Mean Soil Moisture Content Research Articles

IMPACT OF PITCHER MATERIAL AND SALINITY OF WATER USED ON FLOW RATE, WETTING FRONT ADVANCE, SOIL MOISTURE AND SALT DISTRIBUTION IN SOIL IN PITCHER IRRIGATION: A LABORATORY STUDY

ABSTRACTThree types of pitchers made of different materials were used with saline waters of varied concentrations (5, 10, 15 and 20 dS m‐1) separately to study the effect on flow rate, wetting front advance, moisture and salt distribution in the wetted zone of soil around pitchers. It was found that the pitcher made of clay and sand yielded the lowest flow rate, ranging from 0.42 to 0.62%, followed by the pitcher made of clay, sand and resin, 0.51–0.69% and the pitcher made of clay, sand and sawdust, 0.91–1.02% .The wetting front advance was highest for the pitcher made of clay, sand and sawdust, followed by the pitcher made of clay, sand and resin, and the pitcher made of clay and sand. The mean soil moisture content around the pitcher made of clay and sand was found to be the minimum and varied from 8.53 to 13.3%, followed by the pitcher made of clay, sand and resin, and the pitcher made of clay, sand and sawdust with 9.56–13.7% and 14.5–20.8%, respectively. In the case of the pitcher made of clay and sand, and the pitcher made of clay, sand and resin, the maximum salt concentration in the soil profile ranged between 1.09 and 3.88 dS m‐1 and in the pitcher made of clay, sand and sawdust, it ranged from 2.30 to 6.07 dS m‐1. The initial salinity of water was found to be substantially reduced around the pitcher made of clay and sand, and the pitcher made of clay, sand and resin in comparison to the pitcher made of clay, sand and sawdust. In all cases, salinity levels around the pitchers were well within the safe limit of growing crops. The study reveals that pitcher irrigation may be a promising option for growing plants using highly saline waters, sustaining hardly any salinity hazard or moisture stress. Copyright © 2013 John Wiley & Sons, Ltd.

Analysis of soil moisture variation by forest cover structure in lower western Himalayas, India

Soil moisture affects various hydrological processes, including evapotranspiration, infiltration, and runoff. Forested areas in the lower western Himalaya in India constitute the headwater catchments for many hill streams and have experienced degradation in forest cover due to grazing, deforestation and other human activities. This change in forest cover is likely to alter the soil moisture regime and, consequently, flow regimes in streams. The effect of change in forest cover on soil moisture regimes of this dry region has not been studied through long term field observations. We monitored soil matric potentials in two small watersheds in the lower western Himalaya of India. The watersheds consisted of homogeneous land covers of moderately dense oak forest and moderately degraded mixed oak forest. Observations were recorded at three sites at three depths in each watershed at fortnightly intervals for a period of three years. The soil moisture contents derived from soil potential measurements were analyzed to understand the spatial, temporal and profile variations under the two structures of forest cover. The analysis revealed large variations in soil moisture storage at different sites and depths and also during different seasons in each watershed. Mean soil moisture storage during monsoon, winter and summer seasons was higher under dense forest than under degraded forest. Highest soil moisture content occurred at shallow soil profiles, decreasing with depth in both watersheds. A high positive correlation was found between tree density and soil moisture content. Mean soil moisture content over the entire study period was higher under dense forest than under degraded forest. This indicated a potential for soil water storage under well managed oak forest. Because soil water storage is vital for sustenance of low flows, attention is needed on the management of oak forests in the Himalayan region.

