Surface Soil Water Content Research Articles

A Spatial Distribution Empirical Model of Surface Soil Water Content and Soil Workability on an Unplanted Sugarcane Farm Area Using Sentinel-1A Data towards Precision Agriculture Applications

Obtaining soil water content and soil workability data using remote sensing technology with passive sensors has some limitations due to cloud cover, cloud shadow, haze and smoke. This study proposes a method for computing soil water content and soil workability over large areas, faster and in near real-time based on Sentinel-1A (SAR) data. Sample data collected from sugarcane plantations in the Kediri and Sidoarjo districts in East Java, Indonesia, were used to develop a mathematical model of the proposed method using multi-polynomial regression. The performance indicators of the model (RMSE, MAPE and accuracy) were calculated with the results of RMSE = 0.213 and 0.250, MAPE = 16.39% and 18.79%, and accuracy = 83.6% and 81.2% for the training and testing models, respectively. The distribution of soil water content and soil workability can be computed and visualized using a spatial map. The future contribution of this work is to develop a decision support system for the selection of appropriate machinery for sugarcane field operations based on the principles of precision agriculture.

Surface soil water content as an indicator of Hass avocado irrigation scheduling

This study aims to determine whether Hass avocado irrigation can be triggered based on the surface soil water content (SSWC). To address this question, the soil water dynamics from three Hass avocado orchard plots located in Valle del Cauca (Colombia) was simulated using a model provided by Hydrus-1D software, which was calibrated through the genetic algorithm NSGA-II and validated using the soil matric potential measured at several depths at nine monitoring stations installed in the three plots. The influence of each superficial (0–5, 5–10, and 10–15 cm) and deeper (15–30 and 30–60 cm) available water (AW) computed from the simulated moisture on the SWB at 0–60 cm was estimated from the artificial neural network (ANN) trained weights. The most influential depth range was used to predict the soil water balance at 0–60 cm using ANN. For validation, the RMSE slightly increased regarding calibration, varying from 1.73 to 8.20, while the R2 value varied from 0.61 to 0.89 (P < 0.001 for all cases). The AW at 5–10 cm depth had a significant influence on SWB with an average relevance index of 2.87 (Wilcoxon signed-rank test P ≤ 0.05) for Laurentina farm. The AW at 0–5 cm depth had not significant influence on SWB with an average relevance index of 1.34 (independent group) and 0.97 (P < 0.05) for Laurentina and Poncena, respectively. The ANN model predicted the SWB with a RMSE no bigger than 13.76 mm. In conclusion, the SSWC at a depth of 5–10 cm can be used as an indicator for scheduling Hass avocado irrigation.

The Coupling of Soil Water and Leaf Phenology Observed by Satellite During Australian Bushfires in 2019–2020

AbstractWater and energy fluxes at the interface between the surface of the earth and the atmosphere depend strongly on soil moisture. Surface soil moisture (SSM) participates in natural phenomena such as evaporation, infiltration and runoff. From 2019 to 2020, bushfires in Australia caused changes in the runoff of surface water, the transpiration of vegetation, and evapotranspiration of the soil, subsequently affecting the soil water cycle. However, the dynamics of surface soil water content during large‐scale bushfires are still not completely understood. Here, we report on patterns of seasonal variation in SSM and vegetation leaf phenology in Australia, identified using L‐band radiometric measurements of soil moisture taken by the soil moisture and ocean salinity mission from 2011 to 2020. This study reveals a decrease in the leaf area index in affected regions of New South Wales, Victoria, Queensland, Western Australia, Australian Capital Territory, Northern Territory, and Tasmania. The observed seasonal variations in SSM are highly synchronous with those of leaf phenology in northern and northeastern Australia. However, the development of the leaf area lags behind that of SSM for up to 90 days in the southeastern subtropical woodlands. The time lag between leaf area development and SSM in the southwest is about 60 days. Bushfires can lead to the decrease of evapotranspiration hence shortening the time lag between SSM and leaf phenology. Our results offer insights into the variations in SSM during bushfires, the relationship between SSM and leaf phenology in Australia, and lay a foundation for improving models of ecological hydrology during bushfires.

