Interplays between State and Flux Hydrological Variables across Vadose Zones: A Numerical Investigation

Wang Wang,Zhang Zhang

doi:10.3390/w11061295

Abstract

Knowledge of both state (e.g., soil moisture) and flux (e.g., actual evapotranspiration (ETa) and groundwater recharge (GR)) hydrological variables across vadose zones is critical for understanding ecohydrological and land-surface processes. In this study, a one-dimensional process-based vadose zone model with generated soil hydraulic parameters was utilized to simulate soil moisture, ETa, and GR. Daily hydrometeorological data were obtained from different climate zones to drive the vadose zone model. On the basis of the field phenomenon of soil moisture temporal stability, reasonable soil moisture spatiotemporal structures were reproduced from the model. The modeling results further showed that the dependence of ETa and GR on soil hydraulic properties varied considerably with climatic conditions. In particular, the controls of soil hydraulic properties on ETa and GR greatly weakened at the site with an arid climate. In contrast, the distribution of mean relative difference (MRD) of soil moisture was still significantly correlated with soil hydraulic properties (most notably residual soil moisture content) under arid climatic conditions. As such, the correlations of MRD with ETa and GR differed across different climate regimes. In addition, the simulation results revealed that samples with average moisture conditions did not necessarily produce average values of ETa and GR (and vice versa), especially under wet climatic conditions. The loose connection between average state and flux hydrological variables across vadose zones is partly because of the high non-linearity of subsurface processes, which leads to the complex interactions of soil moisture, ETa, and GR with soil hydraulic properties. This study underscores the importance of using soil moisture information from multiple sites for inferring areal average values of ETa and GR, even with the knowledge of representative sites that can be used to monitor areal average moisture conditions.

Highlights

Estimation of state and flux (e.g., actual evapotranspiration (ETa ) and groundwater recharge (GR)) hydrological variables across vadose zones are of great importance for many research and application purposes, and especially for understanding ecohydrological and land-surface processes in Earth’s critical zones [1,2,3]
A synthetic modeling approach with generated soil hydraulic parameters was utilized in this study to investigate the interplays between state and flux hydrological variables across vadose zones in different climate zones
On the basis of the temporal stability analysis (TSA) method, reasonable soil moisture spatiotemporal structures were reproduced from the model

Summary

Introduction

Estimation of state (e.g., soil moisture) and flux (e.g., actual evapotranspiration (ETa ) and groundwater recharge (GR)) hydrological variables across vadose zones are of great importance for many research and application purposes, and especially for understanding ecohydrological and land-surface processes in Earth’s critical zones [1,2,3]. Due to the high non-linearity and extreme complexity of hydrological systems, those state and flux variables tend to display significant spatiotemporal variability. A wealth of field and numerical studies has shown that there was considerable variability in soil moisture at different spatiotemporal scales, as a result of its complex interactions with surrounding environments [4,5]. Given the tight connections between state and flux variables [12,14,15], it is imperative to elucidate the interplays among those variables to improve their estimation across vadose zones

Objectives

Methods

Results

Conclusion