Rainfall uncertainty in the Mediterranean: dryness distribution

Dryness analysis is a major topic in the study of rainfall regime, mainly in regions with water shortage. The present study suggests a new approach for analyzing dry spells and their annual distribution and introduces a new term: dry days since last rain (DDSLR hereafter). The main goals of this study are to analyze and present the different annual courses of the DDSLR across the Mediterranean region. Daily rainfall totals for the period of 1931–2006 at 41 stations served as the main database. Two annual courses of the DDSLR, the median (50 percentile) and the 90 percentile, are presented for each Julian day in each station. Correlation matrices between stations according to their annual courses were calculated. A cluster analysis was performed on these correlations matrices according to which the stations were grouped. The main conclusions of the present study can be summarized as follows: Four regions were found in the Mediterranean basin according to their annual course of the DDSLR: Region Ia spread over the southern Mediterranean and has the most severe dryness conditions reaching maximum dryness in August and September. Region Ib is located mainly in northeastern Iberian Peninsula, south France, and northwestern Italy. Dryness is less severe than in Region Ia. The maximum dryness conditions are in July and August. Region IIa is located in the northeastern study area, with a bi-modal moderate dryness conditions. Maximum dryness is in August–October and a secondary dry period in January–March. Region IIb is located in the northwestern study area with a bi-modal moderate dryness conditions. Maximum dryness is in January–March and a secondary dry period in October. Both regions Ia and Ib can be combined into a single major region I. This region represents the classical Mediterranean rainfall regime with a very distinguishable dry period during summer. Similarly, regions IIa and IIb can be combined into a single major region II. This region benefits from rainfall all year round and therefore is not considered as having a classical Mediterranean climate. Uncertainty regarding the DDSLR distribution (from year to year) is much crucial in region II, since ecosystems are not adapted to long dry periods and their prolongation may have very severe environmental consequences.     

Modelling the spatial and temporal distribution of rainfall intensity at local scale

Summary Accurate estimates of rainfall intensity distribution with high temporal and spatial resolution are necessary in most urban hydrological studies, such as planning, simulation or control of sewer networks. Traditionally, these data are obtained from intensity-duration-frequency (IDF) curves at sites with long rainfall intensity time-series, however, little attention is given to the spatial features of precipitation. In this paper, a mathematical model of a local scale storm that takes account of the spatial variability of rainfall and rain-cell movement is proposed. The model has been calibrated with a dense network of raingauges and a long rainfall intensity timeseries (60 years) and its parameters have been calculated for convective storms of return periods up to 15 years with their most frequently-observed rain-cell velocities (1 to 4 m/s).This work has been supported by the DGICYT, Project NAT91-0596.With 6 Figures     

Rainfall uncertainty in the Mediterranean: Intraseasonal rainfall distribution

The rainfall distribution within the rainy season has crucial implications on a variety of disciplines. According to one approach of analyzing the intraseasonal rainfall distribution, it is essential to examine the date of different accumulated percentage (DAP hereafter), as presented in Paz and Kutiel (Isr J Earth Sci 52:47–63, 2003). The present study identifies various intraseasonal temporal distributions of rainfall, in 41 stations within the Mediterranean basin. Furthermore, classifications of these distributions according to their time, yield, and length are presented. The accumulated percentage was calculated for each Julian day for every available year in all stations. A correlation matrix between every possible pair of years, in each station, was calculated, and a cluster analysis (average linkage method) was performed. Finally, the averages of the entire dataset and the average of every cluster were compared in order to classify the clusters by using three parameters: timing represented by DAP_{(25%, 50%, 75%)} annual rainfall total and the rainy season length (RSL). Between 2 and 5 different types of clusters, with various probabilities, were defined for every station. Out of 132 overall clusters, which were found in 41 stations, the most frequent type (cluster 1) was the median in all three parameters. There were 16 clusters identified as short in their RSL, and 18 were identified as having a long classification. There were 19 dry clusters, and only eight were identified as wet. As for the parameter of timing, 39 clusters were classified as early and 38 as late. One conclusion of this study was that the probability of a dry year is higher than a wet one, and likewise, the probability of a long year is higher than of a short one.     

