Floods In Central Europe Research Articles

Developing Low‐Likelihood Climate Storylines for Extreme Precipitation Over Central Europe

AbstractHeavy precipitation and associated flooding during the cold season, such as the 1993 flood in central Europe (CEU), are a major threat to society and ecosystems. Due to the lack of long homogenous climate data and methodological frameworks, it is challenging to estimate how extreme precipitation could get and what the physical drivers are. This study presents two complementary strategies to extrapolate beyond the precipitation records: (a) statistical estimates based on fitting generalized extreme value distributions, providing their probabilistic information on return periods and, (b) ensemble boosting, a model‐based re‐initialization of heavy precipitation in large ensembles, providing a physical coherent storyline in space and time, however, with no direct quantification of its probability. Both show that 3‐day accumulated precipitation maxima can be substantially exceeded over CEU of around 30%–40%, but even higher magnitudes cannot be ruled out in the near future. An empirical orthogonal function analysis reveals that certain sea level pressure patterns, partly reminding of atmospheric rivers are more often associated with heavy precipitation than more moderate events. Additionally, ensemble boosting is a suitable tool for case studies to analyze how extreme heavy precipitation as for the event in 1993 can be simulated. By boosting a 1993‐analog, one‐quarter of the resulting storylines show increased rainfall than observed, due to a stronger north‐south pressure gradient that may have exacerbated the flooding. Overall, the precipitation estimates demonstrate that ensemble boosting is a complementary method to statistical tools and suitable for stress testing, for example, infrastructure protection measures against potentially unseen heavy precipitation events.

A multi-disciplinary analysis of the exceptional flood event of July 2021 in central Europe – Part 1: Event description and analysis

Abstract. The July 2021 flood in central Europe was one of the five costliest disasters in Europe in the last half century, with an estimated total damage of EUR 32 billion. The aim of this study is to analyze and assess the flood within an interdisciplinary approach along its entire process chain: the synoptic setting of the atmospheric pressure fields, the processes causing the high rainfall totals, the extraordinary streamflows and water levels in the affected catchments, the hydro-morphological effects, and the impacts on infrastructure and society. In addition, we address the question of what measures are possible to generate added value to early response management in the immediate aftermath of a disaster. The superposition of several factors resulted in widespread extreme precipitation totals and water levels well beyond a 100-year event: slow propagation of the low pressure system Bernd, convection embedded in a mesoscale precipitation field, unusually moist air masses associated with a significant positive anomaly in sea surface temperature over the Baltic Sea, wet soils, and steep terrain in the affected catchments. Various hydro-morphodynamic processes as well as changes in valley morphology observed during the event exacerbated the impact of the flood. Relevant effects included, among many others, the occurrence of extreme landscape erosion, rapidly evolving erosion and scour processes in the channel network and urban space, recruitment of debris from the natural and urban landscape, and deposition and clogging of bottlenecks in the channel network with eventual collapse. The estimation of inundation areas as well as the derived damage assessments were carried out during or directly after the flood and show the potential of near-real-time forensic disaster analyses for crisis management, emergency personnel on-site, and the provision of relief supplies. This study is part one of a two-paper series. The second part (Ludwig et al., 2022) puts the July 2021 flood into a historical context and into the context of climate change.

Moisture sources of heavy precipitation in Central Europe in synoptic situations with Vb-cyclones

