Critical analysis of thermal inertia approaches for surface soil water content retrieval

Abstract

The “thermal inertia” method to retrieve surface soil water content maps on bare or sparsely-vegetated soils is analysed. The study area is a small experimental watershed, where optical and thermal images (in day and night time) and in situ data were simultaneously acquired. The sensitivity of thermal inertia to the phase difference between incoming radiation and soil temperature is demonstrated. Thus, to obtain an accurate value of the phase difference, the temporal distance between thermographs using a three-temperature approach is evaluated. We highlight when a cosine correction of the temperature needs to be applied, depending on whether the thermal inertia formulation includes two generic acquisition times, or not. Finally, the deviation in soil water content retrieval is quantifies for given values of each parameter by performing a sensitivity analysis on the basic parameters of the thermal inertia method that are usually affected by calibration errors.

Citation Maltese, A., Bates, P.D., Capodici, F., Cannarozzo, M., Ciraolo, G., and La Loggia, G., 2013. Critical analysis of thermal inertia approaches for surface soil water content retrieval. Hydrological Sciences Journal, 58 (5), 1144–1161.

Editor D. Koutsoyiannis; Associate editor D. Hughes     

Estimation of the temporal autocorrelation structure by the collocation technique with an emphasis on soil moisture studies

Abstract

The collocation technique has become a popular tool in oceanography and hydrology for estimating the error variances of different data sources such as in situ sensors, models and remote sensing products. It is also possible to determine calibration constants, for example to account for an off-set between the data sources. So far, the temporal autocorrelation structure of the errors has not been studied, although it is known that it has detrimental effects on the results of the collocation technique, in particular when calibration constants are also determined. This paper shows how the (triple) collocation estimators can be adapted to retrieve the autocovariance functions; the statistical properties as well as the structural deficencies are described. The coupling between the autocorrelation of the error and the estimation of calibration constants is studied in detail, due to its importance for analysing temporal changes. In soil moisture applications, such time variations can be induced, for example, by seasonal changes in the vegetation cover, which affect both models and remote sensing products. The limitations of the proposed technique associated with these considerations are analysed using remote sensing and in situ soil moisture data. The variability of the inter-sensor calibration and the autocovariance are shown to be closely related to temporal patterns of the data.

Editor D. Koutsoyiannis

Citation Zwieback, S., Dorigo, W., and Wagner, W., 2013. Estimation of the temporal autocorrelation structure by the collocation technique with an emphasis on soil moisture studies. Hydrological Sciences Journal, 58 (8), 1729–1747.     

Comparative performance of soil water balance models in computing semi-arid aquifer recharge

Abstract

Estimating groundwater recharge is essential to ensure the sustainable use of groundwater resources, particularly in arid and semi-arid regions. Soil water balances have been frequently advocated as valuable tools to estimate groundwater recharge. This article compares the performance of three soil water balance models (Hydrobal, Visual Balan v2.0 and Thornthwaite) in the Ventós-Castellar aquifer, Spain. The models were used to simulate wet and dry years. Recharge estimates were transformed into water table fluctuations by means of a lumped groundwater model. These, in turn, were calibrated against piezometric data. Overall, the Hydrobal model shows the best fit between observed and calculated levels (r² = 0.84), highlighting the role of soil moisture and vegetation in recharge processes.

Editor D. Koutsoyiannis; Associate editor X. Chen

Citation Touhami, I., et al., 2014. Comparative performance of soil water balance models in computing semi-arid aquifer recharge. Hydrological Sciences Journal, 59 (1), 193–203.     

