极端干旱区沙漠包气带降水入渗与蒸发规律模拟研究

发布时间：2018-03-13 15:05

本文选题：极端干旱区　切入点：包气带　出处：《兰州大学》2017年博士论文　论文类型：学位论文

【摘要】：包气带水是维系极端干旱区沙漠地带植被生长和沙丘稳定的重要约束因子,降水作为沙区包气带水的主要补给来源,降水对地下水的有效补给是干旱区包气带水文研究的前沿热点,然而受观测条件的限制与实验环境的恶劣,当前对极端干旱区沙漠包气带降水入渗与蒸发规律的认识不足,严重限制了区域地下水补给资源的估算。因此,试图应用大型蒸渗系统,开展包气带水分运移动态的实验模拟、天然条件下降水入渗规律与较长尺度降水入渗规律的模拟验证,揭示极端干旱区沙漠包气带在不同降水类型下蒸发、入渗和补给规律。旨在为认识极端干旱区沙漠包气带水循环规律、促进水资源可持续利用和荒漠化植被恢复提供数据支撑。主要成果如下:(1)实验区所在的敦煌市年均降水37.52~50 mm,年降水变化幅度在3~103.8 mm,降水量与海拔高度正相关关系,且降水变率随海拔增高而变小;区域夏季降雨量占年总降水量的56.69%以上,春夏降水可达到全年降水量的80.38%;日尺度降水小而降水历时短,0~5 mm的日降水类型为区域主导降水事件,占研究区降水事件的91.28%,以日降水量5 mm、10 mm和25 mm为界限将区域日尺度独立降水事件划分为常规降水事件、年内普通降水事件、偶发降水事件和极端降水事件四种类型;实验站2014-2016年降水观测发现,日尺度降水雨量小、集中发生在夏季,独立降水事件间隔时间长,为降水形式的主导,偶发降水事件和极端降水事件发生概率较低。(2)沙土表层0~5 cm为受降水影响最剧烈区域,3 mm以上降水事件就会影响到表层5 cm处的含水量变化;40 cm为常规降水事件、年内普通降水事件以及偶发降水事件的入渗影响深度下限,而50~120 cm等深度仅在强降水事件发生后产生含水量响应,且响应具有滞后性;入渗深度随着降水量的增大而加深,入渗深度与与时间变化具有较好的指数拟合关系。普通降水事件及以上降水会驱动20 cm以下水势变化,雨后沙土表层发散型零通量面的形成与下移是驱动包气带水分运移的根本动力。降水事件的发生会带来沙土温度变化的突变,影响深度一直到120 cm。(3)2014-2016年雨季实际蒸发分别消耗同期天然降水的89.8-155.4%。小于10 mm的降水事件基本属于无效降水:偶发降水事件蒸发消耗同期降水水量的68.7%以上;极端降水事件后雨季储水占降水的15.89%以上。在没有强降水事件发生的时段内,小于10 mm的降水事件不能产生有效的储水,偶发降水事件的土壤储水仅在表层40 cm内,会被蒸发消耗,而在30 mm和35 mm降水事件极端降水事件发生后的666 h、497 h在50 cm以下分别产生3.3 mm和4 mm的入渗量。(4)雨后日尺度实际蒸发与首日蒸发量随雨后时间t倒数变化的相关函数,得出研究区实际蒸发经验公式:Ea=(0.9447E1+0.4097)/t,可以较好的模拟敦煌地区雨后日尺度实际蒸发速率。通过模拟期包气带水平衡观测结果表明,实际蒸发累积消耗为100.94 mm,占同期降水总量的97.5%,包气带水分年补给量仅为1.88 mm,且主要来源于极端降水事件,大于25mm的极端降水事件极端干旱区沙漠包气带有效降水的阈值,但补给量较低,对沙漠包气带地下水补给具有微弱效应。(5)通过对1954-2013年尺度降水入渗模拟结果发现,在极端干旱区沙漠包气带年水平衡为由水分补给和没有水分补给共存,且没有水分补给发生的年份为主。模拟的年均蒸发量与实际降水量分别为38.03 mm和38.87 mm,年均入渗量为0.84 mm,极端干旱沙漠环境下的年入渗量要占年均降水量的2.16%以下,难以形成有效补给。模拟结果同样表明近60年来,随着降水量的增加,降水入渗补给量也呈现增加趋势,极端降水事件的发生时影响极端干旱沙漠区包气带水分补给的重要因素,蒸发环境的造就的较厚干沙层(约40 cm)的存在同样是极端干旱沙漠包气带降水规律的不容忽视的因素。
[Abstract]:The vadose zone water is an important factor to maintain restraint in extreme arid region desert dune vegetation growth and stability, the main recharge sources of precipitation as in the vadose zone water, precipitation recharge of groundwater is hot arid vadose zone hydrology research, however, by observation and experimental conditions limit the bad the desert in extreme arid region of vadose zone of precipitation infiltration and evaporation of the lack of understanding of the law, severely limits the estimation of groundwater recharge resources area. Therefore, trying to use the large lysimeter system, carrying out the simulation of vadose zone migration and dynamic experiments, under the condition of natural precipitation infiltration and long scale precipitation infiltration simulation, reveal the extreme arid area of desert vadose zone in different types of precipitation evaporation, infiltration and recharge. To understand the extreme arid areas. The vadose zone water cycle rules, promote water Provide data support for the sustainable use of resources and restoration of desertification vegetation. The main results are as follows: (1) the annual precipitation of 37.52~50 mm in Dunhuang city where the annual precipitation change in experimentation area, in the range of 3~103.8 mm, precipitation and altitude are related, and the change rate of precipitation with higher elevation and smaller area; summer rainfall accounted for more than the total 56.69% spring and summer precipitation, precipitation can reach 80.38% of the annual precipitation on small scale precipitation; rainfall duration is short, the daily precipitation type 0~5 mm as the dominant regional rainfall events, rainfall events accounted for 91.28% of the study area, with daily rainfall of 5 mm, 10 mm and 25 mm for boundaries will be divided into separate regional precipitation events on the scale of conventional precipitation events, years of ordinary precipitation events, occasional precipitation events and extreme precipitation events in four types of experimental station; found 2014-2016 years precipitation, precipitation, rainfall, occur