scholarly journals Impact of Atmospheric Circulation on Flooding Occurrence and Type in Luxembourg (Central Western Europe)

2020 ◽  
Author(s):  
Judith Meyer ◽  
Audrey Douinot ◽  
Erwin Zehe ◽  
Carol Tamez-Meléndez ◽  
Olivier Francis ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
Large Scale ◽  
Western Europe ◽  
Flash Flood ◽  
Flood Events ◽  
Intense Rainfall ◽  
European Continent ◽  
Rainfall Events ◽  
Area Of Interest ◽  
Winter Flood

<p>In the second half of the 20<sup>th</sup> century, hydrological regimes in central Western Europe were largely characterised by large-scale winter floods. This type of event was predominantly triggered by westerly atmospheric fluxes, bringing moist and mild air masses from the Atlantic Ocean to the European continent. Since the late 1990’s, major flooding events seem to have shifted in time and magnitude. Flash flood events, while being a well-known phenomenon in Mediterranean catchments, are increasingly also reported at higher latitudes. Unlike the large-scale winter flood events, flash floods are of very narrow spatial extension and triggered by rather short, but highly intense rainfall events.</p><p>Here, we focus on the specific case of rivers in Luxembourg that have experienced several flash flood events in recent years, while only small to moderate winter flood events have been reported since the late 1990’s. National hydro-meteorological monitoring and flood forecasting systems have been designed for large-scale floods and are not suited for simulating local flash flood events. Therefore, there is a need to increase our understanding of the hydro-meteorological processes underlying flash flood occurrences in our area of interest.</p><p>While increasing air temperature is known to allow a higher air moisture content that can lead to more intense rainfall events and possible flooding, we moreover hypothesize that the recent increase in flash flood occurrences in Luxembourg is reinforced by a change in atmospheric circulation patterns. To test this hypothesis, we analyse the prevailing atmospheric patterns on rainy days during summer and winter months over the period 1954 - 2019, with a particular focus on rainfall events that lead to moderate and extreme floods. In a next step, we intend to extend our findings for Luxembourg in a larger European context. This analysis should allow to better assess the current situation of hydrological extreme events in central Western Europe in order to take precaution measures and prepare for a diversifying hazard.</p>

Physiographic controls on pre-event hydrological states and hydrological response to extreme precipitation in the Alzette River Basin, Luxembourg

2020 ◽  
Author(s):  
Carol Tamez-Melendez ◽  
Judith Meyer ◽  
Audrey Douinot ◽  
Günter Blöschl ◽  
Laurent Pfister
Keyword(s):  
Land Use ◽  
River Basin ◽  
Urban Areas ◽  
Large Scale ◽  
Western Europe ◽  
Flash Flood ◽  
Potential Evapotranspiration ◽  
Hydrological Regime ◽  
Area Of Interest ◽  
Wide Range

<p>The hydrological regime of rivers in Luxembourg (Central Western Europe) is characterised by summer low flows and winter high flows. In winter, large-scale floods are typically triggered by long-lasting sequences of precipitation events, related to westerly atmospheric fluxes that carry wet and temperate air masses from the Atlantic Ocean. In recent years, several flash flood events have been observed in Luxembourg. While being a common feature of Mediterranean river basins, this type of flooding events is uncommon at higher latitudes. The design of the hydro-meteorological monitoring and forecasting systems operated in Luxembourg is not adapted to this type of extreme events and there is a pressing need for a better mechanistic understanding of flash flood triggering mechanisms.</p><p>Here, we explore two lines of research – focusing on (i) the spatio-temporal variability of flash flood generation across a set of 41 nested catchments covering a wide range of physiographic settings (with mixed land use, soil types and bedrock geology) and (ii) the responsivity (resistance) and elasticity (resilience) of these catchments to global change.</p><p>Our area of interest is the Sûre River basin (4,240 km<sup>2</sup>), characterised by a homogenous climate (temperate oceanic), as well as various bedrock (e.g. sandstone, marls, shale) and land use (e.g. forests, grassland, crops, urban areas) types. Based on 8 years’ worth of daily hydrological data (precipitation, discharge and potential evapotranspiration) we computed the increments of the water balance to determine the maximum storage capacity and pre-event wetness state (expressed as storage deficit). Based on the relationship between storage deficit and discharge we first estimated total storage at nearly zero flow conditions. Second, we compared event runoff ratios (Q/P) to pre-hydrological states (as expressed to storage deficit prior to a rainfall-runoff event) in order to assess each catchment’s sensitivity to antecedent wetness conditions. Third, we assessed the responsivity (resistance) and elasticity (resilience) to climate variations – as expressed through the PET/P and AET/P deviations from the Budyko curve – for each individual catchment. Finally, we investigated potential physiographic controls on catchment responsivity and elasticity across our set of 41 nested catchments.</p>

scholarly journals Extreme Floods in the Eastern Part of Europe: Large-Scale Drivers and Associated Impacts

