The 1921 European drought: impacts, reconstruction and drivers

The European drought of 1921 is assessed in terms of its impacts on society and in terms of its physical characteristics. The development of impacts of the drought are categorized by a systematic survey of newspaper reports from five European newspapers covering the area from England to the Czech Republic and other parts of Europe. This is coupled to a reconstruction of daily temperature and precipitation based on meteorological measurements to quantify the drought severity and extent, and reanalysis data are used to identify its drivers. This analysis shows that the first impacts of the drought started to appear in early spring and lingered on until well into autumn and winter, affecting water supply and agriculture and livestock farming. The dominant impact in western Europe is on agriculture and livestock farming while in central Europe the effects of wildfires were reported on most often. The peak in the number of reports is in late summer. Preceding the first impacts was the dry autumn of 1920 and winter 1920–1921. The area hardest hit by the drought in the following spring and summer was the triangle between Brussels, Paris and Lyon, but a vast stretch of the continent, from Ireland to the Ukraine, was affected. The reported impacts on water supply and water-borne transport in that region were matched by an analysis of the hydrological situation over the Seine catchment. On average, the 1921 summer was not particularly hot, but the heatwave which was observed at the end of July saw temperatures matching those of the heatwaves in modern summers. Similar to modern droughts, an anticyclone was present roughly over the British Isles, maintaining sunny and dry weather in Europe and steering away cyclones to the north. Its persistence makes it exceptional in comparison to modern droughts. The 1921 drought stands out as the most severe and most widespread drought in Europe since the start of the 20th century. The precipitation deficit in all seasons was large, but in none of the seasons in 1920 and 1921 was the precipitation deficit the largest on record. The severity of the 1921 drought relates to the conservative nature of drought which amplifies the lack of precipitation in autumn and winter into the following spring and summer

Long-term changes in drought indices in eastern and central Europe

This study analyses long-term changes in drought indices (Standardised Precipitation Index—SPI, Standardised Precipitation–Evapotranspiration Index—SPEI) at 1 and 3 months scales at 182 stations in 11 central and eastern European countries during 1949–2018. For comparative purposes, the necessary atmospheric evaporative demand (AED) to obtain SPEI was calculated using two methods, Hargreaves-Samani (SPEIH) and Penman-Monteith (SPEIP). The results show some relevant changes and tendencies in the drought indices. Statistically significant increase in SPI and SPEI during the cold season (November–March), reflecting precipitation increase, was found in the northern part of the study region, in Estonia, Latvia, Lithuania, northern Belarus and northern Poland. In the rest of study domain, a weak and mostly insignificant decrease prevailed in winter. Summer season (June–August) is characterized by changes in the opposite sign. An increase was observed in the north, while a clear decrease in SPEI, reflecting a drying trend, was typical for the southern regions: the Czech Republic, Slovakia, Hungary, Romania, Moldova and southern Poland. A general drying tendency revealed also in April, which was statistically significant over a wide area in the Czech Republic and Poland. Increasing trends in SPI and SPEI for September and October were detected in Romania, Moldova and Hungary. The use of SPEI instead of SPI generally enhances drying trends.This study was initiated and financed by the EU JPI WATER project IMDROFLOOD. In addition, it is partly supported by the Ministry of Education and Research of Estonia (grant PRG-352), by the projects “SustES—Adaptation strategies for sustainable ecosystem services and food security under adverse environmental conditions” (ref. CZ.02.1.01/0.0/0.0/16_019/0000797), MZe QK1910269 “Adaptation potential of common wheat in response to drought and extreme temperatures,” and by DAMOCLES COST ACA17109 “Understanding and modelling compound climate and weather events” (2018–2022).Peer reviewe

Documentary evidence as a source of data for studying droughts in the Czech lands

Information about past droughts may be derived from the various kinds of documentary evidence. Documentary data are particularly applicable to the pre-instrumental period but may also be used for the overlapping period with instrumental records. They are extracted from written narrative sources, weather diaries, personal and official letters, newspapers, religious records, epigraphic sources, and other sources. Direct descriptions of weather facilitate identification of meteorological droughts, while descriptions of drought impacts are used to identify agricultural and hydrological droughts. Documentary evidence enabled the creation of series of precipitation indices which classify dry months on a scale of –1 (dry), –2 (very dry), and –3 (extremely dry). In this way, it is possible to study the frequency, seasonality, severity, and impacts of drought episodes in the pre-instrumental period

Počasí v Čechách v letech 1805-1806; konfrontace vizuálních a přístrojových pozorování

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Meteorologická pozorování Alexandra Zawadzkého v Brné v letech 1861-1867

The observations made by Pavel Olexík in 1848 are accepted as the beginning of standardised meteorological measurements in Brno. Three times every day, from September 1861 to December 1867, Professor Alexander Zawadzki, a teacher of physics and botany at a Brno technical secondary school, kept recording the values of air pressure, air temperature, precipitation, wind and atmospheric phenomena. His observation diary also includes phenological data and information about meteorological and other natural events across the Czech Lands and Europe. Because there is neither a great distance nor difference in altitude between the places in which Zawadzki and Olexík made their observations, the pressure and temperature readings show only negligible devergencies. The differences are not significant for wind direction, precipitation totals and days with rain and snow, but they are greater for athmospheric phenomena. The contemporary meteorological activities of Gregor Johann Mendel also vastly contributed to Brno becoming an important centre of meteorology in the eastern part of the Czech Lands in the 1860s.33435