in summer set, alone Vertical precipitation events long time interval, as the leading form of precipitation, occasional precipitation events and extreme precipitation event probability is low. (2) 0~5 cm for the sandy surface affected by precipitation is the most intense region, water content above 3 mm precipitation events will affect the surface at 5 cm; 40 cm for conventional precipitation events in ordinary precipitation events and occasional precipitation events influence the infiltration depth of the lower limit, while 50~120 cm only in the depth of precipitation events occurred after moisture response, and the response is lagging; infiltration depth deepen with the increase of precipitation, infiltration depth index has good fitting relationship with the time change. Common precipitation events and the precipitation will drive below 20 cm water potential changes, the formation of rain sand surface divergent zero flux surface and is driven down the fundamental driving force of vadose zone transport will bring precipitation events. Mutation sand temperature change, the influence depth of up to 120 cm. (3) 2014-2016 precipitation events during the rainy season the actual evaporation respectively consumed in the same period of precipitation is less than 10 89.8-155.4%. of the basic mm is invalid: occasional precipitation evaporation precipitation event precipitation water more than 68.7%; extreme precipitation events after the rainy season water storage accounted for more than 15.89%. In precipitation without the occurrence of heavy precipitation period, precipitation events cannot be less than 10 mm the effective water storage, soil water storage incidental precipitation events only in 40 cm surface, evaporation will be consumed, and in extreme precipitation events in 30 mm and 35 mm precipitation event after 666 H, 497 h in 50 cm the following are 3.3 mm and 4 mm infiltration. (4) after the rain on the scale of the actual evapotranspiration and initial evaporation time correlation function with rain t reciprocal changes, the empirical formula of study area actual evaporation (0.9447E1+0.40: Ea= 97) /t, Dunhuang area on the scale after the rain can better simulate the actual evaporation rate. With the observation results show that the water balance through the simulation period of aeration, the actual evapotranspiration cumulative consumption was 100.94 mm, accounted for 97.5% of the total precipitation, vadose zone recharge amount is only 1.88 mm, and the main source of extreme precipitation events, the threshold of extreme precipitation events than 25mm desert in extreme arid region of vadose zone and effective precipitation, but the supply is low, the desert vadose zone groundwater recharge has weak effect. (5) found by 1954-2013 years of precipitation infiltration simulation results, in the desert in extreme arid region of vadose zone water balance for water supply and no water supply coexist, and no water supply occurred year. The average annual evaporation and actual precipitation simulation is 38.03 mm and 38.87 mm respectively, the average infiltration rate was 0.84 mm, the extremely arid desert environment of the year Infiltration amount to account for an average annual rainfall of 2.16%, it is difficult to form an effective supply. The simulation results also show that in the past 60 years, with the increase of precipitation, the precipitation infiltration recharge also show an increasing trend, the important factors influencing the extreme arid desert region of vadose zone recharge extreme precipitation events, evaporation environment created by the thick dry sand layer (about 40 cm) there is also the extremely arid desert vadose zone of precipitation factor can not be ignored.

【学位授予单位】：兰州大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P426;P641

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