Effect of climate change on the trends of evaporation of phreatic water from bare soil in Huaibei Plain, China

When the soil condition and depth to water table stay constant, climate condition will then be the only determinant of evaporation intensity of phreatic water from bare soil. Based on a series of long-term quality-controlled data collected at the Wudaogou Hydrological Experiment Station in the Huaibei Plain, Anhui, China, the variation trends of the evaporation rate of phreatic water from bare soil were studied through the Mann-Kendall trend test and the linear regression trend test, followed by the study on the responses of evaporation to climate change. Results indicated that in the Huaibei Plain during 1991-2008, evaporation of phreatic water from bare soil tended to increase at a rate of 5% on monthly scale in March, June and July while in other months the increase was minor. On the seasonal basis, the evaporation saw significant increase in spring and summer. In addition, annual evaporation tended to grow evidently over time. When air temperature rises by 1 °C, the annual evaporation rate increases by 7.24–14.21%, while when the vapor pressure deficit rises by 10%, it changes from-0.09 to 5.40%. The study also provides references for further understanding of the trends and responses of regional evapotranspiration to climate change.

Stable Isotopes and Chloride Applied as Soil Water Tracers for Phreatic Evaporation Experiment

A phreatic water evaporation experiment,without rainfall influence,was designed to study the mechanisms of soil water movement through groundwater recharge to the unsaturated zone. Soil moisture content,chloride concentration,and δD and δ~18 O values of soil water were measured. Results showthat with decreasing soil moisture content,the chloride concentration of leachate( ρ_f(Cl)) in the capillary water layer decreases,whereas the ρ_f(Cl) value of the hanging and film water layers above the capillary water layer increases. With the combined δD and δ~18 O values,the soil water in the hanging and film water layers is influenced by evaporation,although a dry sand layer of 39 cm exists above the wet sand layer. The highest evaporation rate and the largest salt accumulation occur at a depth of about 39 cm in columns d,e,and f(Six polyvinyl chloride columns were assigned as column a,b,c,d,e,and f). We deduce that soil water migrates in the form of liquid water above the capillary water layer. In the experiment,a part of phreatic water consumed is used for the movement of soil water,whereas the other part is lost to evaporation. Soil water could continue migrating upward with prolonged experiment duration.

Analysis of phreatic evaporation law and influence factors of typical lithology in Hebei Plain

Based on three typical mediums(sandy loam, loam and sandy clay loam) in Hebei Plain, this paper designs phreatic evaporation experiments under different lithology and phreatic depth. Based on the analysis of experimental data, the phreatic evaporation law and influencing factors of three mediums were studied. The results showed that:(1) The shallower the phreatic depth, the larger the phreatic evaporation.(2) Sandy clay loam has the biggest response to the increase of the phreatic depth, sandy loam is the second and loam is the smallest.(3) The limit depth of phreatic evaporation of sandy clay loam is about 3 m and that of loam and sandy loam is about 2 m and 3 m, seperately.(4) By fitting the daily evaporation of phreatic water and phreatic depth, the results showed that sandy loam and sandy clay loam are exponential functions and loam is power functions.

Analysis of evaporation of high-salinity phreatic water at a burial depth of 0 m in an arid area

High-salinity phreatic water refers to which with total dissolved solids（TDS）>30 g/L. Previous studies have shown that high salinity phreatic water evaporation is different at different depths. High salinity phreatic water evaporation under 0 m depth is the basis of the high salinity phreatic water evaporation studies. In this study, evaporation of high-salinity phreatic water at a burial depth of 0 m in arid area was investigated. New insights were gained on evaporation mechanisms via experiments conducted on high-salinity phreatic water with TDS of 100 g/L at 0 m at the study site at Changji Groundwater Balance Experiment Site, Xinjiang Uygur Autonomous Region in China, where the lithology of the vadose（unsaturated zone） was silty clay. Comparison was made on the data of high-salinity phreatic water evaporation, water surface evaporation(EΦ20) and meteorological data obtained in two complete hydrological years from April 1, 2012 to March 31, 2014. The experiments demonstrated that when the lithology of the vadose zone is silty clay, the burial depth is 0 m and the TDS is 100 g/L, intra-annual variation of phreatic water evaporation is the opposite to the variation of atmospheric evaporation EΦ20 and air temperature. The salt crust formed by the evaporation of high-salinity phreatic water has a strong inhibitory effect on phreatic water evaporation. Large volumes of precipitation can reduce such an inhibitory effect. During freezing periods, surface snow cover can promote the evaporation of high-salinity phreatic water at 0 m; the thicker the snow cover, the more apparent this effect is.

