Analysis of daily rainfall processes in lower extremadura (Spain) and homogenization of the data

Summary In this paper we analyze, from the point of view of stochastic processes, daily rainfall data recorded at the Badajoz Observatory (Southwestern Spain) since the beginning of the century. We attempt to identify any periodicities or trends in the daily rainfall occurrences and their dependence structure, and attempt to select the appropriate point stochastic model for the daily rainfall series.Standard regression analysis, graphical methods and the Cramer statistic show a rise in the number of cases of light rain (between 0.1 and 5 mm/d) and a decline in the number of cases of moderate to heavy rain (> 5 mm/d) in the daily rainfall at least at the 5% significance level.That the homogenization process was satisfactory is shown by the mean interarrival time of the homogenized series and the test of the rate of homogenized daily rainfall occurrences. Our analysis also shows that the behavior of the spectra of the homogenized daily rainfall counts is completely different from that of a Poisson process, so that the hypothesis of a non-homogeneous Poisson process is rejected.With 7 Figures     

一次极端短时强降水天气分析

本文利用常规地面及高空观测资料、加密自动站资料及多普勒雷达资料等,从环境条件及雷达特征等方面对2019年鸡西市一次极端短时强降水天气进行分析,结果表明:强降水发生在宽广且深厚的西风槽稳定维持背景下,降水区中层有冷空气入侵,低层位于槽前暖湿气流中,一致的西南风输送水汽至降水区。850 hPa槽线是本次对流天气的触发系统,上冷下暖及午后地面温度迅速升高造成热力不稳定,另外,低层绝对水汽含量较高是本次短时暴雨发生的重要条件。从雷达产品上看,麻山区的降水是由多单体风暴形成的,其中包含有超级单体风暴,单体依次经过降水区,强对流过程持续3 h,一定的"列车效应"使其出现了短时暴雨天气。     

Basic statistical characteristics of hourly rainfall amounts in Barcelona (Spain)

Summary In order to derive some statistical rainfall characteristics applicable to hydrology, data of continuous rainfall rate recordings of a Jardí gauge installed in Barcelona (Spain) have been converted to an hourly precipitation series. From these data, four useful distributions have been obtained and further compared with some theoretical models. It has been found that the duration of events is distributed exponentially. The duration of rainless intervals follow a generalized Pareto distribution, and the cumulative rainfall in the cumulative rain duration is beta distributed. Concerning the distribution of rain amounts, two models can be accepted, depending on the duration of the events. Comparison with a similar study carried out in Farnborough (United Kingdom) indicates that the events are shorter and that the amounts of rain collected in short events are larger in Barcelona.This work was supported by the DGICYT (Project NAT91-0596) and the CCE (Project PL 910104 Environment).With 7 Figures     

Significant hot and cold events at the Fabra Observatory, Barcelona (NE Spain)

Summary A long series of maximum and minimum daily temperatures recorded at the Fabra Observatory (Barcelona) from 1917 to 1998 has permitted a detailed study of significant hot and cold events, based on the crossing theory and on the Markovian process. The former allows us to obtain statistical distributions of the number of hot and cold events per year, the starting date and the magnitude of an event. The Poisson, the normal and the exponential distributions are the respective models. On the other hand, the Markovian process estimates probabilities for the duration of several hot and cold events above or below different temperature threshold levels. It should be stressed that the threshold levels, which define the significant hot and cold events, are almost coincident with those whose lengths follow a Markovian process. From a more applied point of view, two examples of hot and cold events of high magnitude are shown and their associated synoptic situations discussed. Some other typical synoptic situations leading to relevant hot and cold events in Barcelona and the surrounding areas are also summarised. Received March 1, 2001 Revised July 30, 2001     

Principal Component Analysis of precipitation and rainfall regionalization in Spain

Summary A T-mode Principal Component Analysis (PCA) based on a network including 68 pluviometric gauges and their 12 mean monthly amounts of rainfall is attempted in order to describe the main patterns governing precipitation in Spain. The procedure is applied to a 12 × 12 intermonth covariance matrix; the unrotated components and two additional solutions deduced after varimax and oblimin rotations are presented and discussed. In all cases component scores are computed and their spatial distribution is discussed. Two regionalizations of Spanish rainfall are then obtained and compared in terms of group homogeneity. There follows a discussion concerning the main pluviometric characteristics of each region deduced from the best division.With 7 Figures     

