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The correlation analysis between precipitation indices and aerobiological variables could lead to different results if seasonal rainfall is considered. The number of significant correlations, as well as the ratio of positive/negative correlations, is higher when previous autumn rainfall is taken into account than for annual rainfall. However, the percentage of significant correlations is only 5.1 % of the total possible correlations. The autumn indices showing more correlations are related to rainfall duration and persistence, while those for winter were related to rainfall amount and intensity. Since the influence of moderately extreme rainfall seems to be low, the reported probable increase, due to climate change, of the occurrence of intense and short rainy events in the Mediterranean area in autumn does not seem that will have an appreciable effect by itself on the subsequent pollen production.

A long and complete series of monthly rainfall amounts corresponding to Barcelona city (Catalonia, NE Spain), exceeding two centuries (years 1786–2019), is analysed in detail. The obtained results of periodicity (annual scale), time trends (monthly, seasonal and annual scales), statistical distribution (seasonal and annual scale) and fractal/multifractal structures and self-similarity at monthly scale depict the complex structure of this pluviometric regime, which is characterized by moderate increasing and decreasing trends on rain amounts, varying from +0.08¿mm·year-1 (February) to -0.07¿mm·year-1 (September) and quite evident changes on the pluviometric trends at annual and seasonal scales when the rainfall data are analysed for segments of 50¿years from 1800 up to 2019. A good example could be the relevant change on the annual scale time trend, from +0.77¿mm·year-1 (years 1800–1850) to -0.17¿mm·year-1 (years 1950–2019). Clear evidences of decreasing pluviometry for spring, summer and autumn for the last segment (1950–2019) in comparison with the other three segments, including years 1800–1950, are also detected. Additionally, increasing rainfall patterns complexity, expected difficulties on monthly rainfall forecasting and the increasing irregularity of monthly amounts is also detected by interpreting fractal and multifractal results. Irregularity increases on the monthly rainfall series and on the rainfall regime complexity derived from multifractal parameters, could be associated with the very notable increase of CO2 emissions into the atmosphere, globally varying from 51.1¿×¿106 metric tonnes (year 1820) to 36.6¿×¿109 metric tonnes (year 2019) and the tropospheric concentration increasing from 280.8 ppm (year 1850) to 397.5 ppm (year 2014), being the probable relationship between tropospheric concentrations and changes on rainfall patterns the objective of future researches.

Historically, most precipitation data have been measured by collecting rainfall, usually at intervals of 24 h, with a fixed starting time. Nonetheless, it is known that the use of fixed time intervals to measure rainfall quantities could lead to an underestimation of the true maximum precipitation amounts for the considered duration, so a single multiplicative correction factor is commonly applied, generally without taking into account the rainfall pattern of the place, nor regional or seasonal considerations. In the present work, hourly measurements from 120 stations of Catalonia (northeast of the Iberian Peninsula) have been used to analyse how the ratio between rainfall amounts measured by fixed and unrestricted intervals, i.e. the correction factor, depends on the considered duration and on the specific starting time of the fixed interval (local 00:00, 08:00, 12:00 or 16:00), as well as the influence ofgeographical location and seasonality and actual rainfall duration. For fixed sampling intervals starting at 16:00, the mean correction factor has been found to be higher (1.137) than at the usual 08:00 starting time (1.129). Some geographical patterns of the correction factor over Catalonia arose which, moreover, depend on the season, with a mean value of 1.161 in spring and a value of 1.093 in summer. Also, the value of the correction has been found to increase with the actual duration of the maximum rainfall events used in the analysis. Some of these extreme events had actual mesoscale durations between 6 and 9 h, linked to highly convective mesoscale organisations acting mainly in summer and the beginning of autumn. Other maxima episodes, with more advective rainfall lasting more than 12 h registered in the northern area of the territory, presented the highest values of the correction factor, especially in spring.

