| Volumes and Issues Contents of Issue 2 |
www.hydrol-earth-syst-sci-discuss.net/5/785/2008/
© Author(s) 2008. This work is distributed
under the Creative Commons Attribution 3.0 License.
Is streamflow increasing? Trends in the coterminous United States
1Department of Earth and Planetary Science, University of California at Berkeley, CA, USA
2Department of Environmental Science, Policy, and Management, University of California at Berkeley, CA, USA
Abstract. An increasing trend in global streamflow has been variously attributed to climate change, land use, and a reduction in plant transpiration under higher CO2 levels. To separate these influences, we use a subset of ~1000 United States Geological Survey stream gauges primarily from small, minimally disturbed watersheds to estimate annual streamflow per unit area since 1920 on a uniform grid over the coterminous United States. We find that although streamflow has indeed increased over this period taken as a whole, this increase has not been uniform in time but concentrated in the late 1960s, when precipitation increased. Since the early 1990s, both precipitation and streamflow show nonsignificant declining trends. Multiple regression of streamflow against precipitation, temperature and CO2 suggests that higher CO2 levels may increase streamflow, presumably due to the physiological plant response to CO2, but that this positive response is more than offset by the concomitant increasing evaporation due to global warming, so that the net impact of greenhouse gas emissions has been to increase evaporation and reduce streamflow. The suppression of plant transpiration through higher CO2 levels seems to be particularly important for sustaining high streamflow in recent decades in the Great Plains, where precipitation is concentrated during the growing season.
Discussion Paper (PDF, 708 KB) Interactive Discussion (Final Response, 4 Comments)
Citation: Krakauer, N. Y. and Fung, I.: Is streamflow increasing? Trends in the coterminous United States, Hydrol. Earth Syst. Sci. Discuss., 5, 785-810, 2008. Bibtex EndNote Reference Manager
