Climate Science

Charting Global Runoff

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Science  27 Jun 2008:
Vol. 320, Issue 5884, pp. 1696
DOI: 10.1126/science.320.5884.1696d

One widely expected potential consequence of climate warming is an intensification of the hydrological cycle, including more precipitation and more extreme precipitation events. Evidence that such intensification already has begun is available for some regions, but the question of whether or not the phenomenon is global remains unanswered. Milliman et al. have analyzed the runoff records of 137 rivers located on six continents, covering the last 50 years of the 20th century, in order to provide that answer. They find that global discharge has not changed significantly over that time, although regional changes were clearly apparent: Discharge decreases occurred disproportionately in Africa, Asia, and Australia, while Europe, North America, and South America experienced increases more often. Thus, the evidence seems not to show an intensification of the global hydrological cycle over the last half of the 20th century. That time period is too short, however, to draw firm conclusions about longer-term trends. — HJS

Global Planet. Change 62, 187 (2008).

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