Advantages offered by a pluviometric network in Catalonia (NE Spain) have permitted a detailed analysis of the two primary results derived from the autoregressive ARIMA process applied to monthly rainfall amounts. The first was the spatial distribution of the necessary number of previous monthly amounts needed to predict the next amount. The second was the spatial distribution of discrepancies between the real recorded amount and those derived from the autoregressive process. The heterogeneous spatial distribution of both parameters of the ARIMA process is in accordance with the complex spatial distribution of the monthly rainfall regime in Catalonia and fractal/multifractal analyses of several monthly rainfall time series. The statistical distribution of monthly discrepancies also permits a prediction of the probable evolution at monthly scale of drought episodes in terms of length and accumulated rainfall deficit. The results of the ARIMA algorithm are characterised by a few cases of raingauges with remarkable differences (10-20¿mm/month) between real and autoregressive amounts, a predominant number of emplacements lowering 10¿mm/month and a not negligible number of cases with discrepancies lower than 5¿mm/month. In terms of percentages with respect to average monthly amounts, most of discrepancies do not exceed 15%, and only in a very few cases they are within the 20-40% range. It is also worth mentioning that the discrepancies between real and predicted drought lengths use to be no longer than one month. Results corresponding to monthly series recorded at two Earth Sciences observatories are described with more detail to illustrate the advantages offered by the ARIMA autoregressive process in the prediction of beginning, continuity and end of drought episodes.

The pluviometric regime in the Western Mediterranean and concretely in Catalonia (NE Spain) is characterised by irregular amounts at monthly and annual scales, sometimes with copious short episodes causing foods and, conversely, sometimes with long dry spells exceeding 1 month length, depending on the chosen threshold level to defne the dry episode. Taking advantage of a dense network of rain gauges, most of them with records length of 50–60 years and some others exceeding 85 years, the evolution of these monthly and annual amounts is quantifed by means of their time trends, statistical signif- cance and several irregularity parameters. In agreement with the evolution of the CO2 emissions into the atmosphere and the increasing concentration, in parts per million (ppm), of this greenhouse gas, diferent time trends at annual scale have been detected up to approximately years 1960–1970 in comparison with the interval 1960–1970 to nowadays. Consequently, besides the greenhouse efects on the temperature regime, the infuence on the pluviometric regime could not be negligible. Rainfall data have been supplied by Servei Mete‑ orològic de Catalunya (Generalitat de Catalunya), Fabra Observatory (RACA, Barcelona) and Ebro Observatory (Ramón Llull University and CSIC, Spanish Government). This research was supported by the Spanish Ministry of Science, Innovation and Universities: grant 460 number PID2019-105976RB-I00] and grant number AGL201787658-R. The authors also thank the editor and the anonymous reviewers for their valuable comments and suggestions to improve the manuscript

Collected rainfall records by gauges lead to key forcings in most hydrological studies. Depending on sensor type and recording systems, such data are characterized by different time-resolutions (or temporal aggregations), ta. We present an historical analysis of the time-evolution of ta based on a large database of rain gauge networks operative in many study areas. Globally, ta data were collected for 25,423 rain gauge stations across 32 geographic areas, with larger contributions from Australia, USA, Italy and Spain. For very old networks early recordings were manual with coarse time-resolution, typically daily or sometimes monthly. With a few exceptions, mechanical recordings on paper rolls began in the first half of the 20th century, typically with ta of 1 h or 30 min. Digital registrations started only during the last three decades of the 20th century. This short period limits investigations that require long time-series of sub-daily rainfall data, e.g, analyses of the effects of climate change on short-duration (sub-hourly) heavy rainfall. In addition, in the areas with rainfall data characterized for many years by coarse time-resolutions, annual maximum rainfall depths of short duration can be potentially underestimated and their use would produce errors in the results of successive applications. Currently, only 50% of the stations provide useful data at any time-resolution, that practically means ta = 1 min. However, a significant reduction of these issues can be obtained through the information content of the present database. Finally, we suggest an integration of the database by including additional rain gauge networks to enhance its usefulness particularly in a comparative analysis of the effects of climate change on extreme rainfalls of short duration available in different locations.

The quality control of weather data is a necessity and a responsibility of meteorological services that store, distribute, and use these data. In the present work, a newly designed quality control procedure for daily rainfall data is presented after it has been adjusted and tested with more than 10^7 data from 1726 daily rainfall measurement sites in Catalonia. It is applicable to data from different origins (e.g., automatic weather stations or manual historical measurements). The procedure is focused on relative comparison of daily data with reference stations that are automatically selected after an initial estimation of their quality and a proximity study regarding location and correlation. The presented procedure has been verified taking advantage of an available network in the study area that has been routinely quality controlled by technicians of the Meteorological Service of Catalonia. The newly designed quality control procedure for daily precipitation yields good results, especially for extreme values: type I error under 10% is found for values up to 150 mm (error decreasing for lower values) and type II error is under 16% when reported values are twice a measure of 50 mm or more (error decreasing for more extreme values). After the application of the quality control procedure, a selection of series with the minimum desired quality is achieved.