The economics of climate change impacts and policy benefits at city scale: a conceptual framework

Cities are particularly vulnerable to climate change and climate extremes in part because they concentrate many activities, people and wealth in limited areas. As a result they represent an important scale for assessment and understanding of climate change impacts. This paper provides a conceptual and methodological framework for urban economic impact assessment of climate change. The focus of the paper is on model-based analysis of future scenarios, including a framing of uncertainty for these projections, as one valuable input into the decision-making process. The paper highlights the main assessment difficulties, methods and tools, and selected examples across these areas. A number of challenges are unique to climate change impact assessment and others are unique to the problem of working at local scales. The paper also identifies the need for additional research, including the need for more integrated and systemic approaches to address climate change as a part of the urban development challenge as well as the need to assess the economic impacts of climate change and response policy at local scale.     

Rainfall distribution and regime in Central America

Summary Seasonal variations of the atmospheric circulation on the western flanks of the North Atlantic Anticyclone imply upward motion over the Caribbean Sea during the summer half-year, with a secondary minimum in July and August, while ascending motion decreases from November onward, and a strong subsidence develops towards the end of the winter half-year. This is associated with variations in the persistence of the trade inversion and the development of the Easterly Waves.The precipitation regime over the Caribbean Sea follows closely the seasonal variations in the field of large-scale vertical motion. A large variety in rainfall distribution and regime is found, on the other hand, on the Central American Isthmus. In qualitative terms, this is controlled by the orientation of mountain ranges and the configuration of coast lines relative to the seasonal flow patterns, that is orographic and stress-differential induced divergence and convergence effects. Due to the latitudinal variation of the Coriolis parameter, stress-differential induced divergence effects should be particularly pronounced in the tropics. The causes for the regional variations in the beginning of the rainy season and the secondary rainfall minimum in midsummer are discussed particularly.An altitudinal belt of maximum rainfall below the 1,000 m level is found in large parts of the Central American mountains. Recent climatic fluctuations display regional differences which appear to be greatly due to orographic and stressdifferential induced divergence effects.

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Zusammenfassung Jahreszeitliche Zirkulationsschwankungen auf der Westflanke der Nordatlantischen Hochdruckzelle sind verbunden mit aufsteigender Bewegung über dem Karibischen Meer während des Sommerhalbjahrs, mit einem sekundären Minimum im Hochsommer; von November an wird die Aufwärtsbewegung geringer, und ein starkes Absinken entwickelt sich gegen Ende des Winterhalbjahres. Änderungen der großräumigen Vertikalbewegung gehen mit Schwankungen in der Intensität der Passatinversion und der Ausbildung der Easterly Waves einher.Das Niederschlagsregime über dem Karibischen Meer folgt im wesentlichen den jahreszeitlichen Schwankungen der großräumigen Vertikalbewegung. Starke Gegensätze in Niederschlagsverteilung und-regime prägen sich andererseits auf der mittelamerikanischen Landbrücke aus. Sie sind im wesentlichen bestimmt durch Orientierung der Gebirge und des Küstenverlaufes in bezug zum jahreszeitlich veränderlichen Strömungsfeld. Orographische Effekte und Schubspannungs-unterschiede zwischen Land und Meer haben eine große Bedeutung für horizontale Strömungsdivergenzen in der Reibungsschicht. Wegen der Breitenabhängigkeit des Coriolis-Parameters sollten sich diese Effekte besonders stark in den Tropen auswirken. Die Ursachen für die ausgeprägten regionalen Unterschiede im Beginn der Regenzeit sowie das sekundäre Niederschlagsminimum im Hochsommer werden besonders diskutiert.In weiten Teilen der mittelamerikanischen Gebirge kann eine Höhenstufe maximalen Niederschlags unterhalb des 1000 m-Niveaus festgestellt werden. Klimaschwankungen der letzten Jahrzehnte zeigen regionale Unterschiede, die vor allem durch orographische Effekte und Schubspannungsunterschiede bedingt zu sein scheinen.

