Temporal Stability Of Soil Moisture Research Articles

A near-linear transect sampling method for validation of SMAP surface soil moisture in non-complex terrains

ABSTRACT The global validation for SMAP (Soil Moisture Active Passive) Level-4 surface soil moisture using well-established core validation sites does not comprehensively account for all landscapes on earth’s surface due to the diverse nature of their intrinsic characteristics. Due to the inhibitive cost of implementing a standard validation site, this study presents an alternative sampling approach suitable for localized validation of SMAP data in non-complex terrains. It involves clustering a large heterogeneous study area to smaller units of non-complex terrains where landscape-defining characteristics are largely homogeneous, thus permitting the computation of areal soil moisture as a simple arithmetic mean of near-linear point measurements. This allows optimization of limited resources (a hand-held moisture sensor with site-specific calibrations) to balance the need for spatial representativeness of samples in the sampling unit and the need for temporal proximity of sampled measurements to the aggregation time of the satellite product being validated. For ease of movement, transect sampling is implemented along access roads that run across the sampling units to allow sufficient measurement replications within a reasonably short time. Validations with four different landscapes in Kenya show a good agreement between in situ measurements and SMAP with R2 of 0.76, 0.72, 0.80, and 0.82, and biases of −0.0246, +0.0113, 0.0004, and + 0.0035 m3 m−3, respectively for Mawego, Kuresoi, Sotik and Kapsuser sites. These results only marginally differ from those obtained with a spatially distributed sampling method, indicating the potential of the proposed sampling design for time and cost effectiveness in validations at non-complex terrains. An analysis of the temporal variability of SMAP soil moisture in the watershed is also presented, with an assessment of its significance in the selection of sampling sites for validation. Particularly, the concept of temporal stability of soil moisture as a basis for clustering validation sites is evaluated.

On the Variability in the Temporal Stability Pattern of Soil Moisture Under Mediterranean Conditions

In recent decades, there has been increasing interest in studying the variability in soil water properties and, specifically, the spatiotemporal variability in the soil water content. This is motivated by the notable theoretical and applied research interests in soil moisture dynamics and their implications for many natural processes. This study aimed to study whether there are variations in the spatial pattern of the temporal stability of soil moisture over time and to analyze the possible influences of certain hydroclimatic (soil water content, precipitation, and evapotranspiration) and soil factors (texture, bulk density, and organic matter content) on these variations. This study was conducted within the Soil Moisture Measurement Stations Network of the University of Salamanca (REMEDHUS, Spain) under Mediterranean conditions, with daily surface moisture data (0–5 cm depth) obtained from 20 stations for the 2006-2023 period. The results showed differences between the average pattern obtained with the 18-year data series and that obtained with the data series for each year. In more than half of the years studied, the representative station differed from that derived from the average pattern. The mean annual precipitation and summer precipitation characteristics seem to be the main factors influencing the variability in the spatial pattern of the temporal stability of soil moisture.

Temporal stability of soil moisture in a fixed dune of the Horqin Sand Land in northern China

Temporal stability of soil moisture in a fixed dune of the Horqin Sand Land in northern China

Soil Moisture Distribution and Time Stability of Aerially Sown Shrubland in the Northeastern Margin of Tengger Desert (China)

Considering the importance of soil moisture in hydrological processes, it is crucial to understand the water distribution and time stability of different aerial shrub soils. There are few studies on the soil moisture of aerial vegetation in the northeastern margin of the Tengger Desert. Based on long-term monitoring data from the aerial seeding area in the northeastern margin of the Tengger Desert, the distribution characteristics of soil moisture and the temporal stability of soil moisture were studied. From June to October 2022, the soil moisture monitoring instrument WatchDog was used to monitor the long-term soil moisture changes (0–200 cm) in the four aerial afforestation plots of Hedysarum scoparium, mixed forest land (Hedysarum scoparium dominant species), mixed forest land (Calligonum mongolicum dominant species), and Calligonum mongolicum. The Spearman rank correlation coefficient was used to study the temporal stability of soil moisture in the four plots. Rainfall data were collected through small weather stations. The results show that the average soil water storage of four kinds of aerial shrub land in the study area was the highest in August, and the average soil water storage of different forest lands was different. The soil water content of the surface layer (0–30 cm) fluctuated the most in different months. The variation in soil water content in the shallow layer (30–100 cm) was smaller than that in the surface layer. The fluctuation of soil water content in the middle layer (100–150 cm) and deep layer (150–200 cm) was relatively stable. There was no strong variability in soil moisture content, and the temporal variation coefficient of surface soil moisture was the highest (31.44–39.8%), which showed moderate variability. The temporal variation coefficient of soil moisture in the shallow, middle and deep layers of all kinds of plots was significantly reduced, and the soil moisture stability of different aerial shrub land was the same. Spearman rank correlation analysis showed that the spatial pattern of soil water content in the surface layer (0–30 cm) and deep layer (150–200 cm) was more stable over time, that is, the temporal stability of soil water content was higher, and the temporal stability of soil water content in the middle and shallow layers of different types of shrub land was different. The research results help us to understand the soil hydrological process in the aerial seeding afforestation area in the northeastern margin of Tengger Desert, rationally arrange soil moisture monitoring points, efficiently manage and utilize water resources in the aerial seeding area, and provide a theoretical basis for local vegetation restoration and the optimization of the ecological environment.