Water ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1122
Author(s):  
Monica Ionita ◽  
Viorica Nagavciuc
Keyword(s):  
Water Vapor ◽  
Heavy Rainfall ◽  
Large Scale ◽  
Vapor Transport ◽  
Water Vapor Transport ◽  
Flood Events ◽  
Rainfall Events ◽  
Catchment Areas ◽  
Large Scale Atmospheric Circulation ◽  
Heavy Rainfall Events

The role of the large-scale atmospheric circulation in producing heavy rainfall events and floods in the eastern part of Europe, with a special focus on the Siret and Prut catchment areas (Romania), is analyzed in this study. Moreover, a detailed analysis of the socio-economic impacts of the most extreme flood events (e.g., July 2008, June–July 2010, and June 2020) is given. Analysis of the largest flood events indicates that the flood peaks have been preceded up to 6 days in advance by intrusions of high Potential Vorticity (PV) anomalies toward the southeastern part of Europe, persistent cut-off lows over the analyzed region, and increased water vapor transport over the catchment areas of Siret and Prut Rivers. The vertically integrated water vapor transport prior to the flood peak exceeds 300 kg m−1 s−1, leading to heavy rainfall events. We also show that the implementation of the Flood Management Plan in Romania had positive results during the 2020 flood event compared with the other flood events, when the authorities took several precaution measurements that mitigated in a better way the socio-economic impact and risks of the flood event. The results presented in this study offer new insights regarding the importance of large-scale atmospheric circulation and water vapor transport as drivers of extreme flooding in the eastern part of Europe and could lead to a better flood forecast and flood risk management.

Physiographic controls on pre-event hydrological states and hydrological response to extreme precipitation in the Alzette River Basin, Luxembourg

2021 ◽  
Author(s):  
Carol Tamez Melendez ◽  
Judith Meyer ◽  
Audrey Douinot ◽  
Günter Blöschl ◽  
Laurent Pfister
Keyword(s):  
River Basin ◽  
Large Scale ◽  
Flash Flood ◽  
Potential Evapotranspiration ◽  
Convective Precipitation ◽  
Hydrological Response ◽  
Local Character ◽  
Area Of Interest ◽  
Oceanic Climate ◽  
Precipitation Events

<p>Flash flood events have caused massive damage on multiple occasions between 2016 and 2018 in several catchments in eastern Luxembourg. This region is very well known for being exposed to large-scale winter floods, commonly triggered by long-lasting advective precipitation events related to westerly atmospheric fluxes. However, flash floods - a truly exceptional phenomenon in this region - are have solely occurred in summer in response to intense convective precipitation events. Thus, because of the rare occurrence and local character of this type of events, the mechanisms eventually controlling a flash flood-type response of a catchment remains poorly understood.  </p><p>Here, we focus on four main objectives: i) the role that physiographic characteristics play on the spatial variability of pre-event hydrological states (as expressed via storage) across a set of 41 nested catchments located in the Sûre River basin (4,240 km<sup>2</sup>), Luxembourg, ii) the hydrological response to precipitation controlled by those pre-event hydrological states, iii) the responsivity (resistance) and elasticity (resilience) of the catchments to global change, and iv) the relation between water yields and the offsets from Budyko curve and its related energy limits.</p><p>The area of interest is not only characterised by a homogenous temperate oceanic climate but also by heterogeneous physiographical conditions and land use, which makes it ideal for this study. We used 8 years’ worth hydrological data (precipitation, discharge and potential evapotranspiration) to calculate the increments of the water balance and determine the maximum storage capacity and storage deficits. Second, we used the relationship between storage deficit and discharge to estimate total storage at a hypothetical nearly zero flow condition. Third, we compared the pre-hydrological states and event runoff ratios (Q/P) to the catchments’ physiographical conditions in order to link catchment’s sensitivity to storage metrics. We then assessed the responsivity and elasticity to climate and anthropogenic variations – as expressed through the PET/P and AET/P deviations from the Budyko curve and energy limits– for each individual catchment. Finally, we investigated the catchment’s area control on responsivity, elasticity, water yields and Budyko’s elements across our set of 41 nested catchments.</p>

