The forgotten drought of 1765–1768: Reconstructing and re‐evaluating historical droughts in the British and Irish Isles

Abstract

Historical precipitation records are fundamental for the management of water resources, yet rainfall observations typically span 100-150 years at most, with considerable uncertainties surrounding earlier records. Here, we analyse some of the longest available precipitation records globally, for England and Wales, Scotland and Ireland. To assess the credibility of these records and extend them further back in time, we statistically reconstruct (using independent predictors) monthly precipitation series representing these regions for the period 1748-2000. By applying the Standardized Precipitation Index at 12-month accumulations (SPI-12) to the observed and our reconstructed series we re-evaluate historical meteorological droughts. We find strong agreement between observed and reconstructed drought chronologies in post-1870 records, but divergence in earlier series due to biases in early precipitation observations. Hence, the 1800s decade was less drought prone in our reconstructions relative to observations. Overall, the drought of 1834-1836 was the most intense SPI-12 event in our reconstruction for England and Wales. Newspaper accounts and documentary sources confirm the extent of impacts across England in particular. We also identify a major, "forgotten" drought in 1765-1768 that affected the British-Irish Isles. This was the most intense event in our reconstructions for Ireland and Scotland, and ranks first for accumulated deficits across all three regional series.

Regional Differences in Spatiotemporal Drought Characteristics in Great Britain

“…Our study has also identified six additional droughts not well known until now: an early drought rich period in the 1860s and 1870s particularly in the NW, a severe drought in the "Transition" region in 1937-38, and a severe drought in the NW in 1955-56. Five out of these six "new" droughts were also identified in the recent study by Murphy et al (2020) as "severe" droughts (12-month SPI > −1.5), with the exception of the 1870-1873 one which fell into the category of "moderate" drought. Murphy et al (2020) use single long national-scale rainfall time series for England, Scotland and Ireland (albeit each being a combination of multiple gauges) so the current study adds value by characterising the spatiotemporal signature of these events.…”

“…The earlier instruments were installed before international standards for precipitation measurements were defined and widely adopted (Rodda and Dixon, 2012), and issues such as snowfall undercatch in winter or the effect of wind are likely to overestimate the severity of droughts. However, Murphy et al (2020) found that winter under-catch was identified as being significant mainly for data prior to 1850 in the British Isles, and that observed and reconstructed precipitation time series strongly agreed for the period going from 1870 to present. This gives us confidence in the underlying raingauge data underpinning the gridded dataset used in this study, which starts in 1862, and although we acknowledge the greater uncertainty in the data in the earlier period, this is the best dataset available at the time this study was carried out and is a clear improvement to what was available before.…”

Long‐term variability and trends in meteorological droughts in Western Europe (1851–2018)

“…It is necessary to stress that this study may be affected by some limitations. For example, Murphy et al (2019Murphy et al ( , 2020 have shown that pre-1870 winter precipitation in north West Europe is likely too low due to undercatch of snow. Such changes that affect multiple stations simultaneously may not be detected using relative homogenisation methods and they could affect winter and annual SPI trends for stations in the British and Irish Isles.…”

Reconstructed monthly river flows for Irish catchments 1766–2016

“…Murphy et al (2019) show that pre-1870 winter precipitation observations in the United Kingdom were likely affected by under-catch of snowfall due to gauge design and observer practice. It is likely that early Irish precipitation totals are affected by the same biases during winter months (Murphy et al, 2020).…”