共查询到20条相似文献，搜索用时 31 毫秒
1.
Nachiketa Acharya Ankita Singh U. C. Mohanty Archana Nair Surajit Chattopadhyay 《Natural Hazards》2013,66(2):851-871
The drought during the months of June to September (JJAS) results in significant deficiency in the annual rainfall and affects the hydrological planning, disaster management, and the agriculture sector of India. Advance information on drought characteristics over the space may help in risk assessment over the country. This issue motivated the present study which deals with the prediction of drought during JJAS through standardized precipitation index (SPI) using nine general circulation models (GCM) product. Among these GCMs, three are the atmospheric and six are atmosphere–ocean coupled models. The performance of these GCM’s predicted SPI is examined against the observed SPI for the time period of 1982–2010. After a rigorous analysis, it can be concluded that the skill of prediction by GCM is not satisfactory, whereas the ability of the coupled models is better than the atmospheric models. An attempt has been made to improve the accuracy of predicted SPI using two different multi-model ensemble (MME) schemes, viz., arithmetic mean and weighted mean using singular value decomposition-based multiple linear regressions (SVD-MLR) of GCMs. It is found that among these MME techniques, SVD-MLR-based MME has more skill as compared to simple MME as well as individual GCMs. 相似文献
2.
NACHIKETA ACHARYA S C KAR MAKARAND A KULKARNI U C MOHANTY L N SAHOO 《Journal of Earth System Science》2011,120(5):795-805
The northeast (NE) monsoon season (October, November and December) is the major period of rainfall activity over south peninsular
India. This study is mainly focused on the prediction of northeast monsoon rainfall using lead-1 products (forecasts for the
season issued in beginning of September) of seven general circulation models (GCMs). An examination of the performances of
these GCMs during hindcast runs (1982–2008) indicates that these models are not able to simulate the observed interannual
variability of rainfall. Inaccurate response of the models to sea surface temperatures may be one of the probable reasons
for the poor performance of these models to predict seasonal mean rainfall anomalies over the study domain. An attempt has
been made to improve the accuracy of predicted rainfall using three different multi-model ensemble (MME) schemes, viz., simple arithmetic mean of models (EM), principal component regression (PCR) and singular value decomposition based multiple
linear regressions (SVD). It is found out that among these three schemes, SVD based MME has more skill than other MME schemes
as well as member models. 相似文献
3.
Probabilistic analysis has been used as an effective tool to evaluate uncertainty so prevalent in variables governing rock slope stability. In this study a probabilistic analysis procedure and related algorithms were developed by extending the Monte Carlo simulation. The approach was used to analyze rock slope stability for Interstate Highway 40 (I-40), North Carolina, USA. This probabilistic approach consists of two parts: analysis of available geotechnical data to obtain random properties of discontinuity parameters; and probabilistic analysis of slope stability based on parameters with random properties. Random geometric and strength parameters for discontinuities were derived from field measurements and analysis using the statistical inference method or obtained from experience and engineering judgment of parameters. Specifically, this study shows that a certain amount of experience and engineering judgment can be utilized to determine random properties of discontinuity parameters. Probabilistic stability analysis is accomplished using statistical parameters and probability density functions for each discontinuity parameter. Then, the two requisite conditions, kinematic and kinetic instability for evaluating rock slope stability, are determined and evaluated separately, and subsequently the two probabilities are combined to provide an overall stability measure. Following the probabilistic analysis to account for variation in parameters, results of the probabilistic analyses were compared to those of a deterministic analysis, illustrating deficiencies in the latter procedure. Two geometries for the cut slopes on I-40 were evaluated, the original 75° slope and the 50° slope which has developed over the past 40 years of weathering. 相似文献
4.
水位波动诱发岩溶塌陷的概率分析 总被引：8，自引：8，他引：0
水位波动诱发岩溶塌陷的概率问题可以简化为波动幅度、波动频率和波动时间3个随机变量的极值分布问题。随机变量的极值分布可以通过对水位监测数据进行频谱分析获得。桂林市柘木村水位波动诱发岩溶塌陷概率分析的结果表明: 柘木村2000年水位波动诱发岩溶塌陷的概率为7. 38% , 2001年为1. 47% , 2002年为16. 4%。分析结果与实际情况也比较吻合, 2002年6月柘木村一老塌陷复活,而2000和2001年则未发生塌陷,仅有部分土层发生扰动。因此可以用概率分析来判别某一时段内由水位波动而诱发岩溶塌陷的危险性大小,以便于分时段进行重点防治。 相似文献
5.