During the past century, several extreme summer floods in Central Europe were associated with so-called Vb-cyclones propagating from the Mediterranean Sea north-eastward to Central Europe. The processes intensifying the precipitation in synoptic situations with Vb-cyclones in the Danube, Elbe, and Odra catchments are only partially understood. Our study aims to investigate these processes with Lagrangian moisture-source diagnostics for 16 selected Vb-events. Moreover, we analyse the characteristics of typical moisture source regions during 1107 Vb-events from 1901 to 2010 based on ERA-20C reanalysis dynamically downscaled with COSMO-CLM+NEMO. We observe moisture contributions by various source regions highlighting the complex dynamical interplay of different air masses leading to moisture convergence in synoptic situations with Vb-cyclones. Overall, up to 80% of the precipitation originates from the European continent, indicating the importance of continental moisture recycling, especially within the respective river catchment. Other major moisture uptake regions are the North Sea, the Baltic Sea, the North Atlantic, and for a few events the Black Sea. Remarkably, anomalies in these oceanic source regions show no connection to precipitation amounts in synoptic situations with Vb-cyclones. In contrast, the Vb-cyclones with the highest precipitation are associated with anomalously high evaporation in the Mediterranean Sea, even though the Mediterranean Sea is only a minor moisture source region on average. Interestingly, the evaporation anomalies are not connected with sea-surface temperature but with wind-speed anomalies (Spearman’s rank correlation coefficient Rapprox 0.7, significant with p<0.01) indicating mainly dynamically driven evaporation. The particular role of the Mediterranean Sea hints towards possible importance of Mediterranean moisture for the early-stage intensification of Vb-cyclones and the pre-moistening of the continental uptake regions upstream of the target catchments.

Rivers in the sky, flooding on the ground: the role of atmospheric rivers in inland flooding in central Europe

Abstract. The role of large-scale atmospheric circulation and atmospheric rivers (ARs) in producing extreme flooding and heavy rainfall events in the lower part of the Rhine catchment area is examined in this study. Analysis of the largest 10 floods in the lower Rhine, between 1817 and 2015, shows that all these extreme flood peaks have been preceded up to 7 d in advance by intense moisture transport from the tropical North Atlantic basin in the form of narrow bands also known as atmospheric rivers. 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 toward Europe, and a stable high pressure center over the northern part of Africa and the southern part of Europe and projects on the positive phase of the North Atlantic Oscillation. On the days preceding the flood peaks, lower (upper) level convergence (divergence) is observed over the analyzed region, which indicates strong vertical motions and heavy rainfall. Vertically integrated water vapor transport (IVT) exceeds 600 kg m−1 s−1 for the largest floods, marking these as very strong ARs. The results presented in this study offer new insights regarding the importance of moisture transport as a driver of extreme flooding in the lower part of the Rhine catchment area, and we show, for the first time, that ARs are a useful tool for the identification of potentially damaging floods in inland Europe.

Spatial Development of the 1507–1510 Plague in Poland and Its Consequences. Kalisz District Case Study

Abstract The article discusses the causes and effects of the plague which is said to have spread over many Polish towns in 1507. The focus is on its possible causes, related to the occurrence of droughts and floods in Central Europe in the late 15th and early 16th century. Available sources from the late mediaeval period have also been analysed for the recorded perceptions of the extreme climatic and weather conditions. Special attention has been paid to the issues of intensity and spatial distribution of the effects of the plague on the example of one district. The analysis covered a variety of issues such as settlement changes, prices of basic goods or even some pollen data. The main results of the study indicate that the climatic extremes at the turn of the 16th century exerted a long-term impact on the society and economy of the region. They also contributed to the abandonment of settlements on rural sites.

Successful Small-Scale Household Relocation after a Millennial Flood Event in Simbach, Germany 2016

International and national laws promote stakeholder collaboration and the inclusion of the community in flood risk management (FRM). Currently, relocation as a mitigation strategy against river floods in Central Europe is rarely applied. FRM needs sufficient preparation and engagement for successful implementation of household relocation. This case study deals with the extreme flood event in June 2016 at the Simbach torrent in Bavaria (Germany). The focus lies on the planning process of structural flood defense measures and the small-scale relocation of 11 households. The adaptive planning process started right after the damaging event and was executed in collaboration with authorities and stakeholders of various levels and disciplines while at the same time including the local citizens. Residents were informed early, and personal communication, as well as trust in actors, enhanced the acceptance of decisions. Although technical knowledge was shared and concerns discussed, resident participation in the planning process was restricted. However, the given pre-conditions were found beneficial. In addition, a compensation payment contributed to a successful process. Thus, the study illustrates a positive image of the implementation of the alleviation scheme. Furthermore, preliminary planning activities and precautionary behavior (e.g., natural hazard insurance) were noted as significant factors to enable effective integrated flood risk management (IFRM).

