Dynamics Of Soil Water Balance Research Articles

Biological soil crusts enhance the role of non-rainfall water in the water input in alpine sandy land ecosystems

• High amounts of non-rainfall water (10%–15% of water input) occur in the alpine sandy land. • Biological soil crusts increase the daily mean non-rainfall water amount by 23%–30%. • Biological soil crusts enhance non-rainfall water accumulation and dissipation rates by >20%. • The effects of soil crusts can be attributed to changes in soil physicochemical properties. • The principal source of non-rainfall water is atmospheric vapor (∼60%). Non-rainfall water originating from atmospheric and soil vapors is a major water source that supports dryland ecosystem functioning. The alpine sandy land ecosystem is fragile, where biological soil crusts develop widely on the soil surface and play a critical role in regulating surface hydrological processes. Yet, the effects of biological soil crusts on non-rainfall water in the alpine sandy land remain unclear. Therefore, we investigated the patterns and main sources of non-rainfall water under different biological soil crusts in the Qinghai–Tibet Plateau region during the growing season (May–September 2017). Micro-lysimeters were used to measure the amount of non-rainfall water in surface soil (0–10 cm) covered with moss and algae crusts in an interdune area. The results revealed that non-rainfall water occurred for at least 12 h·d −1 (7 p.m.–7 a.m.) and disappeared for 5 h (7 a.m.–12 a.m.). The daily mean non-rainfall water amount ranged between 0.324 and 0.426 mm. Differences in the physical and chemical properties of surface soil caused by biological soil crusts affected the accumulation and dissipation of non-rainfall water. The accumulation and dissipation rates of non-rainfall water under biological soil crusts were respectively 1.22–1.32-fold ( F = 8.01, P < 0.05) and 1.21–1.27-fold ( F = 8.86, P < 0.05) higher than those of bare sand. Biological soil crusts also increased the amount of total non-rainfall water by 23.41%–30.39% ( F = 5.367, P < 0.05), accounting for 2.4%–3.0% of the total water input. Atmospheric vapor condensation was the principal source of non-rainfall water (>60%). Nevertheless, biological soil crusts increased both atmospheric and soil vapor condensation by 29.44%–39.98% ( F = 12.45, P < 0.05) and 13.09–13.94% ( F = 5.91, P < 0.05), respectively. Although non-rainfall water contributed only 10%–15% of the total water input, it constituted a main water input to the ecosystem during the dry period of less rainfall (up to 20%, 19.72 vs. 95.72 mm). In conclusion, non-rainfall water, especially atmospheric vapor condensation, makes a non-negligible contribution to water input in the alpine sandy land ecosystem, for which biological soil crusts enhance the role of non-rainfall water in the water input in surface soil water balance dynamics.

Analysis of the spatio-temporal variability of soil water dynamics in an arid catchment in South Africa

The accurate quantification of soil water dynamics is critical as it is a key parameter in the soil-plant-atmosphere continuum. This study was conducted to analyse the spatio-temporal variability of soil water dynamics in dry areas. The Soil and Water Assessment Tool (SWAT) was used to estimate the dynamics of soil water balance. The model was calibrated and validated by the regionalization with physical similarity approach. Unlike the revap water (water drawn upwards from shallow groundwater tables), the soil water, percolation and lateral flow increased with precipitation. The Mann Kendall trend test also shows that there was no trend in both the annual and monthly soil water content (SWC) and percolation; however, there was a decreasing trend (1.091 mm per annum) in the revap water. The contribution of the revap water to evapotranspiration (ET) varied from 9% during summer to 32% during spring. The SWC also exhibited a higher spatial variation. Larger part of the catchment recorded a long-term annual mean soil water content varying between 0.1 and 0.2 mm mm−1. The soil water anomaly (SWA) consistently follows the trends of dry and wet seasons in the study area. Although the use of model-derived drought monitoring indices are relevant for farmers and decision makers in arid areas, it requires intensive verification over much larger scales to increase the reliability of model results.

