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Global pattern of trends in streamflow and water availability in a changing climate


Water availability on the continents is important for human health1,2, economic activity3, ecosystem function4 and geophysical processes5. Because the saturation vapour pressure of water in air is highly sensitive to temperature, perturbations in the global water cycle are expected to accompany climate warming6. Regional patterns of warming-induced changes in surface hydroclimate are complex and less certain than those in temperature, however, with both regional increases and decreases expected in precipitation and runoff. Here we show that an ensemble of 12 climate models exhibits qualitative and statistically significant skill in simulating observed regional patterns of twentieth-century multidecadal changes in streamflow. These models project 10–40% increases in runoff in eastern equatorial Africa, the La Plata basin and high-latitude North America and Eurasia, and 10–30% decreases in runoff in southern Africa, southern Europe, the Middle East and mid-latitude western North America by the year 2050. Such changes in sustainable water availability would have considerable regional-scale consequences for economies as well as ecosystems.

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Figure 1: Annual runoff rate (streamflow per unit basin area, in mm yr-1).
Figure 2: Global distributions of trend ( Z ) in streamflow from 1900–70 to 1971–98.
Figure 3: Relative change in runoff during the twentieth century.
Figure 4: Relative change in runoff in the twenty-first century.


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We thank T. Cohn, T. Delworth, I. Held, G. Hodgkins, H. Lins and R. Stouffer for advice. Streamflow data were provided by national hydrometric services through the Global Runoff Data Centre, Koblenz, Germany. Climate-model outputs were provided by modelling centres through PCMDI. We acknowledge the JSC/CLIVAR Working Group on Coupled Modelling and their Coupled Model Intercomparison Project and Climate Simulation Panel for organizing the model data analysis activity, and the IPCC WG1 TSU for technical support. This investigation was performed within the IPCC Global Hydroclimates Analysis Project.

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Correspondence to P. C. D. Milly.

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Milly, P., Dunne, K. & Vecchia, A. Global pattern of trends in streamflow and water availability in a changing climate. Nature 438, 347–350 (2005).

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