The role of vegetation and soil properties on the spatio-temporal variability of the surface soil moisture in a maize-cropped field

• Surface soil moisture dynamic is analysed in a cropped field. • The role of soil and crop properties is quantitatively evaluated. • Strong seasonality of the controls depending on the mean soil moisture content. • Crop seasonality is explicitly considered and it improves the correlations analysis. • Crop affects directly and through interactions in dry and intermediate condition. Soil moisture dynamics are affected by complex interactions among several factors. Understanding the relative importance of these factors is still an important challenge in the study of water fluxes and solute transport in unsaturated media. In this study, the spatio-temporal variability of surface soil moisture was investigated in a 10 ha flat cropped field located in northern Italy. Soil moisture was measured on a regular 50 × 50 m grid on seven dates during the growing season. For each measurement campaign, the spatial variability of the soil moisture was compared with the spatial variability of the soil texture and crop properties. In particular, to better understand the role of the vegetation, the spatio-temporal variability of two different parameters – leaf area index and crop height – was monitored on eight dates at different crop development stages. Statistical and geostatistical analysis was then applied to explore the interactions between these variables. In agreement with other studies, the results show that the soil moisture variability changes according to the average value within the field, with the standard deviation reaching a maximum value under intermediate mean soil moisture conditions and the coefficient of variation decreasing exponentially with increasing mean soil moisture. The controls of soil moisture variability change according to the average soil moisture within the field. Under wet conditions, the spatial distribution of the soil moisture reflects the variability of the soil texture. Under dry conditions, the spatial distribution of the soil moisture is affected mostly by the spatial variability of the vegetation. The interaction between these two factors is more important under intermediate soil moisture conditions. These results confirm the importance of considering the average soil moisture conditions within a field when investigating the controls affecting the spatial variability of soil moisture. This study highlights the importance of considering the spatio-temporal variability of the vegetation in investigating soil moisture dynamics, especially under intermediate and dry soil moisture conditions. The results of this study have important implications in different hydrological applications, such as for sampling design, ranking stability application, indirect measurements of soil properties and model parameterisation.

Responses of soil moisture in different land cover types to rainfall events in a re-vegetation catchment area of the Loess Plateau, China

Implementation of the Grain-for-Green project has resulted in significantly increased vegetative cover on the Loess Plateau of China during the past few decades. The plant communities influence soil moisture recharge and usage processes, particularly the input process, which is directly related to transformation of the limited precipitation into available soil water in the semi-arid Loess Plateau. A study to measure soil moisture dynamics of typical land cover types associated with precipitation events was conducted in a re-vegetated catchment area. Smart probes were inserted at 6 different depths below the ground surface under grass ( Andropogon ), subshrub ( Artemisia scoparia ), shrub ( Spiraea pubescens ), tree ( Robinia pseudoacacia ), and crop ( Zea mays ) vegetation to record volumetric soil moisture at 10-minute intervals for a period of 60 days during the growing season in 2011. The advance of the wetting front and total accumulated infiltrated water were measured. The rainfall events were sporadic with widely different intensities, and the soil moisture was replenished mainly by 3–4 heavy precipitation events during July and August. The mean soil moisture content profiles of the 5 vegetation types can be ordered as crop > grass > subshrub > tree > shrub and this relationship displayed time stability. The different land cover types clearly influenced the water infiltration and water input amounts in the re-vegetated area. The subshrub site showed the highest total infiltration amount (164 mm) with precipitation (227 mm) during the study period. The grass site had an infiltration amount of 156 mm. The tree site had a total precipitation of 154 mm and an infiltration amount of 97 mm. The infiltration amount was 136 mm for the shrub site and was the lowest (83 mm) for the crop site. Natural grasses displayed a rapid infiltration rate and the wetting front was able to reach a greater depth. ► We observe the water infiltration processes under a heavy rainfall. ► We compare the effects of different soil moisture inputs of five plant species. ► The mean soil moisture relationship displayed time stability. ► Natural grasses displayed a rapid infiltration rate and reach a greater depth.