Soil water balance dynamics under plastic mulching in dryland rainfed agroecosystem across the Loess Plateau

In rain-fed semiarid areas, low soil water availability is a major challenge constraining crop productivity and agricultural sustainability. Soil surface mulching with plastic film has been widely used to improve soil water availability in the Loess Plateau of China. However, a systematic assessment on soil water balance dynamics under plastic mulching is still lacking. We conducted a meta-analysis on plastic mulching observations across the Loess Plateau to quantify the intensity of evapotranspiration (ET), spatiotemporal dynamics of soil water storage (SWS), and annual soil water balance in the plastic mulching systems. The results indicated that compared with non-mulching, plastic mulching significantly enhanced ET by 2.6% across the entire dataset. The magnitude of intensified ET was strongly associated with mulching pattern, mean annual precipitation and nitrogen application. Plastic mulching led to a significant increase in SWS by 8.4% at 0−60 cm soil layer, yet a decrease by 0.8% at 60−200 cm layer over the growing season, comparing with non-mulching. Importantly, an effective water recovery effect was observed at the deep soil layer under plastic mulching, as evidenced by the significantly greater SWS (+30%) over the fallow season, in comparison with that of non-mulching. Nitrogen input level and mean annual precipitation proved to be the most important factors in driving SWS. As a result, crop yield and water use efficiency were substantially improved under plastic mulching, and such enhancements were the most pronounced under full plastic mulching and lower annual mean precipitation. Increased vegetation growth due to plastic mulching can turn to impact soil water dynamics in both growing and fallow seasons, but it did not disrupt the annual equilibrium of SWS. Particularly, more precipitation storage at deep soil layer during the non-growing season appeared to fully offset the extra water loss by enhanced ET. Our findings provide critical insight into the success of plastic mulching farming practice regarding field productivity and soil water sustainability.

Soil water balance dynamics on reclaimed mine land in the southwestern United States

Understanding the dynamics of soil water movement in arid and semi-arid environments is critical to successful reclamation of mined lands. Characteristics of applied topsoil impact soil water processes and long-term ecosystem health. The objective of this study was to better understand the soil water balance at a reclaimed mine in the southwestern United States through the investigation of soil hydraulic properties and subsequent one-dimensional water balance modeling. The study was conducted on a mine reclaimed using geomorphic principles. Complementary field and laboratory techniques were used to describe soil properties. Dry bulk density of topsoil at the mine sites increased with depth, while saturated hydraulic conductivity decreased with increasing bulk density. Two discrete one-dimensional models were created to investigate soil water dynamics and results indicate the importance of appropriately describing soil layering to create more accurate model predictions. In addition, results suggest that matric potentials during the study period were often too low for substantial plant growth. Models similar to those created in this study may be helpful in future assessment of seed germination on reclaimed lands as well as the implications that global climate change may have on reclamation strategies in the future.

Satellite soil moisture for agricultural drought monitoring: Assessment of the SMOS derived Soil Water Deficit Index

Abstract Drought is a major cause of limited agricultural productivity and of crop yield uncertainty throughout the world. For that reason, agricultural drought research and monitoring are of increasing interest. Although soil moisture is the main variable to define and identify agricultural drought, the actual soil water content is rarely taken into account because this type of drought is commonly studied using methodologies based on either climatological data or hydrological modeling. Currently, it is possible to use remote sensing to obtain global and frequent soil moisture data that could be directly used for agricultural drought monitoring everywhere. For example, the SMOS (Soil Moisture and Ocean Salinity) satellite was launched in 2009 and provides global soil moisture maps every 1–2 days. In this work, the Soil Water Deficit Index (SWDI) was calculated using the SMOS L2 soil moisture series in the REMEDHUS (Soil Moisture Measurement Stations Network) area (Spain) during the period 2010–2014. The satellite index was thus calculated using several approaches to obtain the soil water parameters and was compared with the SWDI obtained from in situ data. One approach was based directly on SMOS soil moisture time series (using the 5th percentile as an estimator for wilting point and the 95th percentile and the minimum of the maximum value during the growing season as estimators for field capacity). In this case, the results of the comparison were good, but the temporal distribution and the range of the index data were unrealistic. Other approaches were based on in situ data parameters and pedotransfer functions estimation. In this case, the results were better, and the satellite index was able to adequately identify the drought dynamics. Therefore, the final choice to apply the index in one particular site will depend on the availability of data. Finally, a comparison analysis was made with the SMOS SWDI and two indices (Crop Moisture Index, CMI, and Atmospheric Water Deficit, AWD) commonly used for agricultural drought monitoring and assessment. In both cases, the agreement was very good, and it was proven that SMOS SWDI reproduces well the soil water balance dynamics and is able to appropriately track agricultural drought.

