流动沙丘水分深层入渗量与降雨的关系

为分析流动沙丘水分深层入渗与降雨的关系,采用YWB-01型水分深层渗漏记录仪,运用土壤水动力学原理,研究了毛乌素沙地流动沙丘降雨入渗水分传递过程及地表以下150 cm深度入渗补给特征.结果表明:流动沙丘深层土壤水分来源主要为降雨入渗,2010年入渗补给量为141.4 mm,2011年为355.8 mm,分别占同期降雨量的55.1%和68.2%.深层入渗主要补给期为5—11月,期间补给量占全年总量的95%.当土壤水分条件保持在田间持水量范围之内时,降雨过程对土壤150 cm深度的补给作用主要受降雨量和降雨强度的影响,入渗量与降雨量呈极显著正相关(P<0.01),降雨通常在30~48 h后渗透补给到150 cm深层土壤,入渗补给速率在前3~5 h呈快速上升趋势,3~8 h左右达到最大值,此后缓慢下降,整个入渗补给过程可以持续96 h以上.     

Evaluation of TRMM rainfall for soil moisture prediction in a subtropical climate

The Tropical Rainfall Measuring Mission (TRMM) is a joint space mission between NASA and the Japan Aerospace Exploration Agency (JAXA) designed to monitor and study tropical rainfall. In this study, the daily rainfall from TRMM has been utilized to simulate the soil moisture content up to 30 cm vertical soil profile of at an interval depth of 15 cm by using the HYDRUS 1D numerical model for the three plots. The simulated soil moisture content using ground-based rainfall and TRMM-derived rainfall measurements indicate an agreeable goodness of fit between the both. The Nash–Sutcliffe efficiency using ground-based and TRMM-derived rainfall was found in the range of 0.90–0.68 and 0.70–0.40, respectively. The input data sensitivity analysis of precipitation combined with different irrigation treatment indicates a high dependency of soil moisture content with rainfall input. The overall analysis reveals that TRMM rainfall is promising for soil moisture prediction in absence of ground-based measurements of soil moisture.     

Rainfall thresholds for the triggering of landslides considering previous soil moisture conditions (Asturias,NW Spain)

Given its geological and climatic conditions and its rugged orography, Asturias is one of the most landslide prone areas in the North of Spain. Most of the landslides occur during intense rainfall episodes. Thus, precipitation is considered the main triggering factor in the study area, reaching average annual values of 960 mm. Two main precipitation patterns are frequent: (i) long-lasting periods of moderate rainfall during autumn and winter and (ii) heavy short rainfall episodes during spring and early summer. In the present work, soil moisture conditions in the locations of 84 landslides are analysed during two rainfall episodes, which represent the most common precipitation patterns: October–November 2008 and June 2010. Empirical data allowed the definition of available water capacity percentages of 99–100% as critical soil moisture conditions for the landslide triggering. Intensity-duration rainfall thresholds were calculated for each episode, considering the periods with sustained high soil moisture levels before the occurrence of each analysed landslide event. For this purpose, data from daily water balance models and weather stations were used. An inverse relationship between the duration of the precipitation and its intensity, consistent with published intensity-duration thresholds, was observed, showing relevant seasonal differences.     

The role of rainfall in the thermal-moisture dynamics of the active layer at Beiluhe of Qinghai-Tibetan plateau

The active layer in permafrost regions plays an important role in energy exchange between permafrost and atmosphere. Rainfall is one of the dominant factors affecting thermal-moisture dynamics of the active layer. To better understand the thermal-moisture dynamics and the interaction between rainfall and the active layer in-detail, in situ experiment was carried out and soil temperature, soil moisture and soil heat flux of the active layer were measured from 2007 to 2009. The observation data demonstrated that the volumetric soil water content of the active layer remained fairly constant during the winter and had a notable fluctuation resulted from evapotranspiration and rewetting from rainfall events in summer. The daily variation amplitude of soil temperature and soil heat flux in summer was bigger than that in winter. Soil moisture content increased and soil temperature decreased after rainfall. Rainfall in summer led to the change of surface energy balance and caused subsurface soil cooling. The convective heat transfer from water infiltration reduced the temperature gradient along depth and changed near-surface heat fluxes. The increase in rainfall may mitigate permafrost degradation on the Tibetan Plateau.     

