Assessing the most severe subsistence crisis of the 18th century in the northwest of the Iberian Peninsula: a climatological perspective

Abstract

The analysis of climate variability over centuries reveals how environmental forces shaped society and helps contextualize modern climate trends and future projections. The persistent and heavy rains across several regions of the eastern Atlantic in 1768-1769 triggered the last and most severe agricultural crisis in Galicia and northern Portugal, leading to high mortality. The atmospheric conditions of this historical episode were analyzed using the EKF400v2 paleo-reanalysis dataset, which spans from the 18th century to the early 21st century. From June 1768 to May 1769, the rainfall anomaly in Galicia and northern Portugal was positive in 11 out of 12 months. Although the rainfall in northern Portugal appeared less intense than in Galicia, June 1768 had the highest positive rain anomaly of the century, and September 1768 had the second-highest. This excess precipitation agrees with the occurrence of pro-Serenitate rogations and written testimonies indicating an unusually high number of rainy days between June 1768 and May 1769. The atmospheric synoptic patterns for the rainiest months show negative anomalies in both sea level pressure and 500 hPa geopotential height in the northeastern Atlantic. These patterns are associated with troughs in the northeastern Atlantic that induce the formation of surface low-pressure systems and hinder the eastward progression of anticyclones into the region, resulting in more frequent episodes of rain and cold than usual.