Nonsequential Response in Mountainous Areas of Southwest China

Abstract

Nonsequential response is the phenomenon where the change of soil water content at the lower layer is larger than that of the upper layer within a set time interval. It is often ignored because of the lack of spatially distributed measurements at the watershed scale, especially in mountainous areas where extensive monitoring network is expensive and difficult to deploy. In this study, the subsurface nonsequential response in a mountainous watershed in Southwest China was investigated by combining field monitoring and numerical simulation. A physics-based numerical model (InHM) was employed to simulate the soil water movement to explore the occurrence of the subsurface nonsequential response. The topographic wetness index [TWI = ln (a/tan b)] was used to distinguish the topographic zone corresponding to the nonsequential response at different depths. The nonsequential response mainly came from the subsurface lateral flow initiated at the soil–bedrock interface or at a relatively impermeable layer. The results showed that the occurrence depth of the nonsequential response increased with precipitation intensity when the time since last event was more than 24 h and the total amount of this event exceeded 37 mm. During a rainfall event, the nonsequential response occurred at the middle layer in the hillslope zone and the deep soil layer beneath the channel. In case of a rainfall event with two peaks, the region observed with nonsequential response expanded. The soil layer at the interface of the bedrock could be saturated quickly, and became saturated upward. This kind of nonsequential response can be observed on the hillslope at the beginning of rainfall events, and then found beneath stream channels afterward. Furthermore, nonsequential response could also happen after rainfall events. The results improved our understanding of nonsequential response and provided a scientific basis for flash flood research in mountainous areas.

The impacts of rainfall and soil moisture to flood hazards in a humid mountainous catchment: a modeling investigation

“…It has been applied to different catchments and terraces, validated for runoff generation (Ran et al, 2019a;Ran et al, 2019b;Ran et al, 2020), as well as sediment movement simulation (Ran et al, 2012;Ran et al, 2018). It has also been applied to nearby watershed of similar characteristics, and proved its suitability on the study region (Liu et al, 2021).…”

“…The average slope in the catchment is 32.5 °, and the annual mean temperature is 15.2 °C (Liu, 2022). Average annual precipitation is about 1134 mm, with most of it occurring between June and September (Liu et al, 2021). The geological structure of the catchment is complex, with developed folds and faults.…”

The Early Identification of Flash Flood Disasters: Mechanism, Model and Uncertainty

“…As a triggering factor, with strong kinetic energy, the rainstorms in mountainous regions can make the material and energy in the watershed increase sharply in a short time, destroying the watershed's equilibrium state before rain (Ye et al, 2021). Different disasters will occur if the flood submergence area is inhabited or equipped with disaster-bearing bodies such as transportation, communication, factories and mines, enterprises, etc.…”

“…Regarding the occurrence process, water and sediment disasters have nodes such as weather situation, rainfall distribution, topography, river system, water and sediment process, submergence and loss, etc (Li et al, 2023). However, the chain characteristics of water and sediment disasters reflect that various disaster-causing factors are coupled at the watershed scale (Liu et al, 2021;Ran et al, 2022). For the intersection of the gullies, the coupling of disaster-causing factors in the higher-level watersheds of water and sediment deposits should be provided as well.…”

Water-Related Natural Disasters in Mountainous Area, volume II

“…The average slope in the catchment is 32.5 °, and the annual mean temperature is 15.2 °C . Average annual precipitation is about 1134 mm, with most of it occurring between June and September (Liu et al, 2021). The geological structure of the catchment is complex, with developed folds and faults.…”