Preferential flow influences the temporal stability of soil moisture in a headwater catchment

The dynamics and controls of soil moisture spatial organization are crucial to modeling water flux and land–atmosphere interactions across landscapes. Despite this importance, the control of subsurface preferential flow on the temporal stability of soil moisture spatial organization (TSSS) has not been thoroughly examined. This study monitored daily soil moisture at multiple depths (5–162 cm) for three consecutive years at 33 sites across a forested headwater catchment spanning 7.9 ha. The standard deviation of the relative difference in soil moisture between each monitoring location and the catchment mean (i.e., SDRD, a measure of TSSS) was calculated to quantify the influence of controlling factors on TSSS. Factors considered included soil moisture monitoring frequency, soil and terrain attributes, soil wetness condition, and preferential flow. The analysis was conducted separately for wet and dry seasons. The results indicated that (1) soil moisture monitoring frequency had a considerable impact on TSSS, particularly in valley and swales during dry seasons. As the monitoring frequency increased from 1 day to 28 days, the SDRD values of areas with varied soil–terrain attributes all decreased, suggesting a more stable TSSS. However, this also implied that coarser monitoring frequencies might not capture short-term (e.g., daily) soil moisture processes and associated TSSS dynamics. (2) The relationship between soil–terrain attributes and TSSS was stronger during dry seasons than wet seasons (R2 of 0.597 vs. 0.301, P < 0.05). (3) TSSS was significantly correlated with preferential flow frequency (r = 0.611, P < 0.05) at the study catchment. Including preferential flow frequency as a regression variable improved the explanation and prediction of TSSS. This study confirms the vital role of preferential flow in regulating TSSS in complex terrain. These findings underscore the need for high-frequency monitoring to accurately characterize soil moisture distributions over time and space in similar environments.

Variation of soil water stability and dominant influencing factors after sparse forestation in the loess alpine hills of northwest China

Study regionDatong County, located in the loess alpine hills of north-western China. Study focusThis study investigated soil moisture and environmental factors in three catchments (10, 20 and 40 years after afforestation with sparse forests) to examine the influence and dominant factors of afforestation with sparse forests on the stability of soil moisture patterns in the catchment. New hydrological insights for the study regionThe results show that long-term afforestation with sparse forests improved the soil moisture in the catchment. The spatial patterns of soil moisture (SMSP) were highly stable in all three catchments, except for surface (0–20 cm) soil moisture. Afforestation with sparse forests improved the stability of the spatial patterns and the fitting of representative locations (R2:0.818–0.878). In the early and middle afforestation periods, soil moisture was mainly influenced by plant indices such as fine root biomass, shrub grass biomass and leaf area index, whereas in the middle and late periods, the temporal stability of soil moisture gradually became more dependent on soil indices such as the clay content and soil organic carbon. This study provides a scientific basis for improving the understanding of soil hydrological processes in areas afforested with sparse forests and for optimising the selection of sample sites in the loess alpine hilly region.