Active microwave remote sensing for soil moisture measurement: a field evaluation using ERS‐2

Active microwave remote sensing observations of backscattering, such as C‐band vertically polarized synthetic aperture radar (SAR) observations from the second European remote sensing (ERS‐2) satellite, have the potential to measure moisture content in a near‐surface layer of soil. However, SAR backscattering observations are highly dependent on topography, soil texture, surface roughness and soil moisture, meaning that soil moisture inversion from single frequency and polarization SAR observations is difficult. In this paper, the potential for measuring near‐surface soil moisture with the ERS‐2 satellite is explored by comparing model estimates of backscattering with ERS‐2 SAR observations. This comparison was made for two ERS‐2 overpasses coincident with near‐surface soil moisture measurements in a 6 ha catchment using 15‐cm time domain reflectometry probes on a 20 m grid. In addition, 1‐cm soil moisture data were obtained from a calibrated soil moisture model. Using state‐of‐the‐art theoretical, semi‐empirical and empirical backscattering models, it was found that using measured soil moisture and roughness data there were root mean square (RMS) errors from 3·5 to 8·5 dB and r² values from 0·00 to 0·25, depending on the backscattering model and degree of filtering. Using model soil moisture in place of measured soil moisture reduced RMS errors slightly (0·5 to 2 dB) but did not improve r² values. Likewise, using the first day of ERS‐2 backscattering and soil moisture data to solve for RMS surface roughness reduced RMS errors in backscattering for the second day to between 0·9 and 2·8 dB, but did not improve r² values. Moreover, RMS differences were as large as 3·7 dB and r² values as low as 0·53 between the various backscattering models, even when using the same data as input. These results suggest that more research is required to improve the agreement between backscattering models, and that ERS‐2 SAR data may be useful for estimating fields‐scale average soil moisture but not variations at the hillslope scale. Copyright © 2004 John Wiley & Sons, Ltd.     

Event-based estimation of water budget components using a network of multi-sensor capacitance probes

Abstract

A new approach was developed for estimating vertical soil water fluxes using soil water content time series data. Instead of a traditional fixed time interval, this approach utilizes the time interval between two sequential minima of the soil water storage time series to identify groundwater recharge events and calculate components of the soil water budget. We calculated water budget components: surface-water excess (Sw), infiltration less evapotranspiration (I – ET) and groundwater recharge (R) from May 2001 to January 2003 at eight locations at the USDA Agricultural Research Center, Beltsville, Maryland, USA. High uncertainty was observed for all budget components. This uncertainty was attributed to spatial and temporal variation in Sw, I – ET and R, and was caused by nonuniform rainfall distributions during recharge events, variability in the profile water content, and spatial variability in soil hydraulic properties. The proposed event-based approach allows estimating water budget components when profile water content monitoring data are available.

Citation Guber, A., Gish, T., Pachepsky, Y., McKee, L., Nicholson, T. & Cady, R. (2011) Event-based estimation of water budget components using a network of multi-sensor capacitance probes. Hydrol. Sci. J. 56(7), 1227–1241.     

Simulating the water budget of a Prairie Potholes complex from LiDAR and hydrological models in North Dakota,USA

Abstract

Hydrological processes of the wetland complex in the Prairie Pothole Region (PPR) are difficult to model, partly due to a lack of wetland morphology data. We used Light Detection And Ranging (LiDAR) data sets to derive wetland features; we then modelled rainfall, snowfall, snowmelt, runoff, evaporation, the “fill-and-spill” mechanism, shallow groundwater loss, and the effect of wet and dry conditions. For large wetlands with a volume greater than thousands of cubic metres (e.g. about 3000 m³), the modelled water volume agreed fairly well with observations; however, it did not succeed for small wetlands (e.g. volume less than 450 m³). Despite the failure for small wetlands, the modelled water area of the wetland complex coincided well with interpretation of aerial photographs, showing a linear regression with R² of around 0.80 and a mean average error of around 0.55 km². The next step is to improve the water budget modelling for small wetlands.

Editor Z.W. Kundzewicz; Associate editor X. Chen

Citation Huang, S.L., Young, C., Abdul-Aziz, O.I., Dahal, D., Feng, M., and Liu, S.G., 2013. Simulating the water budget of a Prairie Potholes complex from LiDAR and hydrological models in North Dakota, USA. Hydrological Sciences Journal, 58 (7), 1434–1444.     

