Soil Moisture Variations in Response to Precipitation Across Different Vegetation Types on the Northeastern Qinghai-Tibet Plateau

Abstract

An understanding of soil moisture conditions is crucial for hydrological modeling and hydrological processes. However, few studies have compared the differences between the dynamics of soil moisture content and soil moisture response to precipitation infiltration under different types of vegetation on the Qinghai-Tibet Plateau (QTP). In this study, a soil moisture sensor was used for continuous volumetric soil moisture measurements during 2015 and 2016, with the aim of exploring variations in soil moisture and its response to precipitation infiltration across two vegetation types (alpine meadow and alpine shrub). Our results showed that temporal variations in soil moisture at the surface (0-20 cm) and middle soil layers (40-60 cm) were consistent with precipitation patterns for both vegetation types. However, there was a clear lag in the soil moisture response to precipitation for the deep soil layers (80-100 cm). Soil moisture content was found to be significantly positively related to precipitation and negatively related to air temperature. Aboveground biomass was significantly negatively associated with the surface soil moisture content (0-20 cm) during the growing season. Statistically significant differences were observed between the soil water content of the surface, middle, and deep soil layers for the two vegetation types (p < 0.05). Soil moisture (19.81%) in the surface soil layer was significantly lower than that in the deep soil layer (24.75%) for alpine shrubs, and the opposite trend was observed for alpine meadows. The maximum infiltration depth of alpine shrubs was greater than that of alpine meadows under extremely high-precipitation events, which indicates that alpine shrubs might be less susceptible to surface runoff under extreme precipitation events. Furthermore, low precipitation amounts did not affect precipitation infiltration for either vegetation type, whereas the infiltration depth increased with precipitation for both vegetation types. Our results suggest that a series of small precipitation events may not have the same effect on soil moisture as a single large precipitation event that produces the equivalent total rainfall.

Keywords: Qinghai-Tibet Plateau; precipitation infiltration; soil moisture; temporal variations; vegetation type.

FIGURE 1

The location of study area (I), alpine meadow (II), and alpine shrub (III).

FIGURE 2

Number of precipitation event (A) and total precipitation (B) amount across different category precipitation.

FIGURE 3

Daily variations of soil water content for 0–100 cm (A), surface soil layer (B), middle soil layer (C), and deep soil layer (D) across two vegetation types.

FIGURE 4

Monthly variations of soil water content for 0–100 cm (A), surface soil layer (B), middle soil layer (C), and deep soil layer (D) across two vegetation types.

FIGURE 5

Comparison of soil water content for 0–100 cm (A), surface soil layer (B), middle soil layer (C), and deep soil layer (D) across two vegetation types.

FIGURE 6

The relationship between aboveground biomass and soil water content for alpine meadow (A) and alpine shrub (B).

FIGURE 7

The depth of soil water infiltration of alpine meadow at low precipitation event (A), medium precipitation event (B), high-precipitation event (C) and extremely high-precipitation event (D).

FIGURE 8

The depth of soil water infiltration of alpine shrub at low precipitation event (A), medium precipitation event (B), high-precipitation event (C) and extremely high-precipitation event (D).