS–GUI) framework
and its application in medical geography problems. Based on sound theoretical reasoning, the interactive software library
of SEKS–GUI explores heterogeneous (spatially non-homogeneous and temporally non-stationary) health attribute distributions
(disease incidence, mortality, human exposure, epidemic propagation etc.); expresses the health system’s dependence structure
using (ordinary and generalized) spatiotemporal covariance models; synthesizes core knowledge bases, empirical evidence and
multi-sourced system uncertainty; and generates a meaningful picture of the real-world system using space–time dependent probability
functions and associated maps of health attributes. The implementation stages of the SEKS–GUI library are described in considerable
detail using appropriate screens. The wide applicability of SEKS–GUI is demonstrated by reviewing a selection of real-world
case studies.
An erratum to this article can be found at 相似文献
9.
An automatic scheme for baseline correction of strong-motion records in coseismic deformation determination 总被引:2,自引:0,他引:2
Coseismic deformation can be determined from strong-motion records of large earthquakes. Iwan et al. (Bull Seismol Soc Am
75:1225–1246, 1985) showed that baseline corrections are often required to obtain reliable coseismic deformation because baseline offsets lead
to unrealistic permanent displacements. Boore (Bull Seismol Soc Am 91:1199–1211, 2001) demonstrated that different choices of time points for baseline correction can yield realistically looking displacements,
but with variable amplitudes. The baseline correction procedure of Wu and Wu (J Seismol 11:159–170, 2007) improved upon Iwan et al. (Bull Seismol Soc Am 75:1225–1246, 1985) and achieved stable results. However, their time points for baseline correction were chosen by a recursive process with
an artificial criterion. In this study, we follow the procedure of Wu and Wu (J Seismol 11:159–170, 2007) but use the ratio of energy distribution in accelerograms as the criterion to determine the time points of baseline correction
automatically, thus avoiding the manual choice of time points and speeding up the estimation of coseismic deformation. We
use the 1999 Chi-Chi earthquake in central Taiwan and the 2003 Chengkung and 2006 Taitung earthquakes in eastern Taiwan to
illustrate this new approach. Comparison between the results from this and previous studies shows that our new procedure is
suitable for quick and reliable determination of coseismic deformation from strong-motion records. 相似文献
10.
Seung-Jae Lee Elizabeth A. Wentz Patricia Gober 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(2):283-295
Managing environmental and social systems in the face of uncertainty requires the best possible forecasts of future conditions.
We use space–time variability in historical data and projections of future population density to improve forecasting of residential
water demand in the City of Phoenix, Arizona. Our future water estimates are derived using the first and second order statistical
moments between a dependent variable, water use, and an independent variable, population density. The independent variable
is projected at future points, and remains uncertain. We use adjusted statistical moments that cover projection errors in
the independent variable, and propose a methodology to generate information-rich future estimates. These updated estimates
are processed in Bayesian Maximum Entropy (BME), which produces maps of estimated water use to the year 2030. Integrating
the uncertain estimates into the space–time forecasting process improves forecasting accuracy up to 43.9% over other space–time
mapping methods that do not assimilate the uncertain estimates. Further validation studies reveal that BME is more accurate
than co-kriging that integrates the error-free independent variable, but shows similar accuracy to kriging with measurement
error that processes the uncertain estimates. Our proposed forecasting method benefits from the uncertain estimates of the
future, provides up-to-date forecasts of water use, and can be adapted to other socio-economic and environmental applications. 相似文献
11.
Long-term time-dependent stochastic modelling of extreme waves 总被引:4,自引:3,他引:1
Erik Vanem 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(2):185-209
This paper presents a literature survey on time-dependent statistical modelling of extreme waves and sea states. The focus
is twofold: on statistical modelling of extreme waves and space- and time-dependent statistical modelling. The first part
will consist of a literature review of statistical modelling of extreme waves and wave parameters, most notably on the modelling
of extreme significant wave height. The second part will focus on statistical modelling of time- and space-dependent variables
in a more general sense, and will focus on the methodology and models used also in other relevant application areas. It was
found that limited effort has been put on developing statistical models for waves incorporating spatial and long-term temporal
variability and it is suggested that model improvements could be achieved by adopting approaches from other application areas.
In particular, Bayesian hierarchical space–time models were identified as promising tools for spatio-temporal modelling of
extreme waves. Finally, a review of projections of future extreme wave climate is presented. 相似文献
12.
F. Martínez-Ruiz J. Mateu F. Montes E. Porcu 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(4):519-526
Dynamic life tables arise as an alternative to the standard (static) life tables with the aim of incorporating the evolution
of mortality over time. These tables can be considered as a two-way table on a grid equally spaced in either the vertical
(age) or horizontal (year) directions, and the data can be decomposed into a deterministic large-scale variation (trend) plus
a stochastic small-scale variation (residuals). In this context, space–time geostatistical methods can be used for fitting
and predicting the dynamic mortality. We use four different space–time covariance functions for fitting and predicting mortality
in Spain during the period 1980–2005. In particular, we aim at showing the behavior of separable versus nonseparable fitted
structures on one hand, and the behavior of simple structures given by combinations of products and sums versus more complicated
negative structures on the other hand. 相似文献
13.
