發(fā)布時間：2018-03-13 15:05

  本文選題：極端干旱區(qū)　切入點(diǎn)：包氣帶　出處：《蘭州大學(xué)》2017年博士論文　論文類型：學(xué)位論文

【摘要】：包氣帶水是維系極端干旱區(qū)沙漠地帶植被生長和沙丘穩(wěn)定的重要約束因子,降水作為沙區(qū)包氣帶水的主要補(bǔ)給來源,降水對地下水的有效補(bǔ)給是干旱區(qū)包氣帶水文研究的前沿?zé)狳c(diǎn),然而受觀測條件的限制與實驗環(huán)境的惡劣,當(dāng)前對極端干旱區(qū)沙漠包氣帶降水入滲與蒸發(fā)規(guī)律的認(rèn)識不足,嚴(yán)重限制了區(qū)域地下水補(bǔ)給資源的估算。因此,試圖應(yīng)用大型蒸滲系統(tǒng),開展包氣帶水分運(yùn)移動態(tài)的實驗?zāi)M、天然條件下降水入滲規(guī)律與較長尺度降水入滲規(guī)律的模擬驗證,揭示極端干旱區(qū)沙漠包氣帶在不同降水類型下蒸發(fā)、入滲和補(bǔ)給規(guī)律。旨在為認(rèn)識極端干旱區(qū)沙漠包氣帶水循環(huán)規(guī)律、促進(jìn)水資源可持續(xù)利用和荒漠化植被恢復(fù)提供數(shù)據(jù)支撐。主要成果如下:(1)實驗區(qū)所在的敦煌市年均降水37.52~50 mm,年降水變化幅度在3~103.8 mm,降水量與海拔高度正相關(guān)關(guān)系,且降水變率隨海拔增高而變小;區(qū)域夏季降雨量占年總降水量的56.69%以上,春夏降水可達(dá)到全年降水量的80.38%;日尺度降水小而降水歷時短,0~5 mm的日降水類型為區(qū)域主導(dǎo)降水事件,占研究區(qū)降水事件的91.28%,以日降水量5 mm、10 mm和25 mm為界限將區(qū)域日尺度獨(dú)立降水事件劃分為常規(guī)降水事件、年內(nèi)普通降水事件、偶發(fā)降水事件和極端降水事件四種類型;實驗站2014-2016年降水觀測發(fā)現(xiàn),日尺度降水雨量小、集中發(fā)生在夏季,獨(dú)立降水事件間隔時間長,為降水形式的主導(dǎo),偶發(fā)降水事件和極端降水事件發(fā)生概率較低。(2)沙土表層0~5 cm為受降水影響最劇烈區(qū)域,3 mm以上降水事件就會影響到表層5 cm處的含水量變化;40 cm為常規(guī)降水事件、年內(nèi)普通降水事件以及偶發(fā)降水事件的入滲影響深度下限,而50~120 cm等深度僅在強(qiáng)降水事件發(fā)生后產(chǎn)生含水量響應(yīng),且響應(yīng)具有滯后性;入滲深度隨著降水量的增大而加深,入滲深度與與時間變化具有較好的指數(shù)擬合關(guān)系。普通降水事件及以上降水會驅(qū)動20 cm以下水勢變化,雨后沙土表層發(fā)散型零通量面的形成與下移是驅(qū)動包氣帶水分運(yùn)移的根本動力。降水事件的發(fā)生會帶來沙土溫度變化的突變,影響深度一直到120 cm。(3)2014-2016年雨季實際蒸發(fā)分別消耗同期天然降水的89.8-155.4%。小于10 mm的降水事件基本屬于無效降水:偶發(fā)降水事件蒸發(fā)消耗同期降水水量的68.7%以上;極端降水事件后雨季儲水占降水的15.89%以上。在沒有強(qiáng)降水事件發(fā)生的時段內(nèi),小于10 mm的降水事件不能產(chǎn)生有效的儲水,偶發(fā)降水事件的土壤儲水僅在表層40 cm內(nèi),會被蒸發(fā)消耗,而在30 mm和35 mm降水事件極端降水事件發(fā)生后的666 h、497 h在50 cm以下分別產(chǎn)生3.3 mm和4 mm的入滲量。(4)雨后日尺度實際蒸發(fā)與首日蒸發(fā)量隨雨后時間t倒數(shù)變化的相關(guān)函數(shù),得出研究區(qū)實際蒸發(fā)經(jīng)驗公式:Ea=(0.9447E1+0.4097)/t,可以較好的模擬敦煌地區(qū)雨后日尺度實際蒸發(fā)速率。通過模擬期包氣帶水平衡觀測結(jié)果表明,實際蒸發(fā)累積消耗為100.94 mm,占同期降水總量的97.5%,包氣帶水分年補(bǔ)給量僅為1.88 mm,且主要來源于極端降水事件,大于25mm的極端降水事件極端干旱區(qū)沙漠包氣帶有效降水的閾值,但補(bǔ)給量較低,對沙漠包氣帶地下水補(bǔ)給具有微弱效應(yīng)。(5)通過對1954-2013年尺度降水入滲模擬結(jié)果發(fā)現(xiàn),在極端干旱區(qū)沙漠包氣帶年水平衡為由水分補(bǔ)給和沒有水分補(bǔ)給共存,且沒有水分補(bǔ)給發(fā)生的年份為主。模擬的年均蒸發(fā)量與實際降水量分別為38.03 mm和38.87 mm,年均入滲量為0.84 mm,極端干旱沙漠環(huán)境下的年入滲量要占年均降水量的2.16%以下,難以形成有效補(bǔ)給。模擬結(jié)果同樣表明近60年來,隨著降水量的增加,降水入滲補(bǔ)給量也呈現(xiàn)增加趨勢,極端降水事件的發(fā)生時影響極端干旱沙漠區(qū)包氣帶水分補(bǔ)給的重要因素,蒸發(fā)環(huán)境的造就的較厚干沙層(約40 cm)的存在同樣是極端干旱沙漠包氣帶降水規(guī)律的不容忽視的因素。
[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.

【學(xué)位授予單位】：蘭州大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：P426;P641

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