Comparing phreatic evaporation at zero water table depth with water surface evaporation

Salt-affected soils are mostly found in irrigated areas within arid and semi-arid regions where the groundwater table is shallow.Soils of this type have become an increasingly severe problem because they threaten both the environment and the sustainable development of irrigated agriculture.A tool to estimate phreatic evaporation is therefore urgently required to minimize the salinization potential of salt-affected areas.In this context,phreatic evaporation at zero water table depth(E0)is a key parameter for establishing a model for calculating phreatic evaporation.The aim of this study was to explore the law of phreatic evaporation and to develop structurally rational empirical models for calculating phreatic evaporation,based on E0data of six types of soil(i.e.,gravel,fine sand,sandy loam,light loam,medium loam,and heavy loam)observed using the non-weighing lysimeter and water surface evaporation(E601)data observed using a E601 evaporator of same evaporation area with a lysimeter-tube at the groundwater balance station of the Weigan River Management Office in Xinjiang Uygur Autonomous Region,China,during the non-freezing period(April to October)between 1990 and 1994.The relationship between E0and E601was analyzed,the relationship between the ratio of E0to E601and the mechanical compositions of different soils was presented,and the factors influencing E0were discussed.The results of this study reveal that E0is not equal to E601.In fact,only values of the former for fine sand are close to those of the latter.Data also show that E0values are related to soil texture as well as to potential atmospheric evaporation,the ratio of E0to E601and the silt-clay particle content(grain diameter less than 0.02 mm)is negatively exponentially correlated,and that soil thermal capacity plays a key role in phreatic evaporation at E0.The results of this analysis therefore imply that the treatment of zero phreatic depth is an essential requirement when constructing groundwater balance stations to study the law of phreatic evaporation.

Solution and its application of transient stream/groundwater model subjected to time-dependent vertical seepage

Based on the first linearized Boussincsq equation, the analytical solution of the transient groundwater model, which is used for describing phreatic flow in a semiinfinite aquifer bounded by a linear stream and subjected to time-dependent vertical seepage, is derived out by Laplace transform and the convolution integral. According to the mathematical characteristics of the solution, different methods for estimating aquifer parameters are constructed to satisfy different hydrological conditions. Then, tile equation for estimating water exchange between stream and aquifer is proposed, and a recursion equation or estimating the intensity of phreatic evaporation is also proposed. A phreatic aquifer stream system located in Huaibei Plain, Anhui Province, China, is taken as an example to demonstrate tile estimation process of the methods stated herein.

冻融作用下土壤不均匀系数对潜水与土壤水转化的影响

为了揭示冻融过程中土壤不均匀系数对潜水与土壤水转化的影响,在室内进行了-10、-20和-25℃依次降温恒温冻结62 d和自然消融10 d的冻融试验,研究了不均匀系数(Cu)为2.00(土柱A)、3.70(土柱B)、6.36(土柱C)、16.18(土柱D)和20.67(土柱E)的5个土柱在0.5 m地下水位埋深下的土壤温度、潜水蒸发量及潜水回补量变化特征。结果表明:在冻融过程中,土壤颗粒的不均匀系数越大,土壤剖面温度变化幅度越大。随着土壤深度的增加,土柱A和土柱E冻结结束时的温度差减小,不均匀系数对土壤剖面温度的影响减小。冻结0~3 d时,土柱A、B、C、D和E的潜水蒸发速率分别为0.11、0.15、0.23、0.27和0.39 mm/d,潜水蒸发速率相对较小,但不均匀系数越大,潜水蒸发速率越大;冻结结束(第62 d)时土柱A、B、C、D和E的累积潜水蒸发量分别为15.17、21.46、28.23、34.96和38.65 mm,累积潜水蒸发量与土壤不均匀系数较好的符合对数函数的关系,潜水与土壤水的转化量随土壤颗粒不均匀系数增大而增加。

干旱区高盐度潜水蒸发规律初步分析

为分析干旱区高盐度潜水蒸发规律,于2012年4月1日~2014年3月31日在新疆昌吉地下水均衡试验站开展了不同总溶解固体（0.8 g/L、30 g/L和100 g/L）、不同包气带岩性（细砂和粉质黏土）和不同潜水埋深（0 m、0.5m、1.0 m、2.0 m和3.0 m）潜水蒸发量的监测工作。结果表明：当潜水埋深大于0.5 m时,包气带岩性对高总溶解固体（Total Dissolved Solids,TDS）潜水蒸发量的影响与淡水基本一致;潜水埋深0.5 m、TDS为30 g/L时,包气带岩性的差异对潜水蒸发量的影响远小于由于潜水的TDS和外界大气蒸发能力对潜水蒸发共同造成的影响;潜水位埋深为0 m、TDS为100 g/L、包气带为粉质黏土时,年内潜水蒸发趋势与大气蒸发能力EΦ20的趋势相反;潜水埋深0.5~1.0 m时,在非冻结期随着TDS的升高,潜水蒸发量逐渐减小;当潜水埋深为3.0 m时,TDS的变化对潜水蒸发抑制作用存在滞后性。

