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The Global Warming-Global Runoff Connection
Munier, S., Palanisamy, H., Maisongrande, P., Cazenave, A. and Wood, E.F. 2012. Global runoff anomalies over 1993-2009 estimated from coupled Land-Ocean-Atmosphere water budgets and its relation with climate variability. Hydrology and Earth system Sciences 16: 3647-3658.

"As noted by many authors (e.g. Labat, 2004; Huntington, 2006; Gerten et al., 2008; Dai et al., 2009)," in the words of Munier et al., "global runoff may be seen as an indicator of the intensification of the hydrological cycle." And they add that "since global runoff represents an integrated response to continental hydrological dynamics (e.g. Gleick, 2003; Nilsson et al., 2005; Milliman et al., 2008), it has also been used to detect the impact of anthropogenic activities," not the least of which is global warming.

What was done
Munier et al. employed two different ways of estimating global runoff over the period 1993-2009, both of which were derived from the coupling of land-atmosphere and ocean-atmosphere water budgets, and where independent data sets (atmospheric reanalyses, land surface models, satellite altimetry and in situ ocean temperature data) were used to estimate water storage variations in several different water budget compartments.

What was learned
First of all, the five researchers found that the results of both sets of calculations of the 1993-2009 global runoff "correlate very well over the study time span, giving confidence in the [two] method[s]." And secondly, they report that for both approaches to the problem, "no significant trend is observed over the whole period."

What it means
In the concluding words of the research team, "we show that an intensification of the global water cycle due to global warming is not obvious over the last two decades," which is not exactly what one would expect to be the case during a period of supposedly "unprecedented" over-heating of the planet.

Dai, A., Qian, T.T., Trenberth, K.E. and Milliman, J.D. 2009. Changes in continental freshwater discharge from 1948 to 2004. Journal of Climate 22: 2773-2792.

Gerten, D., Rost, S., von Bloh, W. and Lucht, W. 2008. Causes of change in 20th century global river discharge. Geophysical Research Letters 35: 10.1029/2008GL035258.

Gleick, P. 2003. Global freshwater resources: Soft-path solutions for the 21st century. Science 302: 1524-1528.

Huntington, T.G. 2006. Evidence for intensification of the global water cycle: Review and synthesis. Journal of Hydrology 319: 83-95.

Labat, D. 2004. Evidence for global runoff increase related to climate warming. Advances in Water Resources 27: 631-642.

Milliman, J.D., Farnsworth, K.L., Jones, P.D., Xu, K.H. and Smith, L.C. 2008. Climatic and anthropogenic factors affecting river discharge to the global ocean, 1951-2000. Global and Planetary Change 62: 187-194.

Nilsson, C., Reidy, C., Dynesius, M. and Revenga, C. 2005. Fragmentation and flow regulation of the world's large river systems. Science 308: 405-408.

Reviewed 10 April 2013