A climatology of western Mediterranean precipitation extremes focusing on the study of moisture origin

A presente tese enmárcase no estudo da orixe da precipitación extrema e ten como principal obxectivo aclarar definitivamente cales son as principais fontes de humidade que alimentan as chuvias torrenciais do Mediterráneo Occidental. A principal ferramenta empregada para tal fin é unha técnica de rastrexo de humidade coñecida como trazadores de vapor de auga. Esta técnica acóplase a un modelo meteorolóxico, no noso caso o WRF (Weather Research and Forecasting model). O modelo executouse para máis dun cento de casos ocorridos en diferentes países do Mediterráneo entre 1980 e 2015. Isto fixo posible extraer conclusións xerais e robustas, mellorando así o coñecemento previo sobre este asunto, que se baseaba xeralmente no estudo de casos concretos en zonas concretas. A principal conclusión que se extrae da tese é que a aportación do Mar Mediterráneo como fonte de humidade é, en termo medio, menor do que moitas veces se presume, arredor dun 35%. Encontramos que as fontes remotas, nalgúns casos tan remotas coma o Pacífico tropical ou o hemisferio sur, xogan un papel determinante nestes eventos. De feito, a contribución de fontes remotas é en termo medio superior á contribución de fontes locais nun 10%. Polo tanto, se queremos comprender plenamente este tipo de eventos catastróficos, temos que estudalos dende un enfoque máis global e menos local ou rexional, especialmente cando intentan atribuírse ao cambio climático

Análisis de las fuentes de humedad en los episodios de lluvias torrenciales del otoño de 1982 empleando el método de los trazadores

Màster de Meteorologia, Facultat de Física, Universitat de Barcelona, Curs: 2015-2016, Tutors: M. Carmen Llasat Botija, Gonzalo Miguez MachoDurante los días del 19 al 21 de octubre y del 6 al 8 de noviembre de 1982, se produjeron en la Península Ibérica dos eventos de precipitaciones extremas de una magnitud excepcional, que causaron grandes pérdidas materiales y numerosas víctimas mortales. El primero afectó especialmente al Levante y el segundo a Cataluña, Andorra y sur de Francia. Las situaciones meteorológicas que provocaron tales eventos fueron las dos más típicas asociadas con inundaciones en Cataluña y el Levante, por lo que los resultados pueden ser extrapolables a otros casos. En este trabajo nos centraremos en estudiar de forma detallada las posibles fuentes de humedad que, a priori, pudieron jugar un papel relevante para producir las intensísimas precipitaciones. Para ello, hemos empleado el método de los trazadores de humedad instalados en el modelo meteorológico regional WRF. Los resultados obtenidos muestran que en el evento de octubre, la evaporación en el Mediterráneo los días previos a la catástrofe y la inyección de humedad desde África fueron importantes para dar lugar a las precipitaciones, aunque solo explican en torno a la mitad de estas. En el evento de noviembre, la humedad procedente del Atlántico actuó como fuente predominante, si bien es cierto que su predominio en las lluvias del sur de Francia no fue tan claro y en esta región la influencia del Mediterráneo fue considerable

Local and remote moisture sources for extreme precipitation: a study of the two catastrophic 1982 western Mediterranean episodes