Ankita Singh Nachiketa Acharya Uma Charan Mohanty Gopbandhu Mishra 《Comptes Rendus Geoscience》2013,345(2):62-72
The emerging advances in the field of dynamical prediction of monsoon using state-of-the-art General Circulation Models (GCMs) have led to the development of various multi model ensemble techniques (MMEs). In the present study, the concept of Canonical Correlation Analysis is used for making MME (referred as Multi Model Canonical Correlation Analysis or MMCCA) for the prediction of Indian summer monsoon rainfall (ISMR) during June-July-August-September (JJAS). This method has been employed on the rainfall outputs of six different GCMs for the period 1982 to 2008. The prediction skill of ISMR by MMCCA is compared with the simple composite method (SCM) (i.e. arithmetic mean of all GCMs), which is taken as a benchmark. After a rigorous analysis through different skill metrics such as correlation coefficient and index of agreement, the superiority of MMCCA over SCM is illustrated. Performance of both models is also evaluated during six typical monsoon years and the results indicate the potential of MMCCA over SCM in capturing the spatial pattern during extreme years. 相似文献
6.
7.
With the development of regional climate simulation, CWRF, the new generation regional climate model, is increasingly used in climate research because of its advanced capability and high skill. The CWRF application in China was introduced from three aspects: its modifications of WRF physics parameterizations, the construction of modeling domain and lateral boundary conditions, the case simulation study and comparison with RegCM, illustrating the accuracy and advantage of CWRF in regional climate simulations. Furthermore, two major CWRF developmental prospects in China were explored: one was to incorporate more accurate physical parameterization schemes and optimized multi-physics ensemble approach; the other was to nest CWRF in GCMs for short-term climate operational forecast and long-term climate change prediction and impact assessment. The status of CWRF applications in China was summarized and the outlook of its further development was pointed out, which provided a meaningful reference for more general research and application. 相似文献
8.
岩土参数的随机性会直接影响边坡稳定性评价结果的精度。首先,依据边坡参数的常用分布特征,利用拉丁超立方抽样法生成若干组边坡土性参数和几何参数的随机样本,用有限元强度折减法求解各组样本对应的边坡安全系数。再考虑土性参数的空间变异性,在二维随机场模型下将蒙特卡罗模拟和有限元强度折减法相结合求解各组样本对应的边坡失效概率。然后,利用样本数据及其安全系数和失效概率对径向基函数（RBF）神经网络进行训练和测试,从而建立边坡安全系数和失效概率的预测模型。算例表明,二维随机场模型能相对精确地考虑参数的空间变异性;在此基础上建立的神经网络模型对边坡的安全系数和失效概率具有较高的预测精度,且能极大地节省边坡稳定性分析的时间。 相似文献
9.
Experimental real-time multi-model ensemble (MME) prediction of rainfall during monsoon 2008: Large-scale medium-range aspects 总被引：1，自引：0，他引：1
A K MITRA G R IYENGAR V R DURAI J SANJAY T N KRISHNAMURTI A MISHRA D R SIKKA 《Journal of Earth System Science》2011,120(1):27-52
Realistic simulation/prediction of the Asian summer monsoon rainfall on various space–time scales is a challenging scientific
task. Compared to mid-latitudes, a proportional skill improvement in the prediction of monsoon rainfall in the medium range
has not happened in recent years. Global models and data assimilation techniques are being improved for monsoon/tropics. However,
multi-model ensemble (MME) forecasting is gaining popularity, as it has the potential to provide more information for practical
forecasting in terms of making a consensus forecast and handling model uncertainties. As major centers are exchanging model
output in near real-time, MME is a viable inexpensive way of enhancing the forecasting skill and information content. During
monsoon 2008, on an experimental basis, an MME forecasting of large-scale monsoon precipitation in the medium range was carried
out in real-time at National Centre for Medium Range Weather Forecasting (NCMRWF), India. Simple ensemble mean (EMN) giving
equal weight to member models, bias-corrected ensemble mean (BCEMn) and MME forecast, where different weights are given to
member models, are the products of the algorithm tested here. In general, the aforementioned products from the multi-model
ensemble forecast system have a higher skill than individual model forecasts. The skill score for the Indian domain and other
sub-regions indicates that the BCEMn produces the best result, compared to EMN and MME. Giving weights to different models
to obtain an MME product helps to improve individual member models only marginally. It is noted that for higher rainfall values,
the skill of the global model rainfall forecast decreases rapidly beyond day-3, and hence for day-4 and day-5, the MME products
could not bring much improvement over member models. However, up to day-3, the MME products were always better than individual
member models. 相似文献
10.
