Petr Dobrovolný

European summer temperatures since Roman times

The spatial context is criticalwhen assessing present-day climate anomalies, attributing them to potential forcings and making statements regarding their frequency and severity in a long-term perspective. Recent international initiatives have expanded the number of high-quality proxy-records and developed new statistical reconstruction methods. These advances allow more rigorous regional past temperature reconstructions and, in turn, the possibility of evaluating climate models on policy-relevant, spatiotemporal scales. Here we provide a new proxy-based, annually-resolved, spatial reconstruction of the European summer (June-August) temperature fields back to 755 CE based on Bayesian hierarchical modelling (BHM), together with estimates of the European mean temperature variation since 138 BCE based on BHM and composite-plus-scaling (CPS). Our reconstructions compare well with independent instrumental and proxy-based temperature estimates, but suggest a larger amplitude in summer temperature variability than previously reported. Both CPS and BHM reconstructions indicate that the mean 20th century European summer temperature was not significantly different from some earlier centuries, including the 1st, 2nd, 8th and 10th centuries CE. The 1st century (in BHM also the 10th century) may even have been slightly warmer than the 20th century, but the difference is not statistically significant. Comparing each 50 yr period with the 1951-2000 period reveals a similar pattern. Recent summers, however, have been unusually warm in the context of the last two millennia and there are no 30 yr periods in either reconstruction that exceed the mean average European summer temperature of the last 3 decades (1986-2015 CE). A comparison with an ensemble of climate model simulations suggests that the reconstructed European summer temperature variability over the period 850-2000 CE reflects changes in both internal variability and external forcing on multi-decadal time-scales. For pan-European temperatures we find slightly better agreement between the reconstruction and the model simulations with high-end estimates for total solar irradiance. Temperature differences between the medieval period, the recent period and the Little Ice Age are larger in the reconstructions than the simulations. This may indicate inflated variability of the reconstructions, a lack of sensitivity and processes to changes in external forcing on the simulated European climate and/or an underestimation of internal variability on centennial and longer time scales.

Documentary Evidence on Climate in Sixteenth-Century Europe

The known documentary climatic evidence from six European countries - Switzerland, Germany, the Czech Republic, ancient Hungary, Italy and Spain - is presented and classified in this article and then further analyzed in subsequent papers included in this volume. The sixteenth century witnessed an increase in the number and variety of sources in Switzerland, Germany and the Czech Republic as well as in the western and northern parts of ancient Hungary (present Slovakia). In northern Italy, the relevant sources are more abundant and widespread than in central Europe, but they have hardly been explored. Town chronicles written by members of the literate elite comprise the basic type of evidence in central Europe (including northern Italy and Hungary). This kind of source reports exceptional climatic events (e.g. anomalies and natural disasters) along with their impact on the environment and on society. Documentary data are the only evidence known to exist for reconstructing time series of natural disasters prior to the twentieth century. In order to document the extreme character of an event, chroniclers frequently referred to features in the cryosphere, biosphere or hydrosphere that were known to be more accurate yardsticks of temperature and precipitation patterns than subjective impressions. When records of such events are compiled with the description of some of the known effects, the results can be transformed into a severity index. Whereas chroniclers usually focused upon extreme events, long, continuous and seemingly homogeneous series of different kinds of proxy data are drawn from administrative records. Most of them are connected to the timing of certain kinds of agricultural work (hay-making, beginning of grain harvest or vintage) or to the amount and quality of agricultural production (per hectare yield of vineyards, sugar content of wine, etc.). In most cases the timing of these works was found to be directly related to temperature patterns over the preceding months and weeks.All the Iberian peninsula towns, which had an institutionalized municipal authority, have preserved documents generated from the late Middle Ages. These records frequently contain references to floods and meteorological anomalies such as droughts and long wet spells. They also include mention of the system of rogations, those religious rites performed in a standardized way within the Spanish world with a view to putting an end to an alleged meteorological stress.The data for Switzerland, Hungary and Spain as well as much of the data for Germany are stored in the EURO-CLIMHIST database set up at the Institute of History at the University of Bern. At present, EURO-CLIMHIST comprises some 600,000 data for the period from AD 750 to the beginning of the period of instrumental networks. About 120,000 records for Germany are currently stored in a data bank called HISKLID located at the Department of Geography of the University of Würzburg. The database for the Czech Republic includes records for the time-span AD 975-1900 and is housed with the Department of Geography of Masaryk University in Brno. Data on Italy were collected with different purposes and are stored in two data banks, the CNR-ICTIMA (climatic data and natural disasters) and the SGA (extreme events).

