Suchergebnisse

Abstract. A large fraction of extreme precipitation and flood events across western Europe are triggered by atmospheric rivers (ARs). The association between ARs and extreme precipitation days over the Iberian Peninsula has been well documented for western river basins. Since ARs are often associated with high impact weather, it is important to
study their medium-range predictability. Here we perform such an assessment
using the ECMWF ensemble forecasts up to 15 d for events where ARs made
landfall in the western Iberian Peninsula during the winters spanning between 2012–2013 and 2015–2016. Vertically integrated horizontal water vapor transport (IVT) and precipitation from the 51 ensemble members of the ECMWF Integrated Forecasting System (IFS) ensemble (ENS) were processed over a domain including western Europe and the contiguous North Atlantic Ocean. Metrics concerning AR location, intensity, and orientation were computed, in order to compare the predictive skill (for different prediction lead times) of IVT and precipitation. We considered several regional boxes over western Iberia, where the presence of ARs is detected in analysis/forecasts, enabling the construction of contingency tables and
probabilistic evaluation for further objective verification of forecast
accuracy. Our results indicate that the ensemble forecasts have skill in
detecting upcoming AR events, which can be particularly useful to better
predict potential hydrometeorological extremes. We also characterized how
the ENS dispersion and confidence curves change with increasing forecast
lead times for each sub-domain. The probabilistic evaluation, using receiver operating characteristic (ROC)
analysis, shows that for short lead times precipitation forecasts are more
accurate than IVT forecasts, while for longer lead times this reverses
(∼10 d). Furthermore, we show that this reversal occurs for shorter lead times in areas where the AR contribution is more relevant for winter precipitation totals (e.g., northwestern Iberia).

Abstract. Increasing drought conditions under global warming are expected to alter the
frequency and distribution of large and high-intensity wildfires. However,
our understanding of the impact of increasing drought on extreme wildfires
events remains incomplete. Here, we analyzed the weather conditions
associated with the extreme wildfires events that occurred in Mediterranean
France during the exceptionally dry summers of 2003 and 2016. We identified
that these fires were related to two distinct shifts in the fire
weather space towards fire weather conditions that had not been explored before and
resulting from specific interactions between different types of drought and
different fire weather types. In 2016, a long-lasting "press drought"
intensified wind-driven fires. In 2003, a "hot drought" combining a
heat wave with a press drought intensified heat-induced fires. Our findings
highlight that increasing drought conditions projected by climate change
scenarios might affect the dryness of fuel compartments and lead to a higher
frequency of extremes wildfires events.

The task of retrieving information about past flood events is very important to reconstruct flood series data. In this work, a wide range of different sources including newspapers, technical reports, and books was consulted in order to recover information about catastrophic flood events in Badajoz (Spain). A set of 37 catastrophic floods of the Guadiana River that occurred in Badajoz in the winter months (DJFM - December, January, February, and March) have been recovered since 1500 CE. This strong seasonality constrain is due to the important influence of the large-scale circulation patterns in winter affecting the climate of the Iberian Peninsula. Moreover, it is found that there is a clear difference between a higher number of floods in the 19th and 20th centuries and a substantial lower value of floods in the 16th–18th centuries. Finally, we evaluated the long-term evolution and inter-annual variability of the precipitation and the main large-scale atmospheric circulation patterns that govern climate variability in Iberia (NAO and EA modes) for the period 1851–1985. This analysis suggests that most extreme floods observed in this period (26 events) correspond to consecutive months with higher than usual precipitation, driven in part by unusual values of both the NAO and the EA modes of variability. ; This research was supported by the Economy and Infrastructure Counselling of the Junta of Extremadura through project IB16127, IB20080, and grant GR18081 (co-financed by the European Regional Development Fund) and by the Ministerio de Economía y Competitividad of the Spanish Government (CGL2017-87917-P). The research of N. Bravo-Paredes has been supported by the predoctoral fellowship PRE2018-084897 from Agencia Estatal de Investigación (Ministerio de Ciencia, Innovación y Universidades) of the Spanish Government. ; peerReviewed