11.
Progress in Researches on Ensemble Forecasting of Extreme Weather Based on Numerical Models 总被引：1，自引：1，他引：0
Under the background of climate change, extreme weather events (e.g., heavy rainfall, heat wave, and cold damage) in China have been occurring more frequently with an increasing trend of induced meteorological disasters. Therefore, it is of great importance to carry out research on forecasting of extreme weather. This paper systematically reviewed the primary methodology of extreme weather forecast, current status in development of ensemble weather forecasting based on numerical models and their applications to forecast of extreme weather, as well as progress in approaches for correcting ensemble probabilistic forecast. Nowadays, the forecasting of extreme weather has been generally dominated by methodology using dynamical models. That is to say, the dynamical forecasting methods based on ensemble probabilistic forecast information have become prevailing in current operational extreme weather forecast worldwide. It can be clearly found that the current major directions of research and development in this field are the application of ensemble forecasts based on numerical models to forecasting of extreme weather, and its improvement through bias correction of ensemble probabilistic forecast. Based on a relatively comprehensive review in this paper, some suggestions with respect to development of extreme weather forecast in future were further given in terms of the issues of how to propose effective approaches on improving level of identification and forecasting of extreme events. 相似文献
12.
Based on a consistent interpretation of earthquake occurrence as a stochastic process I demonstrate that the mathematical model of Probabilistic Seismic Hazard Analysis (PSHA) as it is in use today is inaccurate and leads to systematic errors in the calculation process. These mathematical errors may be regarded as an important contributor to the unrealistic results obtained by traditional PSHA for low probabilities of exceedance in recent projects. 相似文献
13.
Desmond Manatsa Leonard Unganai Christopher Gadzirai Swadhin K. Behera 《Natural Hazards》2012,64(2):1187-1207
Farmers?? adaptation to climate change over southern Africa may become an elusive concept if adequate attention is not rendered to the most important adaptive tool, the regional seasonal forecasting system. Uptake of the convectional seasonal rainfall forecasts issued through the southern African regional climate outlook forum process in Zimbabwe is very low, most probably due to an inherent poor forecast skill and inadequate lead time. Zimbabwe??s recurrent droughts are never in forecast, and the bias towards near normal conditions is almost perpetual. Consequently, the forecasts are poorly valued by the farmers as benefits accrued from these forecasts are minimal. The dissemination process is also very complicated, resulting in the late and distorted reception. The probabilistic nature of the forecast renders it difficult to interpret by the farmers, hence the need to review the whole system. An innovative approach to a regional seasonal forecasting system developed through a participatory process so as to offer a practically possible remedial option is described in this paper. The main added advantage over the convectional forecast is that the new forecast system carries with it, predominantly binary forecast information desperately needed by local farmers??whether a drought will occur in a given season. Hence, the tailored forecast is easier for farmers to understand and act on compared to the conventional method of using tercile probabilities. It does not only provide a better forecasting skill, but gives additional indications of the intra-seasonal distribution of the rainfall including onsets, cessations, wet spell and dry spell locations for specific terciles. The lead time is more than 3?months, which is adequate for the farmers to prepare their land well before the onset of the rains. Its simplicity renders it relatively easy to use, with model inputs only requiring the states of El Nino Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) climate modes. The developed forecast system could be one way to enhance management of risks and opportunities in rain-fed agriculture among small-holder farmers not only in Zimbabwe but also throughout the SADC region where the impact of ENSO and/or IOD on a desired station rainfall is significant. 相似文献
14.
空间尺度转换是近年来区域生态水文研究领域的一个基本研究问题。其需要主要是源于模型的输入数据与所能提供的数据空间尺度不一致以及模型所代表的地表过程空间尺度与所观测的地表过程空间尺度不吻合。综述了目前区域生态水文模拟研究中常用的空间尺度转换研究方法,包括向上尺度转换和向下尺度转换。详细论述了2种向下尺度转换方法: 统计学经验模型和动态模型。前者是通过将GCM大尺度数据与长期的历史观测数据比较从而建立统计学相关模型, 然后利用这个统计学经验模型进行向下的空间尺度转换. 然而动态模型并不直接对GCM数据进行向下尺度的转换,而是对与GCM进行动态耦合的区域气候模型(RCM) 的输出数据进行空间尺度转换. 通常后者所获得的数据精度要比前者高,但是一个主要缺点就是并不是全球所有的研究区域都有对应的RCM。还详细论述了2种向上尺度转换方法: 统计学经验模型和斑块模型。前者是建立一个能代表小尺度信息在大尺度上分布的密度分布概率函数, 然后利用这个函数在所需的大尺度上进行积分而求得大尺度所需的信息。而后者是根据相似性最大化原则将大尺度划分为若干个可操作的小尺度斑块,然后将计算的每个小尺度斑块的信息平均化得到大尺度所需的信息。通常在计算这种斑块化的小尺度信息的时候,对每个小尺度也会采用统计学经验模型来计算代表整个斑块小尺度的信息。建议用斑块模型与统计学经验模型相集合的方法来实现向上的空间尺度转换 相似文献
15.