Temporal stability of soil moisture: a case study in a small watershed in the subtropical region of Brazil

Temporal stability of soil moisture: a case study in a small watershed in the subtropical region of Brazil

Comparison on moisture dynamics of two different soil types in desert steppe

Based on the positioning monitoring data from 2017 to 2018, we analyzed the spatial-temporal dynamic characteristics of moisture in two different soil types (sierozem and aeolian sandy soil) in the Yanchi desert steppe in the eastern Ningxia. The results showed that the rainfall in the study area was 208.2 and 274.8 mm in the growing season of 2017 and 2018 (May-October), respectively. The distribution of rainfall varied across different months. Except for the extreme rainfall event (129.6 mm) in May in 2018, rainfall in other months was lower than that in 2017. The seasonal dynamics of soil water content was roughly divided into two phases: compensation period (early May to early June) and fluctuation period (mid June to late September). The soil moisture of 0-20 cm layer had a pulse characteristic of rapid increase and decrease after rainfall, while that of the deep soil was relatively stable. The soil water content of sierozem showed a "rise-fall-liter" change with increasing soil depth. The saeolian sandy soil increased sharply from 0 to 60 cm then increased slowly, whereas soil water content gradually increased with increasing soil depth. In 2017, soil moisture in the soil profile (0-100 cm) of the sierozem was accumulated, and the aeo-lian sand soil was in the consumption type. In 2018, both soil water across the full profile in both soil types were the consumption type. The temporal stability of soil moisture of two soil types increased with increasing soil depth. The average soil water content of the whole sections of sierozem and aeolian sandy soil were 80-100 and 40-60 cm, respectively. The two soil types had different spatial and temporal distributions of soil moisture. Aeolian sandy soil was more affected by precipitation than sierozem. Precipitation would reduce the variability of soil moisture and change its temporal stability.

Soil moisture temporal stability and spatio‐temporal variability about a typical subalpine ecosystem in northwestern China

Soil moisture temporal stability and spatio‐temporal variability about a typical subalpine ecosystem in northwestern China

黄土高寒区坡面土壤水分的时间稳定性

黄土高寒区坡面土壤水分的时间稳定性

Temporal instability of soil moisture at a hillslope scale under subtropical hydroclimatic conditions

Temporal instability, a condition of soil moisture with unstable spatiotemporal patterns, may occur when the relative roles of the controlling factors change. It impacts the applicability of the temporal stability in the prediction of soil moisture. However, the occurring frequency, degree and underlying hydrological conditions of the temporal instability are far from clear. This study aimed to examine the presence of temporal instability at the hillslope scale and to characterize and quantify the frequency, degree and underlying hydrological conditions contributing to the phenomenon. Sloping crop lands under subtropical hydrological conditions are known for their frequent transition between dry and wet periods and were chosen for this study. Soil moisture was monitored at 5 locations and at seven soil depths down to 2.2 m along a 160 m hillslope over a period of a year. Relative difference analysis was employed to evaluate the temporal stability of soil moisture. Representative locations (RLs) mainly appeared at locations with a mild slope and relatively high sand content. Daily RLs were not consistent among the study period, which has the highest proportion to be the same to those full dataset based. These proportions were depth dependent, the lowest (40%) at moderate soil layers (i.e. 50 and 80 cm) and the highest (95%) at deep soil layers (i.e. 180 and 220 cm). An obvious temporal instability was observed by the extensive ranges in the daily mean relative difference (MRD) values. If the whole dataset was used to calculate the mean soil moisture of the hillslope, it would be overestimated by 16.1% or underestimated by 18.2%. The frequency of temporal instability was low and varied over time and soil depths. For example, 17% of the time for this period was temporally unstable at 20 cm and 2% time of the study period was unstable at 220 cm. These low proportions confirm that the temporal stability remains a valid and robust tool in mean soil moisture prediction. The rainfall after a long drought period or a storm after successive rainfall probably caused the temporal instability. Therefore, caution should be exercised during the strong dry-wet transition period.

Temporal stability of soil moisture in banana cropping area in the Brazilian semiarid region

ABSTRACT Soil moisture is essential for agricultural production. Knowledge on its spatial-temporal variability is indispensable to support agriculture, and it is strongly influenced by cultural practices, soil cover conditions and irrigation methods. Thus, this study aimed to evaluate the temporal stability and spatial distribution of soil moisture as a function of the use of banana leaves as soil cover in a plot under conventional sprinkler irrigation and cultivated with banana in the Brazilian semiarid region. The study area was divided in two sectors, with and without covering using banana leaves. Soil moisture was monitored before and after irrigation, at 16 times, using FALKER HidroFarm sensors installed on a transect with 11 units spaced by 8 m, in each sector. The data were analyzed using descriptive statistics, temporal stability and Spearman correlation test. The morphology of the banana leaves and the irrigation system used contributed to lower soil moisture in the covered sector at all monitoring times. Variations in the physical-hydraulic properties of the soil promoted variations in soil moisture with the position of the sensors in the ground. The temporal stability technique allowed the identification of points that represent the mean behavior of soil moisture throughout the area. The use of banana leaf residues caused less soil wetting using sprinkler irrigation, indicating the need to pre-grind the material or use localized irrigation systems, practices that are not very accessible to small farmers.