Laboratory experiments of sediment transport from bare soil with a rill

Abstract

Mathematical models developed for quantification of sediment transport in hydrological watersheds require data collected through field or laboratory experiments, but these are still very rare in the literature. This study aims to collect such data at the laboratory scale. To this end, a rainfall simulator equipped with nozzles to spray rainfall was constructed, together with an erosion flume that can be given longitudinal and lateral slopes. Eighty experiments were performed, considering microtopographical features by pre-forming a rill on the soil surface before the start of each experiment. Medium and fine sands were used as soil, and four rainfall intensities (45, 65, 85 and 105 mm h^-1) were applied in the experiments. Rainfall characteristics such as uniformity, granulometry, drop velocity and kinetic energy were evaluated; flow and sediment discharge data were collected and analysed. The analysis shows that the sediment transport rate is directly proportional to rainfall intensity and slope. In contrast, the volumetric sediment concentration stays constant and does not change with rainfall intensity unless the slope changes. These conclusions are restricted to the conditions of experiments performed under rainfall intensities between and 105 mm h^-1 for medium and fine sands in a 136-cm-wide, 650-cm-long and 17-cm-deep erosion flume with longitudinal and lateral slopes varying between 5 and 20%.

Editor Z.W. Kundzewicz; Associate editor G. Mahé

Citation Aksoy, H., Unal, N.E., Cokgor, S., Gedikli, A., Yoon, J., Koca, K., Inci, S.B., Eris, E., and Pak, G., 2013. Laboratory experiments of sediment transport from bare soil with a rill. Hydrological Sciences Journal, 58 (7), 1505–1518.     

Modelling spatio-temporal patterns of sediment yield and connectivity in a semi-arid catchment with the WASA-SED model

Abstract

Rainfall–runoff induced soil erosion causes important environmental degradation by reducing soil fertility and impacting on water availability as a consequence of sediment deposition in surface reservoirs used for water supply, particularly in semi-arid areas. However, erosion models developed on experimental plots cannot be directly applied to estimate sediment yield at the catchment scale, since sediment redistribution is also controlled by the transport conditions along the landscape. In particular, representation of landscape connectivity relating to sediment transfer from upslope areas to the river network is required. In this study, the WASA-SED model is used to assess the spatial and temporal patterns of water and sediment connectivity for a semi-arid meso-scale catchment (933 km²) in Brazil. It is shown how spatial and temporal patterns of sediment connectivity within the catchment change as a function of landscape and event characteristics. This explains the nonlinear catchment response in terms of sediment yield at the outlet.

Citation Medeiros, P. H. A., Güntner, A., Francke, T., Mamede, G. L. & de Araújo, J. C. (2010) Modelling spatio-temporal patterns of sediment yield and connectivity in a semi-arid catchment with the WASA-SED model. Hydrol. Sci. J. 55(4), 636–648.     

Regional spatial pattern of deep soil water content and its influencing factors

Abstract

Plant root systems can utilize soil water to depths of 10 m or more. Spatial pattern data of deep soil water content (SWC) at the regional scale are scarce due to the labour and time constraints of field measurements. We measured gravimetric deep SWC (DSWC) at depths of 200, 300, 400, 500, 600, 800 and 1000 cm at 382 sites across the Loess Plateau, China. The coefficient of variation was high for soil water content (SWC) in the horizontal direction (48%), but was relatively small for SWC in the vertical direction (9%). Semivariogram ranges for DSWC at different depths were between 198 and 609 km. Kriged distribution maps indicated that deep soil layers became moister along northwest to southeast transects. Multiple statistical analyses related DSWC to plant characteristics (e.g. plant age explained >21% of the variability), geographical location and altitude (8–13%), soil texture and infiltrability, evaporation zone and eco-hydrological processes (P < 0.05). Regional land management decisions can be based on our DSWC distribution data to determine land uses and plant species appropriate for the soil type and location that would maintain a stable soil water balance. Maintaining infiltrability is of great importance in this and other water-scarce regions of the world.

Editor D. Koutsoyiannis; Associate editor J. Simunek

Citation Wang, Y.Q., Shao, M.A., Liu, Z.P. and Warrington, D.N., 2012. Regional spatial pattern of deep soil water content and its influencing factors. Hydrological Sciences Journal, 57 (2), 265–281.     

