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Drought (Europe) -- Summary
Climate alarmists typically contend that as the world warms it should experience more frequent and severe droughts. A good reality check on this claim would be to see what happened over the 20th century, when climate alarmists claim the world warmed at a rate and to a level that were unprecedented over the past two millennia. Hence, we here investigate this subject as it pertains to Europe.

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. Specifically, 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 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." Quite to the contrary, they found 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)."

Concentrating on Central Scandinavia, 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 the region. 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 17th century. These results clearly demonstrate that for this portion of the European continent, 20th-century global warming did not result in more frequent or more severe droughts.

In a related study conducted in east central Sweden, Linderholm and Molin (2005) analyzed two independent precipitation proxies, one derived from tree-ring data and one from a farmer's diary, to produce a 250-year record of summer (Jun-Aug) precipitation. This work indicated there had been a high degree of variability in summer precipitation on inter-annual to decadal time scales throughout the record, but with the past century exhibiting less variability than the 150 years that preceded it. One period that stood out vividly was a persistent dry episode between 1806 and 1832, when the tree-ring history revealed its longest consecutive period of below-average tree growth, which was associated with a concomitant period of drought that was documented in the farmer's diary.

Concomitantly, Wilson et al. (2005) used the 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 20th century. Hence, these results, too, fly in the face of climate-alarmist predictions.

Another study of interest concerns the Danube River in western Europe, where several researchers had studied the precipitation histories of adjacent regions and suggested that an anthropogenic signal was present in the latter decades of the 20th century, and that it was responsible for that period's supposedly drier conditions. Determined to investigate further, Ducic (2005) examined 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 5-year discharge value in the pre-instrumental era (1831-1835) was practically equal to the lowest 5-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% less than the 260-year mean, leading to the conclusion that "modern discharge fluctuations do not point to dominant anthropogenic influence."

One year later, van der Schrier et al. (2006) constructed monthly maps of the Self-Calibrating Palmer Drought Severity Index (SC-PDSI, a variant put forward by Wells et al. (2004) of the more common PDSI) for the period 1901-2002 for Europe (35N-70N, 10W-60E), which index, in their words, "improves upon the PDSI by maintaining consistent behavior of the index over diverse climatological regions," which "makes spatial comparisons of SC-PDSI values on continental scales more meaningful." In doing so, they found that "over the region as a whole, the mid-1940s to early 1950s stand out as a persistent and exceptionally dry period, whereas the mid-1910s and late 1970s to early 1980s were very wet." Over the entire study period, however, they found that trends in the continent's summer moisture availability "fail to be statistically significant, both in terms of spatial means of the drought index and in the area affected by drought." In addition, they note that "evidence for widespread and unusual drying in European regions over the last few decades [as suggested by the work of Briffa et al. (1994) and Dai et al. (2004)] is not supported by the current work," in that "values for the total percentage area subject to extreme moisture conditions in the years 1996-99 returned to normal levels at ~2% from a maximum of nearly 10% in 1990." And in further support of their findings, the four researchers note that "the absence of a trend toward summer desiccation has recently also been observed in soil moisture records in the Ukraine (Robock et al., 2005) and supports conclusions in the current study."

Pfister et al. (2006) identified extremely low water stages within the Upper Rhine River Basin via hydrological measurements made since 1808 at Basel, Switzerland, while "for the period prior to 1808, rocks emerging in rivers and lakes in the case of low water were used along with narrative evidence for assessing extreme events." This work revealed that "29 severe winter droughts are documented since 1540," which events, in their words, "occurred after a succession of four months with below-average precipitation" associated with "persistent anticyclones centered over Western Europe." Of most interest, in this regard, was their finding that the "severe winter droughts were relatively rare in the 20th century compared to the former period, which is due to increased winter temperature and precipitation." And in discussing the generality of their findings, they note that "extended droughts in the winter half-year in Central Europe were more frequent, more persistent and more severe during the Little Ice Age than in the preceding 'Medieval Warm Period' and the subsequent 'warm 20th century' (Pfister, 2005)," which facts suggest a relationship that is just the opposite of what climate alarmists typically claim is the case.

