Hydraulic redistribution and its contribution to water retention during short-term drought in the summer rainy season in a humid area

Hydraulic redistribution (HR) in sites with shallow soils and its response to random droughts during the summer rainy season in humid areas remains poorly understood. We investigated the soil moisture dynamics, HR and water buffer of shallow soils by monitoring the soil moisture content at multiple depths during a random drought event in the summer rainy season, in typical forestland and orchard in a subtropical area. Soil moisture sensors were installed at depths of 5, 10, 15, 20 and 30 cm at three sites (forest, peach1, and peach2). The total and net daily water use and water buffer capacity of the root zone were defined and calculated. During the short-term drought, the HR of soil moisture occurred at all sites, suggesting that it could be an important process in both forest and orchard land in response to short-term drought. HR occurred at both daily and multiple-day timescales in the shallow soils. The net daily water use had less difference between the sites than the total daily water use. Principal component analysis of the total and net daily water use showed only evident clustering characteristics for the total daily water use, indicating an important plant-soil interaction effect. The depth-averaged magnitude of daily HR varied from 0.385 mm (0.0077 m3 m−3) at the forest site to 0.725 mm (0.0145 m3 m−3) at the peach1 site. The redistributed water replenished over 75% of the water depleted from the shallow soil. In particular, soil moisture was better retained in 15-20 cm root zone than in other soil layers. Furthermore, the water buffer capacity of the forest site was not higher than those of the two peach sites (where land use converted from forest), indicating that land use conversion does not necessarily weaken soil water retention. The study results highlighted that HR has a significant influence on water recharge and water retention in humid area, thus benefiting plant drought tolerance and total water utilization. This study provides more insights to evaluate HR's effect on water retention and enhance our understanding of HR in shallow soils during random droughts in the summer rainy season in humid areas.