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Trends of 20th-Century River Flow
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.

Climate models predict that one of the potential consequences of CO2-induced global warming is an enhancement of the world's hydrologic cycle, which is projected to result in increased precipitation and floods. At the same time, however, the models also predict longer and more severe droughts due to increased evapotranspiration driven by rising temperatures. Given such predictions, recent major floods and droughts in Europe and North America have led climate alarmists to proclaim they are due to global warming. But is this attribution correct?

What was done
In an effort to evaluate model projections of increased floods and droughts as a result of global warming, the authors examined 20th-century river flow data for a group of 21 stations distributed about the globe that they obtained from the Global Runoff Data Centre in Koblenz, Germany. Individual record lengths of the 21 stations varied from 44 to 100 years, with an average of 68 years. Analyses of the data consisted of computing trends in flood magnitude, flood frequency, and low-flow index series using Mann-Kendall and linear regression methods.

What was learned
In terms of flood magnitude and frequency, the analysis revealed there were slightly more stations exhibiting significant negative trends (reduced flooding) than significant positive trends (increased flooding). With respect to low-flow trends, nearly all stations showed increasing trends, approximately half of which were significant at the 90% level.

What it means
The results of this analysis, according to Svensson et al., indicate "there is no general pattern of increasing or decreasing numbers or magnitudes of floods, but there are significant increases in half of the low-flow series." These real-world observations are not consistent with model predictions of river flow response to global warming, since the world's climate alarmists claim that the planet experienced a warming over the latter part of the 20th century that was unprecedented over the past two millennia. If anything, therefore, and if the warming was truly as great as they claim, the data tend to support just the opposite relationship between warming and flood and drought occurrences.

Reviewed 29 March 2006