Droughts in Europe
From Climate Change Reconsidered, a work of the Nongovernmental International Panel on Climate Change
Linderholm and Chen (2005) derived a 500-year history of winter (September-April) precipitation from tree-ring data obtained within the Northern Boreal zone of Central Scandinavia. This chronology indicated that below-average precipitation was observed during the periods 1504-1520, 1562-1625, 1648-1669, 1696-1731, 1852-1871, and 1893-1958, with the lowest values occurring at the beginning of the record and at the beginning of the seventeenth century. These results demonstrate that for this portion of the European continent, twentieth century global warming did not result in more frequent or more severe droughts.
Another five-century perspective on the issue was provided by Wilson et al. (2005), who used a regional curve standardization technique to develop a summer (March-August) precipitation chronology from living and historical ring-widths of trees in the Bavarian Forest region of southeast Germany for the period 1456-2001. This technique captured low frequency variations that indicated the region was substantially drier than the long-term average during the periods 1500-1560, 1610-1730, and 1810-1870, all of which intervals were much colder than the bulk of the twentieth century.
A third study of interest concerns the Danube River in western Europe, where some researchers had previously suggested that an anthropogenic signal was present in the latter decades of the twentieth century, and that it was responsible for that period’s supposedly drier conditions. Ducic (2005) tested these claims by analyzing observed and reconstructed discharge rates of the river near Orsova, Serbia over the period 1731-1990. This work revealed that the lowest five-year discharge value in the pre-instrumental era (1831-1835) was practically equal to the lowest five-year discharge value in the instrumental era (1946-1950), and that the driest decade of the entire 260-year period was 1831-1840. What is more, the discharge rate for the last decade of the record (1981-1990), which prior researchers had claimed was anthropogenically influenced, was found to be “completely inside the limits of the whole series,” in Ducic’s words, and only 0.7 percent less than the 260-year mean, leading to the conclusion that “modern discharge fluctuations do not point to dominant anthropogenic influence.” In fact, Ducic’s correlative analysis suggests that the detected cyclicity in the record could “point to the domination of the influence of solar activity.”
In much the same vein and noting that “the media often reflect the view that recent severe drought events are signs that the climate has in fact already changed owing to human impacts,” Hisdal et al. (2001) examined pertinent data from many places in Europe. They performed a series of statistical analyses on more than 600 daily streamflow records from the European Water Archive to examine trends in the severity, duration, and frequency of drought over the following four time periods: 1962-1990, 1962-1995, 1930-1995, and 1911-1995. This work revealed, in their words, that “despite several reports on recent droughts in Europe, there is no clear indication that streamflow drought conditions in Europe have generally become more severe or frequent in the time periods studied.” To the contrary, they report that “overall, the number of negative significant trends pointing towards decreasing drought deficit volumes or fewer drought events exceeded the number of positive significant trends (increasing drought deficit volumes or more drought events).”
In conclusion, there is no evidence that droughts in Europe became more frequent or more severe due to global warming in the twentieth century.
Climate Change Reconsidered: Website of the Nongovernmental International Panel on Climate Change. http://www.nipccreport.org/archive/archive.html
Ducic, V. 2005. Reconstruction of the Danube discharge on hydrological station Orsova in pre-instrumental period: Possible causes of fluctuations. Edition Physical Geography of Serbia 2: 79-100.
Hisdal, H., Stahl, K., Tallaksen, L.M. and Demuth, S. 2001. Have streamflow droughts in Europe become more severe or frequent? International Journal of Climatology 21: 317-333.
Linderholm, H.W. and Chen, D. 2005. Central Scandinavian winter precipitation variability during the past five centuries reconstructed from Pinus sylvestris tree rings. Boreas 34: 44-52.
Wilson, R.J., Luckman, B.H. and Esper, J. 2005. A 500 year dendroclimatic reconstruction of spring-summer precipitation from the lower Bavarian Forest region, Germany. International Journal of Climatology 25: 611-630.