Abstract. We present a procedure that allows the operational generation of daily
forecasts of fire danger over Mediterranean Europe. The procedure combines
historical information about radiative energy released by fire events with
daily meteorological forecasts, as provided by the Satellite Application
Facility for Land Surface Analysis (LSA SAF) and the European Centre for
Medium-Range Weather Forecasts (ECMWF). Fire danger is estimated based on
daily probabilities of exceedance of daily energy released by fires occurring
at the pixel level. Daily probability considers meteorological factors by
means of the Canadian Fire Weather Index (FWI) and is estimated using a daily
model based on a generalized Pareto distribution. Five classes of fire danger
are then associated with daily probability estimated by the daily model. The
model is calibrated using 13 years of data (2004–2016) and validated
against the period of January–September 2017. Results obtained show that
about 72 % of events releasing daily energy above 10 000 GJ belong to the
"extreme" class of fire danger, a considerably high fraction that is more
than 1.5 times the values obtained when using the currently
operational Fire Danger Forecast module of the European Forest Fire
Information System (EFFIS) or the Fire Risk Map (FRM) product disseminated by
the LSA SAF. Besides assisting in wildfire management, the procedure is
expected to help in decision making on prescribed burning within the
framework of agricultural and forest management practices.

Abstract. Portugal is recurrently affected by large wildfire events that have serious
impacts at the socio-economic and environmental levels and dramatic
consequences associated with the loss of lives and the destruction of the
landscape. Accordingly, seasonal forecasts are required to assist fire
managers, thus contributing to alter the historically based purely reactive
response. In this context, we present and discuss a statistical model to
estimate the probability that the total burned area during summer will
exceed a given threshold. The statistical model uses meteorological
information that rates the accumulation of thermal and vegetation stress.
Outlooks for the 39-year study period (1980–2018) show that, when the
statistical model is applied from 26 May to 30 June, out of
the six severe years, only one year is not anticipated as potentially severe
and, out of the six weak years, only one is not anticipated as potentially
weak. The availability of outlooks of wildfire potential with an
anticipation of up to 1 month before the starting of the fire season, such
as the one proposed here, may serve to provide clear directions for the fire
community when planning prevention and combating fire events.

A record 500,000 hectares burned in Portugal during the extreme wildfire season of 2017, with more than 120 human lives lost. Here we analyse the climatic factors responsible for the burned area (BA) from June to October series in Portugal for the period 1980–2017. Superposed onto a substantially stationary trend on BA data, strong oscillations on shorter time scales were detected. Here we show that they are significantly affected by the compound effect of summer (June-July-August) drought and high temperature conditions during the fire season. Drought conditions were calculated using the Standardized Precipitation Evapotranspiration Index (SPEI), the Standardized Precipitation Index (SPI) and the Standardized Soil Moisture Index (SSI). Then the extent to which the burned area has diverged from climate-expected trends was assessed. Our results indicate that in the absence of other drivers, climate change would have led to higher BA values. In addition, the 2017 extreme fire season is well captured with the model forced with climate drivers only, suggesting that the extreme fire season of 2017 could be a prelude to future conditions and likewise events. Indeed, the expected further increase of drought and high temperature conditions in forthcoming decades, point at a potential increase of fire risk in this region. The climate-fire model developed in this study could be useful to develop more skilled seasonal predictions capable of anticipating potentially hazardous conditions. ; M. Turco has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 740073 (CLIM4CROP project). S. Augusto was supported by FCT-MCTES (SFRH/BPD/109382/2015). RMT was supported by national funds through Fundação para a Ciência e a Tecnologia, Portugal (FCT) under project FireCast (PCIF/GRF/0204/2017). SJ was supported by the Plan Propio de Investigación of the University of Murcia (Grant No. UMU-2017-10604). Further support was provided under projects: (i) CGL2014-59677-R and CGL2017-87921-R also partially funded by FEDER; (ii) POCI-01-0145-FEDER-006939 (LEPABE -UID/EQU/00511/2013) funded by the European Regional Development Fund (ERDF), through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI) and by national funds, through FCT - Fundação para a Ciência e a Tecnologia; (iii) NORTE-01-0145-FEDER-000005-LEPABE-2-ECO-NNOVATION, supported by North Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the ERDF; (iv) Investigador FCT contract IF/01101/2014 (Nuno Ratola); (v) the Fundación Séneca - Regional Agency for Science and Technology of Murcia through the CLIMAX project (20642/JLI/18). We acknowledge the E-OBS dataset from the EU-FP6 project UERRA (http://www.uerra.eu) and the Copernicus Climate Change Service, and the data providers in the ECA&D project (https://www.ecad.eu); the European Forest Fire Information System-EFFIS (http://effis.jrc.ec.europa.eu) of the European Commission Joint Research Centre for the fire data. ; Peer Reviewed ; Postprint (published version)