Flood Events of Selected European Rivers in the Sixteenth Century

The severity and frequency of sixteenth-century floods of the Rhine, the Main, the middle and upper Elbe with its tributaries, rivers of northern and central Italy, the Garonne and rivers in Catalonia and Andalusia are analyzed using documentary evidence. The basic topographical and hydrological characteristics of the rivers investigated as well as the synoptic causes of their flooding during the instrumental period are presented. Different examples of modifications of the run-off process due to anthropogenic activity are discussed. Prevalence in flood occurrence during the second half of the sixteenth century in comparison to the first half is typical for central European and Andalusian rivers (mainly in the 1560s and 1590s) and agrees with the evolution of precipitation patterns. On the other hand, Italian and Catalonian rivers, in part, had a higher occurrence of floods during the first half of the century. Changes in the flooding seasons in both halves of the century are not unambiguous. Results of an analysis on a broader European scale show floods to be a random natural phenomena with limited areal extent defined by the spatial influence of forcing meteorological factors (continuous heavy rains, sudden melting of thick snow cover, etc.). Despite some limitations of documentary evidence, series of reconstructed historical floods are valuable sources of proxy data which can be utilized for the study of the flooding fluctuations in the pre-instrumental period.

Seasonal Temperature and Precipitation Fluctuations in Selected Parts of Europe During the Sixteenth Century

The article in hand presents a comparative analysis of unweighted thermic and hygric index series of different European regions (northern Switzerland, Germany, the Czech Republic, northern Italy, ancient Hungary, Poland and Spain). Besides methodological aspects about the formation of indices, especially the progress as well as the question of similarity development of these series in the 16th century are discussed and shown on the balance sheet. It becomes evident that with respect to the temperature on the level of unweighted indices the European regions of Germany, the Czech Republic and Switzerland are very similar during all seasons. In winter and summer these correlations are especially evident, during the transitional seasons they are smaller. Larger differences exist between the central European core region and the adjacent areas of research. In principle, the hygric differences are larger than the thermic ones.In the course of the sixteenth century marked cooling phases occurred during all seasons with increasing accentuation. These phases were typical for the climate of the Little Ice Age. In addition to this long-term analysis, some outstanding years of extreme weather like those of 1540, 1573 and 1587 are presented, in the course of which questions of climatic impact are included. Finally, recent instrumental data was used to conduct an analysis that compared the similarities between the respective regions and the similarities between the empirical data and indices. On the one hand, this confirmed the spatial pattern, on the other hand the usability of the indices.

The year-long unprecedented European heat and drought of 1540 – a worst case

The heat waves of 2003 in Western Europe and 2010 in Russia, commonly labelled as rare climatic anomalies outside of previous experience, are often taken as harbingers of more frequent extremes in the global warming-influenced future. However, a recent reconstruction of spring–summer temperatures for WE resulted in the likelihood of significantly higher temperatures in 1540. In order to check the plausibility of this result we investigated the severity of the 1540 drought by putting forward the argument of the known soil desiccation-temperature feedback. Based on more than 300 first-hand documentary weather report sources originating from an area of 2 to 3 million km2, we show that Europe was affected by an unprecedented 11-month-long Megadrought. The estimated number of precipitation days and precipitation amount for Central and Western Europe in 1540 is significantly lower than the 100-year minima of the instrumental measurement period for spring, summer and autumn. This result is supported by independent documentary evidence about extremely low river flows and Europe-wide wild-, forest- and settlement fires. We found that an event of this severity cannot be simulated by state-of-the-art climate models.

Cereal harvest dates in the Czech Republic between 1501 and 2008 as a proxy for March–June temperature reconstruction

Cereal crop harvests reflect the weather patterns of the period immediately preceding them, and thus the dates at which they begin may be used as a source of proxy data on regional climate. Using systematic phenological observations in the Czech Lands (now known as the Czech Republic) after 1845, together with exploration of further surviving documentary evidence (chronicles, diaries, financial accounts etc.), it has proved possible to create series of winter wheat harvest dates for the period 1501–2008. Employing linear regression, the harvesting dates of the main cereal species (wheat, rye, barley, oats) were first converted to winter wheat harvest days and then normalised to the same altitude above sea level. The next step consisted of using series of winter wheat harvest dates to reconstruct mean March–June temperatures in the Czech Republic, applying standard palaeoclimatological methods. Series reconstructed by linear regression explain 70% of temperature variability. A profound cold period corresponding with late winter wheat harvests was noted between 1659 and 1705. In contrast, warm periods (i.e. early winter wheat harvests) were found for the periods of 1517–1542, 1788–1834 and 1946–2008. The period after 1951 is the warmest of all throughout the entire 1501–2008 period. Comparisons with other European temperature reconstructions derived from documentary sources (including grape harvest dates), tree-rings and instrumental data reveal generally close agreement, with significant correlations. Lower correlations around A.D. 1650 and 1750 may be partly related to deterioration of socio-economic conditions in the Czech Lands resulting from prolonged wars. The results obtained demonstrate that it is possible to use widely-available cereal harvest data for climate analysis and also that such data constitute an independent proxy data series for the region of Central Europe crucial to further studies of the potential impact of climatic variability and climate change on agriculture.