Moisture Temporal Stability of a Typic Hapludox under Different Uses and Depths

Temporal stability shows that specific within‐field locations can represent average moisture values for a period of time, reducing efforts of collecting and measurement field observations. The objective of this study was to analyze the temporal stability of soil moisture within a Hapludox, typical of Cerrado, a unique Brazilian biome (similar to savanna), located in the southwestern state of Goiás. Instant readings of volumetric soil moisture were done biweekly from November 2013to February 2014, using a portable TDRSensor with rods of 0.12 m in length, at 0‐ to 0.12‐, from 0.12‐ to 0.24‐, and 0.24‐ to 0.36‐m soil depths. The TDR sensor data were corrected and calibrated by volumetric water content data obtained from gravity method and soil bulk density measurements. To quantify temporal stability, we used nonparametric methods: Spearman correlation coefficient, average relative difference, and temporal stability index. Temporal stability on the field scale differed between the three sites/systems. Average soil moisture can be accurately estimated at only one georeferenced point for each site/management system, reducing measurement effort in long‐term studies.Core Ideas Moisture temporal stability reduce cost of field measurements. It is essential to planning monitoring programs of hydrology and irrigation. Represent a valuable support for future researches related to soil water management.

The role of sampling strategy on apparent temporal stability of soil moisture under subtropical hydroclimatic conditions

Abstract Subtropical regions have clay-rich, weathered soils, and long dry periods followed by intense rainfall that produces large fluctuations in soil water content (SWC) and hydrological behavior. This complicates predictions of spatio-temporal dynamics, as datasets are typically collected at too coarse resolution and observations often represent a duration that is too short to capture temporal stability. The aim of the present study was to gain further insights into the role of temporal sampling scale on the observed temporal stability features of SWC order to aid the design of optimal SWC sampling strategies. This focused on both sampling frequency and total monitoring duration, as previous analyses have not considered both of these sampling aspects simultaneously. We collected relatively high resolution data of SWC (fortnightly over 3.5 years) for various soil depths and under contrasting crops (peanuts and citrus) at the red soil region of southeast China. The dataset was split into a three-year training period and a six-month evaluation period. Altogether 13 sampling frequencies (intervals ranging from 15 to 240 days) and eight monitoring duration periods (between three and 36 months) were derived from the training period to identify temporal stability features and the most time stable location (MTSL). The prediction accuracies of these MTSLs were tested using the independent evaluation data. Results showed that vegetation type did affect the spatio-temporal patterns of SWC, whereby the citrus site exhibited a stronger temporal variation and weaker temporal stability than the peanut site. However, the effects of both sampling frequency and observation duration were more pronounced, irrespective of the role of vegetation type or soil depth. With increasing sampling interval or decreasing monitoring duration, temporal stability of SWC was generally overestimated; by less than 10% when sampling interval increased from every 15 to 240 days and by up to 40% with duration decreasing from 36 to 3 months. Our results suggest that sampling strategies and trade-offs between sampling interval and duration should focus on capturing the main variability in hydro-climatological conditions. For subtropical conditions, we found that sampling once every 45 days over 24 months to be the minimum sampling strategy to ensure errors in SWC temporal stability of less than 10%.

Interplays between State and Flux Hydrological Variables across Vadose Zones: A Numerical Investigation

Knowledge of both state (e.g., soil moisture) and flux (e.g., actual evapotranspiration (ETa) and groundwater recharge (GR)) hydrological variables across vadose zones is critical for understanding ecohydrological and land-surface processes. In this study, a one-dimensional process-based vadose zone model with generated soil hydraulic parameters was utilized to simulate soil moisture, ETa, and GR. Daily hydrometeorological data were obtained from different climate zones to drive the vadose zone model. On the basis of the field phenomenon of soil moisture temporal stability, reasonable soil moisture spatiotemporal structures were reproduced from the model. The modeling results further showed that the dependence of ETa and GR on soil hydraulic properties varied considerably with climatic conditions. In particular, the controls of soil hydraulic properties on ETa and GR greatly weakened at the site with an arid climate. In contrast, the distribution of mean relative difference (MRD) of soil moisture was still significantly correlated with soil hydraulic properties (most notably residual soil moisture content) under arid climatic conditions. As such, the correlations of MRD with ETa and GR differed across different climate regimes. In addition, the simulation results revealed that samples with average moisture conditions did not necessarily produce average values of ETa and GR (and vice versa), especially under wet climatic conditions. The loose connection between average state and flux hydrological variables across vadose zones is partly because of the high non-linearity of subsurface processes, which leads to the complex interactions of soil moisture, ETa, and GR with soil hydraulic properties. This study underscores the importance of using soil moisture information from multiple sites for inferring areal average values of ETa and GR, even with the knowledge of representative sites that can be used to monitor areal average moisture conditions.

