Maria Dolors Martínez

The catastrophic events caused by the DANA (cold drop) on October 29, 2024, in Valencia (Spain) lead us to reflect on whether we are facing a trend toward extreme rainfall events never before seen. The mega-rainfalls of 10/29/24, as well as the resulting flooding, caused 228 deaths, as well as extraordinary economic damage. How could such a catastrophic outcome have occurred in a country like Spain with a long tradition of weather forecasting? Are we facing a mega-event, never seen before?The province of Valencia has suffered torrential rainfall events for as long as recorded memory exists. The extreme rainfall that occurred in Alcira in 1864 is a memory that still remains today. Valencia is a land where "rain doesn't know how to rain" (Raimon, 1984). Extreme events have occurred in 1957 (1,414 hm3), 1982 (2,225 hm3), 1987 (2,656 hm3) and 2000 (2,196 hm3). From this perspective, the 1,526 hm3 accumulated in the province of Valencia in 2024 do not represent an absolute record. However, the torrential rains of October 29, 2024, had catastrophic effects. Why?It's true that political and administrative errors occurred, but the event's uniqueness stems largely from the fact that it occurred in an area where it had never rained to this extent before. DANAs have a very localized territorial effect. They can occur in areas where they have never occurred before.The research seeks to evaluate the return period of rainfall produced at the head of the Chiva torrent (Poyo torrent), where accumulated rainfall in 24 hours exceeded 600 mm. The traditional methodology (based on the Gumbel distribution, using the data series available at the Chiva station) predicted a much lower rainfall than recorded: 248 mm. Meanwhile, the gridded data generated by Copernicus (E-Obs, 0.1°) show an even lower limit for 500 years: 138 mm. From this perspective we would certainly be facing a mega-event of extreme rainfall.The results suggest the need to develop more detailed risk maps. Maps that consider not only the rainfall recorded in a specific location, but also its immediate geographic surroundings. They also highlight the enormous difficulty of developing gridded databases like E-OBS when there is not a large number of meteorological stations in each area.

Objectives: The main goal of this research is to analyze and quantify reduction of surface temperatures (Ts) in systems which retain and especially harvest water with the focus on blue roofs and to check if just infiltrating water is enough to reduce surface temperatures. Theoretical Framework: ODS13, Climate action; ODS11 Sustainable Cities and communities; Water Sensitive Urban Design construction systems thermal behavior and Cooling water effect implemented by Governments and Municipalities. Method: it’s experimental, based on the quantification of different WSUD construction systems which infiltrate, retain and harvest water during a first year and focused on a blue roof prototype during a second year. Tools used are a thermal camera, a hygrometer and an anemometer. Results and Discussion: Surface temperatures gradients were from 5.3ºC at the infiltration basin, to 6ºC in the blue roof prototype to 14.6ºC in the built blue roof. Construction systems which could retain and harvest water had a Ts underneath the environmental one. They also retain less heat during the night contributing less to UHI than those which can’t retain water. Research implications: this research provides the information about water powerful effect in construction systems which infiltrate and harvest water. They contribute to the decrease of UHI. Originality/value: results demonstrate water cooling effect in infiltrating surfaces which can retain it. Results offer one more construction systems choice criteria in urban design.

Daily maximum, TX, and minimum, TN, temperatures recorded at Fabra Observatory, for the period 1914–2020 (from June to September), have permitted to identify the daytime and night time heatwaves, HWs, at the Barcelona Metropolitan Region, BMR, along 107 years. Four heatwaves indices have been computed both for maximum and minimum temperatures: the number of events per season, HWN; their maximum duration, HWD; their frequency of occurrence, HWF; and the amplitude of the hottest day event, HWA. Trends in these indices have been obtained and their statistical significance quantified by means of the Mann-Kendall test. For the whole period (1914–2020), positive significant trends have been detected for the four indices, with a marked positive trend since year 2000 for TX, and since 1985 for TN. Nevertheless, when 31-year moving windows have been analysed, both positive and negative significant trends are obtained, being remarkable the change in trend signs around 1960s. The convenience of using the four HW indices is evaluated applying a Principal Component Analysis, PCA, obtaining two principal components. Additionally, the spatial distributions of the MODIS land surface temperatures, LST, corresponding to some extreme heatwaves, permits the detection of two hotspots in the BMR, one for TX and the other for TN. It is also worth mentioning that correlations between the Western Mediterranean Oscillation index, WeMOi, and HW episodes are detected, being notable that, at the beginning of these episodes, WEMOi values are usually lower. These correlations could improve the HWs forecasting.

