Global Pattern of Trends in Streamflow and Water Availability in a Changing Climate

Changes in the water cycle are expected to accompany global warming. Scientific assessments of the subject have concluded little, because natural hydrologic variability makes detection of hydrologic change intrinsically difficult.

SUBSTANTIAL PREDICTIVE SKILL of climate models was demonstrated by Milly et al. (2005, abstract, paper), who compared 20th-Century trends in climate-model streamflow with observed trends, and found a striking resemblance in the global pattern of regional trends, a resemblance that appears to be too great to be explained by chance. The finding suggests that changes in climate forcing, including both natural and human factors, may be partially responsible for observed late-20th-Century drying in sub-Saharan Africa, southern Europe, and southwestern North America.

the credibility of water-availability projections of climate models has increased substantially as a result of this study. Some of the more robust projections include drying in southwestern North America, southern Europe, northern Africa, the Middle East, and southern Africa.