Function Of Soil Moisture Content Research Articles

Random forest approach to estimate soil thermal diffusivity: Evaluation and comparison with traditional pedotransfer functions

Pedotransfer functions (PTFs) are widely used in science and engineering to calculate soil thermal diffusivity (κ) as a function of soil moisture content and other soil physical properties. However, available data on κ are rather scarce and already developed PTFs suffer from significant uncertainties in applicability and performance. Few studies attempted to systematically review and evaluate these PTFs with large dataset of κ. The objectives of this study were to (1) review and collate currently available PTFs for κ; (2) compile a κ dataset to evaluate performance of these PTFs, (3) build a machine learning (ML) (i.e., random forest-RF) model with three classes of soil physical properties to determine soil physical properties most appropriate to use as predictors for calculating κ, and (4) compare the RF modelling with the traditional PTFs. The correlation coefficient (r), centered root-mean-square (E'), and standard deviation (SD) were used to evaluate the performance of the above PTFs. A total of nine PTFs were synthesized and assessed with a compiled dataset consisting of 998 measurements from 106 soils with a wide range of textures. In general, the PTFs of Lukiashchenko and Arkhangelskaya (2018) (LA2018–1 and LA2018–2) perform the best. While the quadratic equation of Mady and Shein (2018) (MS2018–1 and MS2018–2) showed better performance for coarse and medium textured soil. However, the overall performance of the nine PTFs for predicting κ was not as accurate as RF. RF can satisfactorily calculate κ taking into account sand, silt, clay contents, and soil moisture content as predictors.

New insights into the parameterization of the dry surface layer and its hydrogeochemical mechanism: An experimental study

Knowledge of the parameterization of the dry surface layer (DSL) is essential for evaluating near-surface water flow and water balance in arid and semi-arid areas. Existing studies have parameterized DSL thickness and vapor flow as functions of the soil moisture content (SMC) in the surface layer to predict soil evaporation. However, hydrochemical processes related to DSL development have been ignored, including changes in hydrochemistry, the underlying hydrochemical mechanism, and the role of dissolved substances in the DSL development. Herein, we performed a series of soil evaporation experiments for 260 days and explored the factors influencing DSL development (e.g., soil texture, atmospheric temperature, SMC, solutes). Evaporation experiments were performed using silty loess, sandy loess, and fine sand with a 60-cm water table. Results showed that the cumulative evaporation of silty loess, sandy loess, and fine sand over the experimental period were 1,391.52, 460.10, and 185.53 mm, respectively, which determined by the maximum height of liquid flow continuity. The content of total dissolved solids (TDS) and major ions at the surface soil were significantly higher than the values at deep depths of 5‒55 cm, which largely depend on evaporative water loss. Evolutionary trends of chemical facies in sand media along the liquid water migration were from HCO3-Ca type to SO4·Cl-Na type. This was attributed to mineral dissolution at a depth of 5–55 cm and their transport with liquid water, resulting in the precipitation of salt crystals at the surface soil. Furthermore, a consolidated DSL with a thickness of 3.0–3.5 cm in the sandy loess and a loose DSL with a thickness of 1.5–2.0 cm in fine sand were observed at the end of the experiments. The accumulation of solutes at the surface leads to a reduction in effective porosity and the aggregation of soil particles during continuous drying, which facilitates the consolidation of DSL in sandy loess. This overestimated the DSL thickness, resulting in a difference between the experimental and predicted evaporation rates by Fick's law. Overall, these results highlight the limitations of considering DSL thickness as a function of SMC only, providing new insights into hydrochemical processes and dissolved solutes involving DSL parameterization during continuous soil drying.

The 2022 Pacheco Silva lecture: The influence of residual loads on pile foundation behavior

Residual loads can affect the load transfer and the settlement-induced in-service loadings, although they do not alter the bearing capacity. When residual loads are present and not measured or evaluated, the settlement estimate is greater than predicted if these loads are known. Residual loads can be measured when the pile instrumentation is nullified before pile installation, in the case of displacement piles, or before the first loading in non-displacement piles, such as bored cast-in-place piles, continuous flight auger piles, and micro-piles. In the case of underpinning foundation and piled raft, when the loading transfer is shared by the original and new foundation, or by the piles and the raft, it is essential to know the stiffness of each foundation element to estimate the load partition. If residual loads are present, pile stiffness is greater than when not considered in the design. The paper revisits this theme of practical relevance. A historical review of the most relevant research involving pile residual load measurements, pile loading tests including the interpretation of residual loads locked at a pile toe, and a new procedure for residual loads prediction are provided. A comparison is made of the experimental residual loads observed in some of the instrumented cases and the values estimated with the suggested procedure. The development of residual loads at the pile toe as a function of the toe resistance to total capacity ratio is very similar to the variation of the soil density as a function of soil moisture content in soil compaction.