Floods and flash floods are frequent in the south of Europe resulting from heavy rainfall events that often produce more than 200 mm in less than 24 h. Even though the meteorological conditions favourable for these situations have been widely studied, there is a lingering question that still arises: what humidity sources could explain so much precipitation? To answer this question, the regional atmospheric Weather Research and Forecasting (WRF) model with a recently implemented moisture tagging capability has been used to analyse the main moisture sources for two catastrophic flood events that occurred during the autumn of 1982 (October and November) in the western Mediterranean area, which is regularly affected by these types of adverse weather episodes. The procedure consists in selecting a priori potential moisture source regions for the extreme event under consideration, and then performing simulations using the tagging technique to quantify the relative contribution of each selected source to total precipitation. For these events we study the influence of four possible potential sources: (1) evaporation in the western Mediterranean; (2) evaporation in the central Mediterranean; (3) evaporation in the North Atlantic; and (4) advection from the tropical and subtropical Atlantic and Africa. Results show that these four moisture sources explain most of the accumulated precipitation, with the tropical and subtropical input being the most relevant in both cases. In the October event, evaporation in the western and central Mediterranean and in the North Atlantic also had an important contribution. However, in the November episode tropical and subtropical moisture accounted for more than half of the total accumulated rainfall, while evaporation in the western Mediterranean and North Atlantic played a secondary role and the contribution of the central Mediterranean was almost negligible. Therefore, remote sources were crucial: in the October event they played a similar role to local sources, whereas in the November case they were clearly dominant. In both episodes, long-distance moisture transport from the tropics and subtropics mostly occurred in mid-tropospheric layers, via well-defined moisture plumes with maximum mixing ratios at medium levels

Climatology and ranking of hazardous precipitation events in the western Mediterranean area

The western Mediterranean region often suffers from the devastating effects of flooding, caused by enormous rain accumulations that sometimes resemble the values produced by tropical systems. Despite the climatic and social relevancy of this type of episodes, there are some fundamental questions that would still be difficult to answer today, for example: where within the region are more cases recorded? or, which were the most potentially dangerous episodes? In this study, we identify, and then gather and unify information from, all the daily events occurred from 1980 to 2015. Using the MESCAN high-resolution gridded rainfall dataset, events are detected and for each case, the date and affected regions are recorded. Subsequently, events are ranked according to their magnitude and classified by weather type. In addition, flood data from the FLOODHYMEX and EM-DAT databases are used to check whether the precipitation episodes resulted in flooding. All this information is collected into a publicly available single database. Results show that the highest number of events per year is recorded in the Languedoc-Roussillon region (France) and in the Valencian Community (Spain). The cases of greatest magnitude, which are associated with a larger number of floods, present a very marked seasonality, with about 80% of them occurring in September, October and November. Finally, we show that only four weather types are present in most of the days with hazardous rainfall in the western Mediterranean. The most hazardous situation is characterized by a low-pressure area at all tropospheric levels in the eastern Atlantic, forming a block pattern with an anticyclonic ridge that tends to extend from the Central Mediterranean to Central Europe. About 40% of the most extraordinary cases are associated with this configuration. As an example, the infamous Piedmont (Italy) 1994 episode, in the top 10 of the ranking, was produced by an atmospheric pattern of this typeFunding comes from the Spanish Ministerio de Economia y Competitividad OPERMO (CGL2017-89859-R to GMM and DIC), CLICES (CGL2017-83866-C3-2-R to MLC) and M-CostAdapt (CTM2017-83655-C2-2-R to MCLL) projects, the European Union Interreg V POCTEFA project (EFA210/16 PIRAGUA to MCLL) and the CRETUS strategic partnership (AGRUP2015/02 to GMM and DIC). All these programs are co-funded by the European Union ERDF. DIC and MLC were awarded a pre-doctoral FPI (PRE2018-084425) and FPU (FPU2017/02166) grant, respectively, both from the Spanish Ministry of Science, Innovation and UniversitiesS

On the impact of initial conditions in the forecast of Hurricane Leslie extratropical transition

Hurricane Leslie (2018) was a non-tropical system that lasted for a long time undergoing several transitions between tropical and extratropical states. Its trajectory was highly uncertain and difficult to predict. Here the extratropical transition of Leslie is simulated using the Model for Prediction Across Scales (MPAS) with two different sets of initial conditions (IC): the operational analysis of the Integrate Forecast System (IFS) and the Global Forecast System (GFS).This work was partially supported by the research project PID2019-105306RB-I00/AEI/10.13039/501100011033, and the two ECMWF Special Projects (SPESMART and SPESVALE)

Anthropogenic Warming Had a Crucial Role in Triggering the Historic and Destructive Mediterranean Derecho in Summer 2022

