Fig. 2.

Hydrological year (previous August to current July) runoff reconstruction at the Shanxian gauge station of the YR. Comparison between the observed (blue) and the reconstructed (red) runoff (A). Comparison of the first difference of A (B). Runoff reconstruction (red) from 1492 to 2013 CE based on the calibration period 1920 to 1960 CE, which preceded construction of the Sanmenxia Dam (C). The black curve is the 11-y moving average of the reconstruction. The blue curve superimposed on the reconstruction denotes the observed annual runoff from 1920 to 2013 CE. The shaded area represents the ±2 SE bars. The short pink horizontal line (lower right) represents the average observed runoff from 1987 to 2013 CE. The solid gray horizontal lines indicate the mean value of the reconstruction, and the boundaries for extremely high/low runoff, respectively. The dashed gray horizontal lines indicate the boundaries for high/low runoff, respectively (Materials and Methods).