Effect of spatial variability and seasonality in soil moisture on drainage thresholds and fluxes in a conceptual hydrological model

AbstractThis paper uses soil moisture data from 17 recording sensors within the 50 km2 Mahurangi catchment in New Zealand to determine how measured variability in soil moisture affects simulations of drainage in a typical lumped conceptual model. The data show that variability smoothes the simulated field capacity threshold such that a proportion of the catchment contributes to drainage even when mean soil moisture content is well below field capacity. Spatial variability in soil moisture controls by extension the catchment drainage behaviour: the resulting smoothed shape of the catchment‐scale drainage function is demonstrated and is also determined theoretically under simplifying assumptions. The smoothing effect increases the total simulated discharge by 130%. The analysis explains previous findings that different drainage equations are required at point scale versus catchment scale in the Mahurangi. The spatial variability and hence the emergent drainage behaviour are found to vary with season, suggesting that time‐varying parameters would be warranted to simulate drainage. Copyright © 2012 John Wiley & Sons, Ltd.

On the spatial scaling of field measured soil water and electrical conductivity

In order to explore the impacts of scale on soil variability, a study in a 120 × 40 m agricultural field was carried out. Spatial variations of soil water content (SWC) and electrical conductivity (EC) were analyzed with all the data measured under 5 × 5 m sampling grid. Then, resampling technique was employed with changing sampling extents and spacing, and spatial variation of each scenario was also determined. The results showed that SWC and EC presented weak or moderate spatial variability, and showed apparent mosaic pattern at the field scale. For all data sets the number of measurement (n = 207) effectively collected was much higher, making the field mean soil moisture and salt content data set very accurate. All the spatial indices measured increased with various degrees with increasing extent. However, spacing did not affect coefficient of variation and had inconsistent effects on the geo-statistics parameters, such as the nugget, sill and the correlation length for SWC data and EC data. Key words: Soil water content, electrical conductivity, spatial variability, scale-dependency, sampling design.

Effects of Hay Mulch on Soil Properties and Potato Tuber Yield under Irrigation and Nonirrigation in New Brunswick, Canada

Organic mulching and irrigation are considered to be important soil conservation and agricultural practices. However, the effectiveness of these practices on soil properties and potato production in the relatively cool, moist maritime region of Canada has not yet been well studied. In the growing seasons of 2000–2003, a field experiment was conducted at the Potato Research Centre, Agriculture and Agri-Food Canada, Fredericton, New Brunswick, to assess the benefits of hay mulching on a loamy sand soil under potato production. Treatments consisted of four levels of hay mulching: 0, 2.25, 4.5, and 9.0 Mg ha-1 with four replicates under irrigation or nonirrigation. Results showed that hay mulching could help conserve soil moisture in nonirrigation treatments with an increase of mean soil moisture content by 5.7 to 9.5% under 2.25 to 9.0 Mg ha-1 of hay mulch relative to a control. The greatest conservation effect on soil water in our region would be achieved with a mulch rate of 5.6 Mg ha-1. Under irrigation, mulching slightly increased soil temperature. Without irrigation, soil temperature was affected both positively and negatively by mulching, depending on time of day and quantity of mulch applied. During periods of warmer weather, mulching reduced maximum soil temperature during daytime but increased minimum soil temperature during nighttime. While the magnitude of soil temperature change was slight, it varied linearly with mulch quantity. During periods of cold weather, mulching generally increased soil temperature. The soil organic carbon content in the year following mulching increased proportionally with the amount of mulch applied in the nonirrigated treatments. Thus, thicker mulching treatments resulted in a greater increase in soil organic matter accumulation. Irrigation was found to potentially induce organic matter loss for the lower mulching treatment (2.25 Mg ha-1) and control. No significant effects of hay mulching on total potato tuber yield under irrigation were found, but tuber yield under nonirrigation increased linearly with the amount of mulch applied.