广西汛期不同等级小时强降水时空特征分析

利用2005—2021年4—10月广西91个国家气象站小时降水数据和Oceanic Niño Index (ONI)数据,分析了广西汛期极端短时强降水的特征及其关联因子。结果表明：(1) 广西超过80%站点的极端短时强降水强度在40~70mm·h^-1,强度和频次最高均出现在沿海地区,频次次高区域为桂东北地区,但其强度却为广西最低;(2)每年极端短时强降水频次呈现增多趋势,每年5、6月份极端短时强降水频次最高,但各个月份强度变化不大。(3)每日04—05时、17—18时的极端短时强降水频次最高,各个时次强度均在50~55mm·h^-1,差别不大。(4) 广西极端短时强降水特征不仅与地形密切相关,而且与南海夏季风、厄尔尼诺/拉尼娜事件关联性很大。(5)前一年秋季的ONI和次年前汛期的极端短时强降水呈显著正相关。

     

Multifractal analysis of the rainfall time distribution on the metropolitan area of Barcelona (Spain)

In most of the studies on scale properties in the rainfall process, multifractal behavior has been investigated without taking into account the different rain generation mechanisms involved. However, it is known that rain processes are related to certain scales, determined by climatological characteristics as well as regional and local meteorological features. One of the implications derived from these correspondences is the possibility that the multifractal parameters of the rainfall could depend on the dominant precipitation generation mechanism. Fractal analysis techniques have been applied in this work to rainfall data recorded in the metropolitan area of Barcelona in the period 1994–2001, as well as to a selection of synoptic rainfall events registered in the same city in the period 1927–1992. The multifractal parameters obtained have been significantly different in each case probably showing the influence of the rain generation mechanisms involved. This influence has been revealed also in the analysis of the effects of seasonality on the multifractal behavior of rainfall in Barcelona.     

Trends in extreme rainfall events of Bangladesh

Previous studies have shown that urbanization in the Pearl River Delta (PRD) region in southern China can have significant effect on the land-sea breeze circulation in the region. In this study, some characteristics of this urban heat island (UHI) effect are further investigated by some idealized numerical experiments. This study focuses on three aspects of the UHI effects. Firstly, the interaction of UHI effects associated with different city clusters in the PRD region. Secondly, the UHI effect and the strength of the background wind field. Thirdly, seasonal variation of the UHI effect. Experiment results suggest that the interaction of the UHI effects due to the closely distributed city clusters in the PRD region is not significant, while the UHI effect in the region may depend on the strength of the background wind. The seasonal-mean UHI effect in the region shows a significant variation associated with the change of seasons.     

Analysis of extreme temperatures for four sites across Peninsular Spain

Statistical analyses regarding climate studies have often used the average temperature as one of the main variables. However, the tails of the respective distributions are also crucial and have become increasingly considered in recent years. As the Intergovernmental Panel on Climate Change in its fourth assessment report (IPCC 2007) states, ??the type, frequency and intensity of extreme events are expected to change as Earth??s climate changes??. In this paper, the focus is on the statistical behaviour of extreme (maximum and minimum) values of temperature, both in winter and summer. Under the framework of the Extreme Value Theory, the methodology of block maxima is employed. The generalised extreme value distribution, allowing for a linear trend in the location parameter, is fitted to data in order to capture the time tendency in the non-stationary processes. We are able to approximate expected values with a determined probability and to identify time trends of such events. Particularly, an increasing time trend in maximum and minimum temperature is generally detected which could be of great concern to public and private sectors.     

Temporal and spatial persistence in rainfall records from Northeast Brazil and Galicia (Spain)

Summary Temporal and spatial persistence effects in historical rainfall records are investigated for a large number of stations from Northwest Spain (Galicia) and Northeast Brazil. Quantitative results, expressed by the Hurst or roughness exponent, are obtained by two methods: the R/S analysis and the semi-variogram. Despite rather different climatic conditions and period of analysis for the two regions, the results indicate that persistence and anti-persistence for the temporal and spatial analyses, respectively, are found for both regions. Temporal persistence is known to occur with other climatic fields and in many different regions of the world. Antipersistence in spatial patterns of rainfall is a strong result of this work, despite its apparent contradiction with temporal persistence. The results for Northeast Brazil support previous indications of a geographic stratification of persistence: both temporal and spatial persistence increase as latitude decreases.     