Uno de los rasgos principales de las áreas urbanas es el predominio de las superficies impermeables (suelos sellados). Dependiendo de su densidad y extensión, el sellado de los suelos limita o impide las funciones naturales del suelo, puesto que reduce su capacidad potencial de infiltración del agua y, con ello, la regulación de la escorrentía, aumentando el riesgo de inundaciones. En el caso de precipitaciones muy intensas en áreas urbanas con una elevada proporción de superficies impermeables, el sistema de alcantarillado puede no ser suficiente para hacer frente al exceso de agua de lluvia y, por lo tanto, se pueden producir inundaciones súbitas. En muchas zonas de Europa, la extensión de la urbanización y su densificación han incrementado notablemente la proporción de superficies impermeables (European Environment Agency, 2016). En la conurbación de Barcelona, la mayor parte de las áreas tienen una proporción de suelos sellados del 60-80% y en la ciudad de Barcelona, se supera el 80% (fuente: European Environment Agency, GMES/Copernicus). En esta zona los episodios de precipitación intensa son relativamente frecuentes, especialmente a finales de verano y durante el otoño, y algunos de ellos han dado lugar a inundaciones súbitas. En este trabajo se analizan los registros de una red de 23 estaciones de intensidad de precipitación instaladas en la ciudad de Barcelona. La base de datos consta de series de valores de precipitación acumulada a intervalos de 5 minutos, lo cual proporciona una medida de la intensidad de precipitación (mm/5 minutos). El periodo de registro considerado abarca 16 años (1994-2009). Para los registros de más de 60 minutos de duración y de más de 25 mm (67 episodios, 499 registros) se han calculado el total de precipitación acumulada, la intensidad media y la intensidad máxima. Finalmente, se han estudiado los que exceden al mismo tiempo, el percentil del 95% de estas tres variables. Con ello, se han obtenido 29 registros extremos que podrían dar lugar a situaciones de inundación súbita. Estos registros extremos se agrupan en siete episodios distintos, ocurridos entre finales de julio y octubre. Una buena parte de estos episodios extremos se produce por procesos de origen convectivo a escala local, así como por advecciones del este. Los siete episodios extremos analizados, provocaron importantes afectaciones en las comunicaciones viales, averías en los semáforos y en las líneas telefónicas, así como interrupción del servicio de algunas líneas del metro, del aeropuerto y de la red ferroviaria. Como consecuencia del cambio climático y el calentamiento global, es probable que aumente la frecuencia de los episodios de precipitación muy intensa. El desarrollo de políticas dirigidas a limitar o reducir la proporción de suelos sellados en las áreas urbanas sería un elemento clave para mitigar, en lo posible, este riesgo de inundaciones súbitas. Un dels trets principals de les àrees urbanes és el predomini de les superfícies impermeables (sòls segellats). Depenent de la seva densitat i extensió, el segellat dels sòls limita o impedeix les funcions naturals de terra, ja que redueix la seva capacitat potencial d'infiltració de l'aigua i, amb això, la regulació del vessament, augmentant el risc d'inundacions. En el cas de precipitacions molt intenses en àrees urbanes amb una elevada proporció de superfícies impermeables, el sistema de clavegueram pot no ser suficient per fer front a l'excés d'aigua de pluja i, per tant, es poden produir inundacions sobtades. En moltes zones d'Europa, l'extensió de la urbanització i la seva densificació han incrementat notablement la proporció de superfícies impermeables (European Environment Agency, 2016). A la conurbació de Barcelona, la major part de les àrees tenen una proporció de sòls segellats de l'60-80% i a la ciutat de Barcelona, se supera el 80% (font: European Environment Agency, GMES / Copernicus). En aquesta zona els episodis de precipitació intensa són relativament freqüents, especialment a finals d'estiu i durant la tardor, i alguns d'ells han donat lloc a inundacions sobtades. En aquest treball s'analitzen els registres d'una xarxa de 23 estacions d'intensitat de precipitació instal·lades a la ciutat de Barcelona. La base de dades consta de sèries de valors de precipitació acumulada a intervals de 5 minuts, la qual cosa proporciona una mesura de la intensitat de precipitació (mm / 5 minuts). El període de registre considerat abasta 16 anys (1994-2009). Per als registres de més de 60 minuts de durada i de més de 25 mm (67 episodis, 499 registres) s'han calculat el total de precipitació acumulada, la intensitat mitjana i la intensitat màxima. Finalment, s'han estudiat els que excedeixen a el mateix temps, el percentil de el 95% d'aquestes tres variables. Amb això, s'han obtingut 29 registres extrems que podrien donar lloc a situacions d'inundació sobtada. Aquests registres extrems s'agrupen en set episodis diferents, ocorreguts entre finals de juliol i octubre. Una bona part d'aquests episodis extrems es produeix per processos d'origen convectiu a escala local, així com per adveccions de l'est. Els set episodis extrems analitzats, van provocar importants afectacions en les comunicacions vials, avaries en els semàfors i en les línies telefòniques, així com interrupció del servei d'algunes línies de metro, de l'aeroport i de la xarxa ferroviària. Com a conseqüència del canvi climàtic i l'escalfament global, és probable que augmenti la freqüència dels episodis de precipitació molt intensa. El desenvolupament de polítiques dirigides a limitar o reduir la proporció de sòls segellats en les àrees urbanes seria un element clau per a mitigar, en la mesura possible, aquest risc d'inundacions sobtades. One of the main features of urban areas is the prevalence of impervious surfaces (sealed soils). Depending on its density and extent, soil sealing restricts natural soil functions, since it reduces water infiltration capacity and run-off regulation, thus increasing flash flooding risk. In the case of heavy rainfalls in urban areas with high imperviousness ratio, the sewage system could no longer be able to cope with the excess of rainwater and then pluvial floods develop. In many European zones, urban spread and densification have increased the impervious surface ratio (European Environment Agency, 2016). In Barcelona conurbation, most areas have high fractions of sealed soils (60–80%) and in the city, this fraction exceeds 80% (source: European Environment Agency, GMES/Copernicus). Heavy rainfall episodes are relatively frequent in this area, especially in autumn, and some of them have resulted in flash floods. In this study, rainfall intensity records from an urban network of 23 stations are analysed. The database consists of series of rain amounts collected at 5-minute intervals, which provides a measure of rainfall intensity (mm/5 minutes). The recording period encompasses 16 years (1994-2009). For all the records with durations greater than 60 minutes and total amounts greater than 25 mm (67 episodes, 499 records), the total rain amount, average intensity and maximum intensity are determined. We have selected the records exceeding, simultaneously, the 95th percentile of these three variables, thus obtaining 29 extreme records, which could lead to pluvial flash flood events. These extreme records correspond to seven different episodes, occurred from the end of July to October. Most of these extreme episodes are generated by convective processes at local scale as well as by eastern advections. The seven extreme episodes caused important affectations in road communications, breakdowns at traffic lights and telephone lines, as well as interruption of the service of some suburban lines, the airport and the railway network. Because of climate change and global warming, the frequency of episodes of very heavy precipitation is likely to increase. The development of policies aimed at limiting or reducing the proportion of sealed soils in urban areas would be a key element to mitigate, as far as possible, this risk of flash flooding. Esta investigación ha sido financiada por el Ministerio de Economía y Competitividad (Gobierno de España), a través del proyecto BIA2015-68623-R. Los autores agradecen a CLABSA (Clavegueram de Barcelona, S.A.) los datos pluviométricos facilitados.

