Hydrological Dynamics in Response to Vegetation Restoration in a Typical Wind–Water Erosion Crisscross Catchment

The intricate climate and surface composition of the wind-water erosion crisscross region create a distinctive environment for erosion and sediment production. However, research on the hydrological characteristics and responses to vegetation restoration in this area is limited. This study focuses on a representative catchment (3253 km²) in the northern Loess Plateau of China, examining the streamflow and sediment transport dynamics before (P1: 1977–1988) and after (P2: 2006–2017) vegetation restoration. Our results show that streamflow is relatively evenly distributed throughout the year, while sediment transport is highly concentrated over a few days during the wet season. Flood events account for the majority of sediment yield, contributing over 70% in both periods, with hyperconcentrated flows (SSC_p ≥ 300 kg m⁻³) being particularly significant. Vegetation restoration has resulted in an 85% reduction in annual sediment yield and an 89% decrease in the frequency of hyperconcentrated flood events. Despite these reductions, hyperconcentrated floods remain the dominant sediment transport mechanism, with just 9.7% of events in P2 responsible for nearly half of the sediment transported. Analyses of effective sediment transport discharge and sediment rating curves indicate a higher discharge threshold for hyperconcentrated floods post-vegetation restoration, leading to a greater sediment transport magnitude in P2. Hysteresis analysis shows a predominant counter-clockwise pattern in both periods, driven by abundant sediment sources and the high transport capacity of hyperconcentrated floods. Vegetation restoration has reduced the availability of sediment for transport, resulting in more linear relationships and decreased complexity in hysteresis patterns. Under future scenarios of intensified climate extremes, this region remains at high risk of erosion and sediment yield.