Statistical Assessment of the Impact of Conservation Measures on Streamflow Responses in a Watershed of the Loess Plateau, China

The objective of this study was to examine the trends of changes in streamflow in a watershed of the Loess Plateau, where a series of soil conservation measures were implemented since the late 1950s. Both parametric and non-parametric Mann-Kendall test were used to identify the trends in hydrologic variables over the last 50 years, and it showed significant downward trends in annual runoff, surface runoff and baseflow. The Pettitt's test was used to detect the change points of runoff, which occurred in 1973, and the whole 50-year records could be divided into contrast (from 1957 to 1973) and treated (from 1974 to 2006) periods. It was observed that the average annual runoff during treated period reduced by 60%, surface runoff and baseflow reduced by 65% and 55%, respectively in comparing with the contrast period. But the proportion of baseflow to total runoff showed a significant increasing from 0.57 to 0.63. Seasonal runoff also showed decreased trend with the highest reduction occurring in summer and lowest in winter. Annual precipitation in whole period showed no significant trend, so the changes in hydrologic variables were induced by conservation measures. Comparison of the flow duration curves for the two periods showed that reductions in high and low flows varied greatly. Results showed that conservation measures have resulted obvious changes in the hydrologic variables in a watershed of Loess Plateau.