A methodology based on the fractal properties of rainfall has been applied to obtain the intensity-duration-frequency, IDF, curves for 100 pluviometric Spanish stations over the Iberian Peninsula and the Balearic Islands from their daily precipitation series. The scaling behaviour of maximum rainfall intensities has been investigated and simple scaling has resulted suitable. This methodology has been verified in three emblematic observatories with available sub-daily registers and current known generalized IDF relationships: the Fabra Observatory of Barcelona, the Ebre Observatory near Tortosa (Tarragona) and the Retiro Observatory of Madrid. Despite some general concordance with the mean annual rainfall distribution over Spain, the spatial distribution of the scaling parameter found for the 100 stations shows some discrepancies in diverse areas probably due to the influence of other features, as the inter-annual rainfall variability and the contribution of convective rainfall to total precipitation, on the characteristic rainfall pattern in these areas.

As well as in other natural processes, it has been frequently observed that the phenomenon arising from the rainfall generation process presents fractal self-similarity of statistical type, and thus, rainfall series generally show scaling properties. Based on this fact, there is a methodology, simple scaling, which is used quite broadly to find or reproduce the intensity–duration–frequency curves of a place. In the present work, the relationship of the simple scaling parameter with the characteristic rainfall pattern of the area of study has been investigated. The calculation of this scaling parameter has been performed from 147 daily rainfall selected series covering the temporal period between 1883 and 2016 over the Catalonian territory (Spain) and its nearby surroundings, and a discussion about the relationship between the scaling parameter spatial distribution and rainfall pattern, as well as about trends of this scaling parameter over the past decades possibly due to climate change, has been presented.

