scholarly journals Validation of a mesoscale hydrological model in a small-scale forested catchment

2015 ◽  
Vol 47 (1) ◽  
pp. 27-41 ◽  
Author(s):  
Václav Šípek ◽  
Miroslav Tesař
Keyword(s):  
Soil Moisture ◽  
Lateral Flow ◽  
Small Scale ◽  
Good Correspondence ◽  
Flow Estimation ◽  
Forested Catchment ◽  
Model Soil ◽  
Simulation Efficiency ◽  
Model Response ◽  
Ecohydrological Model

The aim of this study was to examine the abilities of the mesoscale ecohydrological model Soil And Water Integrated Model (SWIM) to simulate discharge, soil moisture, and groundwater dynamics in a small-scale forested catchment. Moreover, the influence of two lateral flow computation techniques on the simulation efficiency was assessed. Generally, the discharges were simulated poorly. Groundwater level was estimated reasonably taking into account that the model was not designed for small-scale catchments. The soil moisture simulation exhibited good correspondence with the observed data in the warmer season (April–August). Both the dynamics and the magnitude were estimated sufficiently well. On the other hand, the colder season does not comply satisfactorily with the modelled data, as the decline of moisture content (in the non-precipitation periods) has no model response. The kinematic storage method was found to be more reliable in the case of a small-scale forested catchment compared to the exponential storage lateral flow estimation approach.

Net precipitation assessment in a grassland and soil moisture response at plot scale in a temperate climate

2021 ◽  
Author(s):  
Gökben Demir ◽  
Johanna Clara Metzger ◽  
Janett Filipzik ◽  
Christine Fischer ◽  
Beate Michalzik ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Spatial Variation ◽  
Canopy Structure ◽  
Sampling Period ◽  
Temperate Climate ◽  
Small Scale ◽  
Spatial Effects ◽  
Mixed Effect ◽  
Canopy Development ◽  
Canopy Effect

<div> <p>Evidence on spatial variation of net precipitation in grasslands is scarce. Challenges arise due to a small-scale canopy structure of grasslands.</p> <p>In this study, we designed and tested a new in-situ measurement device (interception grid) to assess net precipitation in grasslands. The collector allows the natural development of the canopy. We tested the device both in the lab for splash loss and in the field to test its capacity to assess net precipitation. In the field, we installed 25 collectors on a grassland within the Hainich Critical Zone Exploratory (Thuringia, Germany), 23 of which were paired with soil moisture sensors. We conducted weekly measurements gross and net precipitation (above and below the canopy), along with grass height in 2019 (March-August) and 2020 (January -February). We categorized the data into two groups (‘covered,’ ‘uncovered’), accounting for canopy development.</p> <p>In the lab, we found that the drop size strongly affects splash loss. Drops of ca. 2 mm, created more than 16% splash loss, decreasing to less than 3% for drops <1.5 mm. Drop sizes <1.75 mm during the sampling period (2019) suggest low to intermediate splash loss in the field, further decreased in the covered period as the canopy contact slows down the drops. Grid measurements corrected with estimated splash loss during the uncovered period agreed well with gross precipitation. Using linear mixed effect models, we found that wind speed and grass height significantly affected the grid measurements of covered periods. Therefore, grids were able to capture net precipitation variation due to grass development. These steps encouraged us to examine the canopy effect in the soil moisture response to rainfall.</p> <p>Soil moisture response over the entire period was not related to the spatial variation of net precipitation. However, for the drier period (June-August 2019), when the spatial variation in soil moisture is higher, and the overall response to rain events stronger, net precipitation slightly affected soil moisture response. LMEM analysis to estimate factors on soil moisture response showed that grass height, net precipitation are significant predictors. Yet, there is no remarkable difference between using net precipitation and gross precipitation as potential drivers for soil moisture response, indicating that the spatial effects are comparatively small. Overall, our findings suggest that the grids are cable to catch canopy effects on the precipitation, while the effect of wind on under-catch still needs to be investigated further.</p> </div>

scholarly journals A comparison of ASCAT and modelled soil moisture over South Africa, using TOPKAPI in land surface mode

2010 ◽  
Vol 14 (4) ◽  
pp. 613-626 ◽  
Author(s):  
S. Sinclair ◽  
G. G. S. Pegram
Keyword(s):  
South Africa ◽  
Soil Moisture ◽  
Land Surface ◽  
Meteorological Data ◽  
Saturation Index ◽  
Significant Proportion ◽  
Surface Mode ◽  
Good Correspondence ◽  
Percentage Saturation ◽  
Soil Saturation

