Dynamic Change Characteristics of Soil Moisture and Its Relationship with Precipitation in Hani Rice Terraces Water Source Area

Abstract

Precipitation in the Hani Rice Terraces water source area is redistributed through the soil, providing a continuous water flow to the terraces downstream and keeping a healthy regional ecosystem. The dynamic characteristics of soil moisture and its relationship with precipitation need to be further investigated. In this study, we examined the dynamics of soil moisture content (SMC) in different site types (based on vegetation), at varying depths, and at varying time scales from 2012 to 2016, using time-series data. Fitting and fuzzy query methods were used to determine the greatest positive correlation between daily/accumulated precipitation and SMC. The results showed that: (1) the dynamic characteristics of soil moisture at depths between 0–100 cm substantially varied between three site types; (2) the relationship graphs of Pearson’s coefficient r between SMC and prior 0–360 day’s daily precipitation were sine curves in three site types; the daily precipitation in the half a year before the test day has a positive effect on SMC at 0–100 cm depth, and the 2–3 month’s daily precipitation has the greatest effect from the test day’s SMC; (3) the influence of daily precipitation on SMC is limited, while cumulative precipitation is the main factor affecting SMC; and (4) there is a linear relationship between accumulated precipitation and SMC. A linear equation was constructed using the strongest correlation and was used to predict SMC. These models are useful to assess the sustainability of the water supply to the terraces downstream, and also to provide a basic understanding of the effect of different sites (by vegetation type) on soil moisture. This study is of great significance for the protection and sustainable utilization of Hani Rice Terraces.