The 1714 flash flood in the Bohemian-Moravian Highlands – Reconstructing a Catastrophe

The flash flood that occurred at the end of July and beginning of August 1714 on the Sázava River in the Bohemian-Moravian Highlands (550–750 m above sea level) is probably the most important case of flooding in the Czech lands. The extremity of the flood is likely to be ranked among the most notable occurrences of extreme weather in history, even within the larger Central European context. In this study we have focused on the upper and middle parts of the Sázava catchment (approximately 2000 km2). The aim of our study was to check of the reliability of the flood data in 1714. The main question was whether we should confirm or reject the possible dominant role played by local fishponds, especially the large Dářko fishpond. The extraordinarily high water levels documented by the chronicles were viewed a bit suspiciously at first.The hydraulic evaluation of the flood peak discharges and a reconstructed hydrograph, together with an envelope curve of maximum floods, have confirmed the reliability of the data recorded during the 1714 flood. The contribution of the collapsed fishponds was evaluated as a minor source of flooding. Therefore, the hydrological modelling enabled an estimation of causative precipitation equal to approximately 100 mm/3–4 h as the main flood source. The estimated rainfall amount and peak discharge of 700–1000 m3/s in the catchment area of 1000 km2 are likely to be the main results of the study. We also present an overview of flash floods in Central Europe in 1714, a definition of the affected area on 31 July, the damage, fatalities and a possible scenario of the storm's track. Our results indicate that the 1714 flood represented a unique extreme in Czech territory. The only comparable event appears to be the 25 May 1872 flood at the Berounka and Blšanka catchment.

Testing the use of standardised indices and GRACE satellite data to estimate the European 2015 groundwater drought in near-real time

Abstract. In 2015, central and eastern Europe were affected by a severe drought. This event has recently been studied from meteorological and streamflow perspective, but no analysis of the groundwater situation has been performed. One of the reasons is that real-time groundwater level observations often are not available. In this study, we evaluate two alternative approaches to quantify the 2015 groundwater drought over two regions in southern Germany and eastern Netherlands. The first approach is based on spatially explicit relationships between meteorological conditions and historic groundwater level observations. The second approach uses the Gravity Recovery Climate Experiment (GRACE) terrestrial water storage (TWS) and groundwater anomalies derived from GRACE-TWS and (near-)surface storage simulations by the Global Land Data Assimilation System (GLDAS) models. We combined the monthly groundwater observations from 2040 wells to establish the spatially varying optimal accumulation period between the Standardised Groundwater Index (SGI) and the Standardized Precipitation Evapotranspiration Index (SPEI) at a 0.25° gridded scale. The resulting optimal accumulation periods range between 1 and more than 24 months, indicating strong spatial differences in groundwater response time to meteorological input over the region. Based on the estimated optimal accumulation periods and available meteorological time series, we reconstructed the groundwater anomalies up to 2015 and found that in Germany a uniform severe groundwater drought persisted for several months during this year, whereas the Netherlands appeared to have relatively high groundwater levels. The differences between this event and the 2003 European benchmark drought are striking. The 2003 groundwater drought was less uniformly pronounced, both in the Netherlands and Germany. This is because slowly responding wells (the ones with optimal accumulation periods of more than 12 months) still were above average from the wet year of 2002, which experienced severe flooding in central Europe. GRACE-TWS and GRACE-based groundwater anomalies did not capture the spatial variability of the 2003 and 2015 drought events satisfactorily. GRACE-TWS did show that both 2003 and 2015 were relatively dry, but the differences between Germany and the Netherlands in 2015 and the spatially variable groundwater drought pattern in 2003 were not captured. This could be associated with the coarse spatial scale of GRACE. The simulated groundwater anomalies based on GRACE-TWS deviated considerably from the GRACE-TWS signal and from observed groundwater anomalies. The uncertainty in the GRACE-based groundwater anomalies mainly results from uncertainties in the simulation of soil moisture by the different GLDAS models. The GRACE-based groundwater anomalies are therefore not suitable for use in real-time groundwater drought monitoring in our case study regions. The alternative approach based on the spatially variable relationship between meteorological conditions and groundwater levels is more suitable to quantify groundwater drought in near real-time. Compared to the meteorological drought and streamflow drought (described in previous studies), the groundwater drought of 2015 had a more pronounced spatial variability in its response to meteorological conditions, with some areas primarily influenced by short-term meteorological deficits and others influenced by meteorological deficits accumulated over the preceding 2 years or more. In drought management, this information is very useful and our approach to quantify groundwater drought can be used until real-time groundwater observations become readily available.