Spatial variability and patterns of surface soil moisture in a field plot of karst area in southwest China

A field plot (100 m × 50 m) was chosen in a karst depression area of Huanjiang County, Guangxi Province of southwest China, with the aim of characterizing the variability and patterns of upper 15 cm soil moisture. Soil moisture content was measured at 5 m intervals by gravimetric method during dry and rainy seasons in 2005. Results indicated that the surface soil moisture presented a strong spatial dependence at the sampling times in the field scale. The variability of soil moisture by CV values and sill decreased with the increasing mean field soil moisture content either in dry or rainy season. In the dry season, mean soil moisture had a little influence on the sill owing to the previous tillage. But, in the rainy season, a heavy rain event could decrease the variability of soil moisture. The anisotropy characteristics were found that the variance was lower in 0° direction than that in 90° direction based on the northeast axis, and the range had opposite trend except for the sampling on March 15, 2005. The mosaic patterns of soil moisture exhibited the variability and its anisotropy visually. The rainfall (mean soil moisture), topography and micro-relief (rock outcrops) had important influence on the variability of soil moisture. To better understand the variability of soil moisture in the karst depression area, more soil samples should be required in the dry season and in a field with more rock outcrops.

Temporal Dynamics of Soil Moisture Spatial Variability in the Shale Hills Critical Zone Observatory

This study utilized a 4‐yr database consisting of catchment‐wide volumetric soil moisture measurements at 78 locations from the surface down to 1.1 m depth within the 7.9‐ha Shale Hills Critical Zone Observatory in central Pennsylvania. The objectives were to: (i) assess the uncertainty in estimating catchment‐wide mean soil moisture content by characterizing the relationship between soil moisture spatial variability and spatially averaged moisture content and (ii) examine the relationship between temporal changes in soil moisture spatial variability and seasonal and event‐based hydrologic fluxes. Our results showed that soil moisture spatial variability increased exponentially with increasing catchment‐wide wetness across all measurement depths and various soil–landform units. This relationship led to the widening of confidence intervals and an increase in the number of sites needed to obtain 95% confidence in spatially averaged soil moisture as the catchment wets up. This was due to the well‐drained and steep‐sloped hillslope soils in the catchment that confined saturated areas to the swales and the valley floor. Temporal changes in soil moisture spatial variability indicated a seasonal increase in the catchment‐wide soil moisture variability that coincided with the emergence of a shallow water table in the valley during the winter and spring months. Event‐based increases in soil moisture spatial variability associated with large antecedent precipitation were also observed (but with limited resolution because of weekly to biweekly measurements), which indicated the importance of subsurface lateral flow in influencing the catchment‐wide soil moisture spatial variability. Because ephemeral shallow water tables and subsurface lateral flow are common in many temperate forests, our results are useful for guiding soil moisture monitoring campaigns in these catchments and have implications for interpreting and scaling remote sensing footprints of soil moisture in these landscapes during different times of a year.

Evergreen broad-leaved forest improves soil water status compared with tea tree plantation in Ailao Mountains, Southwest China

In this paper, the spatial-temporal dynamics of soil moisture content was investigated in an evergreen broad-leaved forest and a tea tree plantation in Ailao Mountains, which was dominated by Fagaceae (Castanopsis wattii and Lithocarpus xylocarpus). Soil moisture content was studied between January 2005 and December 2006 at different depths (from 0–150 cm) with a neutron probe. The results showed that mean soil moisture content in the evergreen broad-leaved forest was usually higher than in the tea tree plantation in the dry season, whereas it was lower than the tea tree plantation in the rainy season. In addition, mean soil moisture content was depth dependent, and in the 10–50 cm layer the spatial variability was due to the active root zone within this depth area in two types of land use. From 50–150 cm, the spatial variability was slightly increasing in the evergreen broad-leaved forest or relatively stable in the tea tree plantation. Our study also showed that soil moisture content was higher and more stable under the evergreen broad-leaved forest than the tea tree plantation, hence we stress that evergreen broad-leaved forest plays an important role in holding soil moisture. It is suggested that the protection of evergreen broad-leaved forest should be strengthened.

A Seasonal Prediction Model for the Summer Rainfall in Northeast China Using the Year-To-Year Increment Approach

Using the year-to-year increment approach, this study investigated the relationship of selected climatic elements with the increment time series of the summer rainfall between successive years in Northeast China, including the soil moisture content, sea surface temperature, 500 hPa geopotential height, and sea level pressure in the preceding spring for the period 1981–2008. Two spring predictors were used to construct the seasonal prediction model: the area mean soil moisture content in Northwest Eurasia and the 500 hPa geopotential height over Northeast China. Both the cross-validation and comparison with previous studies showed that the above two predictors have good predicting ability for the summer rainfall in Northeast China.