Daily rainfall trend in the Valencia Region of Spain

Summary ?We have analyzed daily rainfall trends throughout the second half of the 20^th century in the western Mediterranean basin (Valencia Region, E of Spain). The area is characterized by high torrentiality, and during the second half of the 20^th century some of the highest daily rainfall values in the Mediterranean basin have been recorded. In this area, mean annual rainfall varies between 500 and 300 mm and is overwhelmingly dependent on just a few days of rain. Daily maximum rainfall varies on average from 120 mm day⁻¹ to 50 mm day⁻¹, and represents a mean of 17% (coastland) to 9% (inland) of annual rainfall. The 10 days in each year with the heaviest rainfall (called “higher events”) provide over 50% of the annual rainfall and can reach more than 400 mm on average. We compared the annual rainfall trend and the trend of higher and minor events defined by percentiles, both in volume and variability. We, therefore, tested whether annual rainfall changes depend on the trend of the higher (rainfall) events. To overlap spatial distribution of trends (i.e.: positive, no significant and negative trends) we have used cross-tab analysis. The results confirm the hypothesis that annual rainfall changes depend on changes found in just a few rainy events. Furthermore, in spite of their negative trend, higher events have increased their contribution to annual rainfall. As a consequence, although torrential events may have diminished in magnitude, future scenarios seem to be controlled by a limited number of rainy events which will become more and more variable year on year. The high spatial density of data used in this work, (97 observatories per 24.000 km², overall mean 1 observatory per 200 km²), suggests to us that extreme caution should be applied when analyzing regional and sub-regional changes in rainfall using GCM output, especially in areas of high torrentiality. Received August 1, 2002; revised November 11, 2002; accepted December 1, 2002 Published online May 19, 2003     

Neyman-Scott cluster model for daily rainfall processes in lower extremadura (Spain): Rainfall Generating Mechanisms

Summary A Neyman-Scott cluster model was fitted to the daily rainfall data recorded at the observatory of Badajoz (southwestern Spain) for the period 1901–1990. The data were previously homogenized. The goodness of the fit that indicated the daily rainfall process follows some Rainfall Generating Mechanism (RGM). Having decided on the criteria that a block of rainfall must fulfill to be considered as a RGM, a method was proposed to classify the days that belong to RGMs according to the 500 hPa and the surface topography. In this method each day is characterized by a string of 22 alphanumeric characters. From the subsequent analysis, the structure of the synoptic patterns associated with each RGM was deduced.With 3 Figures     

印江极端降水和极端强降水日数统计特征

利用印江气象站的逐日降水资料,在对该站点极端降水和极端强降水过程阈值进行科学界定的基础上,对50 a来极端降水和极端强降水过程进行了常规统计。结果表明:印江极端降水和极端强降水过程有弱的增加趋势,极端(强)降水天数与降水量成正相关,20世纪60年代极端降水天数和极端强降水的离散程度最大,21世纪前8 a极端强降水的离散程度最小。极端降水和极端强降水日数变化均达不到气候突变的标准。     

基于RClimDex模型的江西省极端降水时空变化研究

基于赣江流域1964-2013年13个水文站的日降水资料,采用AM抽样和POT抽样相结合的方法,对极端降水序列,选定日最大降水量（RX1）、极端降水量（R95）、极端降水天数（RD95）和极端降水强度（RI95）四个指标,利用Mann-Kendall趋势分析方法、Pettitt变点检验法分别对赣江流域极端降水进行时间变化趋势和突变的分析,并利用普通克里金插值,对各指标进行空间分布的分析。研究结果表明,时间变化上,赣江流域RX1、R95和RD95均表现出一定的增加趋势,但RI95变化不大,各指标在过去50 a没有发生显著突变;空间分布上,RX1、R95和RI95沿着赣江流向从西南向东北增加,而RD95的空间分布没有明显的变化规律,存在多个极大极小值中心。

     

Preliminary aspects of rainfall rates in the north east of Spain

Summary A series of charts of rainfall rates recorded by means of a Jardí pluviograph in Barcelona, Spain, and covering a period of 20 years have been digitised. The time intervals of exceedance of certain pre-set rainfall rate thresholds were computed and expressed in percentages of the whole 20-year period. The average worst month period and the absolute worst month were defined and computed. Results are found to agree well with those obtained elsewhere in Southern Europe; they are also compared with some published results for Kew. Frequency-distribution of rates as well as time of occurrence are presented. Rainfall amounts pertaining to several rainfall rate categories have been analysed in order to obtain the ratio of convective to total rainfall amount. Comparison of this ratio with results of some other authors is inconclusive.