An improvement in drainage flow equation of EPA SWMM green roof module.

Green roofs are among the important green infrastructures which decrease the negative impacts of urbanization. In this study, the green roof modeling capability of U.S. Environmental Protection Agency Storm Water Management Model (EPA SWMM) is evaluated and the modeling methods used in EPA SWMM, which need improvements, are determined. In particular, the drainage flow, which is originally calculated with Manning's equation in SWMM, is improved by introducing the drainage mat void thickness and adapting a new value for the exponential coefficient of depth in the equation. In addition, the capability of the percolation equation is further investigated, i.e., the value of the coefficient of the exponential function of soil moisture content that considers the percolation through the soil layer is determined for different substrates using the existing unsaturated hydraulic conductivity and soil moisture content data from steady-state tests. A comparison of the improved equation of drainage flow results with the existing experimental data shows that the improved equation represents the drainage flow more accurately than the one used in EPA SWMM.

Accuracy and precision of the cosmic‐ray neutron sensor for soil moisture estimation at humid environments

AbstractThe accuracy and precision of the cosmic‐ray neutron sensor (CRNS) neutron count and soil moisture estimate are affected differently by distinct neutron moderating factors. Moreover, whereas the accuracy can be improved by correcting for different hydrogen pools, the precision can only be improved by increasing the surface area of the CRNS sensors or by increasing the integration time. To date, the effects of different neutron moderating factors on CRNS accuracy and precision are not completely understood. We used data from three agricultural and low biomass sites located within a few kilometres distance from each other in South England. We developed an extended version of the COsmic‐ray Soil Moisture Interaction Code (COSMIC), which included the effects of relevant neutron moderating factors on the neutron counts. With sensitivity analysis, we found atmospheric pressure and soil moisture content to be most influential on neutron count accuracy and precision. These two factors were, respectively, seven and four times more important than soil bulk density, lattice water and soil organic matter. Above ground biomass was substantially less influential compared to these variables. However, because the three sites had similar soil organic matter and meteorology, calibration results showed that differences between sites could be mostly explained by differences in above ground biomass and to a lesser extent intercepted water. The neutron count differences due to above ground biomass corresponded with substantial soil moisture estimate differences up to ; a significant effect on soil moisture accuracy. The precision of the soil moisture estimate was 10 times more sensitive to soil moisture than other factors and was therefore mostly a function of soil moisture content itself. The neutron count integration times required to obtain a soil moisture precision were typically less than a day. Our results are indicative for other humid, temperate, agricultural sites.

Validation and analysis of Terra and Aqua MODIS, and SNPP VIIRS vegetation indices under zero vegetation conditions: A case study using Railroad Valley Playa