Spatial-temporal variability of soil moisture: Addressing the monitoring at the catchment scale

Soil moisture plays a fundamental role in the mass and energy balance between the land surface and the atmosphere, making its knowledge essential for several hydrological and climatic applications. The aim of this study is to extend the current knowledge of soil moisture spatial-temporal variability at the catchment scale (up to 500 km2). The main implication is to provide guidelines to obtain soil moisture values representative of the mean behaviour at the medium-sized river basin scale, which is useful for remote sensing validation analysis and rainfall-runoff modeling. To this end, 23 measurements campaigns were carried out during a time span of 14 months at 20 sites located within the Upper Chiascio River Basin, a catchment with a drainage area of about 460 km2 in the Umbria Region (central Italy). The data set allowed the analysis of both soil moisture temporal stability and its dynamics. On the basis of statistical and temporal stability approaches, it was investigated how factors such as climatic regime and geomorphology influence soil moisture behaviour. For the investigated area, the spatial variability of soil moisture was higher in dry periods with respect to wet periods, mainly due to the rainfall pattern characteristics during different periods of the year. Soil moisture values recorded during wet periods showed a better correlation than those recorded during dry periods. The maximum number of required samples, to obtain the mean areal soil moisture with an absolute error of 3% vol/vol, was found equal to 12. The temporal stability analysis showed that during wet periods just one “optimal” measurement point can provide values of soil moisture representative of the catchment-mean behaviour, while during dry periods the number of “optimal” measurement points became equal to two. Therefore, at the adopted spatial scale the use of a single measurement point can lead to significant errors. From the perspective of soil moisture dynamics, the decomposition of the spatial variance showed that the contribution of the time-invariant component (temporal mean of each site) was predominant on respect to the total spatial variance of absolute soil moisture data, for almost the whole observation period. Results provided guidance to optimize soil moisture sampling by performing targeted measurements at a few selected points representative of the catchment-mean behaviour.

Spatial Pattern and Temporal Stability of Root-Zone Soil Moisture during Growing Season on a Larch Plantation Hillslope in Northwest China

Soil moisture plays a decisive role for tree growth and forest ecosystems services supply in dryland regions. Hence, it is necessary to clarify the spatio-temporal variation of soil moisture under field conditions. This study selected a hillslope in the Liupan Mountains covered by the plantation of Larix principis-rupprechtii Mayr (larch), a main afforestation tree species in north and northwest China. The volumetric soil moisture (VSM) in root zone layers was monitored with a time interval of about 15 days during the growing season (from May to October) in 2016 at 48 points on this hillslope. The aim was to evaluate the spatial pattern and temporal stability of soil moisture at slope scale. The results showed a moderate spatial variability of VSM in each soil layer, with the variation coefficients range of 17.12–22.63%. The spatial variability of VSM showed a dependence on the soil wetness and a threshold effect, it increased with rising VSM until the VSM reached a threshold of about 15%, but thereafter decreased. The mean relative difference (MRD) among the 48 points ranged from −30.56% to 27.20%, −29.89% to 39.58%, and −28.13% to 33.71% for the soil layers of 0–20, 20–40, and 40–60 cm, respectively. The associated standard deviation (SDRD) (and range) was 11.38% (5.20–26.06%), 8.28% (4.64–15.63%), and 6.51% (2.00–14.16%) for the soil layers of 0–20, 20–40, and 40–60 cm, respectively. The high Spearman’s rank coefficients (p &lt; 0.05) among the measuring dates at each soil layer indicated that the spatial distribution of VSM in the root zone had strong temporal stability. The decrease of Spearman’ rank correlation coefficient and mean SDRD with rising soil depth indicated an increasing temporal stability of VSM with rising soil depth. The mean VSM of the three soil layers on the entire hillslope can be estimated by the direct method (using representative points determined by the index of temporal stability (ITS)) successfully, and these representative points determined by ITS were mainly located at the points with a ratio of field capacity to leaf area index (LAI) close to the slope mean. Moreover, the mean VSM of the three soil layers on the entire hillslope can also be estimated by indirect method (using the time-stable points determined by mean absolute bias error (MABE) and considering the offset between slope mean VSM and observed VSM at time-stable points), and the prediction accuracy of the indirect method was better than the direct method. Significant correlation between MRD and soil bulk density, field capacity, capillary porosity, and LAI were observed for all soil layers, indicating that both the water-retention ability in root zone soil (expressed mainly by field capacity) and water-consumption ability of trees (expressed mainly by canopy LAI) are the main factors controlling the spatial pattern of root-zone VSM on the larch plantation hillslope studied.