The unusual floods and flood frequency in 1858–1878 dry period in Central and Western Europe

2020 ◽  
Author(s):  
Libor Elleder ◽  
Ladislav Kašpárek ◽  
Jakub Krejčí ◽  
Jolana Šírová ◽  
Stanislav Racko
Keyword(s):  
Western Europe ◽  
Flash Flood ◽  
Flood Frequency ◽  
Point Of View ◽  
Ice Age ◽  
Flood Events ◽  
Dry Period ◽  
Drought Period ◽  
Extreme Flood ◽  
Strong Winds

<p>According to the present knowledge, the second half of the 19<sup>th</sup> century meant the end of the Little Ice Age and gradual warming.  This is, however, undoubtedly a fairly simplified statement.  Our contribution presents the period of 1858–1878: (1) from the point of view of drought but also (2) regarding frequency of floods. The aggregation for this period of weather-driven risks such as droughts, floods, strong winds and high tides, is worth attention.  The length of the drought period of 1858–1878, the absolute value of rainfall deficits and the length of seasonal droughts, as well as their impacts, are a certain warning in terms of our present.</p><p>Surprisingly, in such a dry period we witness an accumulation of important and extreme flood episodes as well. The regional catastrophic floods of 1858, and winter extensive floods of 1862 and 1876, may serve as excellent examples.  Furthermore, the Elbe catchment recorded floods with return periods of 10–20 years in 1860, 1865 and 1872. For this period, an occurrence of intensive mesoscale flash flood events with extreme hydrological parameters, high number of fatalities and large damages are of the utmost importance (e.g. 1868-Switzerland, 1872-Czechlands, 1874- Catalonia, 1875-South France). Our contribution builds on earlier analysed flood events of 1872, 1875 and drought period presented at EGU earlier. The contribution stresses the analogies and differences with present situation in 2014–2019.  We mainly address the situation in Czech lands, Central Europe interpreted in wider European context.</p>

scholarly journals Rivers in the sky, flooding on the ground

2020 ◽  
Author(s):  
Monica Ionita ◽  
Viorica Nagavciuc ◽  
Bin Guan
Keyword(s):  
Atmospheric Circulation ◽  
Heavy Rainfall ◽  
Large Scale ◽  
Rhine River ◽  
Flood Events ◽  
Pressure Center ◽  
Atmospheric Rivers ◽  
Extreme Flooding ◽  
Large Scale Atmospheric Circulation ◽  
Lower Rhine

Abstract. The role of the large scale atmospheric circulation and atmospheric rivers (ARs) in producing extreme flooding and heavy rainfall events in the lower part of Rhine River catchment area is examined in this study. Analysis of the largest 10 floods in the lower Rhine, between 1817–2015, indicate that all these extreme flood peaks have been preceded up to 7 days in advance by intense moisture transport from the tropical North Atlantic basin, in the form of narrow bands, also know as atmospheric rivers. The influence of ARs on the Rhine River flood events is done via the prevailing large-scale atmospheric circulation. Most of the ARs associated with these flood events are embedded in the trailing fronts of the extratropical cyclones. The typical large scale atmospheric circulation leading to heavy rainfall and flooding in the lower Rhine is characterized by a low pressure center south of Greenland which migrates towards Europe and a stable high pressure center over the northern part of Africa and southern part of Europe. The days preceding the flood peaks, lower (upper) level convergence (divergence) is observed over the analyzed region, which is an indication of strong vertical motions and heavy rainfall. The results presented in this study offer new insights regarding the importance of tropical moisture transport as driver of extreme flooding in the lower part of Rhine River catchment area and we show for the first time that ARs are an useful tool for the identification of potential damaging floods inland Europe.

scholarly journals Predictability of prototype flash flood events in the Western Mediterranean under uncertainties of the precursor upper-level disturbance: the HYDROPTIMET case studies

2005 ◽  
Vol 5 (4) ◽  
pp. 505-525 ◽  
Author(s):  
R. Romero ◽  
A. Martín ◽  
V. Homar ◽  
S. Alonso ◽  
C. Ramis
Keyword(s):  
Case Studies ◽  
Large Scale ◽  
Flash Flood ◽  
Heavy Rain ◽  
Western Mediterranean ◽  
Flood Events ◽  
Southern France ◽  
The Alps ◽  
Upper Level ◽  
Level Disturbance

