Impacts of Climate, Pollution, and Land-Use Changes on River Flow
River flow has decreased significantly in recent decades, but the causes are not well understood. DOE scientists investigated how climate (temperature and precipitation changes), rising atmospheric CO2 concentrations (independent of effects on climate), increasing anthropogenic nitrogen deposition, and land-use change influenced continental river flow from 1948 to 2004. Nitrogen and CO2 affect vegetation, which alters ground hydrology. The study used the Community Land Model version 4 (CLM4) with a coupled global river routing scheme. Model results were compared to river flow from the world’s 50 largest rivers. Both mean river flow and river flow trends from model predictions were significantly correlated with observed values. Model results show a significant decreasing trend in global river flow and indicate that climate is the dominant factor responsible for the downward trend. Nitrogen deposition and land-use change account for about 5% and 2.5% of the decrease in simulated global scale river flow, respectively, while rising atmospheric CO2 concentration causes an upward trend. However, the relative role of each driving factor is variable across regions in the simulations. For example, the decreasing trend in river flow for the Amazon River basin is primarily explained by CO2, while land-use change accounts for 27% of the downward trend in river flow for the Yangtze River basin. The study suggests that to better understand river flow trends, it is not only necessary to take climate into account, but also to consider atmospheric composition, carbon-nitrogen interaction, and land-use change. This multi-factor approach to the analysis of Earth system response to climate and anthropogenic forcing is particularly important for understanding regional-scale dynamics.
Shi, X., J. Mao, P. E. Thornton, F. M. Hoffman, and W. M. Post. 2011. “The Impact of Climate, CO2, Nitrogen Deposition, and Land-Use Change on Simulated Contemporary Global River Flow,” Geophysical Research Letters 38, L08704. DOI: 10.1029/2011GL046773.