Spectral vegetation index (VI) time series data from coarse resolution satellite sensors, such as the Moderate Resolution Imaging Spectroradiometer (MODIS), have been utilized in studying vegetation dynamics. Numerous studies have evaluated how well VI products capture variations in vegetation biophysical or physiological conditions. Equally important is to evaluate VI products over “zero vegetation” surfaces consisting of soils, litters, and/or rocks, as they define the lower bound for vegetation detection. VIs, however, vary over zero vegetation surfaces as a function of soil moisture content and surface roughness. In this study, we evaluated the behavior of VIs from Terra MODIS (T-MODIS), Aqua MODIS (A-MODIS), and Suomi-National Polar-orbiting Partnership Visible Infrared Imaging Radiometer Suite (S-VIIRS) at Railroad Valley Playa, Nevada for a period from April 2013 to September 2019. The playa is a dried lakebed devoid of vegetation throughout the year. Long-term in situ reflectance measurements acquired over the 1 km-by−1 km Radiometric Calibration Test Site (RadCaTS) located on the playa were obtained from the Radiometric Calibration Network (RadCalNet) portal and used as a reference. Three VIs were analyzed, including the normalized difference VI (NDVI), enhanced VI (EVI), and two-band EVI (EVI2). RadCaTS NDVI, EVI, and EVI2 of the playa surface increased and decreased occasionally for the time period examined in this study, and the satellite NDVIs, EVIs, and EVI2s had comparable temporal signatures to the RadCaTS counterparts. T-MODIS and A-MODIS NDVI and EVI2 values were comparable to the RadCaTS counterparts, whereas T-MODIS and A-MODIS EVI values were lower than the RadCaTS counterparts by ~0.006 and ~ 0.01 EVI units, respectively. All the three VIs of S-VIIRS were consistently higher than their RadCaTS counterparts by ~0.008 VI units, due to the higher near-infrared (NIR) reflectances of S-VIIRS than the RadCaTS NIR reflectance. The red and NIR, and red and blue reflectances each formed linear relationships (i.e., soil lines) for each of the three sensors. Variations in reflectance due to surface conditions and observation geometries all appeared as variations along these soil lines. The satellite red-NIR soil lines were comparable to the RadCaTS counterparts, whereas the satellite red-blue soil lines had steeper slopes than the RadCaTS counterparts due to a negative bias in the satellite blue reflectances. This translated into the T-MODIS and A-MODIS EVI behaviors different from those depicted by RadCaTS EVI, and the satellite NDVI and EVI2 behaving more comparably with the RadCaTS counterparts and across the three sensors than the satellite EVI.

Sensitivity of CyGNSS Bistatic Reflectivity and SMAP Microwave Radiometry Brightness Temperature to Geophysical Parameters Over Land Surfaces

This paper presents an assessment of the correlation between CyGNSS-derived global navigation satellite systems reflectometry (GNSS-R) bistatic reflectivity, ${\Gamma _{rl}}$ , and soil moisture active passive (SMAP) derived brightness temperature, $T{}_I/2$ , over land surfaces. This parametric study is performed as a function of soil moisture content (SMC), vegetation opacity $\tau $ , and albedo $\omega $ . Several target areas, classified according to the International Geosphere-Biosphere Program (IGBP) land cover types, are selected to evaluate potential differentiated geophysical effects on “active” (as many transmitters as navigation satellites are in view) and passive approaches. Although microwave radiometry has potentially a better sensitivity to SMC, the spatial resolution achievable from a spaceborne platform is poor, ∼40 km. On the other hand, GNSS-R bistatic coherent radar pixel-size is limited by half of the first Fresnel zone, which provides about ∼150 m of spatial resolution (depending on the geometry). The main objective of this “active”/passive combination is twofold: a) downscaling the SMC, b) complement the information of microwave radiometry with GNSS-R data to improve the accuracy in SMC determination. The Pearson linear correlation coefficient of ${\Gamma _{rl}}$ and $T{}_I/2$ obtained over Thailand, Argentinian Pampas, and Amazon is ∼−0.87, ∼−0.7, and ∼−0.26, respectively, while the so-called tau–omega model is used to fit the data. Results over croplands are quite promising and deserve special attention since the use of GNSS-R could benefit agricultural and hydrological applications because of: a) the high spatio-temporal sampling properties, b) the high spatial resolution, and c) the potential combination with microwave radiometry to improve the accuracy of the measurements.

Impact of the Elevation Angle on CYGNSS GNSS-R Bistatic Reflectivity as a Function of Effective Surface Roughness over Land Surfaces

