Climate and direct human contributions to changes in mean annual streamflow in the South Atlantic, USA

Streamflow responds to changing climate patterns as well as human modifications within a basin. Understanding the contribution of these different drivers to changes in streamflow provides important information regarding how to effectively and efficiently address and anticipate changes in water availability. We used Budyko curves to ascribe changes in streamflow due to climate and human factors between two time periods in both natural and human-modified basins in the South Atlantic, USA. We extended the analysis to look at the consistency of climate and human alterations in 5 year increments within those time periods. Budyko curves were calculated for each watershed to describe the average climate control on a watershed given its land cover during the period 1934-1969. We then assessed how climate and human factors contributed to altering streamflow during the period 1970-2005. We found climate contributed to increased streamflow (average of 14%) in the South Atlantic since the 1970s. Human factors varied between basins and either amplified or minimized the effect of climate on streamflow. Human impacts were equivalent to, or greater than, climate impacts in 27% of our basins. The 5 year increments showed greater variability in climate, compared to human, contributions to streamflow change through time. Ordinations showed reservoir storage and population size negatively correlated with streamflow change, while the extent of agricultural land within basins positively correlated with streamflow change. Differentiating between the distinct effects that climate and human impacts have on streamflow is increasingly necessary for managing water resources under dynamic climate and human population scenarios.