Statistical analysis of the temporal stability of soil moisture in three desert regions of northwestern China

Soil moisture and its variations are key factors for understanding hydrological processes, which are characterized by a high temporal variability at different scales. The study was conducted at three field stations in the desert regions of northwestern China, where soil moisture measurements with gravimetric method were used to characterize the temporal stability of soil moisture using various statistical parameters and an index of temporal stability (ITS). The soils are a gray–brown desert soil at the Linze station, an aeolian sandy soil at the Fukang station, and a brown desert soil at the Cele station. Soil textures are accordingly sandy loam at Linze and Cele, and loamy sand at Fukang. The dynamic variation in soil moisture depends strongly on the rainfall pattern (amount and frequency) in these desert ecosystems. Soil moisture content is low and significantly different among the three desert ecosystems, with the maximum at the Linze station (6.61 ± 2.08 %), followed by the Cele (4.83 ± 0.81 %) and Fukang (3.46 ± 0.47 %) stations. The temporal pattern exhibits high variability because soil moisture is characterized by low temporal stability and a high coefficient of variation (CV). The standard deviation, CV, and ITS increase significantly with increasing soil moisture. Soil moisture displays a skewed frequency distribution that follows a logarithmic function at lower soil moisture but a log-normal distribution at higher values.     

An investigation of moisture sources and secondary evaporation in Lanzhou,Northwest China

The purpose of this study is to investigate the atmospheric water cycle in Lanzhou and surrounding areas, a place sensitive to climatic conditions and located in the vertex of the “Monsoon Triangle” of China; this study obtained 243 event-based precipitation samples from four stations in Lanzhou, Yongdeng, Yuzhong and Gaolan for 1 year from April 2011 to March 2012. The seasonal variations of δ ¹⁸O and d excess indicate that westerly water vapor, local moisture and summer monsoon all have an influence in this region on a large scale. The westerlies play a dominant role. However, the impact of monsoon moisture has a seasonal limitation, mainly during the period from June to early August. On a local scale, the transportation of moisture appears via two routes. The contribution rate of recycling moisture, over the region, is only 3.6 % on average due to the deficiency of water resource in arid and semi-arid land. Additionally, the effect of secondary evaporation has also been discussed, and the results show that relative humidity, temperature and precipitation amount have different impacts on the effect. However, the influence of precipitation amount is not obvious when the rainfall amount is below 10 mm, while the meteorological parameters of relative humidity and temperature play a significant role in that scope.     

切沟中土壤水分的空间变化特征

切沟侵蚀不仅破坏土地资源，而且影响下游地区环境。目前的土壤侵蚀预报模型没有包括切沟侵蚀，因此研究切沟中土壤水分空间变化是建立切沟侵蚀模型的基础，也是恢复植被的基础。在陕西省安塞大南沟流域选择一个切沟，从1998-2000年连续 3年在 4～10月间对切沟不同部位土壤水分状况进行了观测。分析结果表明，切沟中浅层土壤水分空间分异规律明显，沟顶土壤水分状况较好，土壤容积湿度达到10．3％。沟坡则较差，但沿沟坡向下到沟底，土壤水分不断增加，分别为 6．3％、6．4％和10．4％。沟坡陡崖的土壤水分条件最差，接近凋萎湿度，容积含水量仅为4.6％～5.9％。沟底土壤湿度有所好转，为 7．7％。从雨季开始到结束，整体上土壤水分呈下降趋势，但随降雨事件发生波动。季节变化比较明显的是土壤水分条件好的部位，如沟顶、沟坡底部和沟底。尤以沟底变化最大。沟坡陡崖土壤湿度随季节没有任何变化。从1998-2000年，随降水量减少，切沟所有部位土壤湿度持续下降，即使在水分条件较好的沟顶和沟坡下部，土壤湿度也仅为 8．1％～8．8％，其它部位则都接近于凋萎湿度。土壤水分亏缺相当严重。切沟不同部位土壤水分的季节和年际变化主要受降雨入渗补给影响，而沟底则与径流的产生有关。因此应进一步研究不同降雨类型与径流产生、以及土壤湿度变化的关系。     

