Sub-theme
1. Water-Human-Economy(Agriculture, Industry, City...)-Ecology Nexus under a Changing Environment
Topic
1-4. Water security challenges in key regions
Body
The Chinese Loess Plateau is a unique Critical Zone, which is one of the most serious areas of soil erosion in the world. Since 1999, the CLP has undergone large-scale vegetation restoration, leading to a 25%–28% increase in the total vegetation coverage. Desertification has been effectively mitigated and river sediment has been significantly reduced. However, the flow-producing capacity of the CLP has also considerably decreased. So far, limited study was conducted in how the flow-producing capacity and mechanism of the CLP are changing and what the future development trend of water resources is. To address this issue, we monitored soil moisture at the 10-min interval at 5 depths (10, 20, 40, 60, and 100 cm) in an afforested catchment and a nearby catchment with natural regrowth of grasses for two years (2017–2018). Two monitoring sites were established in each catchment, one in the downhill gully and the other in the uphill slope. We found that vegetation, topography, and rainfall attributes together determined rainwater infiltration and soil moisture replenishment. An accumulated rainfall amount of 3.6 mm was required to trigger soil moisture response at 10-cm depth at the 2 grassland sites and the forestland uphillslope site, while 6.8 mm of rainfall was required for the forestland gully site covered by dense undergrowth and trees. Larger rainfall totals and higher peak intensities permitted rainwater to infiltrate deeper into the soil. The grassland gully site had the highest soil water storage, whereas soil moisture was depleted the most at the forestland gully site. Results of this study also showed that the efficiency of rainwater infiltration was the highest at the forestland uphill slope site, indicating a lower likelihood of the occurrence of the surface runoff and soil erosion in the uphill slope that is covered by forest. The frequency of preferential flow was highest on the forestland upslope and downslope, followed by grassland downslope, and grassland upslope. This study reveals the dynamic change pattern of soil moisture and flow production after rainfall on the CLP, which illustrates the influence of vegetation and topography on rainwater infiltration.