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Resumen Variaciones estacionales de la circulación atmosférica al lado occidental del Anticiclón del Atlántico del Norte están relacionados con el campo del movimiento vertical sobre el Mar Caribe. Hay un movimiento ascendente durante la mitad vernal del año, mostrando cierta disminución en los meses de Julio y Agosto. Una subsidencia pronunciada, por otra parte, suele desarrollarse hacia el final de la mitad invernal del año. Los cambios estacionales en el campo del movimiento vertical van junto con variaciones en la intensidad de la inversion de alísios y de las Ondas del Este.El régimen de lluvias sobre el Mar Caribe está conforme con las variaciones estacionales en el campo del movimiento vertical. En el Istmo Centroamericano, por otra parte, hay grandes contrastes en la distribucion regional y el régimen de lluvias, las cuales se deben a la orientación de las cordilleras y de las costas con respecto a los flujos atmosféricos dominantes. Diferencias en las condiciones aerodinámicas entre la superficie del mar y superficies terrestres, por otra parte, causan efectos de divergencia o convergencia en la faja costera. Debido a la variación latitudinal del parametro de Coriolis, dichos efectos deberían de ser particularmente importantes en los trópicos. Se discutan especialmente las causas para las differencias regionales que existen respecto al comienzo de la estación lluviosa.En gran parte de las montanas de Centro America hay un piso con lluvias máximas, situado debajo de 1,000 m, con una disminución pronunciada monte arriba. Las fluctuaciones climáticas de los ultimos decénios demuestran un carácter distinto en las varias partes del Istmo, lo que parece ser debido a efectos regionales de divergencia y convergencia.

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Résumé Les variations saisonnières de la circulation atmosphérique sur le flanc ouest de l'anticyclone situé sur l'Atlantique septentrional impliquent un mouvement ascendant de l'air au-dessus de la Mer des Caraïbes durant le semestre d'été. Ce mouvement est interrompu par un minimum secondaire en juillet et août. La durée de ces mouvements ascendants diminue à partir du mois de novembre et un fort courant subsident s'y développe vers la fin du semestre d'hiver. Ces mouvements sont associés aux variations de l'inversion des alizés et à l'évolution de l'ondulation de l'est.Le régime des précipitations de la Mer des Caraïbes suit étroitement les variations saisonnières du champ des mouvements verticaux à grande échelle. On recontre par contre une grande diversité dans les régimes et la distribution des précipitations en Amérique Centrale. Cette constatation se contrôle qualitativement par l'orientation des chaînes de montagne et la configuration des côtes par rapport aux modèles d'écoulement saisonnier. C'est à dire que cette diversité est due à des effets de divergence et de convergence provenant des conditions orographiques et des conditions de frottement différencié entre la terre et la mer. Du fait de la variation du paramètre de Coriolis avec la latitude, les effets de divergence provoquée par le dit frottement différencié doivent être spécialement prononcés sous les tropiques. On discute ici en particulier les causes des variations régionales du début de la saison des pluies et du minimum secondaire des précipitations au milieu de l'été.Une ceinture du maximum des précipitations se retrouve au-dessous de 1000 m d'altitude dans la plus grande partie des montagnes de l'Amérique Centrale. Des fluctuations climatiques récentes présentent des différences régionales qui semblent dues principalement à des effets orographiques et à la divergence produite par le frottement différencié de l'air sur la terre et la mer.

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A financial support by the University of Wisconsin Research Committee during the writing stage of this work is gratefully acknowledged.     

2007年贵州西部一次强降水天气过程的中尺度特征

利用常规观测资料、FY2C卫星资料和由NCEP/NCAR再分析资料计算的多种物理量场,分析了2007年7月30日发生在贵州西部地区的强降水天气过程,发现高空槽、西南低涡、对流层中层"人"字形切变线、对流层中低层强盛的不稳定能量以及充沛而又深厚的水汽等天气条件的有效合理配置,造成了这次历史罕见的范围,"的暴雨到大暴雨.显...     

Rainfall intensity patterns derived from the urban network of Barcelona (NE Spain)

Theoretical and Applied Climatology - An analysis of the normalised rainfall intensity curves in Barcelona (NE Spain) has been undertaken from 41 selected rain rate episodes recorded by an urban...     

