Drought variability in the Spanish Mediterranean Basin during the Dalton Solar Minimum period (1790-1830)

The current climate change scenario is increasing concerns about the frequency of droughts in the Mediterranean region and the management of water resources. For this reason, it is interesting to study the most severe droughts of the recent past in order to better characterise the current phenomenon and future adaptive strategies.

One of these episodes of great magnitude and significant impact on economic and social activity were the droughts that occurred in the first third of the 19th century in the Mediterranean basins of the Iberian Peninsula. This relatively brief period, placed at the end of the Little Ice Age, contains up to four episodes of drought that affected the Spanish Mediterranean Basins. Their occurrence can be linked to known climatic forcing factors. On the one hand, the effects of the Dalton Solar Minimum (1790-1830). On the other hand, the effects of three different volcanic eruptions produced in the intertropical latitudes with a VEI equal or greater than 5: the Unknown eruption of 1809, the Tambora eruption of 1815 and the Galunggung eruption of 1822.

The climatic characterisation of the drought in this period is proposed with the use of historical proxy-data based on rogation ceremonies to monitor situations of rainfall deficit at high temporal resolution (daily/monthly). For drought assessment, a drought information classification system is proposed based on an index that takes into account the basic characteristics of each episode (duration, extent and severity). This classification will be tested to determine the behaviour of the droughts that affected the Spanish Mediterranean Basin during the period of the Dalton Solar Minimum.

The results obtained from the application of these methodologies and materials allow the identification of severe droughts that affected the Spanish Mediterranean Basin during this period. Some of these years with severe droughts are 1807, 1812, 1817-1818, the most severe drought in the overall of the series, and 1822-1825. The description and cartographic representation of the historical data about these droughts allows us to assess their severity due to the extraordinary persistence of the rainfall deficits and their capacity to affect simultaneously distant regions.

Finally, in order to compare the results obtained from the historical data recorded in Barcelona about rainfall deficits, we use the instrumental meteorological series of Barcelona. This data series begun in 1780 recording data on temperature and pressure and begun recording precipitation in 1786. The information from those records allows the comparison with the historical data.