There are concerns that recent climate change is altering the frequency and magnitudes of river floods in an unprecedented way 1 . Historical studies have identified flood-rich periods in the past half millennium in various regions of Europe 2 . However, because of the low temporal resolution of existing data sets and the relatively low number of series across Europe, it has remained unclear whether Europe is currently in a flood-rich period from a long term perspective. We analyze how recent decades compare with the flood history of Europe, using a new database composed of more than 100 high-resolution (sub-annual) historical flood series based on documentary evidence covering all major regions of Europe. Here we show that the past three decades were among the most flood-rich periods in Europe in the last 500 years, and that this period differs from other floodrich periods in terms of its extent, air temperatures and flood seasonality. We identified nine floodrich periods and associated regions. Among the periods richest in floods are 1560-1580 (Western and Central Europe), 1760-1800 (most of Europe), 1840-1870 (Western and Southern Europe), and 1990. In most parts of Europe previous flood-rich periods occurred during cooler than usual phases, however the current flood-rich period has been much warmer. In the past, the dominant flood seasons in flood-rich periods were similar to those during the intervening (interflood) periods, but flood seasonality is more pronounced in the recent period. For example, during previous flood and interflood periods, 41% and 42% of Central European floods occurred in summer respectively, compared to 55% of floods in the recent period. The uniqueness of the present-day flood-rich period calls for process-based flood risk assessment tools and flood risk management strategies that can incorporate these changes.
Extreme meteorological events have had devastating consequences all over the world throughout the ages. In this study, we look into the floods at the mouth of the Douro River (Porto, Portugal) in the eighteenth century to expand the data series of floods in Northern Portugal. Information was gathered mostly from documentary narrative sources, either individual or institutional (administrative and ecclesiastic), some of which include reports of Pro Serenitate ceremonies. A study by the priest Rebelo Costa (1789) and the memories of the merchant Ignacio Henckell from 1717 to 1800 stand out among the individual sources. We concluded that there was great interannual variability in the occurrence of the 54 recorded floods, the highest number of which occurred in the 1780s. The “catastrophic” floods were recorded in 1727, 1739, 1769, 1774, 1777, 1788 and 1798, four of which are studied in detail in this paper. The greatest number of flood events took place in winter and autumn, and most of them lasted between 1 and 3 days. An analysis of the description of the floods, their impacts and the associated meteorological causes was carried out. In most cases, the frontal activity associated with Atlantic cyclonic systems was the cause of positive precipitation anomalies in NW Iberia. The great variability in heavy precipitation was confirmed by the new data. However, hardly any temporal simultaneity was found with other case studies in Southern Europe, except for Spain, especially several localities of Galicia and the mid Douro Valley (Zamora).
SumárioAs cheias do rio Douro ocorridas na cidade do Porto, no século XVIII, permitem fazer uma dupla aproximação à história do clima. Por um lado, procede-se a uma análise serial dos anos de cheias, da sua distribuição cronológica, frequência, duração, fenómenos meteorológicos associados e respetivos impactos, aplicando modelos de tratamento de informação utilizados em alguns estudos mais recentes, aferidores das intensidades das cheias. Por outro lado, tentamos compreender como valores, crenças, atitudes e conhecimentos refletem perceções diferentes dos eventos, entre sensações de vulnerabilidade, de aprendizagem e de mudança. A análise de informação coeva, como sejam, fontes cartográficas, eclesiásticas e municipais, assim como o testemunho de um mercador, ao longo de anos sucessivos (1717-1800), permitirá reconstituir a dimensão do fenómeno e compará-la com contextos climáticos de outros espaços geográficos. Conclui-se que a posição do informador, a fragilidade e, em simultâneo, a potência da informação é uma construção social. AbstractThe floods occurred on the estuary of the river Douro in the eighteenth century, in the city of Porto, allow a double approach to the history of the climate. On the one hand, applying information treatment models used in some more recent studies it is possible to make a serial analysis of the years of floods, their chronological distribution, frequency, duration and intensity associated with meteorological phenomena and their impacts. On the other hand, we tried to understand how va-Inês AmorIm; Luís Pedro sILvA; João CArLos GArCIA: As cheias do rio Douro no Porto (Portugal) do século XVIII lues, beliefs, attitudes, knowledge reflect different perceptions of events, between sensations of vulnerability, learning and change. The analysis of information, such as cartographic, ecclesiastical and municipal sources, as well as the testimony of a merchant, over successive years (1717-1800), allowed reconstituting the dimension of the phenomenon comparing with the climatic contexts of other geographical spaces. We conclude that the informant's position, the fragility and, at the same time, the power of information is also a social construction. INTRODUÇÃOAs cheias do rio Douro fazem parte da memória da cidade do Porto, assinaladas, ainda hoje, em vários muros e edifícios situados nas duas margens do seu estuário, entre a cidade do Porto (margem norte) e de Vila Nova de Gaia (margem sul). Quase todas estas marcas são dos séculos XIX e XX, apesar da construção de barragens entre a sua nascente, em território espanhol, e a sua foz, no Noroeste de Portugal, junto à cidade do Porto.Estes testemunhos contemporâneos são as informações sobreviventes e dispersas, não documentadas, vagas, mas repetidas, de ocorrências anteriores, de momentos em que os caudais elevados submergiam os terrenos marginais. São estes traços mais distantes no tempo que procuramos, para a época moderna, em particular ao longo do século XVIII, dando-lhes uma conexão serial, e, em simultâneo, observando os processos de co...
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