Reconstruction of drought episodes for central Spain from rogation ceremonies recorded at the Toledo Cathedral from 1506 to 1900: a methodological approach

Abstract

Rogation (ceremonies to ask God for rain: pro-pluvia, or to stop raining: pro-serenitate) analysis is an effective method to derive information about climate extremes from documentary data. Weighted annual sum by levels has been a widespread technique to analyze such data but this analysis is liable to be biased to spring values as these ceremonies are strongly related to farming activities. The analysis of the length of pro-pluvia periods (the time span during which rogations are carried out in relation to a drought event) and the combination of annual and seasonal information offers a more objective criterion for the analysis of the drought periods and an increase in the resolution of the study.

Analysis by the pro-pluvia periods method of the rogation series from the Toledo (central Spain) Cathedral Chapter allows a good characterization of the droughts during the 1506–1900 period. Two drought maxima appear during the 1600–1675 and 1711–1775 periods, characterized by rogations during almost all the year, with a middle stage (1676–1710) when droughts were less frequent and their length shortened.

Sea level pressure patterns for the instrumental and documentary periods show that droughts were mostly related to a north-eastern position of the Azores High that displaced the Atlantic low pressure systems towards a northern position. There is a weak relation with the North Atlantic Oscillation but this fact is related to the local character of the series that increases the weight of the local factors.

Comparison of rainfall/drought records around Spain and the Western Mediterranean reveals the heterogeneity of their distribution in time and space as well as stresses the need of more and longer reconstructions. Better knowledge of drought variability would help to improve regional models of climate extremes and the understanding of the atmospheric patterns related to their development.