Soil and water conservation techniques in cashew grown along steep hill slopes

Cashew ( Anacardium occidentale L.), the highest foreign exchange earning perennial horticultural crop in India is generally grown as a rainfed crop along steep slopes of hills or on neglected land unsuitable for any other crop. In India, cashew experiences severe moisture stress from January to May, adversely affects its flowering and fruit set. In order to harvest the rainwater and to make it available to the cashew plant during critical period, an in situ soil and water conservation experiment was conducted at Directorate of Cashew Research, Puttur, Karnataka, India during 2003–2010. This experiment was laid along contour with five treatments namely, modified crescent bunds, coconut husk burial, reverse terraces, catch pits and control plot without any soil and water conservation. Among the treatments, modified crescent bund and coconut husk burial were superior. These two treatments reduced the annual runoff (22.3 and 20.4% of the annual rainfall compared to 36.9% of the annual rainfall in control), soil loss (47 and 49% of control) and nutrient loss. Also it increased the mean soil moisture content, growth of plants, yield of cashew (6.45 and 6.60 t/ha respectively compared to 4.88 t/ha in control for the first 5 harvests) and net profit from cashew garden (40% more than control). In addition to this, the groundwater level in nearby wells and ponds increased. Hence, the barren land even in steep slopes with proper soil and water conservation measures can be effectively utilized for cashew cultivation.

Sensitivity of quantitative precipitation forecast to soil moisture initialization and microphysics parametrization

In contrast to many other aspects of numerical weather prediction, quantitative precipitation forecasts did not gain much from a continuously improved physics over the past decades. A gap of knowledge remains as to how different processes contributing to the uncertainty in precipitation forecasts compare to each other. This research aims at gaining further insight into how two aspects influencing moist processes interrelate in atmospheric models. For this, high-resolution (3000 m) integrations with the non-hydrostatic Advanced Regional Prediction System were performed for two cases of extreme convection in Belgium, one driven by strong buoyancy and no vertical wind shear and the other driven by strong vertical wind shear and moderate buoyancy. Sensitivity experiments consisted of three integrations with different soil moisture initialization and three experiments with different size distribution assumptions in the microphysical parametrization scheme. The gain of spatially distributed soil moisture information was small in our simulations, but it was found important to have at least the mean soil moisture content right for the realistic simulation of cold-pool intensity. A mechanism, based on cold-pool and buoyancy interaction was proposed to explain the inverse relation between surface precipitation and soil moisture content. Changing the size distribution assumptions of the precipitating hydrometeors in the microphysics parametrization had a larger impact on the hydrometeor distribution than on surface precipitation. Weighting the size distribution assumptions of large hail to small graupel led to a poor representation of the general storm structure but did not affect the surface precipitation as much as was found in previous idealized studies. Copyright © 2010 Royal Meteorological Society

Comment on “Field observations of soil moisture variability across scales” by James S. Famiglietti et al.

[1] In a recent paper, Famiglietti et al. [2008] analyzed more than 36,000 ground-based soil moisture measurements to characterize soil moisture variability across spatial scales ranging from 2.5 m to 50 km. They concluded that the relationship between soil moisture standard deviation versus mean moisture content, sq (hqi), has a convex upward behavior with maximum values occurring at mean moisture contents of 0.17 cm cm 3 and 0.19 cm cm 3 for the 800-m and 50-km scale, respectively. On the basis of these data, they derived empirical relationships between the coefficient of variation and the mean soil moisture content in order to estimate the uncertainty in field observations of mean moisture content. The authors are to be commended for providing this valuable database to the scientific community. We agree with the authors that such data are important in improving our understanding about the importance of subgrid moisture variability in the parameterization and simulation of land surface processes. However, the authors limited themselves to an empirical description of the observed data by fitting exponential relationships to the mean moisture content versus coefficient of variation (CV) data. We feel that this is a missed opportunity and would like to argue that an interpretation based on established theories and concepts in soil hydrology and upscaling theories could provide alternative methods and new insights for interpreting such data sets. Specifically, it can be shown from soil physical concepts that for a homogeneous soil, the shape of the moisture retention curve can largely explain observed variations in surface soil moisture, at any specific observation scale. For heterogeneous soils, stochastic upscaling theories may be used to relate sq (hqi) to spatial variability in soil hydraulic properties. These theories can be used to predict sq (hqi) and to examine the sensitivity of this function with respect to soil hydraulic properties.