Abstract. In this paper we compare two independent soil moisture estimates over South Africa. The first estimate is a Soil Saturation Index (SSI) provided by automated real-time computations of the TOPKAPI hydrological model, adapted to run as a collection of independent 1 km cells with centres on a grid with a spatial resolution of 0.125°, at 3 h intervals. The second set of estimates is the remotely sensed ASCAT Surface Soil Moisture product, temporally filtered to yield a Soil Wetness Index (SWI). For the TOPKAPI cells, the rainfall forcing used is the TRMM 3B42RT product, while the evapotranspiration forcing is based on a modification of the FAO56 reference crop evapotranspiration (ET0). ET0 is computed using forecast fields of meteorological variables from the Unified Model (UM) runs done by the South African Weather Service (SAWS); the UM forecast fields were used, because reanalysis is not done by SAWS. To validate these ET0 estimates we compare them with those computed using observed meteorological data at a network of weather stations; they were found to be unbiased with acceptable scatter. Using the rainfall and evapotranspiration forcing data, the percentage saturation of the TOPKAPI soil store is computed as a Soil Saturation Index (SSI), for each of 6984 unconnected uncalibrated TOPKAPI cells at 3 h time-steps. These SSI estimates are then compared with the SWI estimates obtained from ASCAT. The comparisons indicate a good correspondence in the dynamic behaviour of SWI and SSI for a significant proportion of South Africa.

scholarly journals Implications of CO<sub>2</sub> pooling on δ<sup>13</sup>C of ecosystem respiration and leaves in Amazonian forest

2008 ◽  
Vol 5 (3) ◽  
pp. 779-795 ◽  
Author(s):  
A. C. de Araújo ◽  
J. P. H. B. Ometto ◽  
A. J. Dolman ◽  
B. Kruijt ◽  
M. J. Waterloo ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Carbon Isotope ◽  
Isotope Ratio ◽  
Ecosystem Respiration ◽  
Nitrogen Concentration ◽  
Carbon Isotope Ratio ◽  
Dry Season ◽  
Small Scale ◽  
Supporting Evidence ◽  
Co2 Efflux

Abstract. The carbon isotope of a leaf (δ13Cleaf) is generally more negative in riparian zones than in areas with low soil moisture content or rainfall input. In Central Amazonia, the small-scale topography is composed of plateaus and valleys, with plateaus generally having a lower soil moisture status than the valley edges in the dry season. Yet in the dry season, the nocturnal accumulation of CO2 is higher in the valleys than on the plateaus. Samples of sunlit leaves and atmospheric air were collected along a topographical gradient in the dry season to test whether the δ13Cleaf of sunlit leaves and the carbon isotope ratio of ecosystem respired CO2 (δ13CReco) may be more negative in the valley than those on the plateau. The δ13Cleaf was significantly more negative in the valley than on the plateau. Factors considered to be driving the observed variability in δ13Cleaf were: leaf nitrogen concentration, leaf mass per unit area (LMA), soil moisture availability, more negative carbon isotope ratio of atmospheric CO2 (δ13Ca) in the valleys during daytime hours, and leaf discrimination (Δleaf). The observed pattern of δ13Cleaf might suggest that water-use efficiency (WUE) is higher on the plateaus than in the valleys. However, there was no full supporting evidence for this because it remains unclear how much of the difference in δ13Cleaf was driven by physiology or &amp;delta13Ca. The δ13CReco was more negative in the valleys than on the plateaus on some nights, whereas in others it was not. It is likely that lateral drainage of CO2 enriched in 13C from upslope areas might have happened when the nights were less stable. Biotic factors such as soil CO2 efflux (Rsoil) and the responses of plants to environmental variables such as vapor pressure deficit (D) may also play a role. The preferential pooling of CO2 in the low-lying areas of this landscape may confound the interpretation of δ13Cleaf and δ13CReco.

scholarly journals Implications of CO<sub>2</sub> pooling on δ<sup>13</sup>C of ecosystem respiration and leaves in Amazonian forest

2007 ◽  
Vol 4 (6) ◽  
pp. 4459-4506
Author(s):  
A. C. de Araújo ◽  
J. P. H. B. Ometto ◽  
A. J. Dolman ◽  
B. Kruijt ◽  
M. J. Waterloo ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Carbon Isotope ◽  
Isotope Ratio ◽  
Ecosystem Respiration ◽  
Nitrogen Concentration ◽  
Carbon Isotope Ratio ◽  
Dry Season ◽  
Atmospheric Co2 ◽  
Small Scale ◽  
Co2 Efflux