Remotely sensed estimation of water discharge into the rapidly dwindling Dead Sea

Abstract

The Dead Sea is shrinking as its water level drops at the alarming rate of about 1 m year^-1. The Dead Sea is important to the economies of Israel and Jordan due to the extracted minerals (primarily potassium, also magnesium and bromide). It is also central to regional tourism. It is the lowest place on Earth and its endorheic, saline basin attracts international research in various disciplines. Additional to the Lower Jordan River, the discharge of which has been decreased to a small fraction of its original value, fresh to brackish springs are the main source of water to the rapidly dwindling Dead Sea. Although the existence of these springs has been known for decades, until recently estimates of spring water discharge into the Dead Sea were scarce. In this study, we developed a methodology of water discharge estimation for channels incising into a lacustrine bed using remotely sensed data and a single hydraulic geometry variable, water-surface width. Based on calibration of over 400 in situ measurements and simultaneous hydrometric data from aerial images, width–discharge rating curves were established, tested, and found suitable (r² = 0.92, p = 0.001) for the estimation of water discharge, with ±5% uncertainty. Furthermore, we used these relationships to estimate retrospectively the temporal changes in water discharge of seven main channels traceable in historical aerial images. The reconstructed trend reveals a major (63%) reduction in average freshwater inflow between 1990 and 2006. Our results maximize the use of water-surface width information from aerial imagery, and suggest applicability to areas experiencing rapid exposure of sea/lake bed and consequent access difficulties in in situ discharge monitoring.

Editor Z.W. Kundzewicz     

Electromagnetic induction prediction of soil salinity and groundwater properties in a Tunisian Saharan oasis

Abstract

Electromagnetic induction measurements (EM) were taken in a saline gypsiferous soil of the Saharan-climate Fatnassa oasis (Tunisia) to predict the electrical conductivity of saturated soil extract (ECe) and shallow groundwater properties (depth, Dgw, and electrical conductivity, ECgw) using various models. The soil profile was sampled at 0.2 m depth intervals to 1.2 m for physical and chemical analysis. The best input to predict the log-transformed soil salinity (lnECe) in surface (0–0.2 m) soil was the EMh/EMv ratio. For the 0–0.6 m soil depth interval, the performance of multiple linear regression (MLR) models to predict lnECe was weaker using data collected over various seasons and years (R _a ² = 0.66 and MSE = 0.083 dS m^-1) as compared to those collected during the same period (R _a ² = 0.97, MSE = 0.007 dS m^-1). For similar seasonal conditions, for the Dgw–EMv relationship, R ² was 0.88 and the MSE was 0.02 m for Dgw prediction. For a validation subset, the R ² was 0.85 and the MSE was 0.03 m. Soil salinity was predicted more accurately when groundwater properties were used instead of soil moisture with EM variables as input in the MLR.

Editor D. Koutsoyiannis; Associate editor K. Heal

Citation Bouksila, F., Persson, M., Bahri, A., and Berndtsson, R., 2012. Electromagnetic induction predictions of soil salinity and groundwater properties in a Tunisian Saharan oasis. Hydrological Sciences Journal, 57 (7), 1473–1486.     

Assessing the performance and uncertainty analysis of the SWAT and RBNN models for simulation of sediment yield in the Nagwa watershed,India

Abstract

The process-based Soil and Water Assessment Tool (SWAT) model and the data-driven radial basis neural network (RBNN) model were evaluated for simulating sediment load for the Nagwa watershed in Jharkhand, India, where soil erosion is a severe problem. The SWAT model calibration and uncertainty analysis were performed with the Sequential Uncertainty Fitting algorithm version 2 and the bootstrap technique was applied on the RBNN model to analyse uncertainty in model output. The percentage of data bracketed by the 95% prediction uncertainty (95PPU) and the r factor were the two measures used to assess the goodness of calibration. Comparison of the results of the two models shows that the value of r factor (r = 0.41) in the RBNN model is less than that of SWAT model (r = 0.79), which means there is a wider prediction interval for the SWAT model results. More values of observed sediment yield were bracketed by the 95PPU in the RBNN model. Thus, the RBNN model estimates the sediment yield values more accurately and with less uncertainty.