Social disruption by flooding, a European perspective

The Dutch National Risk Assessment (NRA) is a methodology to assess the impact and likelihood of all possible threats and hazards that might hit the Netherlands, including a large-scale flood. This methodology addresses all the physical and social aspects that determine social disruption. The NRA has been applied to six European floods in Central and Western Europe. The results show that the NRA impact score for a flooding scenario can be interpreted as a measure for social disruption. Some comments can be made, however. The all hazards approach of the NRA is designed as a robust instrument that enables covering a wide array of threats and disasters. As a result, the NRA in its ‘original’ form offers little room for detailed differences in the consequences of different flooding scenarios. Tailor-made adjustments to the NRA are needed to insure that, for instance, differences in the number of casualties for different floods do not get lost in the bandwidth of the impact criteria.Socio-psychological factors significantly mark the impact of flooding. This offers opportunities to steer on avoiding or restricting social disruption by flooding by putting an adequate flood risk and crisis communication in place.The floods in Central Europe in 2002 and 2013 more or less present the lower and upper bounds of the impacts of recent large-scale river floods in Central and Western Europe. Compared with this bandwidth, the impact of a scenario of a worst-case river flood in the Netherlands is not unusual in a European context.

Rising Mediterranean Sea Surface Temperatures Amplify Extreme Summer Precipitation in Central Europe.

The beginning of the 21st century was marked by a number of severe summer floods in Central Europe associated with extreme precipitation (e.g., Elbe 2002, Oder 2010 and Danube 2013). Extratropical storms, known as Vb-cyclones, cause summer extreme precipitation events over Central Europe and can thus lead to such floodings. Vb-cyclones develop over the Mediterranean Sea, which itself strongly warmed during recent decades. Here we investigate the influence of increased Mediterranean Sea surface temperature (SST) on extreme precipitation events in Central Europe. To this end, we carry out atmosphere model simulations forced by average Mediterranean SSTs during 1970–1999 and 2000–2012. Extreme precipitation events occurring on average every 20 summers in the warmer-SST-simulation (2000–2012) amplify along the Vb-cyclone track compared to those in the colder-SST-simulation (1970–1999), on average by 17% in Central Europe. The largest increase is located southeast of maximum precipitation for both simulated heavy events and historical Vb-events. The responsible physical mechanism is increased evaporation from and enhanced atmospheric moisture content over the Mediterranean Sea. The excess in precipitable water is transported from the Mediterranean Sea to Central Europe causing stronger precipitation extremes over that region. Our findings suggest that Mediterranean Sea surface warming amplifies Central European precipitation extremes.

Temporal clustering of floods in Germany: Do flood-rich and flood-poor periods exist?

The repeated occurrence of exceptional floods within a few years, such as the Rhine floods in 1993 and 1995 and the Elbe and Danube floods in 2002 and 2013, suggests that floods in Central Europe may be organized in flood-rich and flood-poor periods. This hypothesis is studied by testing the significance of temporal clustering in flood occurrence (peak-over-threshold) time series for 68 catchments across Germany for the period 1932–2005. To assess the robustness of the results, different methods are used: Firstly, the index of dispersion, which quantifies the departure from a homogeneous Poisson process, is investigated. Further, the time-variation of the flood occurrence rate is derived by non-parametric kernel implementation and the significance of clustering is evaluated via parametric and non-parametric tests. Although the methods give consistent overall results, the specific results differ considerably. Hence, we recommend applying different methods when investigating flood clustering. For flood estimation and risk management, it is of relevance to understand whether clustering changes with flood severity and time scale. To this end, clustering is assessed for different thresholds and time scales. It is found that the majority of catchments show temporal clustering at the 5% significance level for low thresholds and time scales of one to a few years. However, clustering decreases substantially with increasing threshold and time scale. We hypothesize that flood clustering in Germany is mainly caused by catchment memory effects along with intra- to inter-annual climate variability, and that decadal climate variability plays a minor role.