潜水埋深为零时塔里木盆地不同土质潜水蒸发与水面蒸发关系分析

根据渭干河灌区潜水蒸发试验站和阿克苏水平衡试验站的实际监测资料,分析了E601型蒸发器与E20蒸发皿观测的水面蒸发的关系、不同土质潜水埋深为零时潜水蒸发与水面蒸发的关系,提出了潜水蒸发能力系数的概念,并分析了其与土壤机械组成的关系.结果表明:塔里木盆地非冻结期E601型蒸发器与E20蒸发皿观测的水面蒸发的折算系数变化在0.65～0.78之间;除细砂土外,E601蒸发器观测的水面蒸发强度不能代替潜水埋深为零时的潜水蒸发强度;不同质地土壤的粉粘粒(d<0.02 mm)含量百分数与潜水蒸发能力系数呈指数相关关系.

干旱区高盐度潜水蒸发溶解性总固体折算系数分析

为分析干旱区高盐度潜水蒸发与淡潜水蒸发间的关系,提出了干旱区潜水蒸发溶解性总固体(TDS)折算系数(KM)。2012年4月1日—2014年3月31日在新疆昌吉地下水均衡试验站开展了不同TDS(30和100 g/L)、不同包气带岩性(细砂和粉质黏土)和不同潜水水位埋深(0.5、1.0、2.0、3.0 m)的蒸渗仪潜水蒸发试验,利用实测的高盐度潜水蒸发数据计算不同条件下的KM。对潜水蒸发系数和KM进行分析,初步得出了以下结论:高TDS潜水蒸发系数冻结期大于非冻结期,在其他条件一定的情况下,潜水TDS越高,潜水蒸发系数越小;非冻结期高盐度潜水蒸发量小于淡潜水蒸发量,且随着观测时间的延续高盐度潜水蒸发量有减少趋势;冻结期高盐度潜水蒸发量大于淡潜水蒸发量,潜水埋深越大,两者的差值越大,且随着观测时间延续,高盐度潜水蒸发量与淡潜水蒸发量间的差值有变大的趋势;在其他条件一定的情况下,潜水TDS为100 g/L的全年潜水蒸发量小于潜水TDS为30 g/L的全年潜水蒸发量。

改进的无作物潜水蒸发经验公式

根据安徽省五道沟水文水资源实验站砂姜黑土和砂壤土2种原状土样1992—1994年的潜水蒸发实验观测数据,在分析无作物条件下潜水蒸发与各种影响因素关系、潜水蒸发系数与水面蒸发关系的基础上,采用非线性最小二乘法,以决定性系数、残差均值和方差为性能指标,对已有的潜水蒸发经验公式——阿维里扬诺夫公式和叶水庭公式进行了非线性回归拟合优度比较,并提出了2个公式的改进形式。结果表明,采用改进后的经验公式进行潜水蒸发的拟合和预测,较原有公式精度有明显提高。

极干旱区深埋潜水蒸发量的测定

在远离降雨的典型极干旱气候条件下,在敦煌莫高窟窟顶戈壁搭建封闭塑料拱棚,在棚内放置空调抑制"拱棚效应"。通过空调的制冷抑制拱棚的增温效应,通过空调的冷凝降低棚内的湿度,使棚内的温湿度与外界靠近,并通过空调冷凝排水量评估潜水蒸发强度。45d的监测表明:在潜水埋深超过200m的敦煌极干旱地区存在不少于0.0219mm/d的潜水蒸发。太阳辐射强度、温度、湿度对潜水蒸发有重要影响。潜水蒸发量的测定为利用潜水进行荒漠化的生态重建提供了基本的评估依据,对揭示极干旱区埋深较深的GSPAC水文循环和潜水开发有重要意义,对莫高窟的文物保护也非常关键。

潜水蒸发研究进展

在有关研究成果的基础上,论述潜水蒸发的主要研究方法,归纳了裸地和植被生长条件下潜水蒸发的常用估算方法。指出未来应加强植被生长条件下潜水蒸发的试验观测,在水循环过程综合研究的基础上深入分析不同条件下的潜水蒸发规律。

西北内陆盆地潜水与土壤水转化关系研究

在天山北麓昌吉地下水均衡试验场,选择天山北麓平原的三种代表性岩性(粘土、细砂、砂砾石)进行天然条件下的潜水入渗补给和潜水蒸发模拟试验研究。观测不同岩性的潜水入渗补给量和潜水蒸发量,计算潜水补耗差,分析岩性和潜水埋深对潜水补耗差的影响。研究成果对于认识西北内陆干旱平原区土壤水与潜水的转化关系、涵养和保护地下水资源具有重要意义。