Factors Controlling Temporal Stability of Surface Soil Moisture: A Watershed‐Scale Modeling Study

Core Ideas Soil moisture data at a watershed scale can be derived from distributed land surface modeling. Factors controlling soil moisture temporal stability can be studied using model simulations. Soil moisture estimation accuracy is improved when dominant factors are considered a priori. The minimum number of sampling points and the shortest sampling periods were investigated. The spatial variability of soil moisture makes it difficult to represent watershed‐scale soil moisture using traditional point‐scale soil moisture sensors. In the temporal stability method, the spatial pattern of soil moisture is assumed to persist with time. Hence, measurements at a representative point can be used to represent the mean soil moisture. We investigated the factors that determine temporal stability and attempted to locate these representative points. Long‐term simulated high‐resolution soil moisture data, at a watershed scale, were used. Results showed that locations with a dominant vegetation cover and a low topographic wetness index (TI) can provide reasonable mean soil moisture estimates. Using vegetation cover and TI information, we minimized the number of the sampling locations needed for identifying the best estimate of the true watershed‐scale mean. The sampling period duration is also a key factor. Using random combination tests, the minimum number of required sampling points and shortest sampling time were estimated. When 10 sampling points were used, a sampling period of 10 mo was required for accurately determining the representative point. Our study results will help apply the temporal stability method to the estimation of areal soil moisture and the calibration and validation of remote sensing data.

Temporal stability of soil moisture in an oasis of northwestern China

AbstractTemporal stability of soil moisture has been widely used in hydrological monitoring since it emerged. However, the spatial analysis of temporal stability at the landscape scale is often limited because of insufficient sampling numbers. This work made an effort to investigate the spatial variations of temporal stability of soil moisture in an oasis landscape. The specific objectives of the study were to explore the spatial patterns of temporal stability and to determine the controlling factors of temporal stability in the desert oasis. A time series of soil moisture measurements were gathered on 23 occasions at 118 locations over 3 years in a rectangular transect of approximately 100 km2. The nonparametric Spearman's rank correlation coefficient, standard deviation of relative difference (SDRD), and mean absolute bias error (MABE) were used to quantify the temporal stability of soil moisture. Results showed that the temporal stability of soil moisture was depth dependent and season dependent. The spatial pattern of soil moisture in a deep soil layer and between two same seasons generally had a high temporal stability. SDRD and MABE were spatially autocorrelated and exhibited strong spatial structures in the geographic space. The concept of temporal stability can be extended to describe the time‐stable areas of soil moisture with geostatistics. There were great differences between SDRD and MABE in describing the temporal stability of soil moisture and in identifying the controlling factors of temporal stability. In this case, MABE was a better alternative to estimate the areal mean soil moisture using representative locations than SDRD. Land use type, soil moisture condition, and soil particle composition were the dominant controls of temporal stability in the oasis. These insights could help to better understand the essence of temporal stability of soil moisture in arid regions.

&lt;b&gt;Temporal stability of soil moisture under effect of three spacings in a eucalyptus stand

Soil moisture temporal variability is an important concept in understanding forest management. The objective of this study was to analyse the effect of planting density on soil profile moisture in a clonal Eucalyptus plantation. Soil moisture was observed every 15 days at 25 points distributed throughout the eucalyptus stand between November 2013 and October 2015 to characterize the moisture according to the following three types of spacings: 3 x 2, 3 x 3, and 3 x 5 m. At each point, the 0 - 10, 10 - 20, 20 - 30, 30 – 40, and 60 - 100 cm layers were evaluated using a Profile Probe PR2 model. Soil moisture showed high spatial variability in the 0 - 10 cm layer, whereas from 30 to 100 cm deep, the moisture tended to become more homogeneous throughout the area. The dry periods presented greater temporal soil moisture stability when compared to the rainy seasons. The 3 x 2 m spacing has greater temporal soil moisture stability when compared to the others, while the 3 x 3 m spacing presented greater temporal variability.