Social media as an information source for rapid flood inundation mapping

Abstract. During and shortly after a disaster, data about the hazard and its consequences are scarce and not readily available. Information provided by eyewitnesses via social media is a valuable information source, which should be explored in a~more effective way. This research proposes a methodology that leverages social media content to support rapid inundation mapping, including inundation extent and water depth in the case of floods. The novelty of this approach is the utilization of quantitative data that are derived from photos from eyewitnesses extracted from social media posts and their integration with established data. Due to the rapid availability of these posts compared to traditional data sources such as remote sensing data, areas affected by a flood, for example, can be determined quickly. The challenge is to filter the large number of posts to a manageable amount of potentially useful inundation-related information, as well as to interpret and integrate the posts into mapping procedures in a timely manner. To support rapid inundation mapping we propose a methodology and develop "PostDistiller", a tool to filter geolocated posts from social media services which include links to photos. This spatial distributed contextualized in situ information is further explored manually. In an application case study during the June 2013 flood in central Europe we evaluate the utilization of this approach to infer spatial flood patterns and inundation depths in the city of Dresden.

Local flash floods in Central Europe: A case study of Poland

Bryndal, T. 2015. Local flash floods in Central Europe: A case study of Poland. Norsk Geografisk Tidsskrift–Norwegian Journal of Geography. Vol. 69, 288–298. ISSN 0029-1951.The article focuses on the seasonality, geographical distribution, and hydrometeorological aspects of local flash floods in Poland, in Central Europe. Scientific articles describing local flash flood events were studied and a database of such floods in Poland was developed and analysed. The results revealed that local flash flood events were usually generated by rainfall lasting less than two hours, with a mean intensity in the range 20–80 mm·h-1. The triggering threshold for local flash floods was P = 20 mm·h-1. Local flash floods may occur from April to October, with higher frequencies in May, June, and July. The floods usually affect mountain and uplands areas differently to lowland and basins regions, and this might be explained by heavy rainfall distribution and topographical conditions. The maxima of the unit discharge (Qs) describe an envelope curve according to the equation Qs = 47A-0.4 (where A is the catchment area in km2). The maxima appear very consistent with envelope curves proposed for other inland continental European countries. The authors conclude that local flash floods in Poland are similar to those recorded in inland continental areas of Europe, but differ from the floods in the Mediterranean part of the continent.

After the extreme flood in 2002: changes in preparedness, response and recovery of flood-affected residents in Germany between 2005 and 2011

Abstract. In the aftermath of the severe flooding in Central Europe in August 2002, a number of changes in flood policies were launched in Germany and other European countries, aiming at improved risk management. The question arises as to whether these changes have already had an impact on the residents' ability to cope with floods, and whether flood-affected private households are now better prepared than they were in 2002. Therefore, computer-aided telephone interviews with private households in Germany that suffered from property damage due to flooding in 2005, 2006, 2010 or 2011 were performed and analysed with respect to flood awareness, precaution, preparedness and recovery. The data were compared to a similar investigation conducted after the flood in 2002. After the flood in 2002, the level of private precautions taken increased considerably. One contributing factor is the fact that, in general, a larger proportion of people knew that they were at risk of flooding. The best level of precaution was found before the flood events in 2006 and 2011. The main reason for this might be that residents had more experience with flooding than residents affected in 2005 or 2010. Yet, overall, flood experience and knowledge did not necessarily result in building retrofitting or flood-proofing measures, which are considered as mitigating damages most effectively. Hence, investments still need to be stimulated in order to reduce future damage more efficiently. Early warning and emergency responses were substantially influenced by flood characteristics. In contrast to flood-affected people in 2006 or 2011, people affected by flooding in 2005 or 2010 had to deal with shorter lead times and therefore had less time to take emergency measures. Yet, the lower level of emergency measures taken also resulted from the people's lack of flood experience and insufficient knowledge of how to protect themselves. Overall, it was noticeable that these residents suffered from higher losses. Therefore, it is important to further improve early warning systems and communication channels, particularly in hilly areas with rapid-onset flooding.