The summers of 2018 and 2019 were characterized by unusually warm conditions over Europe. Here, we describe the intense heatwaves striking the Iberian Peninsula in early August 2018 and late June 2019. The 2018 episode was relatively short-lived but outstanding in amplitude, particularly in western Iberia. Similar to previous mega-heatwaves, the 2019 event was long-lasting and affected large areas of western and central Europe, including eastern Iberia. During these events, many absolute temperature records were broken in western and eastern Iberia, respectively (some of them standing since 2003). In both cases, a cyclonic circulation off the coast in the northeastern Atlantic and a strong subtropical ridge pattern over the affected area promoted the advection of an anomalously warm air mass. This paper highlights the role of these very warm, stable and dry air intrusions of Saharan origin in the western and eastern Iberia heatwave events. Using a thermodynamical classification based on the geopotential height thickness and potential temperature, we show how the magnitude and poleward extension of these Saharan intrusions were unprecedented in the period since 1948. The relationship between Iberian heatwaves and Saharan warm air intrusions is discussed in the long-term context, showing a closer link in southern sectors of the Peninsula. However, a consistent poleward trend in the latitudinal extension of these subtropical intrusions reveals their increasing relevance for heatwaves in northern sectors of Iberia and western Europe. This overall trend is accompanied by an apparent "see-saw" in the occurrence of subtropical intrusions between eastern and western Iberia on multi-decadal scales. ; We acknowledge the E-OBS dataset from the EU-FP6 project ENSEMBLES (http://ensembleseu.metoffice.com) and the data providers in the ECA&D project (http://www.ecad.eu). PMS was supported by the projects IMDROFLOOD – Improving Drought and Flood Early Warning, Forecasting and Mitigation using real-time hydroclimatic indicators (WaterJPI/0004/2014) and HOLMDRIVE – North Atlantic Atmospheric Patterns influence on Western Iberia Climate: From the Lateglacial to the Present [PTDC/CTA-GEO/29029/2017] through Fundação para a Ciência e a Tecnologia, Portugal (FCT). RMT was partially supported by national funds through Fundação para a Ciência e a Tecnologia, Portugal (FCT) under project FireCast (PCIF/GRF/0204/2017). This research was partially funded by the European Union's Horizon 2020 research and innovation programme under Grant agreement No 690462 within the frame of the ERANET "European Research Area for Climate Services –ERA4CS" 2016 Call. AMR was supported by the Scientific Employment Stimulus 2017 from FCT (CEECIND/00027/2017). We thank the Editor and reviewers for their helpful comments on this manuscript.