Rainfall spatial organization and areal reduction factors in the metropolitan area of Barcelona (Spain)

The rainfall spatial organization in the metropolitan area of Barcelona (Spain) has been studied from records of an urban rain gauge network in the period 1994–2009. Using statistical and regional analysis techniques, correlation between data recorded by the different rain gauges has been calculated, and the effective number of independent stations (n _eq) equivalent to the used network has been determined. It has been found out that for durations longer than 20 min, the areal rainfall return period observed for a storm registered by the network approximately decreases by a factor of 1/n _eq in relation to the current point rainfall intensity–duration–frequency relationships for the metropolitan area of Barcelona. Using objective analysis techniques, continuous precipitation fields have been generated on a regular grid with a spatial resolution of 300?×?300 m for the storms registered by the rain gauges from 1994 to 2009, for durations from 10 min to 24 h. The precipitation fields obtained have been useful to estimate the characteristic areal reduction factors in the metropolitan area of Barcelona. A direct relationship has been found between the areal reduction factor for all the area corresponding to the urban rainfall network of Barcelona and the effective number of n _eq for every duration considered.     

Rainfall distribution patterns and their change over time in a Mediterranean area

Summary In dry farming areas, where rainfall is the only source of water for crops, changes in both quantity and distribution of rainfall during the year could affect the economy of an area. Inter-annual variability makes it difficult to assess rainfall variability, especially in areas with Mediterranean climate. In this paper, interannual rainfall variations in the Alt Penedès region were evaluated using 24-h rainfall records at Vilafranca del Penedès (1889–1999) and at Sant Sadurni d’Anoia (1960–1999). The distribution patterns during the year and their changes over the time were also analysed. Rainfall data were normalised and the values corresponding to the percentiles 0.1, 0.25, 0.5, 0.75 and 0.9 were calculated to analyse whether they were very dry, dry, normal, wet and very wet periods. Annual rainfall and the rainfall recorded during the main rainfall periods during the year and its trend were analysed. Annual rainfall did not show a clear tendency, although during the last decade reduced interannual variability occurred. The percentage of dry years did not increase but the percentage of wet and very wet years decreased. During the last decade, an increase of dry spring seasons andwet autumn seasons was observed, even in normal or wetyears. These changes could affect the timing of whencrops receive water and could therefore affect their yields. Received May 31, 2000/Revised February 26, 2001     

The urban heat island of a city in an arid zone: the case of Eilat, Israel

Summary This study presents the results of a preliminary research that was conducted in the city of Eilat, located in an extreme hot and arid zone on the northern coast of the Red Sea. The purpose was to analyse the characteristics of the local urban heat island (UHI). Diurnal pre-dawn and early-afternoon measurements were taken in winter and summer weather conditions on three separate occasions for two consecutive years. The results show the development of a moderate UHI located around the most intensive area of human activity; the city business centre and dense hotel belt. The UHI is more significant at midday during the summer period, while early morning inversions in winter have a weakening effect on the UHI intensity. It was found that the topography and wind regime have a dominant effect on the location and intensity of the UHI, while the sea has a very marginal effect. Due to the UHI influences on the spatial distribution of the heat stress in the city, it is suggested that further applied UHI research should be focused on the summer period.     

Divergence of turbulent fluxes in the surface layer: case of a coastal city

This study quantifies the processes that take place in the layer between the mean building height and the measurement level of an energy balance micrometeorological tower located in the dense old core of a coastal European city. The contributions of storage, vertical advection, horizontal advection and radiative divergence for heat are evaluated with the available measurements and with a three-dimensional, high-resolution meteorological simulation that had been evaluated against observations. The study focused on a summer period characterized by sea-breeze flows that affect the city. In this specific configuration, it appears that the horizontal advection is the dominant term. During the afternoon when the sea breeze is well established, correction of the sensible heat flux with horizontal heat advection increases the measured sensible heat flux up to 100 W m⁻². For latent heat flux, the horizontal moisture advection converted to equivalent latent heat flux suggests a decrease of 50 W m⁻². The simulation reproduces well the temporal evolution and magnitude of these terms.     

