Tree planting and soil conservation measures have strongly attenuated storm runoff response on the Chinese Loess Plateau

Land restoration often consists of tree planting and soil conservation measures to improve infiltration and reduce erosion. Tree planting has been shown to reduce annual water yields, but its effects on peak runoff during intense storms has been difficult to determine, particularly in large basins. Soil conservation measures, such as check dams, terraces, and runoff-trapping soil contours, are expected to reduce peak flows but their effects likely depend on precipitation intensity and antecedent moisture conditions. Here we use Ensemble Rainfall-Runoff Analysis to test how tree planting and soil conservation measures have affected storm runoff responses in five large-scale basins (774-17,180 km²) on the Chinese Loess Plateau. We find that peak runoff responses decreased by up to 86% following tree planting and associated soil conservation measures, and that this decrease was proportional to the percentage increase in the Leaf Area Index (LAI). The attenuation of peak runoff was much larger than the decrease in average runoff (59%) or median runoff (24%). The largest attenuation in peak runoff response occurred during high-intensity rainfall events. This observation implies that the decrease in peak runoff response cannot arise primarily from increased canopy interception or drier soils, because these would be expected to have a larger effect on lower-intensity events. Instead, we hypothesize that the main mechanisms are likely to be reduction in runoff-generating areas and increases in infiltration.