Using beryllium-7 to evaluate soil erosion processes in agricultural lands in semiarid regions of Central Argentina

This work presents the results of a soil erosion study using the ⁷Be technique. This technique estimates the water erosion/deposition from the comparison between ⁷Be soil content of a reference site and an eroded or sedimented site. The soil samples were collected from an agricultural area of the semiarid region of Argentina near San Luis City, which has a marked rainfall season. The area has been used for crop cultivation, being subjected to plowing practices. The ⁷Be in the Reference Site was in the first centimeter of soil, showing the typical exponential decreasing of ⁷Be soil content with depth, with the ⁷Be inventories value being 340?±?50 Bq m^?2 for the dry season and 571?±?48 Bq m^?2 for the rainy season. The ⁷Be technique was applied to a potential eroded site subjected to traditional tillage practices (plowing). A net soil erosion value of 13.5 t ha^?1 (1.35 kg m^?2) was obtained. From the assumptions of the applied technique, we can draw the inference that this erosion was caused by rains produced in the month prior to the date of soil sampling.     

Rainfall and irrigation controls on groundwater rise and salinity risk in the Ord River Irrigation Area,northern Australia

Groundwater beneath the Ord River Irrigation Area (ORIA) in northern Australia has risen in elevation by 10–20 m during the past 40 years with attendant concerns about water logging and soil salinization. Persistent groundwater accession has been attributed to excessive irrigation and surface water leakage; however, analysis of daily water-table records from the past 10 years yielded a contrary result. On a seasonal basis, water-table elevation typically fell during irrigation (dry) seasons and rose during fallow (wet) seasons, conflicting with the conventional view that irrigation and not rainfall must be the dominant control on groundwater accession. Previous investigations of unexpectedly large infiltration losses through the cracking clay soils provide a plausible explanation for the apparent conundrum. Because rainfall is uncontrolled and occurs independently of the soil moisture condition, there is greater opportunity for incipient ponding and rapid infiltration through preferred flow pathways. In contrast, irrigation is scheduled when needed and applications are stopped after soil wetting is achieved. Contemporary groundwater management in the ORIA is focused on improving irrigation efficiency during dry seasons but additional opportunities may exist to improve groundwater conditions and salinity risk through giving equal attention to the wet-season water balance.     

Temporal stability of soil water storage and its influencing factors on a forestland hillslope during the rainy season in China’s Loess Plateau

Large-scale vegetation restoration in China’s Loess Plateau has been initiated by the central government to control soil and water losses since 1999. Knowledge of the spatio-temporal distribution of soil water storage (SWS) is critical to fully understand hydrological and ecological processes. This study analysed the temporal stability of the SWS pattern during the rainy season on a hillslope covered with Chinese pine (Pinus tabulaeformis Carr.). The soil water content in eight soil layers was obtained at 21 locations during the rainy season in 2014 and 2015. The results showed that the SWS at the 21 locations followed a normal distribution, which indicated moderate variability with the coefficients of variation ranging from 14 to 33%. The mean SWS was lowest in the middle slope. The spatial pattern of SWS displayed strong temporal stability, and the Spearman correlation coefficient ranged from 0.42 to 0.99 (p < 0.05). There were significant differences in the temporal stability of SWS among different soil layers (p < 0.01). The spatial patterns of SWS distribution showed small differences in different periods. The best representative locations of SWS were found at different soil depths. The maximum RMSE and MAE at 0–1.6 m soil depth for the rainy season were 4.27 and 3.54 mm, respectively. The best representative locations determined during a short period (13 days) can be used to estimate the mean SWS well for the same rainy season, but not for the next rainy season. Samples of SWS collected over a fortnight during the rainy season were able to capture the spatial patterns of soil moisture. Roots were the main factor affecting the temporal stability of SWS. Rainfall increased the temporal stability of the soil water distribution pattern. In conclusion, the SWS during the rainy season had a strong temporal stability on the forestland hillslope.     

