Climatic effects on grain harvest variations at parish-level in Sweden c. 1665–1810

Several studies have statistically assessed the relationship between climate variability and grain harvest variations in pre-modern Sweden. They have, however, either studied the relationship on a coarse geographical (county to national) scale (Ljungqvist et al., 2023) or for only an individual province (Skoglund 2022, 2023, 2024). Fine-scale (parish-level) studies are entirely lacking. The Swedish 17^th and 18^th century tithe data – i.e., a tax paid on a percentage of the harvest – for different grain types are available at  parish-level and offer excellent estimates of harvest variations from year to year. Adequate palaeoclimate data, with seasonal resolution, is also available for the region and period. This has enabled us to conduct a detailed spatio-temporal investigation of the effects of climate variability on grain harvest variations at a parish-level. We have focused on the two main grain types cultivated in pre-modern Sweden, spring-sown barley and autumn-sown rye, and used 10-year high-pass filtered data to investigate short-term effects and linearly detrended data to also capture more long-term climate–harvest relationships while minimising the effects of spurious trends.

Our results show a consistent relationship in northern, and to a lesser extent also central, Sweden between summer temperature and harvest size. Warmer summers resulted in higher yields while colder summers resulted in lower yields. This effect extended further south in Sweden for the more drought-tolerant rye than for the more drought-sensitive barley. However, for both grain types southern-most coastal Sweden showed an opposite temperature–harvest relationship than the rest of the country: here, cooler summers instead promoted larger harvests than warmer ones.

We found that wetter summer conditions (higher soil moisture) mainly had a positive effect on the harvests in east-central and southern Sweden. The hydroclimatic effect on the harvests was found to be largest when considering only inter-annual variability (i.e., using high-pass filtered data), whereas the temperature-effect is more prominent when also considering relationships over longer time-scales (i.e., using linearly detrended data). Finally, we investigate the influence of soil texture and manure availability for the detected geographical climate–harvest relationship. We conclude that the climate–harvest relationships in southern-most and northern Sweden c. 1665–1810 were rather similar to those of modern times. Due to sensitivity to drought, harvests in the former region were, and still are, favoured by cooler summers, while warmer summers in the north increased, and still increase, the harvests. However, the positive effect of warmer summers in south-central Sweden was found to be much stronger c. 1665–1810 than in modern times, when larger harvests in the region rather follow cooler summers.

References

Ljungqvist, F. C., et al.: Climatic signatures in early modern European grain harvest yields, Climate of the Past, 19, 2463–2491, 2023.

Skoglund, M. K.: Climate variability and grain production in Scania, 1702–1911, Climate of the Past, 18, 405–433, 2022.

Skoglund, M. K.: Farming at the margin: climatic impacts on harvest yields and agricultural practices in central Scandinavia, c. 1560–1920, Agricultural History Review, 71, 203–233, 2023.

Skoglund, M. K.: The impact of drought on northern European pre-industrial agriculture, The Holocene, 34, 120–135, 2024.