Effects of grazing exclusion on soil infiltrability and preferential flow in savannah livestock grazing systems

AbstractAlthough the establishment of grazing exclosures is often considered an important strategy of reducing soil degradation, their effect on hydrological functions is still poorly understood, particularly in dry‐hot savanna systems with heavy livestock grazing. In addition, the different roles played by the herb roots and the niche differentiation of woody plant roots induced by the grazing and exclosure in soil hydrological functions are still unclear. This study aimed to evaluate the effect of exclosure management on hydrological functions and services and assess the role of different functional vegetation types in improving these functions and services. The experiments were conducted in the continuous grazing areas and exclosure areas in a savanna ecosystem in Yuanjiang, southwest China. The root biomass of herb and woody plants, soil physical properties, water infiltration, and preferential water flow were measured in each study site. The results showed a significant improvement in soil physical properties with more termite holes, lower soil bulk density, and higher total and non‐capillary soil porosity in exclosure areas compared with grazing ones. As a result, the initial and average water infiltration, and preferential flow significantly increased by 132.76%, 185.31%, and 30.29%, respectively, in exclosure areas compared with the grazing ones. The results also showed that the exclosure significantly improved the soil surface water content by increasing the root biomass of herb and woody plants in the shallow soil layers. Herb plants probably improved water infiltration and insulated evaporation, while woody plants improved lateral preferential water flow paths and accelerated the water exchange between vertical and horizontal soil layers, thereby improving the water availability for different plants. This study demonstrated that the exclosure‐induced restoration and niche differentiation of herb and woody plants, coupled with improved soil structure in exclosures, could promote hydrological function and services and improve water management in savanna systems. Therefore, the grazing exclosures could be expanded periodically and cautiously to prevent soil degradation in the present savanna systems.

Hydraulic performance of mole drains and validation of steady-state drainage spacing equations for Mollisols

Central Santa Fe (Argentina) is a low-gradient region with impaired natural drainage. Extreme rainfall events are increasingly common and cause significant economic losses to agriculture. There is a growing interest in the use of mole drainage as a cost-effective strategy to mitigate such impacts. However, there is no information available that assists with mole drainage design, installation and maintenance, or the field assessment of a system’s hydraulic performance. This work was conducted with the dual objective of evaluating the hydraulic performance of an existing mole drains system and validating Hooghoudt’s steady-state drainage spacing equation for Mollisols. Three treatments representing different hydrologic conditions were tested; namely: (T1) rainfall of 360-min duration and intensity of 23 mm h-1, (T2) surface water ponding achieved through rainfall intensity of 50 mm h-1 and water depths between 50 and 100 mm, and (T3) similar surface water ponding conditions to treatment T2, but achieved through a rainfall intensity of 65 mm h-1 and either one (T3A) or two (T3B) sequential rainfall events. Following application of water, drainage commenced at 270 and 21 min for T1 and T2, and at 40 and 30 min for T3A and T3B, respectively. Mean drained depths were 1 and 3 mm for T1 and T2, respectively. For T3A, the mean drained depth was about one-third that measured for T3B (2.5 vs. 8.5 mm). Under a dry antecedent soil moisture condition, and rainfall intensity of 23 mm h-1, downward water movement was better described by piston flow. As surface water depth and soil water content increased, water flowed preferentially through the fissures and leg slots created by the mole plough implement at installation. Soil fissuring increased field hydraulic conductivity by factors between approximately three and ten. A 4 m mole drains spacing system was considered to be appropriate for managing excess water in the studied soil type. If the contribution of soil fissures to the field hydraulic conductivity can be accounted for, the Hooghoudt’s equation applied to two-layered soils may be used with confidence to help optimise the design of mole drainage systems for Mollisols. Application of this numerical approach, however, will require that the resultant spacing between mole drains be increased by about 30–40 %. Such an allowance will reduce installation costs and will not compromise the hydraulic efficiency of the drainage system.

Effects of Underground Coal Mining on Soil Spatial Water Content Distribution and Plant Growth Type in Northwest China.

