Spatial analysis of daily rainfall intensity and concentration index in Peninsular Malaysia

This study presents the spatial analysis of daily rainfall intensity and concentration index over Peninsular Malaysia. Daily rainfall data from 50 rainfall stations are used in this study. Due to the limited number of stations, the geostatistical method of ordinary kriging is used to compute the values of daily rainfall concentration and intensity and to map their spatial distribution. The resultant analysis of rainfall concentration indicated that the distribution of daily rainfall is more regular over the west, northwest and southwest regions compared to the east. Large areas of the eastern Peninsula display an irregularity in distribution of daily rainfall. In terms of number of rainy days, analysis of daily rainfall confirms that a large number of rainy days across the Peninsula arise from low-intensity events but only contribute a small percentage of total rain. On the other hand, a low frequency of rainy days with high-intensity events contributes the largest percentage of total rain. The results indicated that the total rain in eastern areas is mainly contributed by the high-intensity events. This finding explains the occurrence of a large number of floods and soil erosions in these areas. Therefore, precautionary measures should be taken earlier to prevent any massive destruction of property and loss of life due to the hazards. These research findings are of considerable importance in providing enough information to water resource management, climatologists and agriculturists as well as hydrologists for planning their activities and modelling processes.     

Relative performance of CMIP5 and CMIP6 models in simulating rainfall in Peninsular Malaysia

Theoretical and Applied Climatology - This study evaluated the skills of global climate models (GCMs) of the fifth and sixth Coupled Model Intercomparison Project (CMIP5 and CMIP6) in simulating...     

Regional analysis of annual maximum rainfall using TL-moments method

Information related to distributions of rainfall amounts are of great importance for designs of water-related structures. One of the concerns of hydrologists and engineers is the probability distribution for modeling of regional data. In this study, a novel approach to regional frequency analysis using L-moments is revisited. Subsequently, an alternative regional frequency analysis using the TL-moments method is employed. The results from both methods were then compared. The analysis was based on daily annual maximum rainfall data from 40 stations in Selangor Malaysia. TL-moments for the generalized extreme value (GEV) and generalized logistic (GLO) distributions were derived and used to develop the regional frequency analysis procedure. TL-moment ratio diagram and Z-test were employed in determining the best-fit distribution. Comparison between the two approaches showed that the L-moments and TL-moments produced equivalent results. GLO and GEV distributions were identified as the most suitable distributions for representing the statistical properties of extreme rainfall in Selangor. Monte Carlo simulation was used for performance evaluation, and it showed that the method of TL-moments was more efficient for lower quantile estimation compared with the L-moments.     

Fitting optimum order of Markov chain models for daily rainfall occurrences in Peninsular Malaysia

The analysis of the daily rainfall occurrence behavior is becoming more important, particularly in water-related sectors. Many studies have identified a more comprehensive pattern of the daily rainfall behavior based on the Markov chain models. One of the aims in fitting the Markov chain models of various orders to the daily rainfall occurrence is to determine the optimum order. In this study, the optimum order of the Markov chain models for a 5-day sequence will be examined in each of the 18 rainfall stations in Peninsular Malaysia, which have been selected based on the availability of the data, using the Akaike’s (AIC) and Bayesian information criteria (BIC). The identification of the most appropriate order in describing the distribution of the wet (dry) spells for each of the rainfall stations is obtained using the Kolmogorov-Smirnov goodness-of-fit test. It is found that the optimum order varies according to the levels of threshold used (e.g., either 0.1 or 10.0 mm), the locations of the region and the types of monsoon seasons. At most stations, the Markov chain models of a higher order are found to be optimum for rainfall occurrence during the northeast monsoon season for both levels of threshold. However, it is generally found that regardless of the monsoon seasons, the first-order model is optimum for the northwestern and eastern regions of the peninsula when the level of thresholds of 10.0 mm is considered. The analysis indicates that the first order of the Markov chain model is found to be most appropriate for describing the distribution of wet spells, whereas the higher-order models are found to be adequate for the dry spells in most of the rainfall stations for both threshold levels and monsoon seasons.     

The spatial distribution of annual rainfall in Israel — a review

Summary This paper summarizes relevant studies dealing with the analysis of the annual rainfall map of Israel. With the aid of multiple regression analysis it was possible to quantify the contribution of each of the five geographical factors determining the annual rainfall map. Although the variance of the north-south component on the rainfall map looks most impressive, the orographic factor seems to be the more important contributor. The contribution of the spatially discrete urban factor has to be isolated from the deliberated cloud seeding augmentation. The statistical tools, spatial regression model and distance correlation matrix technique, were applied for the Central Coastal Plain and the Haifa area downwind, respectively. By applying sophisticated remote sensing methods, it was possible to classify and determine the rainfall yields of the variety of cloud formations appearing in the cold air mass following the cold front.With 8 Figures     

基于三参数Weibull分布的安徽省年最大风速均一性检验

以安徽省56个国家级气象站1980—2018年年最大风速序列为研究对象,采用基于三参数Weibull分布的变点检验方法对年最大风速序列均一性进行检验,以郎溪站数据为例,给出了检验和分析的具体过程,最后将该方法检验结果与PM-FT法、SNHT法检验结果进行了对比分析.结果表明:56个站点的年最大风速序列均通过Weibul...     