Yongqin David Chen Tao Yang Chong-Yu Xu Qiang Zhang Xi Chen Zhen-Chun Hao 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(1):9-18
This paper presents a visually enhanced evaluation of the spatio-temporal patterns of the dam-induced hydrologic alteration
in the middle and upper East River, south China over 1952–2002, using the range of variability approach (RVA) and visualization
package XmdvTool. The impacts of climate variability on hydrological processes have been removed for wet and dry periods,
respectively, so that we focus on the impacts of human activities (i.e., dam construction). The results indicate that: (1)
along the East River, dams have greatly altered the natural flow regime, range condition and spatial variability; (2) six
most remarkable indicators of hydrologic alteration induced by dam-construction are rise rate (1.16), 3-day maximum (0.91),
low pulse duration (0.88), January (0.80), July (0.80) and February (0.79) mean flow of the East River during 1952–2002; and
(3) spatiotemporal hydrologic alterations are different among three stations along Easter River. Under the influence of dam
construction in the upstream, the degree of hydrologic changes from Lingxia, Heyuan to Longchuan station increases. This study
reveals that visualization techniques for high-dimensional hydrological datasets together with RVA are beneficial for detecting
spatio-temporal hydrologic changes. 相似文献
14.
Long-term trends in the ocean wave climate because of global warming are of major concern to many stakeholders within the
maritime industries, and there is a need to take severe sea state conditions into account in design of marine structures and
in marine operations. Various stochastic models of significant wave height are reported in the literature, but most are based
on point measurements without exploiting the flexible framework of Bayesian hierarchical space–time models. This framework
allows modelling of complex dependence structures in space and time and incorporation of physical features and prior knowledge,
yet remains intuitive and easily interpreted. This paper presents a Bayesian hierarchical space–time model with a log-transform
for significant wave height data for an area in the North Atlantic ocean. The different components of the model will be outlined,
and the results from applying the model to data of different temporal resolutions will be discussed. Different model alternatives
have been tried and long-term trends in the data have been identified for all model alternatives. Overall, these trends are
in reasonable agreement and also agree fairly well with previous studies. The log-transform was included in order to account
for observed heteroscedasticity in the data, and results are compared to previous results where a similar model was employed
without a log-transform. Furthermore, a discussion of possible extensions to the model, e.g. incorporating regression terms
with relevant meteorological data, will be presented. 相似文献
15.
E. Porcu P. Gregori J. Mateu 《Stochastic Environmental Research and Risk Assessment (SERRA)》2006,21(2):113-122
Obtaining new and flexible classes of nonseparable spatio-temporal covariances and variograms has resulted a key point of research in the last years. The goal of this paper is to introduce and develop new spatio-temporal covariance models taking into account the problem of spatial anisotropy. Recent literature has focused on the problem of full symmetry and the problem of anisotropy has been overcome. Here we propose a generalization of Gneiting’s (J Am Stat Assoc 97:590–600, 2002a) approach and obtain new classes of stationary nonseparable spatio-temporal covariance functions which are spatially anisotropic. The resulting structures are proved to have certain interesting mathematical properties, together with a considerable applicability.Work partially funded by grant MTM2004-06231 from the Spanish Ministry of Science and Education. 相似文献
16.
Regional frequency analysis of rainfall extremes in Southern Malawi using the index rainfall and L-moments approaches 总被引:3,自引:1,他引:2
Cosmo S. Ngongondo Chong-Yu Xu Lena M. Tallaksen Berhanu Alemaw Tobias Chirwa 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(7):939-955
Rainfall extremes often result in the occurrence of flood events with associated loss of life and infrastructure in Malawi.
However, an understanding of the frequency of occurrence of such extreme events either for design or disaster planning purposes
is often limited by data availability at the desired temporal and spatial scales. Regionalisation, which involves “trading
time for space” by pooling together observations for stations with similar behavior, is an alternative approach for more accurate
determination of extreme events even at ungauged areas or sites with short records. In this study, regional frequency analysis
of rainfall extremes in Southern Malawi, large parts of which are flood prone, was undertaken. Observed 1-, 3-, 5- and 7-day
annual maximum rainfall series for the period 1978–2007 at 23 selected rainfall stations in Southern Malawi were analysed.
Cluster analysis using scaled at-site characteristics was used to determine homogeneous rainfall regions. L-moments were applied
to derive regional index rainfall quantiles. The procedure also validated the three rainfall regions identified through homogeneity
and heterogeneity tests based on Monte Carlo simulations with regional average L-moment ratios fitted to the Kappa distribution.
