Land cover changes the soil moisture response to rainfall on the Loess Plateau

Insight into the rainfall-soil moisture (SM) response to land cover is critical for soil hydrological process modelling and management. In this study, five typical land-cover types (forest, shrub, grass, crop and bare land) and four rainfall patterns (heavy, intermediate, light and continuous rains) were selected to assess the effects of SM response characteristics on the Loess Plateau of China. We monitored SM at five depths on each land-cover type at 1-h intervals over the growing season of 2019. The results showed that rainfall patterns and land-cover types together determined the SM response process and infiltration efficiency. A minimum accumulated rainfall amount of 5 mm was the threshold required to trigger a 10-cm SM response. Rain events with a higher intensity and smaller total rainfall amount triggered a quick surface SM response, while larger amounts could percolate deeper and faster. Land-cover change significantly altered the rainfall-SM response dynamics and rainwater utilization efficiency after 20 years of ecological construction. Revegetation sites (mean values of forest, shrub and grass) increased the soil wetting depth by 14.7%, shortened the SM response time by 27.3%, and accelerated the SM wetting front velocity by 67.2%, which promoted a 35.2% rainfall transformation rate (RTR) across the 1-m profile over all rainfall events (R1-13). Moreover, planted forest showed the highest RTR of R1-13 and the maximal increase in soil water storage, which did not aggravate the soil water deficit across the 1-m profile over the growing season. Therefore, we present evidence that planted forests, instead of shrubs, may be beneficial for water conservation if precipitation is greater than 550 mm. The findings of this study prove the role of revegetation on rainwater infiltration capacity and efficiency and can help improve the management of afforestation in arid and semiarid regions.