Abstract. The HYDROPTIMET case studies (9–10 June 2000 Catalogne, 8–9 September 2002 Cévennes and 24–26 November 2002 Piémont) appear to encompass a sort of prototype flash-flood situations in the western Mediterranean attending to the relevant synoptic and mesoscale signatures identified on the meteorological charts. In Catalogne, the convective event was driven by a low-pressure system of relatively small dimensions developed over the mediterranean coast of Spain that moved into southern France. For Cévennes, the main circulation pattern was a synoptic-scale Atlantic low which induced a persistent southerly low-level jet (LLJ) over the western Mediterranean, strengthened by the Alps along its western flank, which guaranteed continuous moisture supply towards southern France where the long-lived, quasistationary convective system developed. The long Piémont episode, very representative of the most severe alpine flash flood events, shares some similarities with the Cévennes situation during its first stage in that it was controlled by a southerly moist LLJ associated with a large-scale disturbance located to the west. However, these circulation features were transient aspects and during the second half of the episode the situation was dominated by a cyclogenesis process over the Mediterranean which gave place to a mesoscale-size depression at surface that acted to force new heavy rain over the slopes of the Alps and maritime areas. That is, the Piémont episode can be catalogued as of mixed type with regard to the responsible surface disturbance, evolving from a large-scale pattern with remote action (like Cévennes) to a mesoscale pattern with local action (like Catalogne). A prominent mid-tropospheric trough or cut-off low can be identified in all events prior and during the period of heavy rain, which clearly served as the precursor agent for the onset of the flash-flood conditions and the cyclogenesis at low-levels. Being aware of the uncertainty in the representation of the upper-level disturbance and the necessity to cope with it within the operational context when attempting to issue short to mid-range numerical weather predictions of these high impact weather events, a systematic exploration of the predictability of the three selected case studies subject to uncertainties in the representation of the upper-level precursor disturbance is carried out in this paper. The study is based on an ensemble of mesoscale numerical simulations of each event with the MM5 non-hydrostatic model after perturbing in a systematic way the upper-level disturbance, in the sense of displacing slightly this disturbance upstream/downstream along the zonal direction and intensifying/weakening its amplitude. These perturbations are guided by a previous application of the MM5-adjoint model, which consistently shows high sensitivities of the dynamical control of the heavy rain to the flow configuration about the upper-level disturbance on the day before, thus confirming the precursor characteristics of this agent. The perturbations are introduced to the initial conditions by applying a potential vorticity (PV) inversion procedure to the positive PV anomaly associated with the upper-level disturbance, and then using the inverted fields (wind, temperature and geopotential) to modify under a physically consistent balance the model initial fields. The results generally show that the events dominated by mesoscale low-level disturbances (Catalogne and last stage of the Piémont episode) are very sensitive to the initial uncertainties, such that the heavy rain location and magnitude are in some of the experiments strongly changed in response to the "forecast errors" of the cyclone trajectory, intensity, shape and translational speed. In contrast, the other situations (Cévennes and initial stage of the Piémont episode), dominated by a larger scale system wich basically acts to guarantee the establishment and persistence of the southerly LLJ towards the southern France-north Italy orography, exhibit much higher predictability. That is, the slight modifications in the LLJ direction and intensity encompassed by the ensemble of perturbed forecasts are less critical with respect to the heavy precipitation potential and affected area.

scholarly journals Intense Rainfall Events Affecting the La Plata Basin

2006 ◽  
Vol 7 (4) ◽  
pp. 769-787 ◽  
Author(s):  
Viviane B. S. Silva ◽  
Ernesto H. Berbery
Keyword(s):  
Large Scale ◽  
Amazon Basin ◽  
Level Structure ◽  
Intense Rainfall ◽  
Rainfall Events ◽  
La Plata ◽  
La Plata Basin ◽  
Intense Precipitation ◽  
Eta Model ◽  
Precipitation Events