Predicting the June 2013 European Flooding Based on Precipitation, Soil Moisture, and Sea Level Pressure

Abstract Over recent decades Europe has experienced heavy floods, with major consequences for thousands of people and billions of euros worth of damage. In particular, the summer of 2013 flood in central Europe showed how vulnerable modern society is to hydrological extremes and emphasized once more the need for improved forecast methods of such extreme climatic events. Based on a multiple linear regression model, it is shown here that 55% of the June 2013 Elbe River extreme discharge could have been predicted using May precipitation, soil moisture, and sea level pressure. Moreover, the model was able to predict more than 75% of the total Elbe River discharge for June 2013 (in terms of magnitude) by also incorporating the amount of precipitation recorded during the days prior to the flood, but the predicted discharge for the June 2013 event was still underestimated by 25%. Given that all predictors used in the model are available at the end of each month, the forecast scheme can be used to predict extreme events and to provide early warnings for upcoming floods. The forecast methodology could be relevant for other rivers also, depending on their location and their climatic background.

Climate, droughts and floods in Central Europe during past 500 years

Climate, droughts and floods in Central Europe during past 500 years

A simple model for the estimation of the number of fatalities due to floods in central Europe

Abstract. In this paper a model for the estimation of the number of potential fatalities is proposed based on data from 19 past floods in central Europe. First, the factors contributing to human losses during river floods are listed and assigned to the main risk factors: hazard – exposure – vulnerability. The order of significance of individual factors has been compiled by pairwise comparison based on experience with real flood events. A comparison with factors used in existing models for the estimation of fatalities during floods shows good agreement with the significant factors identified in this study. The most significant factors affecting the number of human losses in floods have been aggregated into three groups and subjected to correlation analysis. A close-fitting regression dependence is proposed for the estimation of loss of life and calibrated using data from selected real floods in central Europe. The application of the proposed model for the estimation of fatalities due to river floods is shown via a flood risk assessment for the locality of Krnov in the Czech Republic.

Extreme hydrometeorological events and climate change predictions in Europe

Summary Field meteorological data collected in several European Commission projects (from 1974 to 2011) were re-analysed in the context of a perceived reduction in summer storms around the Western Mediterranean Basin (WMB). The findings reveal some hitherto overlooked processes that raise questions about direct impacts on European hydrological cycles, e.g., extreme hydrometeorological events, and about the role of feedbacks on climate models and climate predictions. For instance, the summer storms are affected by land-use changes along the coasts and mountain slopes. Their loss triggers a chain of events that leads to an Accumulation Mode (AM) where water vapour and air pollutants (ozone) become stacked in layers, up to 4000(+) m, over the WMB. The AM cycle can last 3–5 consecutive days, and recur several times each month from mid May to late August. At the end of each cycle the accumulated water vapour can feed V b track events and generate intense rainfall and summer floods in Central Europe. Venting out of the water vapour that should have precipitated within the WMB increases the salinity of the sea and affects the Atlantic-Mediterranean Salinity valve at Gibraltar. This, in turn, can alter the tracks of Atlantic Depressions and their frontal systems over Atlantic Europe. Another effect is the greenhouse heating by water vapour and photo-oxidants (e.g., O 3 ) when layered over the Basin during the AM cycle. This increases the Sea Surface Temperature (SST), and the higher SST intensifies torrential rain events over the Mediterranean coasts in autumn. All these processes raise research questions that must be addressed to improve the meteorological forecasting of extreme events, as well as climate model predictions.