Climatic and other responses to the Lakagígar 1783 and Tambora 1815 volcanic eruptions in the Czech Lands

Using documentary data and long-term temperature and precipitation series for the years 1775-2007, climatic, weather and other phenomena in the Czech Lands following the 1783 Lakagıgar eruption in Iceland and the 1815 Tambora eruption in Indonesia are investigated. The Lakagıgar eruption had clear post-volcanic effects on the weather in central Europe (dry fog, heavy thunderstorms, optical phenomena), with the occurrence of significant cold temperature anomalies in winter 1783/84, spring 1785 and the summer and autumn of 1786. The Tambora eruption was not accompanied by any particular weather phenomena, but was followed by an extremely cold summer in 1816. A comparison of the two eruptions shows that the effects of the Lakagıgar eruption were climatologically stronger than those of the Tambora eruption.14716

Central Europe, 1531–1540 CE: The driest summer decadeof the past five centuries?

Based on three drought indices (SPI, SPEI, Z-index) reconstructed from documentary evidence and instrumental records, the summers of 1531–1540 were identified as the driest summer decade during the 1501–2015 period in the Czech Lands. Based on documentary data, extended from the Czech scale to central Europe, dry patterns of various intensities (represented, for example, by dry spells, low numbers of precipitation days, very low rivers, and drying-out of water sources) occurred in 1532, 1534–1536, 1538, and particularly 1540, broken by wetter or normal patterns in 1531, 1533, 1537, and 1539. Information relevant to summer droughts extracted from documentary data in central Europe was confirmed in summer precipitation totals from a multi-proxy reconstruction for Europe by Pauling et al. (2006) and further by self-calibrated summer Palmer Drought Severity Index (PDSI) reconstruction from tree ring widths in Old World Drought Atlas (OWDA) by Cook et al. (2015). The summer patterns described are consistent with the distribution of sea level pressure deviations from a modern reference period. Summer droughts were responsible for numerous negative impacts, such as bad harvests of certain crops, reduction and lack of water sources, and frequent forest fires, while in the wetter summers central Europe was affected by floods. However, there are no indications of severe impacts of a multi-country or multi-year effect. Reconstructions based on documentary data indicate that the summers of 1531–1540 constitute the driest summer decade in central Europe for the past five centuries between 1501 and 2010 CE

Changes in Weather-Related Fatalities in the Czech Republic during the 1961–2020 Period

Fatalities associated with severe weather, collected from newspapers and other documentary sources, were used to create a corresponding database for the 1961–2020 period for the Czech Republic. Fatalities attributed to floods, windstorms, convective storms, snow and glaze ice, frost, fog, and other severe weather, on the one hand, and vehicle accident fatalities connected with rain, snow, glaze ice, fog, and inclement weather, on the other, were analysed separately for two standard periods, 1961–1990 and 1991–2020. The number of weather-related fatalities between these two periods increased in the flood, windstorm, and especially frost categories, and decreased for the convective storm and fog categories. For snow and glaze ice they were the same. Despite significant differences in both 30-year periods, the highest proportions of fatalities corresponded to the winter months, and in individual fatality characteristics to males, adults, direct deaths, deaths by freezing or hypothermia, and to hazardous behaviour. A statistically significant (p < 0.05) Spearman rank correlation between fatalities and climate variables was only found in the 1991–2020 period for snow/glaze ice-related fatalities, with the number of days with snow cover depth and frost-related fatalities having days with daily minimum temperatures below −5 °C or −10 °C. Despite the highest proportions of the rain and wet road categories being in the number of vehicle accident fatalities, a statistically significant correlation was only found for the category of snow-related fatalities in the number of days with snowfall. The results and conclusions of this study have to be evaluated in the broader context of climatological, political, economic, and societal changes within the country, and have the potential to be used in risk management

Documentary and instrumental-based drought indices for the Czech Lands back to AD 1501

This study addresses the reconstruction of 4 slightly different drought indices in the Czech Lands (now the Czech Republic) back to 1501 AD. Reconstructed monthly temperatures for Central Europe that are representative for the Czech territory, together with reconstructed seasonal precipitation totals from the same area, are used to calculate monthly, seasonal and annual drought indices (SPI, SPEI, Z-index, and scPDSI). The resulting time series reflect interannual to multi-decadal drought variability. The driest episodes cluster around the beginning and end of the 18th century, while 1540 emerges as a particularly dry extreme year. The temperature-driven dryness of the past 3 decades is well captured by SPEI, Z-index and scPDSI, whereas precipitation totals show no significant trend during this period (as reflected in SPI). Data and methodological uncertainty associated with Czech drought indices, as well as their position in a greater European context, are critically outlined. Comparison with fir tree-rings from southern Moravia and a spatial subset of the ‘Old World Drought Atlas’ (OWDA) reveals statistically significant correlation coefficients, of around 0.40 and 0.50, respectively. This study introduces a new documentary-based approach for the robust extension of standardised drought indices back into pre-instrumental times, which we also believe has great potential in other parts of the world where high-resolution paleoclimatic insight remains limited