Editor D. Koutsoyiannis; Associate editor H. Aksoy

Citation Singh, A., Imtiyaz, M., Isaac, R.K., and Denis, D.M., 2014. Assessing the performance and uncertainty analysis of the SWAT and RBNN models for simulation of sediment yield in the Nagwa watershed, India. Hydrological Sciences Journal, 59 (2), 351–364.     

Effects of streamflow reductions on aquatic macroinvertebrates: linking groundwater withdrawals and assemblage response in southern New Jersey streams,USA

Abstract

A comprehensive hydro-ecological investigation was conducted to determine the ecological response of increased groundwater withdrawals from the Kirkwood-Cohansey aquifer system, an important source of water supply in southern New Jersey, USA. Collocated observations were made of aquatic-macroinvertebrate assemblages and stream hydrologic attributes to develop flow–ecology response relations. A sub-regional transient groundwater flow model (MODFLOW) was used to simulate three plausible high-stress groundwater-withdrawal scenarios which resulted in stream baseflow reductions of approximately 0.12, 0.20, and 0.26 m³ s^-1. These reduction scenarios were used to construct flow-alteration ecological response models to evaluate aquatic-macroinvertebrate response to streamflow reduction. For example, flow-alteration ecological response models indicate that if groundwater withdrawals diminish mean annual streamflow from 1.1 to 0.6 m³ s^-1, the abundance of intolerant taxa could be reduced by as much as 20%. These flow-alteration ecological response modelling results could be used by resource professionals to evaluate alternative water management strategies to determine maximum basin withdrawal rates that meet ongoing human water demand while protecting biological integrity.

Editor D. Koutsoyiannis; Guest editor M. Acreman

Citation Kennen, J.G., Riskin, M.L., and Charles, E.G., 2014. Effects of streamflow reductions on aquatic macroinvertebrates: linking groundwater withdrawals and assemblage response in southern New Jersey streams, USA. Hydrological Sciences Journal, 59 (3–4), 545–561.     

Historical aspects of soil erosion in the Mejerda catchment,Tunisia

Abstract

Agricultural use and related water erosion may lead to significant changes in the sedimentological and hydrological characteristics of watersheds, and therefore negative consequences for rural development. This research aimed to put present-day soil erosion of the important Mejerda catchment into a historical context. The catchment of Wadi Mejerda in northern Tunisia has experienced soil erosion due to weather and human impacts for thousands of years. We used historical texts and results from archaeological research that go back to 1000 BC, as well as data collected during the last century. Soil erosion from different types of agricultural landscape management was analysed together with information on the soils' production potential, the hydrographic network and flood frequency. The results showed that water erosion has increased the hydrographic network by 65 km and increased the deltaic plain by as much as 15 km²/century. However, soil productivity has decreased significantly. Moreover, due to in channel sedimentation and river choking, the number of flooding occurrences has multiplied over the last century. Finally, it is shown that water erosion follows a specific cycle of degradation throughout the watershed. These findings should be considered for better water and soil management in the context of semi-arid areas.

Editor Z.W. Kundzewicz

Citation Jebari, S., Berndtsson, R., Lebdi, F., and Bahri, A., 2012. Historical aspects of soil erosion in the Mejerda catchment. Hydrological Sciences Journal, 57 (5), 901–912.     