Reply to comment by H. Vereecken et al. on “Field observations of soil moisture variability across scales”

Reply to comment by H. Vereecken et al. on “Field observations of soil moisture variability across scales”

Hillslope scale soil moisture variability in a steep alpine terrain

Summary In this study we analyse space–time variability of soil moisture data collected at 0–6, 0–12 and 0–20 cm depth over three hillslopes with contrasting steep relief and shallow soil depth in the Dolomites (central-eastern Italian Alps). The data have been collected during two summer seasons (2005 and 2006) with different precipitation distribution. Analysis of soil moisture data shows that different physical processes control the space–time distribution of soil moisture at the three soil depths, with a marked effect of dew on the 0–6 cm soil depth layer. The range of skewness values decreases markedly from the surface to deeper layers. More symmetric distributions, characterised by relatively low skewness, are found for mid-range soil moisture contents, while highly skewed distributions (generally with more log–normal shape) are found at dry and wet conditions. Scatter plots drawn for the whole data set and the analysis of the correlation coefficients suggest a good persistence of soil moisture with depth: the highest degree of correlation was observed between data collected at 0–12 and 0–20 cm. Examination of correlation between soil moisture fields and topographical attributes shows that, notwithstanding the steep relief and the humid conditions, terrain indices are relatively poor predictors of soil moisture spatial variability. The slope and the topographic wetness index, which are found here the best univariate spatial predictors of soil moisture, explains up to 42% of the time-averaged moisture spatial variation. A negative relationship between the soil moisture spatial mean and the corresponding spatial standard deviation is found for mean water contents exceeding 25–30%, while a transition to a positive relationship is observed with drier conditions. Overall, soil moisture variability shows the highest values at moderate moisture conditions (23–29%) and reduced values for wetter and drier conditions for all depths. A negative linear relationship between mean soil moisture content and the coefficient of variation was observed. A soil moisture dynamics model proved to successfully capture the soil moisture variability at the hillslope scale. The simulated time series of hillslope-averaged soil moisture are in good agreement with the observed ones. Moreover, the model reproduces consistently the observed relationships between soil moisture spatial mean and corresponding variability.

Fertiliser induced nitrous oxide emissions during energy crop cultivation on loamy sand soils

Nitrous oxide (N 2O) fluxes from a loamy sand soil have been collected at an experimental field since 1999. To study the nitrogen (N) fertiliser induced emissions, annual crops and perennial plants received three different levels of N fertilisation: 0, 75, and 150 kg N ha −1. N 2O was measured by gas chromatography and closed chamber technique. Water content of the soil was determined gravimetrically and the soil content of mineral N by ion chromatography. The N 2O fluxes were below 30 μg N 2O m −2 h −1 during the winter season and varied from 10 to more than 1000 μg N 2O m −2 h −1 in the course of the vegetation season. N 2O emissions after N fertilisation were assigned to fertiliser induced emissions. High N 2O emissions at the end of the vegetation period are the result of increased mineralisation of soil organic matter. N 2O emissions from freeze–thaw cycles gave only a small contribution to the total annual N 2O emission budget from all blocks studied. Since the mean soil moisture content is very low (10%) and the water-filled pore space (WFPS) correlates negatively with N 2O emissions, nitrification is considered the main source for N 2O emissions. Evaluation of the data regarding dependence on fertilisation level indicates that N 2O fluxes are positively correlated to soil NO 3-N content. The N 2O fluxes from annual crop plots are higher than those from plots with perennial plants (grass, willow, poplar). The mean N 2O-N emission factor for fertiliser induced emissions from tilled soil is 1.0% in contrast to that of non-tilled soil with 0.7%. The mean fertiliser induced N 2O-N emissions, averaged over all crops and the total period of nine years, are in the range of 0.8 ± 0.2% of the N fertiliser applied.