Based on assessments of the accuracy of the derived index rainfall quantiles, it was concluded that the performance of this
regional approach was satisfactory when validated for sites not included in the sample data. The study provides an estimate
of the regional characteristics of rainfall extremes that can be useful in among others flood mitigation and engineering design. 相似文献
17.
Spatio-temporal estimation of precipitation over a region is essential to the modeling of hydrologic processes for water resources management. The changes of magnitude and space–time heterogeneity of rainfall observations make space–time estimation of precipitation a challenging task. In this paper we propose a Box–Cox transformed hierarchical Bayesian multivariate spatio-temporal interpolation method for the skewed response variable. The proposed method is applied to estimate space–time monthly precipitation in the monsoon periods during 1974–2000, and 27-year monthly average precipitation data are obtained from 51 stations in Pakistan. The results of transformed hierarchical Bayesian multivariate spatio-temporal interpolation are compared to those of non-transformed hierarchical Bayesian interpolation by using cross-validation. The software developed by [11] is used for Bayesian non-stationary multivariate space–time interpolation. It is observed that the transformed hierarchical Bayesian method provides more accuracy than the non-transformed hierarchical Bayesian method. 相似文献
18.
Gabriel Kuhn Shiraj Khan Auroop R. Ganguly Marcia L. Branstetter 《Advances in water resources》2007,30(12):2401-2423
A quantification of the spatio-temporal dependence among precipitation extremes is important for investigating the properties of intense storms as well as flood or flash-flood related hazards. Extreme value theory has been widely applied to the hydrologic sciences and hydraulic engineering. However, rigorous approaches to quantify dependence structures among extreme values in space and time have not been reported in the literature. Previous researchers have quantified the dependence among extreme values through the concept of (pairwise bivariate) tail dependence coefficients. For estimation of the tail dependence coefficients, we apply a recently developed method [Kuhn G. On dependence and extremes. PhD thesis (Advisor: C. Klüppelberg), Munich University of Technology, 2006] which utilized the multivariate tail dependence function of a subclass of elliptical copulas. This study extends the previous approach in the context of space and time by considering pairs of spatial grids in South America and quantifying the dependence among precipitation extremes based on the time series at each spatial grid. In addition, Kendall’s τ is used to estimate the pairwise copula correlation (for an elliptical copula) of precipitation between all grids in South America. The geospatial–temporal dependence measures are applied to precipitation observations from 1940 to 2005 as well as simulations from the Community Climate System Model version 3 (CCSM3) for 1940–2099. New insights are obtained regarding the spatio-temporal dependence structures for precipitation over South America both with regard to correlation as well as tail dependence. 相似文献
19.
The 3 310-m-high Chia-min Lake records the climatic history since 4 ka B. P. in Taiwan. The warm/wet period before 2.2 ka
B.P. seemed to correspond to the later part of the Holocene Megathermal, and the cold/dry period during 0–2.2 ka B. P. corresponded
to the Katathermal. Before the termination of the Megathermal, an especially warm and humid segment (2.2–2.4 ka B. P.) emerged.
The paleoclimatic records from Yuen-yang and Chi-tsai Lakes support the notion that the Megathermal in Taiwan terminated during
2—2.3 ka B. P. A warm segment (820–1 320 AD) in the Katathermal could be considered the Medieval Warm Period. The climate
turned cold and dry after 1 320 AD and this indicated the onset of the Little Ice Age. These paleoclimatic variations are
also in good agreement with those recorded in Great Ghost Lake. 相似文献
20.
Validation and use of rainfall radar data to simulate water flows in the Rio Escondido basin 总被引:2,自引:1,他引:1
Sami Eleuch Alin Carsteanu Khalidou Bâ Ramata Magagi Kalifa Goïta Carlos Diaz 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(5):559-565
This paper presents a combined validation method of radar-sensed rainfall, using rain gauge data and hydrologic closure, with
an application to the Rio Escondido basin (North-East of Mexico). The space–time scaling behavior of rainfall between rain
gauge and radar scales is compared with the intrinsic variability of rainfall, for a statistical validation of space–time
variability. For hydrological validation purposes, the CEQUEAU model is used to perform rainfall-runoff routing. It provides a basin-wide water balance, to be compared with the measured
water flow at the Villa de Fuentes hydrometric station, for mean-value gauging closure. A good qualitative agreement in terms
of hydrograph shape and timing is obtained between the simulated and the observed water flows, and a multiplicative correction
factor of an initially proposed Z–R relationship is adopted for the watershed under study, which agrees approximately with
other authors’ findings about that relationship. The results are considered particularly useful as a validation-and-correction
methodology of radar rainfall estimates for areas sparsely covered by rain gauges. 相似文献