Hydrochemical characteristics of irrigation return flow in semi-arid regions of Iran

Abstract

The study area is located on the Harat plain, in the central region of Iran. Four local-soil filled, free-drainage lysimeters were installed in wheat and barley farms operating under traditional farm management practices. The volume, electrical conductivity (EC), nitrate and major ions of the applied irrigation water and irrigation return flow (IRF) were measured during the growing season. The total dissolved solids (TDS) of IRF increased three to five times compared to that of the applied water. This enhancement was the same as for the chloride ion ratio, indicating the major impact of evapotranspiration in IRF salinity enhancement. Geochemical modelling using PHREEQCI confirmed the significant role of evapotranspiration and the minor effects of processes such as calcite precipitation, gypsum dissolution, fertilizer nitrification and ion exchange on the values of the IRF TDS. Time variations of EC were functions of the type of flow (preferential or matrix), lithology and soil type. The controlling parameters of the nitrate time series were the frequent applications of N fertilizer and the nitrification process. The annual N loads (NO₃-N) of IRF varied from 22 to 195 kg ha^-1. These variations were due to the different N loads in the applied water, the amount of fertilizer, soil texture, N uptake and volume of IRF. The annual salt loads of IRF were mainly controlled by the volume of IRF.

Editor Z.W. Kundzewicz

Citation Jafari, H., Raeisi, E., Hoehn, E. and Zare, M., 2012. Hydrochemical characteristics of irrigation return flow in semi-arid regions of Iran. Hydrological Sciences Journal, 57 (1), 173–185.     

Treatment of anchor pixels in the METRIC model for improved estimation of sensible and latent heat fluxes

Abstract

Reliable estimation of sensible heat flux (H) is important in energy balance models for quantifying evapotranspiration (ET). This study was conducted to evaluate the value of adding the Priestley-Taylor (PT) equation to the METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration) model. METRIC was used to estimate energy fluxes for 10 Landsat images from the 2005, 2006 and 2007 crop growing seasons in south-central Nebraska, USA, where each image owing to recent rainfall exhibited high residual moisture content even at the hot pixel. The METRIC model performed satisfactorily for net radiation (R_n ) and soil heat flux (G) estimation with a root mean square error (RMSE) of 52 and 24 W m^-2, respectively. A RMSE of 122 W m^-2 for H indicated the limitation of the METRIC model in estimating H for high residual moisture content of the hot pixel (Alfalfa reference ET fraction, ET _r F > 0.15). The modified METRIC model (wet METRIC or wMETRIC) incorporating the PT equation was applied to calculate H at the anchor pixels (hot and cold) for high residual moisture content of the hot pixel. The α coefficient of the PT equation was locally calibrated using hourly meteorological data from an automatic weather station and R_n and G data from a Bowen ratio flux tower. The mean α coefficient value was 1.14. The wMETRIC model reduced the RMSE of H from 122 to 64 W m^-2 and that of latent heat flux, LE, from 163 to 106 W m^-2. The RMSE of daily ET decreased from 1.7 to 1.1 mm d^-1 with wMETRIC. The results indicate that treatment of anchor pixels for high residual moisture content with the PT approach gives improved estimation of H, LE and daily ET. It is recommended that the wMETRIC model be used for estimating ET if the hot pixel has high residual moisture (i.e. reference ET fraction > 0.15).

Citation Singh, R. K. & Irmak, A. (2011) Treatment of anchor pixels in the METRIC model for improved estimation of sensible and latent heat fluxes. Hydrol. Sci. J. 56(5), 895–906.     

Identifying effects of local and nonlocal factors of soil water storage using cyclical correlation analysis

There are various factors governing the spatial and temporal variability of soil water storage including soil properties, topography and vegetation. Some factors act locally, whereas others act nonlocally, which means that a factor measured at one location has effect on soil water storage at another location. The objective of this study was to examine the effects of local and nonlocal controls of soil water storage in a hummocky landscape using cyclical correlation analysis. Soil water storage, soil properties and terrain indices were measured along a 128‐point transect of 576 m long from the semiarid, hummocky, prairie pothole region of North America. There are large coefficients of determination (r²) between soil water storage and sand content (r² = 0.32–0.53), organic carbon content (r² = 0.22–0.56), depth to carbonate layer (r² = 0.13–0.63), wetness index (r² = 0.25–0.45) and other variables at the measurement scale at different times, indicating strong local effects from these variables. The correlation coefficients were also calculated by physically shifting the spatial series of soil water storage with respect to that of controlling factors. The shifting improves the correlation between the spatial series, and the length of shifting indicated the difference in the response of soil water to its controlling factors. For example, the value of r² increased more than eightfold (r² = 0.47–0.64) after shifting the spatial series of soil water storage by 54 m, almost equal to the average length of existing slope, compared with the very weak correlation (r² = 0.02–0.08) at the measurement scale. This indicated the nonlocal effect from the relative elevation. The identification of nonlocal effects from factors improves the prediction of soil water storage. Copyright © 2011 John Wiley & Sons, Ltd.     