An analysis of annual maximum streamflows in Terengganu, Malaysia using TL-moments approach

TL-moments approach has been used in an analysis to determine the best-fitting distributions to represent the annual series of maximum streamflow data over 12 stations in Terengganu, Malaysia. The TL-moments with different trimming values are used to estimate the parameter of the selected distributions namely: generalized pareto (GPA), generalized logistic, and generalized extreme value distribution. The influence of TL-moments on estimated probability distribution functions are examined by evaluating the relative root mean square error and relative bias of quantile estimates through Monte Carlo simulations. The boxplot is used to show the location of the median and the dispersion of the data, which helps in reaching the decisive conclusions. For most of the cases, the results show that TL-moments with one smallest value was trimmed from the conceptual sample (TL-moments (1,0)), of GPA distribution was the most appropriate in majority of the stations for describing the annual maximum streamflow series in Terengganu, Malaysia.     

Statistical analysis of annual maximum rainfall in North-East India: an application of LH-moments

An attempt has been made to determine the best fitting distribution to describe the annual series of maximum daily rainfall data for the period 1966 to 2007 of nine distantly located stations in North East India. The LH-moments of order zero (L) to order four (L₄) are used to estimate the parameters of three extreme value distributions viz. generalized extreme value distribution (GEV), generalized logistic distribution (GLD), and generalized Pareto distribution (GPD). The performances of the distributions are assessed by evaluating the relative bias (RBIAS) and relative root mean square error (RRMSE) of quantile estimates through Monte Carlo simulations. Then, the boxplot is used to show the location of the median and the associated dispersion of the data. Finally, it can be revealed from the results of boxplots that zero level of LH-moments of the generalized Pareto distribution would be appropriate to the majority of the stations for describing the annual maximum rainfall series in North East India.     

利用对数正态分布计算年最大风速

本文提出用对数正态分布计算年最大风速,这种方法与当前使用的计算方法主要的不同是,它具有较完善的子样检验方法,并且能计算最大风速的容忍上限。     

Statistical distributions of extreme dry spell in Peninsular Malaysia

Statistical distributions of annual extreme (AE) series and partial duration (PD) series for dry-spell event are analyzed for a database of daily rainfall records of 50 rain-gauge stations in Peninsular Malaysia, with recording period extending from 1975 to 2004. The three-parameter generalized extreme value (GEV) and generalized Pareto (GP) distributions are considered to model both series. In both cases, the parameters of these two distributions are fitted by means of the L-moments method, which provides a robust estimation of them. The goodness-of-fit (GOF) between empirical data and theoretical distributions are then evaluated by means of the L-moment ratio diagram and several goodness-of-fit tests for each of the 50 stations. It is found that for the majority of stations, the AE and PD series are well fitted by the GEV and GP models, respectively. Based on the models that have been identified, we can reasonably predict the risks associated with extreme dry spells for various return periods.     

江苏省年最大风速的时空分布及突变分析

根据江苏省34a年最大风速资料,用EOF、REOF方法研究了江苏省年最大风速的空间分布形式和长期变化趋势。结果表明:(1)34a年最大风速基本在11m/s以上,其中最大值区位于盐城的南部和南通的北部,在15m/s以上。近34a来具有明显的波动,整体上呈减小的趋势。(2)EOF分解的第一特征向量场空间分布绝大部分为正值,说明其变化具有极好的一致性,第一时间系数的变化相当于年变化。但是各特征向量场之间的特点相差明显。(3)REOF分析方法表明其可以被分为5个区,分别为西北区、西南区、东南区、中部地区、东北区,各个区域的年最大风速均呈现减小的趋势,但是减小的程度各不相同。突变特征各个区域表现也不同。     

基于GIS的气象要素空间分布拟合

根据四川复杂的气候和地形特点,针对不同的气象要素,分别采用最优子集回归分区域建立分布模式,再利用GIS合并方法,GIS三次样条插值方法等方法来拟合四川省的气象要素空间分布,其结果精确、合理,误差小,已在四川省气候资源开发利用和农业气候区划中得到验证和应用.     

