Historical and Future Changes in Streamflow and Continental Runoff: A Review

Streamflow trends from 1948 to 2012 are statistically significant only in 55 (27.5%, 29 negative vs. 26 positive) of the world's largest 200 rivers. Continental runoff decreased slightly from 1949 to 1993, it then recovered to slightly above the 1950-1980 mean. The streamflow and runoff changes are consistent with precipitation records, and they all show decreases from 1950 to 2012 over most Africa, East and South Asia, eastern Australia, the southeast and northwest United States; but increases over Argentina and Uruguay, central and northern Australia, the central and northeast United States, most of Europe, and Russia. These changes resulted partly from the Interdecadal Pacific Oscillation (IPO) and other climate variations, with low (high) land precipitation and runoff during El Niño (La Niña) events. Under the RCP8.5 scenario, models project mean streamflow to increase in the 21st century by 5%-80% over most of Asia, northern Europe, northern and eastern North America, central and eastern Africa, southeastern and northwestern South America, and central and northern Australia; but decrease by 5%-50% over the Mediterranean region, southwestern North America and Central America, northern and southern South America, southern Africa, and southwestern and southeastern Australia. The projected change patterns in precipitation, runoff, and streamflow are similar, with a fairly constant runoff ratio during the 21st century.