The impact of coal mining subsidence on surface ecology involves the influence of several ecological elements such as water, soil, and vegetation, which is systematic and complex. Given the unclear understanding of the synergistic change patterns of the water–soil–vegetation ecological elements in the influence of coal mining in the west, this paper investigates the impact of coal mining on the surface ecology, especially the distribution of soil water content (SWC). In 2020, this study collected 3000 soil samples from 60 sampling points (at depth of 0–10 m) and tested the SWC. All samples come from three different temporal and spatial areas of coal mining subsidence in the desert mining area of Northwest China where soil types are mainly aridisols. At the same time, the interactions among deep SWC and surface soil physical and chemical properties, surface SWC and soil fertility, and pH were analyzed. The spatial variability of soil moisture is reflected by kriging interpolation, and SWC values at different depths are predicted as a basis for monitoring the environmental impact of different coal mining subsidence years. The research has shown that the ground subsidence leads to a decrease in SWC value and changes in surface soil pH, physical and chemical properties, and covering vegetation, which have occurred from the beginning of coal mining. The impact of coal mining on the SWC of the unsaturated zone is mainly at the depth of 0–6 m, where SWC is not directly related to the nutrient content of the surface soil. The overall settlement of the ground will stir up simultaneous decline in the quality of deep SWC and topsoil. The findings of this investigation suggest that changes in the soil structure caused by coal mining subsidence are the key factor in SWC loss. Timely monitoring and repairing 0–6 m ground fissures, as well as selecting shrubs on the surface is the best choice for the restoration of the ecological environment and prevention of soil erosion in this area.

Surface Soil Water Content Before and After Coal Mining and its Influencing Factors—A Case Study of the Daliuta Coal Mine in Shaanxi Province, China

Surface Soil Water Content Before and After Coal Mining and its Influencing Factors—A Case Study of the Daliuta Coal Mine in Shaanxi Province, China

Does deadwood moisture vary jointly with surface soil water content?

AbstractDeadwood moisture plays a major role in regulating deadwood decomposition rates and may also affect forest microclimate. Despite this, the temporal variability of deadwood moisture at 15‐min time scales remains relatively unknown because techniques for using high‐frequency sensors for tracking moisture at appropriate spatial and temporal intensities have been lacking. We installed a high‐density sensor array in and around a downed log to gain a detailed assessment regarding the temporal variation of volumetric water content at multiple locations within one downed dead log, the source snag, and the surrounding soil. We also measured micrometeorological variables near the log in order to predict variability of the deadwood moisture. We found that the deadwood varied in similar fashion as the soil moisture, and that this similarity allowed us to make accurate predictions of deadwood moisture using micrometeorological data and soil moisture. The primary driver of deadwood moisture was rainfall; however, diurnal cycles of subcanopy humidity and temperature seemed to cause variation in the deadwood moisture between rain events. Our findings highlight the need for applying similar techniques to a variety of forest types, deadwood types, and different forest management strategies to gain a broader understanding of high‐frequency deadwood moisture dynamics and their feedbacks with ecosystem processes, like decomposition and forest fire hazards.

Spatial and temporal characteristics of surface soil moisture in a disturbed coal mining area of Chinese Loess Plateau.

Soil water content is an important variable in hydrology and many related disciplines. It affects runoff from precipitation, groundwater recharge, and evapotranspiration. This research used the coal mining area of the Changhe River Basin in the Loess Plateau as a study and using SAR (Synthetic Aperture Radar) data, the surface soil water in 24 days (From Jan 25, 2018 to Dec 10, 2019) was estimated using a radar signal change detection algorithm. The temporal and spatial variation characteristics of surface soil water inside and outside the disturbed area were compared and analyzed. An empirical orthogonal function (EOF) analysis method was used to analyze the potential temporal and spatial variation of surface soil water, and to detect the regional soil water variation under coal mining disturbances to better understand the different potential modes of spatial variation of soil water in the unobserved time. The results showed that the average surface soil water content in the study area changed with season, showing a dry-wet-dry variation. Moreover, it was significantly affected by precipitation factors, and its response to precipitation had a hysteresis effect. From the perspective of spatial variation, the influence of coal mining disturbance on surface soil moisture was not obvious. From the perspective of time series change, moving from wet to dry conditions, the soil in the disturbed area dried faster than the soil in the undisturbed area after soil wetted. When moving from drying to wetting, the soil in the disturbed area was quickly wetted. The EOF analysis showed that most observed spatial variability of soil moisture was stable in time. The study was conducted in a disturbed area and an undisturbed area for single EOF analysis, and the results showed that the EOF mode of the disturbed area was closer to that of the whole study area. By comparing the two subregions and the entire study area, it was found that the changes of correlation values were related to soil texture, bulk density, altitude and slope, indicating that the soil texture of the two subregions may be different at different elevations, and may also be related to the change of the original soil structure in the disturbed area. Overall, the EOF mode of the disturbed area determined the EOF mode of the entire study area.