The explosive cyclogenesis of extratropical cyclones and the occurrence of atmospheric rivers are characteristic features of a baroclinic atmosphere, and are both closely related to extreme hydrometeorological events in the mid-latitudes, particularly on coastal areas on the western side of the continents. The potential role of atmospheric rivers in the explosive cyclone deepening has been previously analysed for selected case studies, but a general assessment from the climatological perspective is still missing. Using ERA-Interim reanalysis data for 1979–2011, we analyse the concurrence of atmospheric rivers and explosive cyclogenesis over the North Atlantic and North Pacific basins for the extended winter months (ONDJFM). Atmospheric rivers are identified for almost 80% of explosive deepening cyclones. For non-explosive cyclones, atmospheric rivers are found only in roughly 40% of the cases. The analysis of the time evolution of the high values of water vapour flux associated with the atmospheric river during the cyclone development phase leads us to hypothesize that the identified relationship is the fingerprint of a mechanism that raises the odds of an explosive cyclogenesis occurrence and not merely a statistical relationship. These new insights on the relationship between explosive cyclones and atmospheric rivers may be helpful to a better understanding of the associated high-impact weather events. ; Jorge Eiras-Barca was financially supported by the Spanish government (MINECO) and Xunta de Galicia (CGL2013-45932-R, GPC2015/014 – ERDF), and contributions by the COST action MP1305 and CRETUS Strategic Partnership (AGRUP2015/02). Alexandre M. Ramos was supported through a postdoctoral grant (SFRH/BPD/84328/2012) from the Portuguese Science Foundation (Fundação para a Ciência e a Tecnologia, FCT). Alexandre M. Ramos and Ricardo M. Trigo were supported by the project IMDROFLOOD – Improving Drought and Flood Early Warning, Forecasting and Mitigation using real-time hydroclimatic indicators (WaterJPI/0004/2014), ...

Abstract. The floods that struck the lower Tagus valley in February 1979 correspond to the most intense floods in this river and affected the largest number of people in a river flow event in Portugal during the last 150 years. In fact, the vast area affected significantly impacted circa 10 000 people in the lower Tagus sector (and an additional 7000 in other regions of Portugal), including thousands of people evacuated or made homeless. In this context, the present study focuses on an in-depth analysis of this event from a hydrodynamic perspective by means of the Iber+ numerical model and on developing strategies to mitigate the flood episodes that occur in the lower section of the Tagus River using the exceptional floods of February 1979 as a benchmark. In this sense, dam operating strategies were developed and analyzed for the most important dam along the Tagus River basin in order to propose effective procedures to take advantage of these infrastructures to minimize the effect of floods. Overall, the numerical results indicate a good agreement with watermarks and some descriptions of the 1979 flood event, which demonstrates the model capability to evaluate floods in the area under study. Regarding flood mitigation, results obtained indicate that the frequency of floods can be reduced with the proposed strategies, which were focused on providing optimal dam operating rules to mitigate flooding in the lower Tagus valley. In addition, hydraulic simulations corroborated an important decrease in water depth and velocity for the most extreme flood events, and also a certain reduction in the flood extension was detected. This confirms the effectiveness of the proposed strategies to help in reducing the flood impact in the lower Tagus valley through the efficient functioning of dams.

Abstract. To mark the 20th anniversary of Natural Hazards and Earth System Sciences (NHESS), an interdisciplinary and international journal dedicated
to the public discussion and open-access publication of high-quality studies
and original research on natural hazards and their consequences, we
highlight 11 key publications covering major subject areas of NHESS that
stood out within the past 20 years. The papers cover all the topics contemplated in the European Geosciences Union (EGU) Division on Natural Hazards including dissemination, education, outreach and teaching. The selected articles thus represent excellent scientific contributions in the major areas of natural hazards and risks and helped NHESS to become an exceptionally strong journal representing interdisciplinary areas of natural hazards and risks. At its 20th anniversary, we are proud that NHESS is not only used by scientists to disseminate research results and novel ideas but also by practitioners and decision-makers to present effective solutions and strategies for sustainable disaster risk reduction.

