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20th-Century North American Streamflow Trends
Reference
Rood, S.B., Samuelson, G.M., Weber, J.K. and Wywrot, K.A.  2005.  Twentieth-century decline in streamflow from the hydrographic apex of North America.  Journal of Hydrology 306: 215-233.

Background
One of the primary predictions of climate alarmists is that global warming will increase evaporation rates from the world's oceans, resulting in an enhancement of the planet's hydrologic cycle and increased precipitation and river runoff.  They also claim that the global warming of the past century has been unprecedented over the past one to two millennia.  Consequently, analyses of river runoff records for this period of time would be expected to provide evidence for the validity of these claims ... but only, of course, if they are true.

What was done
The authors performed an empirical analysis of stremflow trends from rivers fed by relatively pristine watersheds in the central Rocky Mountain Region of North America that extends from Wyoming through British Columbia.  In doing so, they applied both parametric and non-parametric statistical analyses to assess nearly a century of annual discharge (ending about 2002) along 31 river reaches that drain this region.

What was learned
Overall, the analyses revealed that river flows declined over the past century by an average of 0.22% per year, with four of them exhibiting recent decline rates exceeding 0.5% per year.  As for future streamflow trends, Rood et al. extrapolate from observed historical patterns of interannual variability, suggesting "it is likely that there will be continuing decline in future decades," perhaps by a further 10% by the year 2050.

What it means
To state the obvious, the results of this empirical study show a century-long decline in historic streamflow from the hydrographic apex of North America, which finding, in the words of Rood et al., "contrasts with the many current climate change predictions that the region will become warmer and wetter in the near-future."  Once again, therefore, the models appear to have gotten it all wrong for a large portion of North America.

Reviewed 24 August 2005