The study has obtained a classification of the synoptic patterns associated with a selection of extreme rain episodes registered in the Ebre Observatory between 1905 and 2003, showing a return period of not less than 10 years for any duration from 5 min to 24 h. These episodes had been previously classified in four rainfall intensity groups attending to their meteorological time scale. The synoptic patterns related to every group have been obtained applying a multivariable analysis to three atmospheric levels: sea-level pressure, temperature, and geopotential at 500 hPa. Usually, the synoptic patterns associated with intense rain in southern Catalonia are featured by low-pressure systems advecting warm and wet air from the Mediterranean Sea at the low levels of the troposphere. The configuration in the middle levels of the troposphere is dominated by negative anomalies of geopotential, indicating the presence of a low or a cold front, and temperature anomalies, promoting the destabilization of the atmosphere. These configurations promote the occurrence of severe convective events due to the difference of temperature between the low and medium levels of troposphere and the contribution of humidity in the lowest levels of the atmosphere.

For a few decades the local rainfall measurements are generally obtained by tipping bucket sensors, that allow to record each tipping time corresponding to a well-known rain depth. However, a considerable part of rainfall data to be used in the hydrological practice is available in aggregated form within constant time intervals. This can produce undesirable effects, like the underestimation of the annual maximum rainfall depth, Hd, associated with a given duration, d, that is the basic quantity in the development of rainfall depth-duration-frequency relationships. The errors in the evaluation of Hd from data characterized by a coarse temporal aggregation, ta, and a procedure to reduce the non-homogeneity of the Hd series are here investigated. Our results show that for ta = 1 min the underestimation is practically negligible, whereas for larger temporal aggregations with d = ta the error in a single Hd can reach values up to 50% and in a series of Hd in the average up to 17%. Relationships between the non-dimensional ratio ta/d and the average underestimation of Hd, derived through continuous rainfall data observed in many stations of Central Italy, are presented to overcome this issue. These equations allow to improve the Hd estimates and the associated depth-duration-frequency curves at least in areas with similar climatic conditions. The effect of the correction of the Hd series on the rainfall depth-duration-frequency curves is quantified. Our results indicate that the improvements obtained by the proposed procedure are of the order of 10%.

This is a copy of the author 's final draft version of an article published in the journal Theoretical and applied climatology. The final publication is available at Springer via http://dx.doi.org/10.1007/s00704-016-1998-0 The fractal behavior of extreme rainfall intensities registered between 1940 and 2012 by the Retiro Observatory of Madrid (Spain) has been examined, and a simple scaling regime ranging from 25 min to 3 days of duration has been identified. Thus, an intensity-duration-frequency (IDF) master equation of the location has been constructed in terms of the simple scaling formulation. The scaling behavior of probable maximum precipitation (PMP) for durations between 5 min and 24 h has also been verified. For the statistical estimation of the PMP, an envelope curve of the frequency factor (k m ) based on a total of 10,194 station-years of annual maximum rainfall from 258 stations in Spain has been developed. This curve could be useful to estimate suitable values of PMP at any point of the Iberian Peninsula from basic statistical parameters (mean and standard deviation) of its rainfall series.

The final publication is available at Springer via http://dx.doi.org/10.1007/s00704-015-1476-0 Relationship between maximum rainfall rates for time intervals between 5 minutes and 24 hours has been studied from almost a century (1905-2003) of rainfall data registered in the Ebre Observatory (Tarragona, Spain). Intensity-duration-frequency (IDF) curves and its master equation for every return period in the location have been obtained, as well as the probable maximum precipitation (PMP) for all the considered durations. In particular, the value of the 1-day PMP has resulted 415 mm, very similar to previous estimations of this variable for the same location. Extreme rainfall events recorded in this period have been analyzed and classified according to their temporal scale. Besides the three main classes of cases corresponding to the main meteorological scales, local, mesoscale and synoptic, a fourth group constituted by complex events with high intense rates for a large range of durations has been identified also, indicating the contribution of different scale meteorological processes acting together in the origin of the rainfall. A weighted intensity index taking into account the maximum rainfall rate in representative durations of every meteorological scale has been calculated for every extreme rainfall event in order to reflect their complexity.