15 Pag., 3 Tabl., 10 Fig. ; This work provides a first assessment of the outstanding characteristics of the anomalous precipitation occurrence in the winter of 2010 over the Iberian Peninsula, as well as on the associated atmospheric driving mechanisms. Large areas of Iberia, those located in the western and southern sectors, registered a new historical maximum in winter precipitation values. Simultaneously, the most extreme, negative North Atlantic Oscillation (NAO) index for winter was recorded in 2010. The anomalous pressure gradient in the North Atlantic region steered a large number of low pressure systems via an unusually southern path, directly influencing Iberia and northern Africa. Storms were frequent, and a high number of days occurred with weather types prone to cause precipitation. In addition, the most extreme daily precipitation episodes were recorded during the period with the strongest negative NAO index. Global climate models for the entire 21st century show that strong negative NAO winters, similar to that which occurred in 2010, may be expected in the future. ; This work was supported by the research projects CGL2008-01189/BTE and CGL2006-11619/ HID, financed by the Spanish Commission of Science and Technology and FEDER; by EUROGEOSS (FP7-ENV-2008-1- 226487) and ACQWA (FP7-ENV-2007-1-212250), financed by the VII Framework Programme of the European Commission; and 'La nieve en el Pirineo aragonés: distribución espacial y su respuesta a las condiciones climáticas', financed by 'Obra Social La Caixa' and the Aragón Government. Ricardo Trigo's work was partially supported by the FCT (Portugal) through project ENAC (PTDC/AAC-CLI/103567/2008). ; Peer reviewed

Near-surface wind speed trends recorded at 67 land-based stations across Spain and Portugal for 1961-2011, also focusing on the 1979-2008 subperiod, were analyzed. Wind speed series were subjected to quality control, reconstruction, and homogenization using a novel procedure that incorporated the fifth-generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model (MM5)-simulated series as reference. The resultant series show a slight downward trend for both 1961-2011 (-0.016ms-1 decade-1) and 1979-2008 (-0.010ms-1 decade-1). However, differences between seasons with declining values in winter and spring, and increasing trends in summer and autumn, were observed. Even though wind stilling affected 77.8% of the stations in winter and 66.7% in spring, only roughly 40% of the declining trends were statistically significant at the p < 0.10 level. On the contrary, increasing trends appeared in 51.9% of the stations in summer and 57.4% in autumn, with also around 40% of the positive trends statistically significant at the p < 0.10 level. In this article, the authors also investigated (i) the possible impact of three atmospheric indices on the observed trends and (ii) the role played by the urbanization growth in the observed decline. An accurate homogenization and assessment of the long-term trends of wind speed is crucial for many fields such as wind energy (e.g., power generation) and agriculture-hydrology (e.g., evaporative demand). © 2014 American Meteorological Society. ; The authors wish to acknowledge the editor and three anonymous reviewers for their detailed and helpful comments to the original manuscript. This research was supported by (i) the JAE-DOC043 (CSIC; European Social Fund, FSE) and the JCI-2011-10263 Grants; (ii) A. S.-L. received a postdoctoral fellowship from the Secretaria per a Universitats i Recerca del Departament d'Economia i Coneixement, de la Generalitat de Catalunya i del programa Cofund de les Accions Marie Curie del 7è Programa marc d'R+D de la Unió Europea (2011 BP-B 00078); (iii) Projects CGL2011-27574-C02-02, CGL2011-27536/HID, CGL2011-29263-C02-01, and PSE.120000.2007.14, financed by the Spanish Commission of Science and Technology and FEDER; ACQWA (FP7-ENV- 2008-1-212250), financed by the European Comission; Efecto de los escenarios de cambio climático sobre la hidrología superficial y la gestión de embalses del Pirineo Aragonés, financed by Obra Social La Caixa; CTTP1/12 Creación de un modelo de alta resolución espacial para cuantificar la esquiabilidad y la afluencia turística en el Pirineo bajo distintos escenarios de cambio climático, financed by the Comunidad de Trabajo de los Pirineos; ENAC (PTDC/AAC-CLI/103567/2008), financed by the Portuguese Science Foundation; and (iv) the Climatology Group (2009 SGR 443, Catalan Government). The authors thank the AEMET and the IPMA institutions for the observed wind data and particularly José-Antonio Guijarro (AEMET-Baleares) and Juan-José Vizcaíno (AEMET-Valencia) for their useful comments and information. We thank Ptr Stepanek for providing the AnClim software and the MAR research group of the University of Murcia for providing the MM5-simulated wind speed series, particularly the assistance of Raquel Lorente-Plazas and Juan Pedro Montávez. ; Peer Reviewed

