Early nineteenth century drought in east central Sweden inferred from dendrochronological and historical archives

Scots pine tree-ring width data and entries from a farmer's diary were combined to assess early nineteenth century drought in east central Sweden. Tree-ring data were used to reconstruct drought, in the form of the standardized precipitation index (SPI), back to 1750. Daily weather observations in the farmer's diary were translated to temperature and degree of drought for each growing season from 1815 to 1833. During this period, Scots pine growth was constantly below average, and radial growth in 89% of the years between 1806 and 1832 indicated dry summers. Within the same period, severe drought was reported in the diary during several years. Although individual summers have been drier before and after this period, the record suggests that 1806 to 1835 was the longest continuous drought in the last 250 yr, possibly even the last 300 yr. Furthermore, this event seems to have been of regional extent, as indicated by meteorological, historical and tree-ring data from northern and central Europe. The present study showed that a combination of dendrochronological and historical records yields more useful information about past droughts, in terms of impact and long-term context, than one or the other of these sources can provide alone.