Temperature scenarios for Norway: from regional to local scale

Scenarios with daily time resolution are frequently used in research on the impacts of climate change. These are traditionally developed by regional climate models (RCMs). The spatial resolution, however, is usually too coarse for local climate change analysis, especially in regions with complex topography, such as Norway. The RCM used, HIRHAM, is run with lateral boundary forcing provided from two global medium resolution models; the ECHAM4/OPYC3 from MPI and the HadAM3H from the Hadley centre. The first is run with IPCC SRES emission scenario B2, the latter is run with IPCC SRES emission scenarios A2 and B2. All three scenarios represent the future time period 2071–2100. Both models have a control run, representing the present climate (1961–1990). Daily temperature scenarios are interpolated from HIRHAM to Norwegian temperature stations. The at-site HIRHAM-temperatures, both for the control and scenario runs, are adjusted to be locally representative. Mean monthly values and standard deviations based on daily values of the adjusted HIRHAM-temperatures, as well as the cumulative distribution curve of daily seasonal temperatures, are conclusive with observations for the control period. Residual kriging are used on the adjusted daily HIRHAM-temperatures to obtain high spatial temperature scenarios. Mean seasonal temperature grids are obtained. By adjusting the control runs and scenarios and improving the spatial resolution of the scenarios, the absolute temperature values are representative at a local scale. The scenarios indicate larger warming in winter than in summer in the Scandinavian regions. A marked west–east and south–north gradient is projected for Norway, where the largest increase is in eastern and northern regions. The temperature of the coldest winter days is projected to increase more than the warmer temperatures.     

2000—2017年山地城市百色气候承载力定量评价

利用2000—2017年百色市气象资料和城市社会经济发展数据,构建以气候天然容量、极端气候事件压力、城市气候压力和城市协调发展能力四个评价指数组成的城市气候承载力综合函数,客观定量评价广西西部山地城市百色2000—2017年的气候承载力变化。结果表明：21世纪以来,百色市的气候承载力整体呈现一种波动上升的状态,反映百色的城市建设与气候之间的协调力增强,城市建设发展仍有较大的气候承载空间。百色城市气候承载力对极端天气气候事件,特别是干旱事件较为敏感;人为影响因子对气候承载力具有重要影响。提升气候承载力和应对气候变化能力应从提高防御自然灾害能力和城市协调发展能力、降低城市气候压力着手,建立可持续发展的城市气候生态系统。     

The global scale,distribution and growth of aviation: Implications for climate change

Prior to the COVID-19 crisis, global air transport demand was expected to triple between 2020 and 2050. The pandemic, which reduced global air travel significantly, provides an opportunity to discuss the scale, distribution and growth of aviation until 2018, also with a view to consider the climate change implications of a return to volume growth. Industry statistics, data provided by supranational organizations, and national surveys are evaluated to develop a pre-pandemic understanding of air transport demand at global, regional, national and individual scales. Results suggest that the share of the world’s population travelling by air in 2018 was 11%, with at most 4% taking international flights. Data also supports that a minor share of air travelers is responsible for a large share of warming: The percentile of the most frequent fliers – at most 1% of the world population - likely accounts for more than half of the total emissions from passenger air travel. Individual users of private aircraft can contribute to emissions of up to 7,500 t CO₂ per year. Findings are specifically relevant with regard to the insight that a large share of global aviation emissions is not covered by policy agreements.     

塔克拉玛干沙漠腹地区域性与局地性沙尘暴特征分析——以塔中为例

塔克拉玛干沙漠近几年来沙尘暴发生频率增加,强度增大,为了研究不同尺度沙尘暴的规律,利用2005-2014年塔克拉玛干沙漠腹地塔中及周边14个气象台站沙尘暴资料,给出塔克拉玛干沙漠腹地塔中区域性与局地性沙尘暴天气过程的定义,从区域性与局地性沙尘暴持续时间,能见度,类型,时间变化等特征进行分析。研究结果表明：(1)10塔中发生沙尘暴170d比沙漠南缘和北缘高,比肖塘少,其中区域性沙尘暴80d,局地性沙尘暴90d,天气过程区域性64次,局地性80次;(2)塔中区域性沙尘暴不论是持续时间还是能见度总体上比局地性沙尘暴持续时间长,能见度低;(3)区域与局地沙尘暴可以按主导风向分为5类,但各类沙尘暴在区域性与局地性沙尘暴中表现出季节分布;(4)区域性与局地性沙尘暴10a波动增长,区域性沙尘暴多发生在春季,局地性沙尘暴多发生在夏季,区域性沙尘暴年际和年内变差系数都小于局地沙尘暴,一日中区域性与沙尘暴白天多于夜晚。     