Investigating soil thermodynamic parameters of the active layer on the northern Qinghai-Tibetan Plateau

The soil thermodynamic parameters, including thermal conductivity, diffusivity and volumetric capacity within the active layer on the northern Tibetan Plateau, were calculated using the measured data of soil temperature gradient, heat flux, and moisture at four stations from October 2003 to September 2004. The results showed that the soil thermodynamic parameters exhibited clear seasonal fluctuation. The thermal conductivity and diffusivity in summer and autumn at Beiluhe, Kexinling, and Tongtianhe were larger than those in winter. The volumetric thermal capacity causes an opposite change; it was larger in autumn and winter than in summer. In spring, the soil thermal conductivity at the Kekexili station was larger than that in summer. Generally, fine-grained soils and lower saturation degrees in the topsoil might be a reason for the lower soil thermal conductivity in winter. For a given soil, soil moisture was the main factor influencing the thermodynamic parameters. The unfrozen water content that existed in frozen soils greatly affected the soil thermal conductivity, whose contribution rate was estimated to be 55 %. The thermodynamic parameters of frozen soils could be expressed as a function of soil temperature, volumetric ice content and soil salinity, while for the unfrozen ground the soil moisture content is the dominant factor for those thermal parameters. As for the soil thermal diffusivity, there exists a critical value of soil moisture content. When the soil moisture content becomes less than a critical value, the soil thermal diffusivity increases as the soil moisture content rises.     

Spatial estimation of soil erosion risk using RUSLE/GIS techniques and practices conservation suggested for reducing soil erosion in Wadi Mina watershed (northwest,Algeria)

The Wadi Mina Watershed, western area of Algeria is characterized by rare and irregular rains and a fragile and weak vegetable cover. The sediments resulting from erosion are transported and contributed to silting dam Sidi Mhamed Benaouda. The combination of the thematical maps of the various erosive factors according to the Revised Universal Soil Loss Equation (RUSLE) in SIG by ArcGIS 10.2 software provided a reliable forecast of the annual rates of soil loss by delimiting the areas prone to erosive risk in the catchment above mentioned. The estimated potential average annual soil loss is 11.2 t/ha/yr., and the potential erosion rates from recognized erosion classes ranged from 0.0 to plus 100 t/ha/yr. About 50% of the catchment area was predicted to have very low to low erosion risk, with soil loss between 0 and 7.4 t/ha/yr. Erosion risk is moderate over 13.9% of the catchment, where calculated soil loss is between 7.4 and 12 t/ha/yr. Erosion risk is high to dangerous over 36.1% of the catchment, where calculated soil loss is more than 12 t/ha/yr. According to this study, it appeared clearly that we must intervene quickly by using reliable and effective conservation techniques.     

Impact of monsoon rainfall on the total foodgrain yield over India

The study focuses on understanding the variations of precipitation during summer monsoon season and its impact on Kharif and Rabi foodgrain yield over India. Total foodgrain yield over India during Kharif (summer) season is directly affected by variations in the summer monsoon precipitation (June–September). An increase (decrease) in rainfall is generally associated with an increase (decrease) in foodgrain yield. A similar correspondence during the Rabi (winter) foodgrain yield is not evident. The Rabi crop is not directly affected by variations in the post-monsoon precipitation (October–December) alone, also the summer season precipitation influences the Rabi crop through water and soil moisture availability over many parts of India. Though the reduction of rainfall activity during the entire summer monsoon season leads to reduction in crop yields, the occurrence of prolonged rainfall breaks also causes adverse effect on the crop growth resulting in reduced crop yields.     

Flux of nutrients and heavy metals from the Melai River sub-catchment into Lake Chini, Pekan, Pahang, Malaysia

