Causes of change in 20th century global river discharge

A global vegetation and hydrology model (LPJmL) was applied to quantify the contributions of changing precipitation, temperature, atmospheric CO2 content, land use and irrigation to worldwide trends in 20th century river discharge (Q). Consistently with observations, Q decreased in parts of Africa, central/southern Asia and south‐eastern Europe, and increased especially in parts of North America and western Asia. Based on the CRU TS2.1 climatology, total global Q rose over 1901–2002 (trend, 30.8 km3 a−2, equaling 7.7%), due primarily to increasing precipitation (individual effect, +24.7 km3 a−2). Global warming (−3.1), rising CO2 (+4.4), land cover changes (+5.9) and irrigation (−1.1) also had discernible effects. However, sign and magnitude of trends exhibited pronounced decadal variability and differed among precipitation forcing datasets. Since recent trends in these and other drivers of Q are mainly anthropogenic, we conclude that humans exert an increasing influence on the global water cycle.