Assessment of the MODIS global evapotranspiration algorithm using eddy covariance measurements and hydrological modelling in the Rio Grande basin

Abstract

Remote sensing is considered the most effective tool for estimating evapotranspiration (ET) over large spatial scales. Global terrestrial ET estimates over vegetated land surfaces are now operationally produced at 1-km spatial resolution using data from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the MOD16 algorithm. To evaluate the accuracy of this product, ground-based measurements of energy fluxes obtained from eddy covariance sites installed in tropical biomes and from a hydrological model (MGB-IPH) were used to validate MOD16 products at local and regional scales. We examined the accuracy of the MOD16 algorithm at two sites in the Rio Grande basin, Brazil, one characterized by a sugar-cane plantation (USE), the other covered by natural savannah vegetation (PDG) for the year 2001. Inter-comparison between 8-day average MOD16 ET estimates and flux tower measurements yielded correlations of 0.78 to 0.81, with root mean square errors (RMSE) of 0.78 and 0.46 mm d^-1, at PDG and USE, respectively. At the PDG site, the annual ET estimate derived by the MOD16 algorithm was 19% higher than the measured amount. For the average annual ET at the basin-wide scale (over an area of 145 000 km²), MOD16 estimates were 21% lower than those from the hydrological model MGB-IPH. Misclassification of land use and land cover was identified as the largest contributor to the error from the MOD16 algorithm. These estimates improve significantly when results are integrated into monthly or annual time intervals, suggesting that the algorithm has a potential for spatial and temporal monitoring of the ET process, continuously and systematically, through the use of remote sensing data.

Editor D. Koutsoyiannis; Associate editor T. Wagener

Citation Ruhoff, A.L., Paz, A.R., Aragao, L.E.O.C., Mu, Q., Malhi, Y., Collischonn, W., Rocha, H.R., and Running, S.W., 2013. Assessment of the MODIS global evapotranspiration algorithm using eddy covariance measurements and hydrological modelling in the Rio Grande basin. Hydrological Sciences Journal, 58 (8), 1658–1676.     

Soil water dynamics in cropped and uncropped fields in northern Greece using a dual-permeability model

Abstract

This study focuses on the calibration and validation of a dual-permeability soil water flow model for simulating soil water dynamics during the growing period in an irrigated corn field and during the rainy winter period in an uncropped field in northern Greece. The 1D numerical transient dual-permeability model MACRO 5.0 was used to describe the soil water dynamics, the water balance and deep percolation considering both macropore (two-domain) flow and non-macropore (one-domain) flow. The simulated results were compared with measurements of total soil water content at different depths in the soils. The values of the statistical criteria RMSE, E and CRM were better when macroporosity flow was considered; the soil water content showed better redistribution in the soil profile. The limited irrigation of the corn field during the growing period and the irrigation rates did not create conditions for deep percolation of water. In the uncropped field (bare soil), the wet conditions and the high rainfall during the simulation period created conditions for significant deep percolation, whether macropore flow was included in the model or not. The two-domain approach significantly affects the actual evaporation and the deep percolation. The difference between these two approaches is in the amount of deep percolation and the flow path of drainage flow. In the two-domain approach, most deep percolation follows the macropore domain (79.8%). The errors due to macropore parameter uncertainty and to the difficulties of measuring the macropore water content and flow were estimated by a sensitivity analysis for the more important parameters of the model.

Editor Z.W. Kundzewicz

Citation Antonopoulos, V.Z., Georgiou, P.E., and Kolotouros, C.A., 2013. Soil water dynamics in cropped and uncropped fields in northern Greece using a dual-permeability model. Hydrological Sciences Journal, 58 (8), 1748–1759.