This study was carried out to determine the flux of nutrients and heavy metals from the Melai sub-catchment into Lake Chini through the process of erosion. Melai River is one of the seven feeder rivers that contributed to the present water level of Lake Chini. Three properties of soils, such as particle size, organic matter content, and soil hydraulic conductivity and three chemical soil properties, such as available nutrients, dissolved nutrients, and heavy metals, were analyzed and interpreted. Potential soil loss was estimated using the revised universal soil loss equation model. The results show that the soil textures in the study area consist of clay, silty clay, clay loam, and sandy silt loam. The organic matter content ranges from 3.40 to 9.92 %, while the hydraulic conductivity ranges from 5.2 to 25.3 cm/h. Mean values of available P, K, and Mg amount was 8.5 ± 3.7 μg/g, 24.5 ± 3.4 μg/g, and 20.7 ± 18.6 μg/g, respectively. The highest concentration of soluble nutrients was SO ₄ ^?2 (815.8 ± 624.1 μg/g), followed by NO₃ ^?-N (295.5 ± 372.7 μg/g), NH₄ ⁺-N (24.5 ± 22.1 μg/g) and PO₄ ^3? (2.0 ± 0.8 μg/g). The rainfall erosivity value was 1658.7 MJ mm/ha/h/year. The soil erodibility and slope factor ranges from 0.06 to 0.26 ton h/MJ/mm and 7.63 to 18.33, respectively. The rate of soil loss from the Melai sub-catchment in the present condition is very low (0.0028 ton/ha/year) to low (18.93 ton/ha/year), and low level flow of nutrients and heavy metals, indicating that the Melai River was not the contaminant source of sediments, nutrients, and heavy metals to the lake.     

Influence of soil moisture content on surface albedo and soil thermal parameters at a tropical station

Half hourly data of soil moisture content, soil temperature, solar irradiance, and reflectance are measured during April 2010 to March 2011 at a tropical station, viz., Astronomical Observatory, Thiruvananthapuram, Kerala, India (76°59’E longitude and 8°29’N latitude). The monthly, seasonal and seasonal mean diurnal variation of soil moisture content is analyzed in detail and is correlated with the rainfall measured at the same site during the period of study. The large variability in the soil moisture content is attributed to the rainfall during all the seasons and also to the evaporation/movement of water to deeper layers. The relationship of surface albedo on soil moisture content on different time scales are studied and the influence of solar elevation angle and cloud cover are also investigated. Surface albedo is found to fall exponentially with increase in soil moisture content. Soil thermal diffusivity and soil thermal conductivity are also estimated from the subsoil temperature profile. Log normal dependence of thermal diffusivity and power law dependence of thermal conductivity on soil moisture content are confirmed.     

Deforestation effects on soil properties,runoff and erosion in northern Iran

Improper cultivation practices are seriously degrading native forest ecosystems in northern Iran. Hence, the objectives of this study are to compare selected soil properties, runoff amount, erosion and also introducing equations to predict the runoff and soil erosion in three types of land use (forest, garden and cultivated). A simple portable rainfall simulator has been set in 90 random points to create experimental rainfall. Result showed that changes in natural forest led to a significant clay, organic carbon of soil, total N and antecedent soil moisture decrease and sand, pH and bulk density increasing. The rainfall runoff experiments indicate that runoff content of the natural forest soils was 35 % and respectively 38.45 % higher than the garden and cultivated land soils .This result could be related to the higher antecedent soil moisture in natural forest compared with the other land uses. According to the obtained results, garden soil erosion and cultivated land was 1.351 and respectively 1.587 times higher than the forest. The correlation matrix revealed that runoff content was positively correlated with antecedent soil moisture, bulk density and silt, and negatively with soil organic carbon, total N and sand. Also, soil organic carbon, total N, clay and sand showed negative correlation with soil erosion, while there is a positive correlation between erosion and silt, bulk density, pH and antecedent soil moisture. The results of multiple linear regression showed that runoff in forest, garden and cultivated land can be predicted with correlation coefficient of 0.637, 0.547 and 0.624, respectively. The correlation coefficients of 0.798, 0.628 and 0.560 in equations indicate their moderate potential in simulating soil erosion.     

典型岩溶峰丛洼地坡面土壤水分空间变异性

采用网格法测量典型坡面上旱季（12月）和雨季（5月）的表层(0~5 cm)土壤含水量,以地统计学方法分析其空间变异性,结果表明:（1）与单一土地利用坡面相比,人为扰动强、土地利用多样的岩溶峰丛坡地表层土壤含水量表现为坡上未被扰动的自然植被区明显高于坡下人为改造的区域;旱季时坡地林地表层土壤平均含水量（32.8%）明显高于位于坡下的梯田空闲地（24.2%）、梯田橘园（20.0%）、梯田菜园（22.0%）、坡地裸地（23.5%）;雨季时,坡地裸地（30.2%）和梯田橘园（32.1%）有明显增大,梯田空闲地（17.8%）剧烈减小,坡地林地（32.2%）土壤含水量依然最高;（2）旱、雨季整个坡面上空间结构比分别为21.0%、8.7%,表现为雨季的空间相关性更好;旱、雨季表层土壤含水量变异系数分别为20.1%和31.7%,属中等程度变异;雨季表层土壤含水量的变程（77.5 m）显著高于旱季（8.0 m）,雨季的土壤含水量具有较好的空间变异结构;（3）裸岩周围空间的土壤含水量随与裸岩的距离增大而减小,梯田石坎周围空间的土壤含水量随与梯田石坎的距离增大而递减。      