Fluctuations of floods of the River Morava (Czech Republic) in the 1691- 2009 period: interactions of natural and anthropogenic factors

Abstract Floods from the middle part of the River Morava (eastern Czech Republic) are considered over the course of the past three centuries, the study being based on data derived from documentary evidence (1691–1880), measured peak water stages, Hk (1881–1920) and peak discharges, Qk (1916–2009), evaluated with respect to their N-year return period (HN and QN ). Changes in land use and water management (water reservoirs, channel modifications) are discussed, as are factors influencing runoff conditions in the Morava catchment. Decadal synthesis of flood series identifies the highest flood activity in the decades of 1911–1920 and 1961–1970 (11 floods each), 1831–1840, 1891–1900, 1901–1910 and 1931–1940 (10 floods each). Uncertainty in this series is related to some incompleteness of documentary data in the pre-1881 period. Very low flood frequency occurred in the 1990s–2000s, although the most disastrous floods were recorded in this particular period (July 1997 at Q 100 and March/April 2006 at Q 20–Q 50). Changes in flood frequency correspond partly to long-term changes in temperature and precipitation patterns. Citation Brázdil, R., Řezníčková, L., Valášek, H., Havlíček, M., Dobrovolný, P., Soukalová, E., Řehánek, T. & Skokanová, H. (2011) Fluctuations of floods of the River Morava (Czech Republic) in the 1691–2009 period: interactions of natural and anthropogenic factors. Hydrol. Sci. J. 56(3), 468–485.

Documentary evidence on strong winds related to convective storms in the Czech Republic since AD 1500

This article summarizes information about the occurrence of strong winds connected with convective storms in the Czech Republic for the last 500 years obtained on the basis of the study of historical documentary sources. Documentary evidence about strong winds is characterized with respect to its advantages and drawbacks. Principles are stated for setting up the database of strong winds and the classification of those cases from the point of view of the type of the phenomenon, extent and character of the damage caused. The chronology of strong winds is presented since AD 1500 with particular respect to the occurrence of tornadoes. For tornadoes, their occurrence during the year is analyzed, as well as their dimensions, intensity and the character of the damage caused. All cases of tornadoes, so far recorded in the Czech Republic, are listed and characterized in the appendix. The impacts of strong winds during convective storms and tornadoes are evaluated. The importance of documentary evidence about strong winds from pre-instrumental period is pointed out.

July 1432 and August 2002—two millennial floods in Bohemia?

Abstract This paper describes an enormous flood that occurred in Bohemia in August 2002, which is considered to be one of the most disastrous to take place in the past 1000 years. Data on the catastrophic flood of July 1432 are also presented, derived from documentary records. The two floods are compared and analysed with respect to other heavy floods in Bohemia from the viewpoint of epigraphic and further documentary sources for the Vltava in Prague (water levels with respect to the relief of Bradáč, the “Bearded Man”) and for the Elbe at Děčn (flood marks cut into Castle Rock). Documentary evidence thus makes it possible to compile a chronology of the heaviest floods in Bohemia since the 12th century. However, the summer rain floods of July 1432 and August 2002 stand out as the greatest, while the case of September 1118 must be ranked near them. The concentration of four disastrous winter floods in the years 1784–1862 is also worthy of note, because it corresponds to the last stage of the Little Ice Age.

Historical and recent floods in the Czech Republic: causes, seasonality, trends, impacts

The paper presents results of analysis of flood series (variability, seasonality, trends) and their synoptic causes (based on Principal Component Analysis) in the instrumental period for the Elbe-Děcin, the Vltava-Prague, the Ohře-Louny, the Odra-Bohumin and the Morava-Kroměřiž. Series of floods from the pre-instrumental period based on documentary evidence since the 16th century for parts of the same rivers are shown. The most disastrous floodings in the Czech Lands were in years 1118, 1272, 1342, 1432, 1501, 1598, 1655, 1675, 1784, 1845, 1872, 1890, 1897, 1903, 1997, 2002. Conclusions concerning flooding in the Czech Republic following from synthesis of documentary and instrumental data are formulated.