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Lanzhou University (2017)

Modeling the Water Infiltration and Evaporation in Unsaturated Zone of the Extremely Arid Area

孙朋;

Titre : Modeling the Water Infiltration and Evaporation in Unsaturated Zone of the Extremely Arid Area

Auteur : 孙朋;

Grade : Doctoral Dissertation 2017

Université : Lanzhou University

Résumé partiel
Soil water is an important constraint factor of the stability of unsaturated zone of extremely arid area and dune.Precipitation is the main recharge source of soil water in desert area,and which type of precipitation event will supply soil water and groundwater is a hotspot of the research in unsaturated zone of arid desert field.However,because of the limit of observation and the difficulty of conducting experiments,people still have little knowledge about the water infiltration rule in unsaturated zone of extremely arid aeea.Therefore,new researches and findings on the water infiltration rule in unsaturated zone of extremely arid aeea brings essential scientific influence on the field of the regional water balance.Based on the observation and simulation experiments in the Lanzhou University eco-hydrological laboratory in Dunhuang,we conduct the related experiments and analyze the precipitation feature in the “rainfall season”,soil moisture,temperature and the dynamics of soil water potential between 2014 and 2016 on the basis of the precipitation and climate factor in this region.After that,we analyze the water balance rule between the evaporation and infiltration,and simulate the soil water movement.Finally,we could reveal the rule of different types of precipitation between evaporation,infiltration and recharge in extremely arid area.This could provide the statistic support and scientific research to the rule of water cycle,sustainable utilization of water resources and the stability of desert in the unsaturated zone of extremely arid aeea.This paper shows:The observation of annual precipitation in research area is between 37.52 to 50 mm,and the variation range is between 3 to 103.8mm.There is a positive correlation relationship between the precipitation and the altitude of observation spot,and the precipitation variability decreases with the increase of altitude.The type of precipitation in this region is summer-rainfall,and the amount of precipitation in summer accounts for 56.69% of the annual rainfall ;the maximum of precipitation mainly happens in June and July ;the rainfall in spring and summer is over 80.38% of the total ;the day-scale precipitation is little and its time is short ;0-5mm precipitation,as the main precipitation events,occupies 91.28% of the total precipitation events.The diurnal precipitation events are clarified to CP,OAP,RP and EP by the boundary of day precipitation of 5mm,10 mm and 25 mm.We could see that CP is the main type of precipitation,and the probability of RP and EP are low by the observation from 2014 to 2016.By the artificial modelling precipitation experiments and the observation of natural rainfall,we find that the soil from 0 to 5 mm is impacted greatly by the precipitation events in the research area,and the precipitation over 3 mm could influence the moisture content in the 0-5mm sand zone,and this zone is the area where the volumetric water content changes most.In this zone,the water content gets to peek immediately after rainfall,and then decrease rapidly.During 3 to 5 days,the water content in this area becomes the initial number,and in the condition of none natural water recharge,the surface water content ranges in 0.056±0.003m3m-3,which is the steady condition of dry sand water content in laboratory.40 cm is the lower limiting depth of infiltration influence of CP,OAP and RP events in this region,and the sensor in the soil from the depth of 50 to 120 cm only respond to the heavy rainfall events with hysteresis quality,for example,the response time of the water content in 120 cm soil zone after the 35 mm rainfall event is 520 hours.Similarly,the depth of infiltration increases as the precipitation rises,and there is good exponential curve fitting relationship between the infiltration depth and time changes.The dynamic change of soil water potential proves that the moisture movement,OAP and over OAP could make the response of soil water potential(under 20 cm)change,and the form and moving down of zero flux potential after rainfall events are the fundamental power to drive the movement of soil moisture.The temperature of ground surface and the air temperature have close relationship,and the impact to ground temperature from air temperature decreases with the depth increasing.

Mots clés : Extremely arid area; unsaturated zone; water infiltration; moisture migration; evaporation; modeling;

Présentation (CNKI)

Page publiée le 13 janvier 2018