黄土旱塬区不同覆盖措施对土壤水分及冬小麦水分利用效率的影响

田间试验研究了不同覆盖措施对冬小麦农田土壤含水量及小麦生长状况和水分利用效率的影响.试验包括4个处理:作物生育期秸秆覆盖600 kg/ha(M600)、秸秆覆盖300 kg/ha(M300)、地膜覆盖(PM)和无覆盖处理(CK).结果表明:覆盖处理下的土壤贮水量均高于不覆盖,M600处理能显著增加土壤含水量(0～1m和...     

Extraction of soil moisture from RADARSAT-1 and its role in the formation of the 6 December 2008 landslide at Bukit Antarabangsa,Kuala Lumpur

Active microwave has a huge potential in the estimation of soil moisture especially over large areas where the meteorological observations are seldom. The large contrast in dielectric constant between different types of soil is considered as the main factor for measuring the moisture content. This study is aimed at the extraction of soil moisture over the areas of Bukit Antarabangsa, Malaysia using active microwave remote sensing technique in order to examine the impact of moisture content dynamically on landslides occurrence, which have been a basic challenge that threaten Bukit Antarabangsa area, particularly in falling of monsoon seasons. This study addressed a specific event that took place in 6 December 2008 due to a very high level of precipitation that resulted in a raise in ground water table causing the occurrence of landslide. One Radarsat-1 image acquired in July 2008 before the landslide was used for generating the moisture content map. The resultant moisture content map showed a reasonable distribution of the moisture concentrated over the forest areas which has previous records landslides. Moreover, it was found that the previous landslide events were within the high moisture zone indicating the presence of high moisture content. Subsequently, three moisture maps were extracted from Landsat-7 ETM+, which were then used for validation process. A statistically based validation technique was used by calculating area under the curve that correlates the high moisture values of three images. In order to validate the Landsat-7 ETM+ moisture content, monthly rainfall data was plotted against the high moisture values derived from three Landsat-7 images. The validation result indicated an acceptable compatibility. The spatial relation between high moisture areas in Landsat-7 ETM+ images along the year resulted in a good fitting in the high–low moisture distribution areas with sensitivity ranged of 60–70 %. Finally, the moisture content map generated by Radarsat-1 was validated using a landslide inventory map. The resultant validation produced an area under curve of 0.704 (70 %).     

降雨入渗下非饱和坡残积土湿润锋运移试验研究

我国东南沿海地区丘陵山地发育，降雨入渗到土体中的水分是导致滑坡灾害频发的关键因素。以福建省泉州市德化县地质灾害点为主要研究对象，考察典型地质灾害点具有代表性的坡积土与花岗岩残积土的渗透特性。利用自行研制的土体入渗装置，分别在降雨强度为15、30、60 mm/h条件下，考虑降雨历时一致（180 min）与过程降雨量一致（90 mm）两种工况开展一维土柱入渗试验，得到相应的各个土柱含水率、湿润锋、入渗率随时间变化的响应规律。试验结果表明：（1）土体渗透系数越大、雨强越大，土体湿润蔓延距离越深、速度越快。（2）降雨入渗过程中，土体含水率由浅及深逐次对降雨进行响应。不同雨强对含水率的影响主要体现在第一次响应时间以及饱和速度上，雨强越大，响应时间越快，饱和速度也越快。（3）提出可表征在不同雨强作用下，德化县马坪滑坡与崩土岭滑坡的湿润锋入渗公式。该研究成果对台风暴雨型滑坡的孕灾机制分析以及精细化监测预警具有重要的理论及实际意义。