Towards moss-dominated biocrust effects on soil temperature across seasons in drylands: Insight from continuous measurements of soil thermal properties and solar radiation

Globally widespread, biocrusts form a “living skin” on most dryland soils, helping govern fundamental ecosystem functions, particularly water and heat balances in drylands. Nevertheless, the underlying mechanisms of biocrust effects on topsoil thermal properties and temperature (T) are still unclear. In this study, we continuously measured thermal properties of moss-dominated biocrusts and bare soil (aeolian sand) at 1 cm depth by utilizing heat pulse probes for one year on the Chinese Loess Plateau. The surface soil water content (θ), net all-wave radiation (Jn), surface albedo (α), heat flux (G), and other properties were further measured to analyze their connections with soil thermal properties. Our results indicated that biocrusts decreased (F ≥ 1.91, P ≤ 0.031) heat capacity (C), thermal conductivity (λ), and thermal diffusivity (κ) by 1.6% (1.36 vs. 1.38 MJ m−3 K−1), 11.6% (0.62 vs. 0.69 W m−1 K−1), and 8.7% (0.62 vs. 0.69 × 10−7 m2 s−1) on average, respectively, in contrast to bare soil. Moreover, biocrusts variously regulated soil thermal properties in dry and wet seasons owing to the influences of rainfall events and θ. As compared with bare soil, the C, λ, and κ of biocrusts in dry season (Nov.–Apr.) were decreased by 5.7%, 19.0%, and 12.2%, respectively; while only the C was increased by 2.2% by biocrusts in wet season, but the λ and κ of biocrusts were similar to that of bare soil. Furthermore, biocrusts increased θ both in dry (by 5.0 times) and wet (by 3.5 times) seasons as compared with bare soil. Especially, biocrusts decreased α by 32.1% (0.19 vs. 0.28) and G (at 8 cm depth) by 20.0% (0.8 vs. 1.0 W m−2 s−1), and increased Jn by 30.1% (73.0 vs. 56.1 W m−2) in comparison to bare soil. Lastly, combining with the higher θ and lower α as well as the lower soil thermal properties, biocrusts greatly increased T by 1.7 ℃ (up to 4.5 °C; P < 0.001) on average. In conclusion, moss-dominated biocrusts have great regulating effects on surface soil thermal properties and T, and these effects are mostly attributed to their lower bulk density and α but higher porosity and water-holding capacity, which further change surface θ and T regimes and play a vital role in soil water and heat balances as well as other critical processes in drylands.

Limitations and the value of land surface models and their role in remote sensing

ABSTRACT This essay distills the thoughts of the author who has spent over 30 years developing land surface models, including those for use in remote sensing. The latter includes models whose function is to serve both as a mathematical interface between remotely sensed optical/thermal measurements and land surface evapotranspiration and soil water content and as description of the physiological behaviour of plants and their interaction with atmosphere and soils.

Spatial variability of surface soil water content and its influencing factors on shady and sunny slopes of an alpine meadow on the Qinghai–Tibetan Plateau

Soil moisture is a vital factor that influences soil characteristics and vegetation distributions in alpine meadow regions. Previous studies have mainly focused on the effects of alpine gradient change, climate change, and human activities on soil hydrological characteristics and vegetation distributions worldwide. However, the spatial variability of the surface soil water content and its influencing factors between shady and sunny slopes in alpine regions are seldom conducted, especially on the alpine meadow regions of the Qinghai–Tibetan Plateau. Based on soil sample collection, combined with statistical, geostatistical, stepwise regression, and geographical detector analysis, this study explores the spatial variability of the surface soil water content and its influencing factors on the shady and sunny slopes of the Mila Mountain pass area on the Qinghai–Tibetan Plateau. Results show that the average soil water content of various depths ranges from 23.14% to 35.52%. The soil moisture content of different soil layers on the shady and sunny slopes shows moderate variability. On the sunny slope, the spatial distribution of the soil water content in different soil layers is mostly patched and banded, while the soil water content on the shady slope shows patchy distribution. The correlation analysis shows that the soil water content of each soil layer has a very significant correlation (P < 0.01). Stepwise regression analysis shows that the main influencing factors of water content of different soil layers on the shady and sunny slopes are soil physical property indexes. Meanwhile, the vegetation coverage factor has a higher explanatory power except the physical indexes on the shady and sunny slopes. The index interaction detection shows interaction among all the evaluation indexes. On the shady slope, all the interactive combinations of the evaluation indexes in each soil layer shows a double-factor enhanced relationship. On the sunny slope, 60% of the interactive combinations of the evaluation indexes show a double-factor enhancement relationship, but 40% of the interactive combinations show a nonlinear enhancement relationship. This study contributes to knowledge on the variability of surface soil water content and its influencing factors on the shady and sunny slopes in the alpine meadow of the Tibetan Plateau, and provides guidance on artificial vegetation restoration and soil structure analysis in the alpine regions.

