Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Accueil du site → Doctorat → Chine → 2019 → Soil Hydrological Characteristics under Different Land Covers in the Upper Stream of the Heihe River Watershed

Lanzhou University (2019)

Soil Hydrological Characteristics under Different Land Covers in the Upper Stream of the Heihe River Watershed

田杰;

Titre : Soil Hydrological Characteristics under Different Land Covers in the Upper Stream of the Heihe River Watershed

Auteur : 田杰;

Grade : Doctoral Dissertation 2019

Université : Lanzhou University

Résumé partiel
The arid region in Northwest China covers 24.5%of the national territory and is home to over 26 million people.Mountain areas are the“water towers”of the arid area because of their importance in providing water resources for the downstream areas.Thus,knowledge about the soil hydrological processes is essential to understand the mechanisms of rainfall-runoff processes,and to improve hydrological modelling and water resources management in arid and semi-arid watersheds.However,the spatial heterogeneity of soil hydraulic properties and the mechanism of soil hydrological processes are still poorly understood in high elevation,complex-terrain mountainous areas,which restricts the parameterization and the test of the underlying mechanism of the hydrological models,and in turn impeding the hydrological modelling and water resources management in the mountainous areas.Accordingly,it is urgently needed to understandthe spatial heterogeneity of soil hydraulic properties and the soil hydrological processes in the mountainous area.To this end,this study aims to understand the soil hydrological responses under different land covers based on a soil moisture monitoring network in the Upper Reach of the Heihei River Watershed,Northwest China.The soil moisture monitoring network consists of 32 observation stations,monitoring soil moisture at profile of 0-70 cm with five layers(0-10,10-20,20-30,30-50,50-70 cm)during the growing seasons of 2014-2016 at a 30 min interval.First,soil samples under different land cover types:forestland,meadow,high coverage grassland(HCG),medium coverage grassland(MCG)and barren land in the study area are sampled to measure the saturated hydraulic conductivity(KS).Vertical variation of KS,in combination with precipitation intensity are used to analyze the dominant stormflow pathways of the profile under different land covers.Second,eight soil moisture stations with the same soil textural class and slope but different land covers(forestland,meadow,high coverage grassland(HCG),medium coverage grassland(MCG)and barren land)are used to investigate the effects of different land covers on soil moisture response.Several indices are evaluated to quantitatively describe soil moisture dynamics based on soil wetting events.In addition,HYDRUS-1D simulation is used to further analyze the effect of land cover on soil moisture dynamics.Third,Cross-correlation analysis is conducted to analyze the coupling strength between surface(0-10 cm)and subsurface(10-20,20-30,30-50,50-70 cm,and profile of 0-70 cm)soil moisture.Afterwards,three different methods are tested to estimate subsurface soil moisture from in-situ surface observations:the exponential filter(ExpF)method,artificial neural networks(ANN)and cumulative distribution function(CDF)matching methods.The major findings are described below:1.The influence of land cover on the vertical variation of soil hydraulic propertiesResults show that KS value in layer 5 is significantly lower than the values of above4 layers.KS decreases in the order of forestland,meadow,MCG,HCG,and barren land,corresponding to the degree of vegetation degradation.The KS decreases with depth under forestland,HCG and barren land,but increases first and then decreases under meadow and MCG.The dominant stormflow paths(DSP)for different land covers are different:forestland is dominated by deep percolation(DP),HCG is dominated by subsurface flow(SSF),meadow is prevailed by Hortonian overland flow(HOF)and has no SSF,while MCG and barren land are also dominated by HOF,but still form SSF.This result provides important information for improving the accuracy of mountainous hydrological modeling,and in turn leading to sustainable management of water resources in the study watershed.2.The response pattern of profile soil moisture to rainfall under different land coversOur results show that soil moisture response amplitudes along profile are similar under MCG and barren land,but significantly different under scrubland,meadow and HCG.The rate of soil moisture increment decreases significantly with depth for all land covers,except for the HCG.The temporal pattern of soil moisture increase is highly variable along the soil profiles depending on land cover type.In particular,the difference of response time between the adjacent layers vary from negative values to280 hours with depth.Preferential flow occurres mostly in soils covered by scrubland.Water transferability is higher in deeply rooted soil.

Mots clés : soil hydrology; the Heihe River Watershed; land cover; saturated hydraulic conductivity; soil moisture pattern; soil moisture estimation;

Présentation (CNKI)

Page publiée le 13 février 2020