Reconstructing Historical Droughts in Spain (1806–1865): Atmospheric Dynamics Versus Qualitative Impact Records

Abstract. Significant droughts occurred during the nineteenth century in the Iberian Peninsula causing severe social and economic consequences. Although such events are typically studied through quantitative indices like the Standardized Precipitation Index (SPI); in this case study, instrumental rainfall data only cover the last thirty years of the century. The limited spatial coverage of these early instrumental data justifies the use of historical documentary sources for the study of droughts during this transitional century between the purely pre-instrumental period and the modern instrumental era. This study aims to reconstruct nineteenth-century droughts in the Iberian Peninsula and to assess the extent to which documentary drought records reflect large-scale atmospheric dynamics.

In this work, we developed drought indices based on rogation ceremonies from municipal documentary sources compiled in the AMARNA® Repository and analyzed two atmospheric indicators from the 20CRv3 reanalysis: sea-level pressure and geopotential height at 500 hPa (Z500). The correlation between drought indices and the atmospheric variables reveals a sustained decrease in the sensitivity of historical drought records starting in the mid-19th century, likely due to social, political and other long-term changes. This decline delimits a more reliable period for the documentary-based analysis.

Our findings reveal that years with the most drought records were accompanied by persistent sea-level pressure and Z500 anomalies over the Iberian Peninsula, consistent with known circulation patterns associated with drought. These anomalies occurred predominantly during the preceding winter (DJF), indicating that atmospheric conditions favorable to drought had already developed several months before the late-winter/spring social response captured in the documentary record.

This underscores the value of combining documentary and reanalysis data to reconstruct pre-instrumental climate variability, while highlighting the need to account for both source reliability and temporal lags in future historical drought studies.