05/04/2018

Contribution of Environmental Forcings to U.S. Runoff Changes for the Period 1950-2010

Understanding and attributing long-term trends of US runoff changes.

The Science

This study examines the annual and seasonal trends of U.S. runoff for the 1950-2010 period. Models and measurements are used to study how and why run-off has changed in different regions and seasons of the U.S.

The Impact

Statistical methods, modeling, and observations were used to show significant changing trends and quantification of the environmental driving mechanisms for the US runoff during the 1950-2010 period.

Summary

Runoff in the United States is changing, and this study finds that the measured change is dependent on the geographic region and varies seasonally. Specifically, observed annual total runoff had an insignificant increasing trend in the U.S. between 1950 and 2010, but this insignificance is due to regional heterogeneity with both significant and insignificant increases in the eastern, northern, and southern U.S., and a greater significant decrease in the western U.S. Trends for seasonal mean runoff also differs across regions. By region, the season with the largest observed trend is autumn for the east (positive), spring for the north (positive), winter for the south (positive), winter for the west (negative), and autumn for the U.S. as a whole (positive). Based on the detection and attribution analysis using gridded WaterWatch runoff observations along with semi-factorial land surface model simulations from the Multi-scale Synthesis and Terrestrial Model Intercomparison Project (MsTMIP), we find that while the roles of CO2 concentration, nitrogen deposition, and land use and land cover appear inconsistent regionally and seasonally, the effect of climatic variations is detected for all regions and seasons, and the change in runoff can be attributed to climate change in summer and autumn in the south and in autumn in the west. We also find that the climate-only and historical transient simulations consistently underestimated the runoff trends, possibly due to precipitation bias in the MsTMIP driver or within the models themselves.

Principal Investigator(s)

Jiafu Mao
Oak Ridge National Laboratory
maoj@ornl.gov

Funding

W. Forbes, J. Mao, X. Shi, D.M. Ricciuto, P.E. Thornton, and F.M. Hoffman are supported by DOE Office of Science, Biological and Environmental Research, including support from the following programs:
Terrestrial Ecosystem Science Program, Regional and Global Climate Modeling Program (RUBISCO SFA), and the Earth System Modeling Program (the Energy Exascale Earth System Model (E3SM) project).

References

Forbes, W., J.  Mao, M. Jin*, S.-C. Kao, W. Fu, X. Shi, D.M. Riccuito, P. E. Thornton, A. Ribes, Y. Wang, S. Piao, T. Zhao, C.R. Schwalm, F.M. Hoffman, J.B. Fisher, A. Ito, B. Poulter, Y. Fang, H. Tian, A. Jain, and D. Hayes. “Contribution of environmental forcings to US runoff changes for the period 1950-2010.” Env. Res. Lett. 13 054023 (2018). DOI:10.1088/1748-9326/aabb41