Evaluating three measurement methods of soil ground heat flux based on actively heated distributed temperature sensing technology

Soil ground heat flux (G0) is a key parameter in analyzing soil-atmosphere interaction. It is not only an indispensable component in the surface energy balance, but also an essential boundary condition in the coupled hydro-thermal-mechanical (HTM) numerical analysis of soil-atmosphere interaction. In this study, three G0 measurement methods (gradient method, calorimetric method and combination method) are evaluated based on the measurements (temperature, volumetric water content and thermal conductivity) using the actively heated distributed temperature sensing (AH-DTS) technology. In addition, through a series of in-situ tests, the feasibility of these methods is verified, and their applicability and application potential are compared and analyzed. The results indicate that the G0 values measured by the three AH-DTS technology-based methods are in the same order of magnitude, indicating that the three methods are feasible. Among them, the G0 measured by the gradient method is an instantaneous value which is closely related to the soil surface water content, while the G0 measured by the calorimetric method and combination method is an average values over a period of time. The gradient method is applicable for all types of soil, including the frozen soils. The calorimetric method and the combination method are suitable for soils of which water content can be measured by the AH-DTS sensor. It is recommended that an appropriate G0 measurement method based on the AH-DTS technology be selected according to the site situations.

Physiological and climate controls on foliar mercury uptake by European tree species

Abstract. Despite the importance of vegetation uptake of atmospheric gaseous elemental mercury (Hg(0)) within the global Hg cycle, little knowledge exists on the physiological, climatic, and geographic factors controlling stomatal uptake of atmospheric Hg(0) by tree foliage. We investigate controls on foliar stomatal Hg(0) uptake by combining Hg measurements of 3569 foliage samples across Europe with data on tree species' traits and environmental conditions. To account for foliar Hg accumulation over time, we normalized foliar Hg concentration over the foliar life period from the simulated start of the growing season to sample harvest. The most relevant parameter impacting daily foliar stomatal Hg uptake was tree functional group (deciduous versus coniferous trees). On average, we measured 3.2 times higher daily foliar stomatal Hg uptake rates in deciduous leaves than in coniferous needles of the same age. Across tree species, for foliage of beech and fir, and at two out of three forest plots with more than 20 samples, we found a significant (p&lt;0.001) increase in foliar Hg values with respective leaf nitrogen concentrations. We therefore suggest that foliar stomatal Hg uptake is controlled by tree functional traits with uptake rates increasing from low to high nutrient content representing low to high physiological activity. For pine and spruce needles, we detected a significant linear decrease in daily foliar stomatal Hg uptake with the proportion of time during which water vapor pressure deficit (VPD) exceeded the species-specific threshold values of 1.2 and 3 kPa, respectively. The proportion of time within the growing season during which surface soil water content (ERA5-Land) in the region of forest plots was low correlated negatively with foliar Hg uptake rates of beech and pine. These findings suggest that stomatal uptake of atmospheric Hg(0) is inhibited under high VPD conditions and/or low soil water content due to the regulation of stomatal conductance to reduce water loss under dry conditions. Other parameters associated with forest sampling sites (latitude and altitude), sampled trees (average age and diameter at breast height), or regional satellite-observation-based transpiration product (Global Land Evaporation Amsterdam Model: GLEAM) did not significantly correlate with daily foliar Hg uptake rates. We conclude that tree physiological activity and stomatal response to VPD and soil water content should be implemented in a stomatal Hg model to assess future Hg cycling under different anthropogenic emission scenarios and global warming.