9 Pags., 6 Figs. The Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the of the work, journal citation and DOI. ; We use high quality climate data from ground meteorological stations in the Iberian Peninsula (IP) and robust drought indices to confirm that drought severity has increased in the past five decades, as a consequence of greater atmospheric evaporative demand resulting from temperature rise. Increased drought severity is independent of the model used to quantify the reference evapotranspiration. We have also focused on drought impacts to drought-sensitive systems, such as river discharge, by analyzing streamflow data for 287 rivers in the IP, and found that hydrological drought frequency and severity have also increased in the past five decades in natural, regulated and highly regulated basins. Recent positive trend in the atmospheric water demand has had a direct influence on the temporal evolution of streamflows, clearly identified during the warm season, in which higher evapotranspiration rates are recorded. This pattern of increase in evaporative demand and greater drought severity is probably applicable to other semiarid regions of the world, including other Mediterranean areas, the Sahel, southern Australia and South Africa, and can be expected to increasingly compromise water supplies and cause political, social and economic tensions among regions in the near future. ; This work has been supported by research projects CGL2011-27574-CO2-02, CGL2011-27536 and CGL2011–24185 financed by the Spanish Commission of Science and Technology and FEDER, 'Demonstration and validation of innovative methodology for regional climate change adaptation in the Mediterranean area (LIFE MEDACC)' financed by the LIFE programme of the European Commission, CTTP1/12, financed by the Comunidad de Trabajo de los Pirineos, and QSECA (PTDC/AAG-GLO/4155/2012) funded by the Portuguese Foundation for Science and Technology (FCT). ASL was supported by a postdoctoral fellowship from the Catalan Government (2011 BP-B 00078) and CAM was supported by a Juan de la Cierva fellowship by the Spanish Government. ; Peer reviewed

14 Pags., 4 Figs. ; We evaluated the response of the Earth land biomes to drought by correlating a drought index with three global indicators of vegetation activity and growth: vegetation indices from satellite imagery, tree-ring growth series, and Aboveground Net Primary Production (ANPP) records. Arid and humid biomes are both affected by drought, and we suggest that the persistence of the water deficit (i.e., the drought time-scale) could be playing a key role in determining the sensitivity of land biomes to drought. We found that arid biomes respond to drought at short time-scales; that is, there is a rapid vegetation reaction as soon as water deficits below normal conditions occur. This may be due to the fact that plant species of arid regions have mechanisms allowing them to rapidly adapt to changing water availability. Humid biomes also respond to drought at short time-scales, but in this case the physiological mechanisms likely differ from those operating in arid biomes, as plants usually have a poor adaptability to water shortage. On the contrary, semiarid and subhumid biomes respond to drought at long time-scales, probably because plants are able to withstand water deficits, but they lack the rapid response of arid biomes to drought. These results are consistent among three vegetation parameters analyzed and across different land biomes, showing that the response of vegetation to drought depends on characteristic drought time-scales for each biome. Understanding the dominant time-scales at which drought most influences vegetation might help assessing the resistance and resilience of vegetation and improving our knowledge of vegetation vulnerability to climate change. ; This work was supported by projects financed by the Spanish Commission of Science and Technology (CGL2011-27574-CO2-02, CGL2011-27536 and CGL2011-26654) and the Aragón Government. C.G. and R.T. were supported by Project MEDIATIC (PTDC/AAC-CLI/103361/2008) funded by the Portuguese Foundation for Science and Technology (FCT). J.J.C. thanks the support of ARAID and A.S-L. was supported by a postdoctoral fellowship from the Generalitat de Catalunya (2009 BP-A 00035). ; Peer reviewed