Comparison of meteorological conditions during May and August 2010 floods in Central Europe

We compared May and August 2010 precipitation events that produced catastrophic flooding. In May, large rivers (Vistula, Oder) were affected, while smaller rivers (e.g. Lausitzer Neisse) were affected in August. Similarities in precipitation characteristics (duration of several days, daily total maximum of approximately 180 mm) can be explained by similarities in the meso-a scale (thermo-dynamic indicia connected with a cyclonic system of Mediterranean origin). These indicia were more significant in May (extreme and deep vertical wind speed, extreme northerly flux of moisture) than in August (strong but non-extreme northerly flux of moisture) when conditional instability was additionally detected. Obviously more intensive orographic enhancement in the first case and the strong effect of convection in the latter case produced differences in the return periods of precipitation totals (longer return periods in August). Subsequently, the hydrological response was rapid and particularly strong in smaller streams in August. <b>Srovnání meteorologických podmínek ve střední Evropě během povodní v květnu a srpnu 2010</b> Článek porovnává některé aspekty dvou případů silných srážek ve střední Evropě v roce 2010, které zde způsobily významné povodně: v květnu především na Visle a Odře a jejich přítocích, v srpnu spíše na menších tocích, jako je Lužická Nisa. Podobnost některých srážkových charakteristik (vícedenní trvání, maximální denní úhrn přibližně 180 mm) může být vysvětlena podobností meteorologických veličin v meso-a měřítku (termodynamické anomálie spojené s cyklonou středomořského původu). Tyto anomálie byly výraznější při květnové události (extrémní vertikální rychlost větru skrz celou troposféru, extrémní tok vlhkosti od severu) než při události srpnové (silný, ne však extrémní tok vlhkosti od severu), kdy byla naopak dodatečně detekována podmíněná instabilita. Zjevně výraznější orografické navýšení srážek v prvním případě a silný podíl konvekce v druhém případě způsobily odlišnosti v dosažených dobách opakování srážkových úhrnů, které byly při srpnové události větší. Následně i hydrologická odezva na menších tocích byla rychlá a silná.

Reconstructions of late Holocene paleofloods and glacier length changes in the Upper Engadine, Switzerland (ca. 1450 BC–AD 420)

The relationship between summer-autumn floods in Central Europe and climate warming is poorly constrained by available instrumental, historical, proxy and model data. To investigate this relationship, a complete record of paleofloods, regional glacier length changes (and associated climate phases) and regional glacier advances and retreats (and associated climate transitions) are derived from the varved sediments of Lake Silvaplana (ca. 1450 BC–AD 420; Upper Engadine, Switzerland). In combination, these records provide insight into the behavior of floods (i.e. frequency) under a wide range of climate conditions. Eighty-five paleofloods are identified from turbidites in the sediments of Lake Silvaplana. Regional glacier length changes (and associated cool and/or wet and warm and/or dry climate phases) are inferred from centennial anomalies in the square root of low-pass (LP) filtered Mass Accumulation Rates (MAR LP 1/2). Regional glacier advances and retreats (and associated cooling and/or wetting and warming and/or drying climate transitions) are inferred from centennial trends in MAR LP. This is the first continuous record of glacier length changes in the Lake Silvaplana catchment for this time period. These data agree with regional records of land-use, glacier activity and lake levels. More frequent turbidites are found during cool and/or wet phases of ca. 1450 BC to AD 420. However, no relationship to climate transitions is discerned. Consistently, June–July–August (JJA) temperatures dating ca. 570 BC–AD 120 are inversely correlated to the frequency of turbidites. The rate that turbidite frequency increases with cooler JJA temperatures is not linear. Finally, 130 analogues for a 21st century climate in the Alps between ca. 570 BC–AD 120 (i.e. 50 year windows with a warming trend and average JJA temperature exceeding AD 1950–AD 2000 values from nearby meteo station Sils Maria) are considered. These reveal that turbidites are less frequent than between ca. 1450 BC–AD 420.