Effects of Irrigation Strategy and Plastic Film Mulching on Soil N2O Emissions and Fruit Yields of Greenhouse Tomato

Agriculture is a major source of global greenhouse gas emissions. Approximately 1/3 of vegetables in China are produced in greenhouses. However, the effects of different irrigation strategies and plastic film (PF) mulching combinations on N2O emissions and tomato fruit yields in greenhouses are unclear. The aims of this study were to explore the effects of micro-sprinkler irrigation under plastic film (MSPF), drip irrigation under plastic film (DIPF) and micro-sprinkler irrigation (MSI) on the soil nutrients, enzyme activity, nirS-type denitrifying bacterial community, N2O emissions and fruit yields of tomato. The results showed that MSPF could improve the uniformity of soil water distribution and surface (0–40 cm) soil water content. Film mulching could increase soil temperature at depths of 5–25 cm. Both MSPF and DIPF increased microbial nitrogen, promoted the activity of rhizosphere soil urease and leucine aminopeptidase, changed the community of denitrifying bacteria, accelerated the turnover of soil nutrients and improved yield and water use efficiency. PF mulching had a greater impact on the nirS-type denitrifying bacterial community when compared to irrigation strategy. We conclude that MSPF can be used to configure commercially available installation and operation. The comprehensive benefit of MSPF treatment is that it is more profitable than that of DIPF.

Applications of a thermal-based two-source energy balance model coupled to surface soil moisture

The two-source energy balance (TSEB) model using the land surface temperature (LST) as a key boundary has been used to estimate land surface evapotranspiration (ET) over various landcovers and environmental conditions. However, LST may not always provide an adequate boundary condition to simultaneously constrain the soil evaporation and plant transpiration especially under water limited conditions. A refinement to TSEB model by coupling surface soil moisture information to derive the soil and vegetation component temperatures and a new transpiration algorithm was developed (TSEB-SM). The TSEB-SM model was evaluated under a wide range of surface soil water content values and vegetation cover conditions and compared with the performance with the original TSEB model using only LST. While the results showed that the TSEB-SM model produced similar agreement in the fluxes and ET as the original TSEB for the cropland and grassland sites, TSEB-SM model performance was notably improved at the shrub-forest and desert steppe sites with a significant reduction in mean absolute percent difference in daily ET from nearly 65% to 25% and from approximately 50% to 40%, respectively. It also appears to be more reliable in partitioning ET into soil evaporation and plant transpiration when compared to the partitioning using the water use efficiency (uWUE) approach in combination with the eddy covariance measurements. With satellite data such as MODIS LST and leaf area index, and surface soil moisture retrievals from microwave satellite observations, the TSEB-SM model may potentially be a more reliable tool for monitoring regional ET partitioning under sparse canopy cover conditions.

Substrate and Topsoil Impact on Soil Water and Soil Temperature in Arctic Diamond Mine Reclamation

Soil properties in the Arctic are insufficiently explored and documented, particularly extensive monitoring of soil water and soil temperature over a period of time. Soil water and soil temperature are critical for understanding land surface and atmosphere interactions and are considered key factors for revegetation during mine reclamation. This study assessed how substrate and topsoil influenced soil temperature and soil water content at a reclaimed diamond mine in the Northwest Territories of Canada. Three substrates (crushed rock, processed kimberlite, and lake sediment) with and without topsoil were used. Mean air temperature changed little from year to year, although summer temperature showed a slightly increasing trend. Both annual and summer precipitation sharply declined over time. Soil water was influenced more by substrate than by placing 10 cm of topsoil on it. Processed kimberlite had greater water retention characteristics and water content than lake sediment and crushed rock substrates (significantly). Surface soil water content was lower with than without topsoil, suggesting that 10 cm of topsoil was not enough to influence it. Soil temperatures were not influenced by either substrate or topsoil. This study suggests processed kimberlite could be used as a substrate component for water and temperature management during reclamation of this extreme environment.