The rainfall regime in Catalonia, NE Spain, has a typical Mediterranean behaviour with irregular monthly amounts, sometimes the result of copious and intense torrential episodes for a few months, while for others precipitation is scarce. In addition, the varied topography of this region is related to significant rainfall differences between its different areas. The monthly precipitation from 97 stations spread throughout the territory, from 1950 to 2016, has allowed a detailed study of the spatial distribution of rainfall irregularity, based on the concept of disparity, D. The disparities have been calculated for every calendar month, to characterise the rainfall amount inter-annual oscillations, and also for all the consecutive months, to evaluate the rainfall disparity along the year. The spatial distribution of D has been obtained for all cases, showing a main general increase from North to South, and a secondary increase from West to East, in some months such as July. The winter months, especially January, have the highest values of D, which can reach the value of 2.0. The dependence of D on altitude and distance from the coast has also been analysed. The correlation is predominantly negative in both cases, although in some months, such as January, this correlation is not so clear. Additionally, the histograms of D show statistical characteristics, such as signs of a Gaussian distribution for some calendar months, as well as clear asymmetry in others. The obtained results could be interesting to detect the calendar months with the highest uncertainty on their expected rain amounts, contributing to a better knowledge of the complex structure of the rainfall Mediterranean regime.

Time trends and their statistical significance for daily minimum, Tmin, and maximum, Tmax, temperatures recorded at the Fabra Observatory (Barcelona) along 102 years (1917–2018) permit to analyse the evolution of every one of the 365 calendar days along the recording period. Relevant changes in the daily temperature regime have been quantified not only by time trends and the Mann–Kendall test, but also by the multifractal analysis applied to consecutive segments of daily temperature data. The evolution of several multifractal parameters (the central Hölder exponent, the spectral asymmetry and spectral amplitude, the complexity index and the Hurst exponent) provides a complementary viewpoint to describe the evolution of the thermometric regime along the 102 recorded years. At monthly scale, the effects of the climate change are characterised by significant positive trends from September to December and very moderate negative trends from April to July. With respect to changes in the calendar-day structure, it is noticeable a shift of the highest minimum and maximum daily temperature from July to August (year 2018) to the beginning of September (projections for years 2030 and 2050) and the projected highest maximum calendar-day temperature exceeding 30 °C.

