Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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Beerkan multi-runs for characterizing water infiltration and spatial variability of soil hydraulic properties across scales
Lassabatere, Laurent ; Prima, Simone Di; Angulo-Jaramillo, Rafael ; Keesstra, Saskia ; Salesa, David - \ 2019
Hydrological Sciences Journal 64 (2019)2. - ISSN 0262-6667 - p. 165 - 178.
beerkan - BEST methods - field scale - multi-runs - spatial variability - transect scale

A method is presented for characterizing the spatial variability of water infiltration and soil hydraulic properties at the transect and field scales. The method involves monitoring a set of 10 Beerkan runs distributed over a 1-m length of soil, and running BEST (Beerkan estimation of soil transfer parameters) methods to derive hydraulic parameters. The Beerkan multi-runs (BMR) method provides a significant amount of data at the transect scale, allowing the determination of correlations between water infiltration variables and hydraulic parameters, and the detection of specific runs affected by preferential flow or water repellence. The realization of several BMRs at several transects on the same site allows comparison of the variation between locations (spatial variability at the field scale) and at the transect scale (spatial variability at the metre scale), using analysis of variance. From the results, we determined the spatial variability of water infiltration and hydraulic parameters as well as its characteristic scale (transect versus field).

The Wageningen Lowland Runoff Simulator (WALRUS): application to the Hupsel Brook catchement and Cabauw polder
Brauer, C.C. ; Torfs, P.J.J.F. ; Teuling, A.J. ; Uijlenhoet, R. - \ 2014
Hydrology and Earth System Sciences 18 (2014). - ISSN 1027-5606 - p. 4007 - 4028.
surface parameterization schemes - distributed hydrological model - flow route contributions - land-surface - groundwater interactions - spatial variability - rainfall - scale - netherlands - validation
The Wageningen Lowland Runoff Simulator (WALRUS) is a new parametric (conceptual) rainfall–runoff model which accounts explicitly for processes that are important in lowland areas, such as groundwater-unsaturated zone coupling, wetness-dependent flowroutes, groundwater–surface water feedbacks, and seepage and surface water supply (see companion paper by Brauer et al., 2014). Lowland catchments can be divided into slightly sloping, freely draining catchments and flat polders with controlled water levels. Here, we apply WALRUS to two contrasting Dutch catchments: the Hupsel Brook catchment and the Cabauw polder. In both catchments, WALRUS performs well: Nash–Sutcliffe efficiencies obtained after calibration on 1 year of discharge observations are 0.87 for the Hupsel Brook catchment and 0.83 for the Cabauw polder, with values of 0.74 and 0.76 for validation. The model also performs well during floods and droughts and can forecast the effect of control operations. Through the dynamic division between quick and slow flowroutes controlled by a wetness index, temporal and spatial variability in groundwater depths can be accounted for, which results in adequate simulation of discharge peaks as well as low flows. The performance of WALRUS is most sensitive to the parameter controlling the wetness index and the groundwater reservoir constant, and to a lesser extent to the quickflow reservoir constant. The effects of these three parameters can be identified in the discharge time series, which indicates that the model is not overparameterised (parsimonious). Forcing uncertainty was found to have a larger effect on modelled discharge than parameter uncertainty and uncertainty in initial conditions.
Improved management of winter operations to limit subsurface contamination with degradable deicing chemicals in cold regions
French, H.K. ; Zee, S.E.A.T.M. van der - \ 2014
Environmental Science and Pollution Research 21 (2014)15. - ISSN 0944-1344 - p. 8897 - 8913.
penetrating radar data - solute transport - spatial variability - soil heterogeneity - dc resistivity - porous-media - water - snow - flow - polarization
This paper gives an overview of management considerations required for better control of deicing chemicals in the unsaturated zone at sites with winter maintenance operations in cold regions. Degradable organic deicing chemicals are the main focus. The importance of the heterogeneity of both the infiltration process, due to frozen ground and snow melt including the contact between the melting snow cover and the soil, and unsaturated flow is emphasised. In this paper, the applicability of geophysical methods for characterising soil heterogeneity is considered, aimed at modelling and monitoring changes in contamination. To deal with heterogeneity, a stochastic modelling framework may be appropriate, emphasizing the more robust spatial and temporal moments. Examples of a combination of different field techniques for measuring subsoil properties and monitoring contaminants and integration through transport modelling are provided by the SoilCAM project and previous work. Commonly, the results of flow and contaminant fate modelling are quite detailed and complex and require post-processing before communication and advising stakeholders. The managers’ perspectives with respect to monitoring strategies and challenges still unresolved have been analysed with basis in experience with research collaboration with one of the case study sites, Oslo airport, Gardermoen, Norway. Both scientific challenges of monitoring subsoil contaminants in cold regions and the effective interaction between investigators and management are illustrated.