Estimate Cotton Water Consumption from Shallow Groundwater under Different Irrigation Schedules

Shallow groundwater is considered an important water resource to meet crop irrigation demands. However, limited information is available on the application of models to investigate the impact of irrigation schedules on shallow groundwater depth and estimate evaporation while considering the interaction between meteorological factors and the surface soil water content (SWC). Based on the Richards equation, we develop a model to simultaneously estimate crop water consumption of shallow groundwater and determine the optimal irrigation schedule in association with a shallow groundwater depth. A new soil evaporation function was established, and the control factors were calculated by using only the days after sowing. In this study, two irrigation scheduling methods were considered. In Method A, irrigation was managed based on the soil water content; in Method B, irrigation was based on the crop water demand. In comparison with Method B, Method A was more rational because it could use more groundwater, and the ratio of soil evaporation to total evapotranspiration was low. In this model, the interaction between meteorological factors and the SWC was considered to better reflect the real condition; therefore, the model provided a better way to estimate the crop water consumption.

Evaluation of Soil Water Content Using SWAT for Southern Saskatchewan, Canada

Soil water content (SWC) is one of the most important hydrologic variables; it plays a decisive role in the control of various land surface processes. We simulated SWC using a Soil and Water Assessment Tool (SWAT) model in southern Saskatchewan. SWC was calibrated using measured data and Soil Moisture Active Passive (SMAP) Level-4 for the surface (0–5 cm) SWC for hydrological response units (HRU) at daily and monthly (warm season) intervals for the years 2015 to 2020. We used the SUFI-2 technique in SWAT-CUP, and observed daily instrumented streamflow records, for calibration (1995 to 2004) and validation (2005–2010). The results reveal that the SWAT model performs well with a monthly PBIAS &lt; 10% and Nash–Sutcliffe efficiency (NS) and R2 ≥ 0.8 for calibration and validation. The correlation coefficient between ground measurement with SMAP and SWAT products are 0.698 and 0.633, respectively. Moreover, SMAP data of surface SWC coincides well with measurements in terms of both amount and trend compared with the SWAT product. The highest r value occurred in July when the mean r value in SWAT and SMAP were 0.87 to 0.84, and then in June for r value of 0.75. In contrast, the lowest values were in April and May (0.07 and 0.04, respectively) at the beginning of the growing season in southern Saskatchewan. Furthermore, calibration in the SWAT model is based on a batch form whereby parameters are adjusted to corresponding input by modifying simulations with observations. SWAT underestimates the abrupt increase in streamflow during the snowmelt months (April and May). This study achieved the objective of developing a SWAT model that simulates SWC in a prairie watershed, and, therefore, can be used in a subsequent phase of research to estimate future soil moisture conditions under projected climate changes.

Rainfall-runoff characteristics and their threshold behaviors on a karst hillslope in a peak-cluster depression region

Water balance characteristics and rainfall-runoff relationships of karst slope, are poorly understood worldwide, even though karst landscapes occupy 10–15% the planet’s land surface. Dynamic hydrological responses were monitored for 43 rainfall events on a karst slope in southwest China over two years (2018–2019). The responses included surface, subsurface, and epikarst seepage runoff (abbreviated as SR, SSR, and ESR, respectively) and soil water content at different depths (10 cm, 30 cm, and the soil-epikarst interface) in twelve plots (5 m× 20 m, total 1200 m2). Results showed that: (1) The hillslope-scale SR, SSR, and ESR coefficients were 2.2% (0.4%–5.2%), 3.8% (0.2%–12.4%), and 31.2% (0.6%–89.1), respectively. SR and SSR were relatively rare and of short duration, while ESR was a crucial component of the karst hillslope water balance and its duration was longer, demonstrating the critical role of epikarst zone in regulating flow functions such as water storage and release; (2) Soil depth exerted the greatest direct effect on SR, which increased as soil deepened. Factors controlling the rainfall-SSR response were difficult to identify. They require other geophysical exploration methods; (3) Threshold-like runoff responses to rainfall inputs were observed on karst slope, and the rainfall depth (P) runoff initiation thresholds for SR and SSR were 36±2 mm and 43±7 mm, respectively. The strength of the threshold-like input–output relationships was slightly greater when the P + ASI (antecedent soil water content index) was used as the hydrological input variable rather than without consideration of ASI. The differing shapes of nonlinear hydrological behaviours, such as the ‘hockey stick’, ‘heaviside’ function, or the sigmoid function were detected in karst slope. This suggests karst hydrological system complexity. Threshold values should be determined according to the shapes of nonlinear hydrological behaviours. These results extend the understanding of karst hydrological processes.