Abstract. The carbon isotope of a leaf (δ13Cleaf) is generally more negative in riparian zones than in areas with low soil moisture content or rainfall input. In Central Amazonia, the small-scale topography is composed of plateaus and valleys, with plateaus generally being drier than the valley edges in the dry season. The nocturnal accumulation of CO2 is higher in the valleys than on the plateaus in the dry season. The CO2 stored in the valleys takes longer to be released than that on the plateaus, and sometimes the atmospheric CO2 concentration (ca) does not drop to the same level as on the plateaus at any time during the day. Samples of sunlit leaves and atmospheric air were collected along a topographical gradient to test whether the δ13Cleaf of sunlit leaves and the carbon isotope ratio of ecosystem respired CO2 (δ13CR) may be more negative in the valley than those on the plateau. The δ13Cleaf was significantly more negative in the valley than on the plateau. Factors considered to be driving the observed variability in δ13Cleaf were: leaf nitrogen concentration, leaf mass per unit area (LMA), soil moisture availability, more negative carbon isotope ratio of atmospheric CO2 (δ13Ca) in the valleys during daytime hours, and leaf discrimination (Δleaf). The observed pattern of δ13Cleaf suggests that water-use efficiency (WUE) may be higher on the plateaus than in the valleys. The ;13CR was more negative in the valleys than on the plateaus on some nights, whereas in others it was not. It is likely that lateral drainage of CO2 enriched in 13C from upslope areas might have happened when the nights were less stable. Biotic factors such as soil CO2 efflux (Rsoil) and the responses of plants to environmental variables such as vapor pressure deficit (D) may also play a role.

scholarly journals Large-scale lateral saturated soil hydraulic conductivity as metric for the connectivity of the subsurface flow paths at hillslope scale

2021 ◽  
Author(s):  
Mario Pirastru ◽  
Massimo Iovino ◽  
Hassan Awada ◽  
Roberto Marrosu ◽  
Simone Di Prima ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Hydraulic Conductivity ◽  
Spatial Scale ◽  
Water Table ◽  
Subsurface Flow ◽  
Lateral Flow ◽  
Saturated Soil ◽  
Flow Paths ◽  
Soil Hydraulic Conductivity ◽  
Hillslope Scale

Lateral saturated soil hydraulic conductivity, Ks,l, is the soil property governing subsurface water transfer in hillslopes, and the key parameter in many numerical models simulating hydrological processes both at the hillslope and catchment scales. Likewise, the hydrological connectivity of lateral flow paths plays a significant role in determining the intensity of the subsurface flow at various spatial scales. The objective of the study is to investigate the relationship between Ks,l and hydraulic connectivity at the hillslope spatial scale. Ks,l was determined by the subsurface flow rates intercepted by drains, and by water table depths observed in a well network. Hydraulic connectivity of the lateral flow paths was evaluated by the synchronicity among piezometric peaks, and between the latter and the peaks of drained flow. Soil moisture and precipitation data were used to investigate the influence of the transient hydrological soil condition on connectivity and Ks,l. It was found that the higher was the synchronicity of the water table response between wells, the lower was the time lag between the peaks of water levels and those of the drained subsurface flow. Moreover, the most synchronic water table rises determined the highest drainage rates. The relationships between Ks,l and water table depths were highly non-linear, with a sharp increase of the values for water table levels close to the soil surface. Estimated Ks,l values for the full saturated soil were in the order of thousands of mm h-1, suggesting the activation of macropores in the root zone. The Ks,l values determined at the peak of the drainage events were correlated with the indicators of synchronicity. The sum of the antecedent soil moisture and of the precipitation was correlated with the indicators of connectivity and with Ks,l. We suggest that, for simulating realistic processes at the hillslope scale, the hydraulic connectivity could be implicitly considered in hydrological modelling through an evaluation of Ks,l at the same spatial scale.

scholarly journals Flow Prediction Using Remotely Sensed Soil Moisture in Irish Catchments

Water ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 2202
Author(s):  
Chanyu Yang ◽  
Fiachra E. O’Loughlin
Keyword(s):  
Soil Moisture ◽  
Remote Sensing Data ◽  
Remotely Sensed ◽  
Coefficient Of Determination ◽  
Energy Budgets ◽  
Care Needs ◽  
Soil Moisture Accounting ◽  
Model Soil ◽  
Ungauged Basin ◽  
Behavioural Parameter