Abstract The circulation features associated with intense precipitation events over the La Plata Basin (LPB) during the austral summers of 2001/02 and 2002/03 are investigated using the Eta Model runs generated at the University of Maryland. Based on the main mode of variability over LPB, two regions were selected: (i) the region of Brazil that is at the core of the South American summer monsoon system (SAMS) and (ii) the central region of LPB in southeastern South America (SESA). First, a comparison between the 24-h total precipitation in the Eta Model and the 24-h observed precipitation was made. Results show that the Eta Model captures well the temporal variability of precipitation events in both regions, although a positive bias is noticed over SAMS. Likewise, the model reproduces the distribution of precipitation rate over SESA, but not over SAMS. Nevertheless, the distribution of the moisture flux convergence intensity, which represents the dynamical forcing, is closer in shape to the observed precipitation distribution, suggesting that the model can be a useful tool in identifying the forcing for heavy precipitation events over both regions. Composites of atmospheric and surface variables were constructed for intense precipitation events during austral summer over both regions. Intense rainfall over the central La Plata Basin (SESA) is linked to an amplified upper-tropospheric midlatitude wave pattern in which rainfall occurs just east of an enhanced cyclonic circulation. Accompanying this circulation pattern, an enhanced low-level jet (LLJ) transports warm, moist air from the Amazon toward the region, contributing to an increase in the thermal contrast over SESA. The combined patterns of thermal and dynamical variables suggest that large-scale systems, like frontal systems, are important in producing intense rainfall events. The SAMS region events have a similar upper-level structure as in SESA, but they are longer lived. In this case, the moisture fluxes are determined by an eastward shift of the LLJ, but also directly from the Amazon Basin to the north. As expected, precipitation events produce large increases of simulated runoff. The largest impact is on the SESA region, affecting the streamflow of the Paraná, Paraguay, and Uruguay, the three main rivers of the LPB.

scholarly journals Past long-term summer warming over western Europe in new generation climate models: role of large-scale atmospheric circulation

2020 ◽  
Vol 15 (8) ◽  
pp. 084038
Author(s):  
Julien Boé ◽  
Laurent Terray ◽  
Marie-Pierre Moine ◽  
Sophie Valcke ◽  
Alessio Bellucci ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
Large Scale ◽  
Western Europe ◽  
Climate Models ◽  
Summer Warming ◽  
New Generation ◽  
Large Scale Atmospheric Circulation

scholarly journals More frequent flash flood events and extreme precipitation favouring atmospheric conditions in temperate regions of Europe

2021 ◽  
Author(s):  
Judith Meyer ◽  
Malte Neuper ◽  
Luca Mathias ◽  
Erwin Zehe ◽  
Laurent Pfister
Keyword(s):  
Extreme Precipitation ◽  
Western Europe ◽  
Flash Flood ◽  
Flash Floods ◽  
Water Levels ◽  
Specific Humidity ◽  
Atmospheric Conditions ◽  
Flood Events ◽  
Extreme Precipitation Events ◽  
Precipitation Events

Abstract. In recent years, flash floods repeatedly occurred in temperate regions of central western Europe. Unlike in Mediterranean catchments, this flooding behaviour is unusual. In the past, and especially in the 1990s, floods were characterized by predictable, slowly rising water levels during winter and driven by westerly atmospheric fluxes (Pfister et al., 2004). The intention of this study is to link the recent occurrence of flash floods in central western Europe to extreme precipitation and specific atmospheric conditions to identify the cause for this apparent shift. Therefore, we hypothesise that an increase in extreme precipitation events has subsequently led to an increase in the occurrence of flash flood events in central western Europe and all that being caused by a change in the occurrence of flash flood favouring atmospheric conditions. To test this hypothesis, we compiled data on flash floods in central western Europe and selected precipitation events above 40 mm h−1 from radar data (RADOLAN, DWD). Moreover, we identified proxy parameters representative for flash flood favouring atmospheric conditions from the ERA5 reanalysis dataset. High specific humidity in the lower troposphere (q ≥ 0.004 kg kg−1), sufficient latent instability (CAPE ≥ 100 J kg−1) and weak deep-layer wind shear (DLS ≤ 10 m s−1) proved to be characteristic for long-lasting intense rainfall that can potentially trigger flash floods. These atmospheric parameters, as well as the flash flood and precipitation events were then analysed using linear models. Thereby we found significant increases in atmospheric moisture contents and increases in atmospheric instability. Parameters representing the motion and organisation of convective systems occurred slightly more often or remained unchanged in the time period from 1981–2020. Moreover, a trend in the occurrence of flash floods was confirmed. The number of precipitation events, their maximum 5-minute intensities as well as their hourly sums were however characterized by large inter-annual variations and no trends could be identified between 2002–2020. This study therefore shows that the link from atmospheric conditions via precipitation to flash floods cannot be traced down in an isolated way. The complexity of interactions is likely higher and future analyses should include other potentially relevant factors such as intra-annual precipitation patterns or catchment specific parameters.

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