Droughts in Portugal in the 18th century: A study based on newly found documentary data

摘要

A renewed interest in historical droughts is due to the current climate change issues and also to the recent extreme drought of 2017 in Portugal. This work aims to lengthen the historical drought series and help improve projections for the future. 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 the records had been assembled in the KlimHist database (http://clima.ul.pt/Klimhist-project). A summary statistical analysis of the drought evidence including its impacts was performed to assess its temporal distribution and geographical incidence. A strong precipitation variability was detected, which, similar to the present times, hardly presents trends in long series. The main years of drought during the 18th century in Portugal are highlighted, particularly the severe and long-lasting 1737-38 and 1753-54 droughts that, together with their atmospheric causes, were studied in detail. There are more drought records for Southern Portugal (SP) than for Northern Portugal (NP). It was also observed that spring March, April and May (MAM) and winter December, January and February (DJF) drought evidence are more frequent in SP, whereas in NP there are more records concerning summer June, July and August (JJA). The results obtained agree with those of others of the Iberian Peninsula (IP). Despite Portugal being a small country, our results confirm the existence of an important climatic boundary between the NP and the SP with different precipitation variability.