The Earth’s surface bistatic reflectivity Γ L H C P , C y G N S S is experimentally characterized using the novel Global Navigation Satellite Systems Reflectometry (GNSS-R) L-band passive multistatic radar technique from the Cyclone Global Navigation Satellite Systems (CyGNSS) eight-microsatellite constellation. The focus of this study is to evaluate the influence of the GNSS satellites’ elevation angle θ e on Γ L H C P , C y G N S S , as a function of soil moisture content (SMC) and effective surface roughness parameter h . As the average response, the change of the scattering regime at a global scale and considering also vegetated surfaces appears at θ e ≈ 55°. This empirical observation is understood as a change on the dominant scattering term, from incoherent to coherent. Then, the correlation of Γ L H C P , C y G N S S and SMC is evaluated as a function of θ e over specific sparsely vegetated target areas. The smoother the surface, the higher the angular variability of the Pearson correlation coefficients. Over croplands (e.g., Argentinian Pampas), an improved correlation coefficient is achieved over angular ranges where the coherent scattering regime becomes the dominant one. As such, this function depends on the surface roughness. The maximum correlation coefficients are found at different θ e for increasing mean roughness levels: r P a m p a s ≈ 0.78 at θ e ≈ [60,70]°, r I n d i a ≈ 0.72 at θ e ≈ [50,60]°, and r S u d a n ≈ 0.74 at θ e ≈ [30,40]°. SMC retrieval algorithms based on GNSS-R multi-angular information could benefit from these findings, so as to improve the accuracy using single-polarized signals.

Improved Water Allocation under Limited Water Supplies Using Integrated Soil-Moisture Balance Calculations and Nonlinear Programming

Water allocation under limited water supplies is becoming more important as water becomes scarcer. Optimization models are frequently used to provide decision support to enhance water allocation under limited water supplies. Correct modelling of the underlying soil-moisture balance calculations at the field scale, which governs optimal allocation of water is a necessity for decision-making. Research shows that the mathematical programming formulation of soil-moisture balance calculations presented by Ghahraman and Sepaskhah (2004) may malfunction under limited water supplies. A new model formulation is presented in this research that explicitly models deep percolation and evapotranspiration as a function of soil-moisture content. The new formulation also allows for the explicit modelling of inefficiencies resulting from nonuniform irrigation. Modelling inefficiencies are key to the evaluation of the economic profitability of deficit irrigation. Ignoring increasing efficiencies resulting from deficit irrigation may render deficit irrigation unprofitable. The results show that ignoring increasing efficiencies may overestimate the impact of deficit irrigation on maize yields by a maximum of 2.2 tons per hectare.

Relationships between soil moisture and dust emissions in a bare sandy soil of Mongolia

This study presents experimental results of the change in threshold friction velocity and dust emission strength as a function of soil moisture content. The dust and soil moisture data were obtained from irrigated plots of a bare, sandy soil (no vegetation) situated in the Mongolian steppe. Dust flux was measured using the PI-SWERL® device, while soil moisture was measured using gravimetric methods. Our results demonstrate the strong controlling effects of soil moisture on both the threshold friction velocity and dust emission strengths. Threshold friction velocity increased from 0.44m/s for dry soil (0.002g/g) to 0.67m/s for wet soil (0.06g/g), confirming the importance of soil moisture for controlling dust events. Dust emission strength was significantly depressed for wet soils, starting at a soil moisture value of 0.02g/g. From these results, we developed a simple dust diagram that may be useful as part of a warning system to identify initial sensitivity to threshold conditions as well as conditions that could lead to potentially significant dust emissions. Overall, the research findings in this study could be used to provide foreknowledge of conditions that would be conducive to high dust emissions for this area of Mongolia.

High-Resolution Subsurface Imaging of Deeply Submerged Targets Based on Distributed Near-Ground Sensors

A high-resolution subsurface imaging technique based on distributed near-ground sensor networks that utilize ultrawideband waveforms in the very high frequency (VHF) range is presented. An accurate scattering model for a target buried in realistic subsurface environment, modeled as a vertically stratified medium, is presented first. Then an inversion technique that uses ultrawideband near-field focusing is described. The signal penetration depth as a function of frequency and various subsurface parameters is calculated based on the developed forward model. The imaging resolution as it relates to the accuracy of background retrieval is also analyzed. A semi-empirical soil dielectric model that is originally developed for the ultra high frequency band is modified and validated at the VHF range with measured results available in the literature. For a given soil textural composition and frequency, the model predicts the real and imaginary parts of the dielectric constant as a function of soil moisture content. This soil dielectric model is utilized to make the inversion more efficient. To address the challenge associated with the design of compact and ultrawideband VHF antennas, a scheme utilizing multiple antennas and reduced number of frequency points is proposed. The sensor arrangement both in terms of spatial distribution and polarization of each antenna as it relates to the lateral resolution, as well as minimizing the direct coupling between the Tx and Rx antennas, is analyzed. The proposed subsurface imaging approach is validated based on numerical techniques and a laboratory scale model measurement results.