Owing to a scarcity of in situ streamflow data in ungauged or poorly gauged basins, remote sensing data is an ideal alternative. It offers a valuable perspective into the dynamic patterns that can be difficult to examine in detail with point measurements. For hydrology, soil moisture is one of the pivotal variables which dominates the partitioning of the water and energy budgets. In this study, nine Irish catchments were used to demonstrate the feasibility of using remotely sensed soil moisture for discharge prediction in ungagged basins. Using the conceptual hydrological model “Soil Moisture Accounting and Routing for Transport” (SMART), behavioural parameter sets (BPS) were selected using two different objective functions: the Nash Sutcliffe Efficiency (NSE) and Coefficient of Determination (R2) for the calibration period. Good NSE scores were obtained from hydrographs produced using the satellite soil moisture BPS. While the mean performance shows the feasibility of using remotely sensed soil moisture, some outliers result in negative NSE scores. This highlights that care needs to be taken with parameterization of hydrological models using remotely sensed soil moisture for ungauged basin.

scholarly journals A quasi-three-dimensional model for predicting rainfall-runoff processes in a forested catchment in Southern Finland

2000 ◽  
Vol 4 (1) ◽  
pp. 65-78 ◽  
Author(s):  
H. Koivusalo ◽  
T. Karvonen ◽  
A. Lepistö
Keyword(s):  
Soil Moisture ◽  
Water Table ◽  
Unsaturated Soil ◽  
Water Movement ◽  
Three Dimensional ◽  
Moisture Distribution ◽  
Richards Equation ◽  
Rainfall Runoff ◽  
Forested Catchment ◽  
Soil Moisture Distribution

Abstract. Runoff generation in a forested catchment (0.18 km2) was simulated using a quasi-three-dimensional rainfall-runoff model. The model was formulated over a finite grid where water movement was assumed to be dominantly vertical in the unsaturated soil zone and horizontal in the saturated soil. The vertical soil moisture distribution at each grid cell was calculated using a conceptual approximation to the one-dimensional Richards equation. The approximation allowed the use of a simple soil surface boundary condition and an efficient solution to the water table elevation over the finite grid. The approximation was coupled with a two-dimensional ground water model to calculate lateral soil water movement between the grid cells and exfiltration over saturated areas, where runoff was produced by the saturation-excess mechanism. Runoff was an input to a channel network, which was modelled as a nonlinear reservoir. The proposed approximation for the vertical soil moisture distribution in unsaturated soil compared well to a numerical solution of the Richards equation during shallow water table conditions, but was less satisfactory during prolonged dry periods. The simulation of daily catchment outflow was successful with the exception of underprediction of extremely high peak flows. The calculated water table depth compared satisfactorily with the measurements. An overall comparison with the earlier results of tracer studies indicated that the modelled contribution of direct rainfall/snowmelt in streamflow was higher than the isotopically traced fraction of event-water in runoff. The seasonal variation in the modelled runoff-contributing areas was similar to that in the event-water-contributing areas from the tracer analysis.

scholarly journals Comparison of soil moisture fields estimated by catchment modelling and remote sensing: a case study in South Africa

2008 ◽  
Vol 12 (3) ◽  
pp. 751-767 ◽  
Author(s):  
T. Vischel ◽  
G. G. S. Pegram ◽  
S. Sinclair ◽  
W. Wagner ◽  
A. Bartsch
Keyword(s):  
South Africa ◽  
Remote Sensing ◽  
Soil Moisture ◽  
Hydrological Model ◽  
Regional Scale ◽  
Remotely Sensed ◽  
Hydrological Models ◽  
Good Correspondence ◽  
Physically Based

Abstract. The paper compares two independent approaches to estimate soil moisture at the regional scale over a 4625 km2 catchment (Liebenbergsvlei, South Africa). The first estimate is derived from a physically-based hydrological model (TOPKAPI). The second estimate is derived from the scatterometer on board the European Remote Sensing satellite (ERS). Results show a good correspondence between the modelled and remotely sensed soil moisture, particularly with respect to the soil moisture dynamic, illustrated over two selected seasons of 8 months, yielding regression R2 coefficients lying between 0.68 and 0.92. Such a close similarity between these two different, independent approaches is very promising for (i) remote sensing in general (ii) the use of hydrological models to back-calculate and disaggregate the satellite soil moisture estimate and (iii) for hydrological models to assimilate the remotely sensed soil moisture.

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