A record-breaking marine heatwave and anthropogenic climate change have substantially contributed to the development of an extremely anomalous and vigorous convective windstorm in August 2022 over the Mediterranean Sea

Characterisation of Extreme Precipitation Events in the Pyrenees: From the Local to the Synoptic Scale

Mountain systems within the Mediterranean region, e.g., the Pyrenees, are very sensitive to climate change. In the present study, we quantified the magnitude of extreme precipitation events and the number of days with torrential precipitation (daily precipitation ≥ 100 mm) in all the rain gauges available in the Pyrenees for the 1981-2015 period, analyzing the contribution of the synoptic scale in this type of event. The easternmost (under Mediterranean influence) and north-westernmost (under Atlantic influence) areas of the Pyrenees registered the highest number of torrential events. The heaviest events are expected in the eastern part, i.e., 400 mm day−1 for a return period of 200 years. Northerly advections over the Iberian Peninsula, which present a low zonal index, i.e., implying a stronger meridional component, give rise to torrential events over the western Pyrenees; and easterly advections favour extreme precipitation over the eastern Pyrenees. The air mass travels a long way, from the east coast of North America, bringing heavy rainfall to the western Pyrenees. In the case of the torrential events over the eastern Pyrenees, the trajectory of the air mass causing the events in these areas is very short and originates in the Mediterranean Basin. The North Atlantic Oscillation (NAO) index has no influence upon the occurrence of torrential events in the Pyrenees, but these events are closely related to certain Mediterranean teleconnections such as the Western Mediterranean Oscillation (WeMO)

Towards an atmosphere more favourable to firestorm development in Europe

Deep pyroconvection associated with the development of firestorms, can significantly alter wildfire spread, causing severe socioeconomic and environmental impacts, and even posing a threat to human’s lives. However, the limited number of observations hinders our understanding of this type of events. Here, we identify the environmental conditions that favour firestorm development using a coupled fire–atmosphere numerical model. From climate model projections for the 21st century, we show that the number of days with deep pyroconvection risk will increase significantly in southern Europe, especially in the western Mediterranean region, where it will go from between 10 and 20 days per year at present to between 30 and 50 days per year by the end of the century. Our results also suggest fuel reduction as an effective landscape management strategy to mitigate firestorm risks in the future

Record-shattering 2023 Spring heatwave in western Mediterranean amplified by long-term drought

Abstract The western Mediterranean region experienced an exceptional and unprecedented early heatwave in April 2023. By shattering historical temperature records, especially in the Iberian Peninsula and northwestern Africa, this extreme offers a stark illustration of a drought–heatwave compound event. Here, we investigate the soil moisture–temperature interactions that underpinned this event, using the most up-to-date observations and a robust statistical analysis. Our results reveal that soil moisture deficit preconditions, concurring with a strong subtropical ridge as a synoptic driver, had a key contribution to the amplification and duration of this record-breaking heatwave. Specifically, we estimate that the most extreme temperature records would have been 4.53 times less likely and 2.19 °C lower had the soils been wet. These findings indicate that soil moisture content may be a crucial variable for seasonal forecasting of early HW in this region and in other Mediterranean climate regimes that are already suffering an increment in the frequency of compound drought–heatwave events

Reply to Comment on ‘The central role of forests in the 2021 European floods’ by Arie Staal and Gerbrand Koren

In their comment, Staal and Koren replicate our experiment using a different methodology, namely a Lagrangian moisture tracking method. Their results largely agree with ours, which is therefore a good indication of the high robustness and accuracy of these findings. Although this comparison is of great value, to a large extent their comment is a criticism of our interpretation of the results, with which we disagree. Their main objection refers to the fact that, since they show that the relative contribution of forests to the precipitation recorded during the event was not anomalous (above average), their ‘central role’ would not be justified. However, a relevant or even a dominant contribution does not necessarily have to be anomalous, so that claim does not hold. In other words, forests played a ‘central role’ because their contribution (adding transpiration and interception loss) was greater than 50%, regardless of what their average contribution to precipitation in the first half of July might be