---

Zusammenfassung Eine Anzahl von Tabellen über Niederschlagsraten, die in Barcelona (Spanien) durch einen Jardí Niederschlagsmesser über eine Zeitspanne von 20 Jahren aufgezeichnet wurden, werden bearbeitet. Die Andauer von gewissen festliegenden Niederschlagsraten wurde berechnet und in Prozenten von der gesamten 20jährigen Zeitspanne ausgedrückt. Die durchschnittliche Dauer im schlechtesten Monat, sowie der absolut schlechteste Monat werden definiert und berechnet. Die Ergebnisse stimmen im allgemeinen mit solchen anderer südeuropäischer Gebiete überein; sie werden mit schon veröffentlichten Ergebnissen aus Kew verglichen. Häufigkeits- als auch Verteilungsraten sowie die Eintrittszeit der Ereignisse werden angegeben. Die Niederschlagsmengen, die jeweils zu verschiedenen Niederschlagsraten gehören, wurden analysiert, um das Verhältnis des konvektiven zum gesamten Niederschlag zu ermitteln. Ein Vergleich dieses Verhältnisses mit den Ergebnissen anderer Autoren sind noch nicht abgeschlossen.

---

---

With 7 Figures     

华北地区持续性极端暴雨过程的分类特征

利用1960—2015年日降水资料,筛选出华北地区56次持续性极端暴雨过程。基于距平相关系数的客观聚类分析方法和天气学检验,将它们进行分类,并使用NCEP(2.5°×2.5°)再分析资料进行分类合成,对比分析不同环流背景下华北地区持续性极端暴雨过程的基本特征。结果表明,这些持续性极端暴雨事件按照环流背景可分为经向型、纬向型、减弱的登陆热带气旋型和初夏型4类。它们一般都与不同天气系统配置结构下的锋面动力学过程有关,由于锋面结构特征、环境大气层结状态以及与低空急流有关的暖湿气流输送通道和强度不同,造成不同环流形势背景下,暴雨日的高频站点与过程平均累计降水量在空间分布上存在差异。(1)纬向型对应的锋区强度明显强于经向型,但是其对应的层结稳定度与整个夏季状态相当,而经向型存在弱的层结不稳定异常,这表明,纬向型的对流活动一般不如经向型强,持续性锋面降水特征更清晰,造成站点上日降水量超过50 mm的最大频率明显低于经向型,但是过程累计平均最大降雨量却比经向型大。(2)从水汽输送通道来看,源于西太平洋副热带高压南侧的水汽通道只在纬向型环流主导下的华北区域持续性极端暴雨过程中起主导作用。初夏型以及减弱...     

近年华中地区不同级别强降水事件变化趋势

利用1981—2017年近37 a华中区域241个气象观测站年最大小时降水资料,分析了该区域年极端小时降水的时空分布特征。结果表明：阈值分别为30~ < 40 mm·h^-1、40~ < 50 mm·h^-1和≥50 mm·h^-1的年极端小时降水频次,河南和湖北中东部均较高,湖南则随其阈值增大而降低;年极端小时降水频次日变化特征较为明显,午后至傍晚发生最多,前半夜至凌晨次之,后半夜至早晨、上午至午后明显减少;年极端小时降水平均强度大值区多集中在河南和湖北的中东部地区,湖北最强年极端小时降水大值区主要位于沿江汉平原边缘地带;年极端小时降水频次日峰值主要出现在午后至傍晚和后半夜至早晨,其区域性差异较为明显;不同阈值的年极端小时降水频次均表现出明显的年际和年代际变化特征,1980年代呈波动减小趋势,1990年代呈波动增加趋势,21世纪初期呈现低频波动变化,之后波动加大;不同阈值的极端小时降水频次日变化均表现为明显的单峰型特征,峰值出现在17时前后。

     

Periodicities and irregularities of indices describing the daily pluviometric regime of the Fabra Observatory (NE Spain) for the years 1917–1999

Summary Several patterns of a daily pluviometric regime are obtained from an homogeneous set of daily rainfall recorded at the Fabra Observatory (NE Spain) for the period 1917–1999. Power spectral analyses of four annual pluviometric indices, determined from different daily rain amount percentiles, are performed. Periodicities of the quasi-biannual oscillation (QBO), North Atlantic Oscillation (NAO) and sunspot cycles are correlated in some cases with empirical spectral peaks of the indices exceeding Markov red-noise with a confidence level of 95%. Depending on the rainy day percentiles, a set of short periods (2.1–4.6 years), a second group of intermediate periods (5.5 and 9.2 years) and, finally, a third group of long periods of 11.8, 20.8 and 41.5 years can be distinguished. These periods are compared with those derived for other European and African emplacements. Additionally, the consecutive irregularity of every annual series is quantified by means of a concept similar to the entropy.