On the importance of accurate depiction of infiltration processes on modelled soil moisture and vegetation water stress

AbstractThe description of soil moisture dynamics is a challenging problem for the hydrological community, as it is governed by complex interactions between climate, soil and vegetation. Recent research has achieved significant advances in the description of temporal dynamics of soil water balance through the use of a stochastic differential equation proposed by Laio et al. (2001). The assumptions of the Laio et al. model simplify the mathematical form of the soil water loss functions and the infiltration process. In particular, runoff occurs only for saturation excess, the probability distribution function (PDF) of which is well‐represented by a simple expression, but the model does not consider the limited infiltration capacity of soil. In the present work, we extend the soil moisture model to include limitations on soil infiltration capacity with the aim of understanding the impact of varying infiltration processes on the soil water balance and vegetation stress. A comparison between the two models (the original version and the modified one) is carried out via numerical simulations. The limited infiltration capacity influences the soil moisture PDF by reducing its mean and variance. Major changes in the PDFs are found for climates characterized by storms of short duration and high rainfall intensity, as well as in humid climates and in cases where soils have moderate permeability (e.g. loam and clay soils). In the case of limited infiltration capacity, modifications to the dynamics of soil moisture generally lead to higher amounts of vegetation water stress. An investigation of the role of soil texture on vegetation water stress demonstrates that loam soil provides the most favorable condition for plant‐growth under arid and semi‐arid conditions, while vegetation may benefit from the presence of more permeable soils (e.g. loamy sand) in humid climates. Copyright © 2009 John Wiley &amp; Sons, Ltd.

A stochastic approach for the description of the water balance dynamics in a river basin

Abstract. The present paper introduces an analytical approach for the description of the soil water balance dynamics over a schematic river basin. The model is based on a stochastic differential equation where the rainfall forcing is interpreted as an additive noise in the soil water balance. This equation can be solved assuming known the spatial distribution of the soil moisture over the basin transforming the two-dimensional problem in space in a one dimensional one. This assumption is particularly true in the case of humid and semihumid environments, where spatial redistribution becomes dominant producing a well defined soil moisture pattern. The model allowed to derive the probability density function of the saturated portion of a basin and of its relative saturation. This theory is based on the assumption that the soil water storage capacity varies across the basin following a parabolic distribution and the basin has homogeneous soil texture and vegetation cover. The methodology outlined the role played by the soil water storage capacity distribution of the basin on soil water balance. In particular, the resulting probability density functions of the relative basin saturation were found to be strongly controlled by the maximum water storage capacity of the basin, while the probability density functions of the relative saturated portion of the basin are strongly influenced by the spatial heterogeneity of the soil water storage capacity. Moreover, the saturated areas reach their maximum variability when the mean rainfall rate is almost equal to the soil water loss coefficient given by the sum of the maximum rate of evapotranspiration and leakage loss in the soil water balance. The model was tested using the results of a continuous numerical simulation performed with a semi-distributed model in order to validate the proposed theoretical distributions.

The Interplay between Transpiration and Runoff Formulations in Land Surface Schemes Used with Atmospheric Models

Abstract The Project for Intercomparison of Land-surface Parameterization Schemes (PILPS) has shown that different land surface models (LSMs) driven by the same meteorological forcing can produce markedly different surface energy and water budgets, even when certain critical aspects of the LSMs (vegetation cover, albedo, turbulent drag coefficient, and snowcover) are carefully controlled. To help explain these differences, the authors devised a monthly water balance model that successfully reproduces the annual and seasonal water balances of the different PILPS schemes. Analysis of this model leads to the identification of two quantities that characterize an LSM’s formulation of soil water balance dynamics: 1) the efficiency of the soil’s evaporation sink integrated over the active soil moisture range, and 2) the fraction of this range over which runoff is generated. Regardless of the LSM’s complexity, the combination of these two derived parameters with rates of interception loss, potential evaporation, ...