辽西北沙地裸地潜水蒸发试验研究

基于阿尔乡沙地潜水蒸发试验场2010年4月中旬～10月上旬的实测资料,分析了裸地条件下沙地潜水蒸发的影响因素及其相关规律。试验结果表明,潜水蒸发与水面蒸发的变化趋势一致,降雨对潜水蒸发和入渗补给过程的影响大于蒸发对其的影响;地下水埋深对潜水蒸发的影响主要集中于0.0～1.0m之间;地下水埋深1.5m处,入渗补给量达到最大值;沙地的潜水零补耗差深度在0.5～1.0m之间,最佳潜水埋深为1.5m。

干旱区荒漠植被生态需水量计算方法研究

潜水蒸发法和面积定额法是计算植被生态需水量的常用方法,而目前研究中,仅运用一种方法进行干旱区生态需水量的计算,为了解决其计算方法单一、研究结果合理性存在争议,并确定干旱区荒漠植被合理生态需水量计算方法的问题,研究以2013年塔里木河干流上游区为参考区域,通过遥感技术解译该地区各荒漠植被的面积,运用潜水蒸发法和面积定额法计算该区荒漠植被生态需水量,并计算其相对差值百分比,且与前人的研究成果进行比较,结果分别为54.33%、41.39%、52.78%,其值皆为50%左右,相差较小,表明了潜水蒸发法及面积定额法计算干旱区荒漠植被生态需水的合理性,并通过均值计算确定干旱区荒漠植被合理的生态需水量,即2.65亿m3,可应用于其他干旱地区荒漠植被合理生态需水量的确定。

应用拱棚-空调法对极干旱区降水的模拟回收

拱棚法监测表明极干旱区存在潜水蒸发,而土壤温湿度监测表明,土壤水分具备向下运转的条件,这意味着拱棚所监测的水分可能来自降水,极干旱区并不存在深埋潜水蒸发。因此,研究降水的最终去向非常重要。为此笔者应用拱棚-空调法进行对极干旱区降雨模拟回收。结果表明,在极干旱条件下占该区85%以上频次的5 mm的降水经90 d可完全蒸发和回收。回收过程中,棚内地上50 cm的相对湿度(RH)和绝对湿度(AH)分别较棚外增高12.10%和3.50 g/m3,这使降水的回收时间大为延长;另外,土壤内部的温湿度监测表明,洒水后30 cm土壤的温度、RH、AH分别高于棚外对照1.46℃、4.17%和2.50 g/m3,说明有一定数量的降水通过膜下土壤侧向流向了外部,增加了收集时间。回收实验证明极干旱区降水可完全蒸发,该区存在潜水蒸发与GSPAC(Groundwater-Soil-Plant-Atmosphere Continuum)水分的向上运转。

豫东平原潜水蒸发试验研究

为了探讨潜水蒸发规律,为水资源评价提供依据,根据河南省惠北试验站地下水量均衡观测试验场内同一时期不同潜水埋深、不同土壤质地及有无种植作物的测筒试验,通过对潜水蒸发影响因素及其规律的探讨,得到潜水蒸发与气象因素、地下水埋深、上壤质地等影响因素之间的关系。并利用柯夫达公式分别计算出在不同土质下有无种植作物的潜水蒸发量。由于考虑因素更多,故比以往用单一值计算潜水蒸发量的精度更高。

淮北平原有无作物生长条件下潜水蒸发规律试验

为进一步探索淮北平原不同土壤有无植被生长条件下潜水蒸发与地下水位的变化规律,该文依据五道沟实验站地中蒸渗仪60个原状测筒观测资料,从零埋深、埋深增加和临界埋深3个方面,比较了不同土壤有无植被潜水蒸发的差异,分析了潜水蒸发与气象要素的相关关系。通过逐日和逐旬参数拟合,得到砂礓黑土和黄潮土6个潜水蒸发最优公式及相关参数,建议使用彭曼公式计算的蒸发能力代替实测水面蒸发以提高拟和效果;沿着裸土潜水蒸发加作物多耗水量计算作物潜水蒸发的思路,推荐采用作物各生育期和埋深的多耗水量统计方法计算有作物潜水蒸发量,该方法较简便且适用性强,精度较高。

石羊河流域天然植被生态需水量计算

利用ArcView 3.2对2003年石羊河流域TM卫星影像数据进行分析处理,获取了流域植被覆盖状况,应用基于生态适宜性理论的天然植被生态需水量计算模型对研究区域天然植被生态需水量进行定量计算。结果表明,计算结果与潜水蒸发法相近,植被概率与地下水位埋深变化呈单峰形,分布概率越高对应越适宜的地下水位埋深。