Carbon and water fluxes in an arid-zone Acacia savanna woodland: An analyses of seasonal patterns and responses to rainfall events

The study of landscape gas exchange in arid and semi-arid regions is less common than those of more mesic environments, despite their large geographical extent, their importance to regional climate, their socioeconomic values and the carbon and water balances of such regions. In this study we used eddy covariance measurements to examine net ecosystem exchange and water fluxes of a landscape dominated by a N-fixing tree (Acacia aneura; Mulga) as a function of soil moisture content, vapour pressure deficit, leaf area index and pulses of rain. Seasonal budgets of carbon and water, ecosystem-scale water-use-efficiency (the ratio of net ecosystem exchange to evapotranspiration) and inherent water-use-efficiency (ecosystem water-use-efficiency×vapour pressure deficit) were also examined. Across the 12 month study, the landscape was a net sink for carbon, despite prolonged periods of zero rain.Changes in both net ecosystem exchange and evapotranspiration were tightly coupled to changes in the moisture content of the upper (10cm) soil profile, but not the deeper profile and both responded rapidly to changes in soil moisture content. As vapour pressure deficit increased over the course of several consecutive days in the wet season there was no significant response of ecosystem water-use-efficiency. In contrast, in the dry season, as vapour pressure deficit increased ecosystem water-use-efficiency declined curvilinearly. However, in both wet and dry seasons, ecosystem water-use-efficiency declined with increasing soil moisture content. Daily inherent water-use-efficiency increased gradually following each rainfall event. As daily mean vapour pressure deficit increased between rain events, inherent water-use-efficiency increased in both the wet and dry seasons but with a steeper slope in the wet season. However, inherent water-use-efficiency decreased with increasing soil moisture in both seasons, and the slope of a semi-log plot of inherent water-use-efficiency versus soil moisture content decreased faster in the dry season than in the wet season. Similarly, the marginal carbon cost of water was smaller (0.3) in the wet than dry season (0.6). Variations in ecosystem leaf area index were correlated with the under storey component, which was highest in the wet season and lowest in the dry season. We therefore conclude that changes in under storey leaf area index were significant drivers of seasonal changes in canopy gas exchange. Mulga, despite maintaining leaf area index through the dry season in a semi-arid environment, supports little dry season evapotranspiration and relies, to a very large extent, on soil moisture in the upper soil profile rather than deeper stores of water.

Spatio-temporal surface soil heat flux estimates from satellite data; results for the AMMA experiment at the Fakara (Niger) supersite

This paper describes a method that employs Earth Observation (EO) data to calculate spatiotemporal estimates of soil heat flux, G, using a physically-based method (the Analytical Method). The method involves a harmonic analysis of land surface temperature (LST) data. It also requires an estimate of near-surface soil thermal inertia; this property depends on soil textural composition and varies as a function of soil moisture content. The EO data needed to drive the model equations, and the ground-based data required to provide verification of the method, were obtained over the Fakara domain within the African Monsoon Multidisciplinary Analysis (AMMA) program. LST estimates (3 km × 3 km, one image 15 min −1) were derived from MSG-SEVIRI data. Soil moisture estimates were obtained from ENVISAT-ASAR data, while estimates of leaf area index, LAI, (to calculate the effect of the canopy on G, largely due to radiation extinction) were obtained from SPOT-HRV images. The variation of these variables over the Fakara domain, and implications for values of G derived from them, were discussed. Results showed that this method provides reliable large-scale spatiotemporal estimates of G. Variations in G could largely be explained by the variability in the model input variables. Furthermore, it was shown that this method is relatively insensitive to model parameters related to the vegetation or soil texture. However, the strong sensitivity of thermal inertia to soil moisture content at low values of relative saturation (<0.2) means that in arid or semi-arid climates accurate estimates of surface soil moisture content are of utmost importance, if reliable estimates of G are to be obtained. This method has the potential to improve large-scale evaporation estimates, to aid land surface model prediction and to advance research that aims to explain failure in energy balance closure of meteorological field studies.