乌鲁木齐城市化进程对局地气候变化的影响研究

利用1976—2014年乌鲁木齐城区和郊区两个气象站的气温、降水、相对湿度和风速气象数据及1995—2014年乌鲁木齐市城市发展数据,运用线性趋势对比分析城区和郊区各气候要素的年际变化特征;采用相关分析法对城市化因子和气候要素进行了探讨。结果表明:城、郊区气温均呈明显的上升趋势,城区的年均气温高于郊区;城区降水量是郊区的3.93倍,增长速率是郊区的3.98倍;各年代城区相对湿度比郊区大,但呈下降趋势,郊区呈上升趋势;各年代郊区风速大于城区,郊区风速约为城区的2.35倍,均呈下降趋势。近20 a,乌鲁木齐城市化进程加快,对局地气候影响明显,其中对平均气温和相对湿度的影响最为显著。     

Statistical distribution and spectral analysis of rainfallanomalies for Barcelona (NE Spain)

Summary  Rainfall anomaly patterns are obtained for the city of Barcelona from a statistical and a spectral point of view. The time series consists of monthly rainfall amounts recorded over 128 years without interruption. Monthly positive and negative anomalies, obtained as the difference between monthly amounts and monthly threshold values, are used for both types of analyses. The threshold levels are derived form the deciles of theoretical monthly rainfall distributions, which have been previously modelled by the gamma distribution. Positive and negative anomalies of the monthly rain amounts are investigated for these threshold levels. The statistical analysis is applied to each decile considered, yielding empirical exponential laws that can be used to forecast the cumulative number of episodes of consecutive months with either positive or negative anomalies equalling or exceeding a fixed length. A set of linear laws, relating the expected rainfall amount cumulated during an episode of a fixed length, is also deduced. It is worthy of mention that, independently of the decile considered, all the exponential and linear laws have satisfactory regression coefficients. At the same time, it has also been possible to establish the evolution of the coefficients of these laws with respect to the different deciles considered. The exponential laws for episodes of positive and negative anomalies are the starting point, together with two hypotheses, to model probabilities of repeated long episodes over an arbitrary number of years and their return periods in terms of the Poisson distribution model. Moreover, power spectra are derived for anomalies relative to the 50% decile at monthly and seasonal scale. The spectral estimates obtained are then compared with theoretical spectra deduced from possible Markovian or random behaviour of the time series of anomalies. Finally, the significant spectral peaks are discussed and compared with other significant spectral components deduced for some areas of the Mediterranean domain. Received November 11, 1999 Revised February 28, 2000     

江西省汛期局地短时强降水的时空分布特征

利用江西省89个测站1998—2013年汛期(3—9月)逐小时降水量资料,定义局地短时强降水过程,并对局地短时强降水的时空间分布进行了分析;利用常规观测资料基于天气学方法,对局地短时强降水进行天气学分类,统计了不同类型短时强降水的时空分布特征。结果表明:1)江西省汛期局地短时强降水天气主要集中在5—8月,8月出现的次数最频繁。局地短时强降水集中出现在武夷山以东的鹰潭和上饶南部、抚州东部;其次是在九岭山脉以南的宜春北部到南昌一带及环鄱阳湖地区,以及罗霄山脉以东的吉安西南部和赣州西部。2)4—8月局地短时强降水过程呈逐月增多趋势。4月的空间分布为东北多、西南少,集中在江西省北部和中东部;5月强降水高频带明显南移;6月与4月很相似但更为集中;7月,上饶东北部、景德镇、赣州市区的短时强降水逐渐增多;8月,除了江西省最北部和最南部外,全省出现强降水的概率比较均匀。3)根据影响系统的不同,将局地短时强降水分为4类。其中,低槽类出现最多,占50.3%,热带系统类占23.0%,副热带高压控制类占13.7%,副热带高压边缘类占9.9%。     

阿克苏地区初夏一次大降水天气分析

综合分析了阿克苏地区2002年6月15～17日夜间大降水天气发生的气象条件和高低层天气形势演变，同时揭示了大降水出现前能量指数、云顶亮温与大降水落区具有较好的对应关系。