基于GIS的气象要素空间分布拟合

根据四川复杂的气候和地形特点，针对不同的气象要素，分别采用最优子集回归分区域建立分布模式，再利用GIS合并方法，GIS三次样条插值方法等方法来拟合四川省的气象要素空间分布，其结果精确、合理，误差小，已在四川省气候资源开发利用和农业气候区划中得到验证和应用。     

Seasonal distribution of rainfall in Australia analysed by Fourier methods

Summary A harmonic or Fourier analysis of mean monthly rainfall data is found useful in objectively describing and mapping the seasonality of rainfall within Australia. Over large areas the seasonal component is well described by the first and second harmonic terms, leaving as a residual variance only a small proportion of the observed total variance. Care must be taken in the interpretation of second harmonic contributions within those areas of tropical Australia under strong monsoonal influences. This is because pecularities in the form of the annual rainfall regime make the first harmonic term inadequate in itself to fully describe the annual trend. The technique is found particularly useful in defining the boundaries of areas of similar seasonality, and maps based upon the first and second harmonic amplitudes are shown to bear a close relationship with known physical controls.

---

Zusammenfassung Zur objektiven Beschreibung der jahreszeitlichen Schwankung der Regenfälle in Australien und ihrer kartenmäßigen Darstellung wird mit Erfolg die harmonische Analyse der mittleren Monatsmengen des Niederschlags angewendet. Über weiten Gebieten wird die jahreszeitliche Schwankung durch die ersten beiden harmonischen Schwingungen gut dargestellt; die Reststreuung macht nur einen kleinen Bruchteil der beobachteten Gesamtstreuung aus. Vorsicht erscheint jedoch geboten bei der Interpretation des Anteils der zweiten Harmonischen in den Gebieten des tropischen Australien, die unter starkem Monsuneinfluß stehen. Hier machen Besonderheiten im Niederschlagsregime selbst die erste Harmonische ungenügend zur Beschreibung des Jahresganges. Die angewandte Methode ist besonders geeignet, die Grenzen zwischen Gebieten mit gleichartigem Jahreszeiteneinfluß festzulegen. Karten, die auf der ersten und zweiten harmonischen Schwingung beruhen, zeigen einen engen Zusammenhang mit bekannten physikalischen Faktoren.

---

Résumé Afin de décrire objectivement les variations saisonnières des précipitations en Australie, on se sert avantageusement de l'analyse harmonique des sommes mensuelles moyennes. Cette méthode est également utilisée pour la représentation cartographique des dites variations. Les amplitudes saisonnières sont bien rendues par les deux premières harmoniques et cela pour de grandes étendues. L'amplitude qui reste ne représente qu'une faible fraction de l'amplitude totale observée. Il faut cependant procéder avec prudence lors de l'interprétation de la part revenant à la seconde harmonique dans les contrées tropicales de l'Australie, contrées qui subissent fortement l'influence de la mousson. Dans ce cas précis, les particularités du régime des précipitations ne permettent même pas d'utiliser la première harmonique pour décrire l'évolution des pluies au cours de l'année. La méthode proposée est surtout intéressante pour délimiter les régions soumises aux mêmes régimes. Des cartes basées sur la première et la seconde harmonique montrent un rapport étroit entre les précipitations et certains facteurs physiques connus.

---

---

With 9 Figures     

Numerical case study of an extreme rainfall event during 9–11 December 2004 over the east coast of Peninsular Malaysia

Summary An exceptional rainstorm affected the eastern coast of Peninsular Malaysia during 9–11 December 2004 as a result of a westward propagating tropical disturbance known as the Borneo vortex. Rainfall totals near the storm center exceeded 600 mm and led to flash floods, loss of life and severe damage in the area. This study presents the results of a numerical simulation of this event using the fifth generation of the Penn State – NCAR Mesoscale Model (MM5). The model successfully simulated the synoptic circulation and reproduced the episode with comparable spatial patterns and total accumulated amount of precipitation to the observed. Various sensitivity experiments showed that the local topography is decisive in shaping the rainfall distribution during the storm episode. The role of the terrain elevation appears to be to block the westward progression of the system and inhibit excessive rainfall in the inland areas of Peninsular Malaysia. To the north of the storm center where coastal terrain elevation is relatively high, orography plays an important role in the rainfall by providing an additional forcing for moist air lifting. An additional fake dry simulation suggested that latent heat release is crucial for the development of the storm. Without latent heating, the vertical coupling of low-level convergence and upper level divergence is weakened and the vertical motion associated with the storm is suppressed.     

基于正态分布拟合与检验的闪电定位资料控制

选取福州地区2007—2012年闪电定位资料,使用Matlab对数正态分布拟合方法以及STATA的正态分布检验方法对数据进行质量控制,研究闪电定位数据误差修正方法。结果表明:利用Matlab对数正态分布拟合方法与STATA正态分布检验方法,可以定量找到闪电定位资料小幅值电流干扰区间,对于有效利用闪电定位资料有较好的参考价值。福州地区小幅值雷电流干扰区间为0~1 kA,剔除此区间资料后正闪拟合效果最佳。在使用福州地区闪电定位资料时可先将此区间小幅值闪电误差数据删除,该结论可为福州地区闪电定位数据修正提供参考。