More recently, Renard et al. (2008) employed four different procedures for assessing field significance and regional consistency with respect to trend detection in both high- and low-flow hydrological regimes of French rivers, using daily discharge data obtained from 195 gauging stations having a minimum record length of 40 years. These analyses revealed that "at the scale of the entire country, the search for a generalized change in extreme hydrological events through field significance assessment remained largely inconclusive." In addition, they say that at the smaller scale of hydro-climatic regions, there were also no significant results for most regions, although they add that "consistent changes were detected in three geographical areas."

Although small geographical areas often display trends in hydrological regimes of one extreme or the other (high- or low-flow), when scaling up to larger regions such as countries, there is typically less consistent change in extreme behavior. Consequently, as a result of their own findings and those of several others, Renard et al. concluded that "when considered at the global scale," the impact of climate change on hydrological regimes "is still an open question, as illustrated by the lack of a clear signal emerging from large-scale studies (Knudzewicz et al., 2005; Svensson et al., 2005)."

This state of affairs must be rather embarrassing for the world's climate alarmists, who vociferously contend that the latter part of the 20th century experienced a warming that was unprecedented over the past one to two millennia, and who claim that such extreme warming should significantly enhance the frequency and severity of extreme hydrological events (such as droughts) the world over, when they clearly don't.

References
Briffa, K.R., Jones, P.D. and Hulme, M. 1994. Summer moisture variability across Europe, 1892-1991: An analysis based on the Palmer Drought Severity Index. International Journal of Climatology 14: 475-506.

Dai, A., Trenberth, K.E. and Qian, T. 2004. A global dataset of Palmer Drought Severity Index for 1870-2002: Relationship with soil moisture and effects of surface warming. Journal of Hydrometeorology 5: 1117-1130.

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.

Knudzewicz, Z.W., Graczyk, D., Maurer, T., Pinskwar, I., Radziejewski, M., Svensson, C. and Szwed, M. 2005. Trend detection in river flow series: 1. Annual maximum flow. Hydrological Sciences Journal 50: 797-810.

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.

Linderholm, H.W. and Molin, T. 2005. Early nineteenth century drought in east central Sweden inferred from dendrochronological and historical archives. Climate Research 29: 63-72.

Pfister, C. 2005. Weeping in the snow. The second period of Little Ice Age-type impacts, 1570-1630. In: Behringer, W., Lehmann, H. and Pfister, C. (Eds.) Kulturelle Konsequenzen der "Kleinen Eiszeit," Vandenhoeck, Gottingen, Germany, pp. 31-86.

Pfister, C., Weingartner, R. and Luterbacher, J. 2006. Hydrological winter droughts over the last 450 years in the Upper Rhine basin: a methodological approach. Journal des Sciences Hydrologiques 51: 966-985.

Renard, B., Lang, M., Bois, P., Dupeyrat, A., Mestre, O., Niel, H., Sauquet, E., Prudhomme, C., Parey, S., Paquet, E., Neppel. L. and Gailhard, J. 2008. Regional methods for trend detection: Assessing field significance and regional consistency. Water Resources Research 44: 10.1029/2007WR006268.

Robock, A., Mu, M., Vinnikov, K., Trofimova, I.V. and Adamenko, T.I. 2005. Forty-five years of observed soil moisture in the Ukraine: No summer desiccation (yet). Geophysical Research Letters 32: 10.1029/2004GL021914.

Svensson, C., Kundzewicz, Z.W. and Maurer, T. 2005. Trend detection in river flow series: 2. Flood and low-flow index series. Hydrological Sciences Journal 50: 811-824.

van der Schrier, G., Briffa, K.R., Jones, P.D. and Osborn, T.J. 2006. Summer moisture variability across Europe. Journal of Climate 19: 2818-2834.

Wells, N., Goddard, S. and Hayes, M.J. 2004. A self-calibrating Palmer Drought Severity Index. Journal of Climate 17: 2335-2351.

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.

Last updated 2 September 2009