Potential impacts of global warming on the frequency and magnitude of heavy precipitation 总被引：5，自引：0，他引：5
It is now widely recognised that the most significant impacts of global warming are likely to be experienced through changes in the frequency of extreme events, including flooding. This paper reviews physical and empirical arguments which suggest that global warming may result in a more intense hydrological cycle, with an associated increase in the frequency and/or magnitude of heavy precipitation. Results derived from enhanced-greenhouse experiments using global climate models (GCMs) are shown to be consistent with these physical and empirical arguments. Detailed analysis of output from three GCMs indicates the possibility of substantial increases in the frequency and magnitude of extreme daily precipitation, with amplification of the effect as the return period increases. Moreover, return period analyses for locations in Australia, Europe, India, China and the USA indicate that the results are global in scope. Subsequent discussion of the limitations of GCMs for this sort of analysis highlights the need for caution when interpreting the precipitation results presented here. However, the consistency between physically-based expectations, empirical observations, and GCM results is considered sufficient for the GCM results to be taken seriously, at least in a qualitative sense, especially considering that the alternative seems to be reliance by planners on the fundamentally flawed concept of a stationary climate. 相似文献
16.
Conceptual climate models, based on the workings of the present-day climate system, provided a first-order approach to ancient climate systems. They are potentially very subjective in character. Their main drawback was that they involved the relocation of continents beneath a stable atmospheric circulation modelled upon that of the present. General circulation models (GCMs) use the laws of physics and an understanding of past geography to simulate climatic responses. They are objective in character. However, they require super computers to handle vast numbers of calculations. Nonetheless it is now possible to compare results from different GCMs for a range of times and over a wide range of parameterisations. GCMs are currently producing simulated climate predictions which compare favourably with the distributions of climatically sensitive facies (e.g. coals, evaporites and palaeosols). They have been used effectively in the prediction of oceanic upwelling sites and the distribution of petroleum source-rocks and phosphorites. Parameterisation is the main weakness in GCMs (e.g. sea-surface temperature, orography, cloud behaviour). Sensitivity experiments can be run on GCMs which simulate the effects of Milankovitch forcing and thus provide insights into possible patterns of climate change both globally and locally (i.e. provide predictions that can be evaluated against the rock record). Future use of GCMs could be in the forward modelling of sequence stratigraphic evolution and in the prediction of the diagenetic characteristics of reservoir units in frontier exploration areas. The sedimentary record provides the only way that GCMs may themselves be evaluated and this is important because these same GCMs are being used currently to predict possible changes in future climate. 相似文献
17.
《Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy》2000,25(6-7):571-579
Assessments of the probability and the consequences of future volcanic activity can be critical aspects when evaluating the safety of the population and of industrial plants. A new methodology has been developed for the probabilistic modelling of volcanic hazards based on regional volcanic data that facilitates the production of probabilistic hazard maps for various volcanic scenarios (lava flows, tephra). The stochastic model is based on Cox processes and allows account to be taken of the observed temporal and spatial correlation inherent in volcanic eruptions. The model is applied to the Quaternary field of the Osteifel region where the forecast number of future eruptions and the probabilities related to the different scenarios are estimated using a Monte Carlo approach. The obtained hazard maps of future volcanic events are part of a comprehensive hazard analysis and serve as a major input for the risk analysis that will determine the consequences of forecast volcanic activity at the site. 相似文献
18.
The present study describes an analysis of Asian summer monsoon forecasts with an operational general circulation model (GCM)
of the European Centre for Medium Range Weather Forecasts (ECMWF), U.K. An attempt is made to examine the influence of improved
treatment of physical processes on the reduction of systematic errors. As some of the major changes in the parameterization
of physical processes, such as modification to the infrared radiation scheme, deep cumulus convection scheme, introduction
of the shallow convection scheme etc., were introduced during 1985–88, a thorough systematic error analysis of the ECMWF monsoon
forecasts is carried out for a period prior to the incorporation of such changes i.e. summer monsoon season (June–August)
of 1984, and for the corresponding period after relevant changes were implemented (summer monsoon season of 1988).
