Episódios de seca extrema em Portugal no século XVIII / Episodes of Extreme Drought in Portugal in the 18th Century

Abstract

Throughout the ages, mankind has been severely affected by extreme weather events. These phenomena have been the subject of several studies, with a considerable number of works focusing in particular on rainfall variability, past droughts and their impacts. The current issues on climate change and the recent extreme drought of 2017 in Portugal raise a renewed interest for the study of historical droughts. As the available instrumental data series are relatively short, past droughts have also been extensively studied using historical documentary data. The present work aims to lengthen the historical drought series in Portugal, thus contributing to the understanding of the drought phenomena and, consequently, to the improvement of projections for the future. Here the main droughts of the 18th century in mainland Portugal were identified using mostly direct documentary sources: individual (poems, letters, memoirs, manuscripts and printed newspapers) and institutional (ecclesiastical and administrative), as well as accounts of Pro pluvia ceremonies and processions. All documentary data were obtained from the KlimHist database, where all records are assembled as a result of previous studies developed during the KlimHist project (http://clima.ul.pt/Klimhist-project). Based on the database records, a summary statistical analysis of the drought evidences including their impacts was performed to assess their temporal distribution and geographical incidence. Strong precipitation variability is detected, as in the present times. The main drought years of the 18th century in Portugal were highlighted, particularly the severe and long-lasting 1737-38 and 1753-54 droughts that, together with their atmospheric causes, were studied in detail. It is noticed that there are more drought records for Southern Portugal (SP) than for Northern Portugal (NP). In addition, it is observed that the spring (MAM) and winter (DJF) drought evidences are more frequent in SP, whereas in NP there are more records concerning summer (JJA). The results of this study corroborate the idea that (as it is well known in our days), despite Portugal is a small country, there is an important climatic limit between NP and SP with different precipitation regimes. Moreover, the results obtained in the present work are in agreement with those of previous studies for the Iberian Peninsula, carried out by different authors.