Impact of Gypsum on Electromagnetic Properties of Desert Soils

Radar remote sensing of soil requires an understanding about the electromagnetic properties of soils. Propagation velocities and attenuation rates at ground-penetrating radar frequencies (0.25-4 GHz) were measured as a function of soil moisture content for soils from Iraq and Afghanistan. Soil samples in the study include two with and two without gypsum (CaSO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ·2H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O) as a major mineral component. When measured at 100°C, volumetric moisture content of gypsum-rich soils ranged from 12% to 24%. In addition to the high moisture content, the propagation velocities were higher than expected, and attenuation rates were lower than expected for soils with moisture contents in this high range. The apparently anomalous relationship between high moisture content and low attenuation rate is explained by the presence and characteristics of gypsum in the soil. Radar signals are not affected by the chemically bound water molecules in gypsum which dehydrates at 100°C. These results show that soil mineralogy is critically important to the interpretation of dielectric properties.

Fate of nitrogen for subsurface drip dispersal of effluent from small wastewater systems

Subsurface drip irrigation systems apply effluent from onsite wastewater systems in a more uniform manner at a lower rate than has been possible with other effluent dispersal methods. The effluent is dispersed in a biologically active part of the soil profile for optimal treatment and where the water and nutrients can be utilized by landscape plants. Container tests were performed to determine the fate of water and nitrogen compounds applied to packed loamy sand, sandy loam, and silt loam soils. Nitrogen removal rates measured in the container tests ranged from 63 to 95% despite relatively low levels of available carbon. A Hydrus 2D vadose zone model with nitrification and denitrification rate coefficients calculated as a function of soil moisture content fit the container test results reasonably well. Model results were sensitive to the denitrification rate moisture content function. Two-phase transport parameters were needed to model the preferential flow conditions in the finer soils. Applying the model to generic soil types, the greatest nitrogen losses (30 to 70%) were predicted for medium to fine texture soils and soils with restrictive layers or capillary breaks. The slow transport with subsurface drip irrigation enhanced total nitrogen losses and plant nitrogen uptake opportunity.

Seasonal climate change impacts on evapotranspiration, precipitation deficit and crop yield in Puerto Rico

The purpose of this study was to estimate precipitation ( P), reference evapotranspiration (ET o), precipitation deficit (PD = P − ET o) and relative crop yield reduction (YR) for a generic crop under climate change conditions for three locations in Puerto Rico: Adjuntas, Mayagüez, and Lajas. Reference evapotranspiration was estimated by the Penman–Monteith method. Precipitation and temperature data were statistically downscaled and evaluated using the DOE/NCAR PCM global circulation model projections for the B1 (low), A2 (mid-high) and A1fi (high) emission scenarios of the Intergovernmental Panel on Climate Change Special Report on Emission Scenarios. Relative crop yield reduction was estimated from a water stress factor, which is a function of soil moisture content. Average soil moisture content for the three locations was determined by means of a simple water balance approach. Results from the analysis indicate that the rainy season will become wetter and the dry season will become drier. The 20-year average September precipitation excess (i.e., PD > 0) increased for all scenarios and locations from 121 to 321 mm between 2000 and 2090. Conversely, the 20-year average February precipitation deficit (i.e., PD < 0) changed from −27 to −77 mm between 2000 and 2090. The results suggest that additional water could be saved during the wet months to offset increased irrigation requirements during the dry months. The 20-year average relative crop yield reduction for all scenarios decreased on average from 12% to 6% between 2000 and 2090 during September, but increased on average from 51% to 64% during February. Information related to the components of the hydrologic water budget (i.e., actual evapotranspiration, surface runoff, aquifer recharge and soil moisture storage) is also presented. This study provides important information that may be useful for future water resource planning in Puerto Rico.