PÉREZ CAMBRA, María del MarTechnical University of Catalonia (UPC) Barcelona School of ArchitectureDepartment of Architectural Technology I (TA), Centre of Land Policy and Valuations (CPSV)Assistant Professor, Ph.D. Candidate.Av. Diagonal 649, 08028, Barcelona, SpainOrcid : 0000-0003-2456-3302E-mail: mar.perez@upc.eduTelephone: +34 934012576Dr. MARTÍNEZ SANTAFÉ, DolorsTechnical University of Catalonia (UPC) Barcelona School of ArchitectureDepartment of Architectural Technology I (TA), Centre of Land Policy and Valuations (CPSV)ProfessorAv. Diagonal 649, 08028, Barcelona, SpainOrcid : 0000-0001-8200-183XE-mail: dolors.martinez@upc.eduTelephone: +34 934016378Dr.ROCA CLADERA, JosepTechnical University of Catalonia (UPC)Department of Architectural Technology I(TA), Centre of Land Policy and Valuations (CPSV)Full ProfessorAv. Diagonal 649, 08028, Barcelona, Spain.Orcid : 0000-0003-3970-6505E-mail: josep.roca@upc.eduTelephone: +34 934016396Key words: WSUDs; thermal behavior; water“Reduction in water consumption and environmental improvements in Barcelona through WSUDs (Water Sensitive Urban Design Systems”The aim of this communication is showing the research done during the last years to try to reduce water consumption in Barcelona with the WSUDs (Water Urban Design Systems) while reducing surface temperatures with the chosen WSUDs and reducing rainwater runoff especially in the flood areas of the city.Water sensitive urban design (WSUD) have been chosen in this research as an approach to planning and designing urban areas of Barcelona as a resource to reduce the damage urban areas cause to water cycle when we change natural pervious surfaces into impervious ones. Thus, while recuperating in some areas water cycle we can reduce rainwater runoff.This same WSUDs used to reduce rainwater runoff can not only infiltrate and transport water but also to harvest it where it can be more efficient. Water harvesting and reducing he rainwater runoff in a floods area calculations for an area as an example will be shown in this communication. This descentralization of the water treatment will save energy by saving the transportation a long distance away to the water sewage treatment plants. It also avoids diffuse pollution of the runoff since water quality is not worsed due to its transportation to the depuration plant.On the other hand, since we have climate change not all the materials and construction systems are the proper ones. This part is mainly experimental and has taken almost three years measuring surfaces temperatures of some WSUDs of Barcelona and treating its data to stablish a criteria to choose WSUDs which can help to reduce surface temperatures, even in some cases, underneath the environmental temperatures. It means we can produce a better thermal effect while planning and implementing the WSUDs in this case in Barcelona and in homoclimatic cities.Therefore, with this WSUDs specific urbanistic micro-acupuncture we can improve some effects of climatic change such as: water scarcity, floods and heat island effect. This communication will focus and deep on it.

The multifractal detrended fluctuation algorithm is applied to a series of distances and elapsed times between consecutive earthquakes recorded along the years 2000–2018 in the Canterbury region (New Zealand). The time evolution of several multifractal parameters (Hurst exponent, Hölder central and maximum exponents, spectral amplitude, asymmetry, and complexity index) is analyzed. Peaks of multifractal parameters, with statistical significance exceeding 95%, are associated with three earthquakes of notable magnitude (equaling or exceeding Mw = 5.7). Additionally, some other peaks are also associated with the swarm of earthquakes of moderate magnitude. Possible shortcomings created by this assignment to mainshocks or swarms can be removed by comparing the results corresponding to elapsed times and interevent distances between consecutive events. Additionally, the Buishand test, which is used to verify the statistical significance of the detected peaks, also discriminates between mainshocks of notable seismic magnitude and swarms of earthquakes with moderate magnitude. The obtained results, based on the multifractal structure of the seismic activity, could also represent some advances in predicting, with sufficient time, forthcoming mainshocks of high magnitude and mitigate their destructive effects.

The complex non-linear regime of the monthly rainfall in Catalonia (NE Spain) is analyzed by means of the reconstruction fractal theorem and the multifractal detrended fluctuation analysis algorithm. Areas with a notable degree of complex physical mechanisms are detected by using the concepts of persistence (Hurst exponent), complexity (embedding dimension), predictive uncertainty (Lyapunov exponents), loss of memory of the mechanism (Kolmogorov exponent), and the set of multifractal parameters (Hölder exponents, spectral asymmetry, spectral width, and complexity index). Besides these analyses permitting a detailed description of monthly rainfall pattern characteristics, the obtained results should also be relevant for new research studies concerning monthly amounts forecasting at a monthly scale. On one hand, the number of necessary monthly data for autoregressive processes could change with the complexity of the multifractal structure of the monthly rainfall regime. On the other hand, the discrepancies between real monthly amounts and those generated by some autoregressive algorithms could be related to some parameters of the reconstruction fractal theorem, such as the Lyapunov and Kolmogorov exponents.

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...