Monsoon forecasts of the ECMWF demonstrate an increasing trend of forecast skill after the implementation of the major changes
in parameterizations of radiation, convection and land-surface processes. Further, the upper level flow is found to be more
predictable than that of the lower level and wind forecasts display a better skill than temperature. Apart from this, a notable
increase in the magnitudes of persistence error statistics indicates that the monsoon circulation in the analysed fields became
more intense with the introduction of changes in the operational forecasting system.
Although, considerable reduction in systematic errors of the Asian summer monsoon forecasts is observed (up to day-5) with
the introduction of major changes in the treatment of physical processes, the nature of errors remain unchanged (by day-10).
The forecast errors of temperature and moisture in the middle troposphere are also reduced due to the changes in treatment
of longwave radiation. Moreover, the introduction of shallow convection helped it further by enhancing the vertical transports
of heat and moisture from the lower troposphere. Though, the hydrological cycle in the operational forecasts appears to have
enhanced with the major modifications and improvements to the physical parameterization schemes, certain regional peculiarities
have developed in the simulated rainfall distribution over the monsoon region. Hence, this study suggests further attempts
to improve the formulations of physical processes for further reduction of systematic forecast errors. 相似文献
19.
Naoyuki Kurita Kimpei Ichiyanagi Jun Matsumoto Manabu D. Yamanaka Tetsuo Ohata 《Journal of Geochemical Exploration》2009,102(3):113
General circulation models (GCMs) fitted with stable isotope schemes are widely used to interpret the isotope–climate relationship. However, previous studies have found that the spatiotemporal isotope/precipitation correlation simulated by GCMs is stronger and more widespread than the observed value. To understand the reason for this failure, we investigated the factors influencing the empirically well-known isotope/precipitation relationship, or precipitation amount effect, in the tropics using newly obtained daily precipitation isotope monitoring data over Asia. As in previous studies, we found an apparent correlation between the long-term monthly mean isotopic content and the corresponding precipitation amount (local precipitation) observed at sub-tropical island stations. Furthermore, on a monthly timescale, the isotopic variability of precipitation for these stations was more clearly related to the regional precipitation amount than to local precipitation. This correlation of isotopic content with the regional precipitation amount was observed at the equatorial (Maritime Continent) stations. For these stations, isotope/local precipitation relationships only appeared over longer timescales, with different regression line slopes at each station. However, at the coastal stations, there was a strong linear relationship between the monthly mean isotopic content and corresponding regional precipitation, and regression line slopes were spatially uniform. For the two sub-tropical terrestrial (Indochina Peninsula) stations, the isotopic minimum appeared without any relationship to rainfall amount but usually occurred at the leeward station during the rainy season. These results suggest that the isotopic variations of precipitation did not depend on the ’local’ rain-out history but on the rain-out process in the surrounding region. However, local rainfall events were associated not only with large-scale disturbances but also with regional circulation. Thus, the scale difference of controlling factors between local rainfall amount and isotopic value results in the weakening of the rainfall amount effect at the observation site and in the discrepancy between GCM simulations and observations. This finding suggests that regional precipitation–isotope relationships should be compared with GCM results. Additionally, because the isotope signal reflects the rain-out history at a regional scale, evaluation of the isotopic field using isotopic GCMs will be useful not only to reconstruct paleoclimate conditions but also to examine how GCMs can reproduce real atmospheric circulation over the tropics. 相似文献
20.
A Hidden Markov Model (HMM) has been developed for prediction of quantitative snowfall in Pir-Panjal and Great Himalayan mountain ranges of Indian Himalaya. The model predicts snowfall for two days in advance using daily recorded nine meteorological variables of past 20 winters from 1992–2012. There are six observations and six states of the model. The most probable observation and state sequence has been computed using Forward and Viterbi algorithms, respectively. Baum–Welch algorithm has been used for optimizing the model parameters. The model has been validated for two winters (2012–2013 and 2013–2014) by computing root mean square error (RMSE), accuracy measures such as percent correct (PC), critical success index (CSI) and Heidke skill score (HSS). The RMSE of the model has also been calculated using leave-one-out cross-validation method. Snowfall predicted by the model during hazardous snowfall events in different parts of the Himalaya matches well with the observed one. The HSS of the model for all the stations implies that the optimized model has better forecasting skill than random forecast for both the days. The RMSE of the optimized model has also been found smaller than the persistence forecast and standard deviation for both the days. 相似文献