Temporally weighted average curve number method for daily runoff simulation

AbstractThe modified Soil Conservation Service curve number (CN) method is widely used in long‐term continuous models to predict daily surface runoff. However, it has been shown that this method gives poor results in reproducing peak flows in high rainfall periods. This is because there is an inaccuracy stemming from the model algorithm as it adjusts the daily runoff curve number as a function of soil moisture content at the end of the previous day. This paper proposes an alternative daily based curve number technique that can provide better prediction of daily runoff during the high flow season. The proposed method uses the temporally weighted average curve number (TWA‐CN) to estimate daily surface runoff, while considering the effect of rainfall during a given day as well as the antecedent soil moisture condition. To test the applicability of the TWA‐CN method, it was incorporated with the long‐term, continuous simulation watershed models SWAT and SWAT‐G. Simulations were conducted for the Miho River watershed located in the middle of South Korea. The graphical displays and statistics of the determination coefficient (R2) and the Nash–Sutcliffe model efficiency (NSE) of the observed and simulated daily runoff indicated that the modified SWAT with the TWA‐CN method may provide better runoff prediction (R2 = 0·837, NSE = 0·833) than the original SWAT (R2 = 0·815, NSE = 0·824). Likewise, the determination coefficient (R2 = 0·816) and the Nash–Sutcliffe efficiency (NSE = 0·834) for the modified SWAT‐G are also higher than the original version (R2 = 0·782, NSE = 0·825). It is expected that the improved capability in predicting surface runoff using the suggested CN estimate method will provide a sound contribution to the accurate simulations of water yield. Copyright © 2008 John Wiley &amp; Sons, Ltd.

개념적 강우-침투 과정을 고려한 탱크 모형의 유도

This study derives an event-based tank model with a conceptual rainfall-infiltration process, modifying conventional tank models. The model comprises two serial tanks, one parallel tank and an infiltration regulating element. The infiltration process within the element is not represented as a function of only time, but as a function of soil moisture content for three possible cases owing to the relationship between rainfall intensity and infiltration capacity. This study considers the previous soil moisture condition of a watershed by using antecedent precipitation index. Six parameters of the model are identified by using the real coded genetic algorithm. The applicability and validity of the proposed model are assessed for the observed stormwater data from the research basin of the International Hydrological Program, the Pyeongchanggang River basin, Republic of Korea. The results computed streamflows show relatively good agreement with observed ones.

Variation of surface albedo and soil thermal parameters with soil moisture content at a semi-desert site on the western Tibetan Plateau

Almost three years of continuous measurements taken between January 2001 and May 2003 at the Gaize (or Gerze) automatic weather station (32.30 °N, 84.06 °E, 4420 m), a cold semi-desert site on the western Tibetan Plateau, have been used to study seasonal and annual variations of surface albedo and soil thermal parameters, such as thermal conductivity, thermal capacity and thermal diffusivity, and their relationship to soil moisture content. Most of these parameters undergo dramatic seasonal and annual variations. Surface albedo decreases with increasing soil moisture content, showing the typical exponential relation between surface albedo and soil moisture. Soil thermal conductivity increases as a power function of soil moisture content. The diffusivity first increases with increasing soil moisture, reaching its maximum at about 0.25 (volume per volume), then slowly decreases. Soil thermal capacity is rather stable for a wide range of soil moisture content.

Runoff of Nitrate Nitrogen and Phosphorus from Turfgrass After Watering-In

Fertilizer nutrients could be transported from turfgrass areas to surface waters, especially those areas intensively managed, such as golf courses. An experiment was initiated to determine effects of “watering-in” fertilizer on the amounts of nitrate nitrogen and phosphorus that is found in runoff water. Three rates of 10–10–10 fertilizer were added to bermudagrass [Cynodon dactylon (L.) Pers.] on a 5% slope and a 0.64 cm irrigation applied. Three days later a 50-mm simulated rainfall was applied [72 h after treatment (HAT)] with three subsequent events. A second experiment was similar except no watering-in was done and the first event was at 4 HAT. Phosphorus and nitrate nitrogen mass transported increased step-wise with rate increases for the first two runoff events. Watering-in and waiting three days greatly decreased the volume of runoff water and the amounts of phosphorus and nitrate nitrogen transported. Runoff volume was a function of soil moisture content before the simulated rainfall events. Percent runoff water of that applied ranged from 24.3 to 43.5% for the first two events where no watering-in was done, but only 12.1–29.7% where watering-in was done. Total percent of phosphorus in runoff of that added was 13.8% for without and 3.4% with watering-in for the high rate (11 kg P/ha) and total nitrate-nitrogen was 1.5 and 0.8%, respectively. Results indicate that watering-in fertilizer with a small amount of irrigation after application is beneficial in decreasing runoff of fertilizer nutrients. Other best management practices are to limit fertilizer amounts applied in one treatment and to avoid application when soils are very moist or when heavy rain is expected.