Stability and variability of long‐term streamflow and its components in watersheds under vegetation restoration on the Chinese Loess Plateau

Abstract Assessing ecological restoration effects on hydrological regimes is important for water resources management, especially under semi‐arid conditions. Here, the stability and long‐term variability of streamflow components were analyzed for three less forested watersheds (LFWs, vegetation coverage 16–23% in 1970) undergoing major vegetation restoration (57–80% coverage in 2019), and for two largely forested watersheds (FWs, 65–68% cover in 1970 increasing to 88–92% in 2019) within the Beiluo River Basin on the Chinese Loess Plateau. Daily flow data for each watershed and year were normalized by rainfall to eliminate effects of non‐stationary rainfall. Mean annual streamflow totals for the ~60‐year study period were 25.1–34.1 and 21.6–48.1 mm y −1 for the LFWs and FWs, respectively. Average contributions of baseflow to total streamflow were 32–44% for the LFWs and 58–61% for the FWs. Mann‐Kendall tests showed significant decreasing trends for annual streamflow and stormflow (0.23–0.54% y −1 ) from the LFWs throughout. Mean streamflow from the LFWs between 2000 and 2019 decreased by 58% compared to the pre‐2000 period, while the average contribution of stormflow decreased from 66% to 35% (2010s). However, winter baseflow increased with time since start of restoration. Conversely, streamflow (components) for the FWs showed only slight fluctuations in decadal, annual and seasonal trends. Both total streamflow and stormflow exhibited strong power relationships with vegetation coverage, illustrating a tendency towards stable flow regimes for vegetation coverage >60–70%. Large‐scale vegetation restoration has fundamentally changed amounts and temporal distribution of streamflow (components) on the Loess Plateau mainly by regulating stormflow. After 20 years of restoration, the trend and proportion of streamflow components from the LFWs approximated those of the FWs. These results underpin the planning of sustainable management of natural resources vis‐á‐vis socio‐economic development during long‐term ecological restoration on the Loess Plateau.