Spatial variability of surface soil moisture content in a re-vegetated desert area in Shapotou, Northern China

Surface soil moisture content exhibits a high degree of spatial and temporal variability. The purpose of this study was (a) to characterize the spatial and temporal variations in soil moisture contents in the depths of 0–15 and 0–30 cm soil layer in an artificially re-vegetated desert area in Shapotou, China; and (b) to make inferences regarding the environmental factors that influence such variability. Over a period of 7-month experiment, soil moisture contents were measured with Time Domain Reflectometry (TDR) at an interval of every half a month at a grid space with 10 m intervals horizontally covering 4500 m 2 area, which include a topography from dune crest to dune hollow, and again to dune crest. Results indicated that the distribution of soil moisture at the grid scale was in a pattern of normal distribution with a significant temporal–spatial variability; the variability of soil moisture decreased with decreased mean soil moisture content, and it was higher in the depth of 0–15 cm than that in the depth of 0–30 cm. Relative elevation was a main influence factor of soil moisture variability especially after rainfall events and its influence was more tremendous in the depth of 0–30 cm than that in the depth of 0–15 cm. There was a consistent time-series pattern between the vegetation cover and the soil moisture content and the relative elevation, which increased under the rainstorm events. Soil texture (particle size distribution) had an opposite time-series pattern with relative elevation and vegetation cover, and the correlation was higher in the depth of 0–15 cm than that in the depth of 0–30 cm. We may conclude that local topography and vegetation cover were the main influencing factors of soil moisture variations immediately after the rainstorm events, whereas the soil texture was an important influencing factor as the soil dried up in the study area.

Evaluation of European Land Data Assimilation System (ELDAS) products using in situ observations

Three land-surface models with land-data assimilation scheme (DA) were evaluated for one growing season using in situ observations obtained across Europe. To avoid drifts in the land-surface state in the models, soil moisture corrections are derived from errors in screen-level atmospheric quantities.With the in situ data it is assessed whether these land-surface schemes produce adequate results regarding the annual range of the soil water content, the monthly mean soil moisture content in the root zone and evaporative fraction (the ratio of evapotranspiration to energy available at the surface). DA considerably reduced bias in net precipitation, while slightly reducing RMSE as well. Evaporative fraction was improved in dry conditions but was hardly affected in moist conditions. The amplitude of soil moisture variations tended to be underestimated. The impact of improved land-surface properties like Leaf Area Index, water holding capacity and rooting depth may be as large as corrections of the DA systems. Because soil moisture memorizes errors in the hydrological cycle of the models, DA will remain necessary in forecast mode. Model improvements should be balanced against improvements of DA per se. Model bias appearing from persistent analysis increments arising from DA systems should be addressed by model improvements.

Soil moisture variability across climate zones

Variability in soil moisture is controlled by temporal variability in atmospheric conditions and spatial variability in land‐surface conditions. Observations of soil moisture have revealed a variety of patterns – generally, in semiarid regions variance increased as mean soil moisture content increased, in humid regions variance decreased as mean soil moisture content increased, and in temperate regions variance peaked at intermediate moisture contents. We collected soil moisture data at Big Meadows, an upland wetland in Shenandoah National Park, Virginia, and we observed peak variance at intermediate moisture contents, consistent with other sites in temperate climate zones. A modified soil moisture dynamics model was used to examine how soil moisture patterns evolve through time, how topography, soil, and vegetation affect these patterns, and how the trends observed across climate zones can be explained. The trends observed relate to theoretical bounds on soil moisture distributions, i.e., the wilting point and the porosity.