Background
The authors write that "the impact of climate change on the hydrological regime of rivers is still a subject of active research, especially regarding extreme hydrological events such as floods or droughts," which climate alarmists contend should become more frequent and extreme as the earth warms.

What was done
Renard et al. employed four different procedures for assessing field significance and regional consistency with respect to trend detection in both high-flow 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.

What was learned
The twelve researchers report 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."

What it means
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 others they cite, Renard et al. conclude 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)."

Clearly, 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 the world over.

References
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.

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.