Surface and atmospheric controls on the onset of moist convection over land
Gentine, P. ; Holtslag, A.A.M. ; Andrea, F. D'; Ek, M. - \ 2013
Journal of Hydrometeorology 14 (2013). - ISSN 1525-755X - p. 1443 - 1462.
large-eddy simulation - fraction diurnal behavior - probabilistic bulk model - coupled mixed-layer - boundary-layer - soil-moisture - evaporative fraction - relative-humidity - hydrologic perspective - spatial variability
The onset of moist convection over land is investigated using a conceptual approach with a slab boundary layer model. We here determine the essential factors for the onset of boundary layer clouds over land, and study their relative importance. They are: 1) the ratio of the temperature to the moisture lapse rates of the free troposphere, i.e. the inversion Bowen ratio, 2) the mean-daily surface temperature, 3) the relative humidity of the free troposphere and 4) the surface evaporative fraction. A clear transition is observed between two regimes of moistening of the boundary layer as assessed by the relative humidity at the boundary layer top. In the first so-called wet soil advantage regime, the moistening results from the increase of the mixed-layer specific humidity, which linearly depends on the surface evaporative fraction and inversion Bowen ratio through a dynamic boundary layer factor. In the second so-called dry soil advantage regime, the relative humidity tendency at the boundary layer top is controlled by the thermodynamics and changes in the moist adiabatic induced by the decreased temperature at the boundary layer top and consequent reduction in saturation water vapor pressure. This regime pertains for very deep boundary layers under weakly stratified free troposphere over hot surface conditions. In the context of the conceptual model, a rise in free-tropospheric temperature (global warming) increases the occurrence of deep convection and reduces the cloud cover over moist surfaces. This study provides new intuition and predictive capacity on the mechanism controlling the occurrence of moist convection over land
Diagnosing evaporative fraction over land from boundary-layer clouds
Gentine, P. ; Ferguson, C.R. ; Holtslag, A.A.M. - \ 2013
Journal of Geophysical Research: Atmospheres 118 (2013)15. - ISSN 2169-897X - p. 8185 - 8196.
large-aperture scintillometer - large-eddy simulation - relative-humidity - mixed-layer - cumulus convection - diurnal behavior - soil-moisture - atmosphere interaction - surface-temperature - spatial variability
The potential use of continental fair-weather shallow cumuli as a way to retrieve the daily surface evaporative fraction over land is evaluated in convective conditions. The proposed method utilizes the fact that both the timing of cloud occurrence and the cloud base height at the time of occurrence provide strong constraints on the surface energy balance and evaporative fraction. The retrieval is especially reliable in the presence of relatively stable and humid free troposphere profiles. The advantage of the method is that it provides a more direct estimate of the surface evaporative fraction than indirect estimation based on inversion of a highly parameterized land surface model. In addition, the evaporative fraction is obtained at a scale of a few kilometers, which is more pertinent for weather and climate studies. The retrieval strategy is tested and validated for three contrasting climates: the U.S. southern Great Plains, West Africa, and the Netherlands. We suggest that the use of satellite observations of shallow cumuli can help constrain the retrieval of the surface evaporative fraction within a data assimilation scheme/reanalysis
Soil erosion, soil fertility and crop yield on slow-forming terraces in the highlands of Buberuka, Rwanda
Kagabo, M.D. ; Stroosnijder, L. ; Visser, S.M. ; Moore, D. - \ 2013
Soil & Tillage Research 128 (2013). - ISSN 0167-1987 - p. 23 - 29.
spatial variability - andes region - conservation - systems - water - land - agroforestry - hedgerows - ecuador - strips
Crop productivity in Rwanda is declining as a result of intensive farming on steep slopes, which leads to soil loss and declining soil fertility particularly in the northern highlands. Slow-forming terraces have been widely adopted in the northern highlands of Rwanda to control soil erosion however not much been done to evaluate their efficiency. We hypothesized that slow-forming terraces reduce soil loss and soil fertility gradients compared with non-conserved land. A field experiment compared the soil erosion rates and fertility gradients of 20+ year old terraces where sole grass strips (Pennisetum purpureum) or grass strips combined with infiltration ditches were used with those of land where no soil conservation technologies were applied. The experiment was conducted in the year 2010 on three landscape positions (Upperslope, Hillslope and Footslope) along a representative toposequence using farmers’ fields where potato and maize were grown in two consecutive cropping seasons. The highest annual soil loss (41.5 t ha-1) was recorded with plots receiving no soil conservation practices while the lowest annual soil loss (18 t ha-1) was recorded with grass strips combined with infiltration ditches. The slow-forming terraces showed a marked “within” spatial difference in both soil quality and crop yield. The soil in the lower part of the terraces showed as much as 57% more organic carbon content and 31% more available phosphorous than the soil in the upper part. Organic carbon (OC) was higher (OC = 2.1%) on the upperslope than on hillslope (OC = 1.9%). Less than 2.3 t ha-1 of the mean potato yield (23 t ha-1) and only 0.5 t ha-1 of the mean maize yield (5 t ha-1) were recorded on the uppermost third of the terraces on all three landscape positions. The marked soil fertility gradients indicate that the sustainability of slow-forming terraces is threatened, unless a site-specific fertilizer strategy is developed. For the sustainability of these terraces, the current practice of “harvesting” the fertile soil from the lower edge of the grass strip and using it as fertilizer for the nutrient deficient upper parts of terraces needs to be stopped
Evaluation of MODIS gross primary productivity for Africa using eddy covariance data
Sjostrom, M. ; Zhao, M. ; Archibald, S. ; Veenendaal, E.M. - \ 2013
Remote Sensing of Environment 131 (2013). - ISSN 0034-4257 - p. 275 - 286.
net primary production - deciduous broadleaf forest - primary production gpp - light use efficiency - ecosystem exchange - soil-water - spatial variability - terrestrial gross - savanna ecosystem - carbon-dioxide
MOD17A2 provides operational gross primary production (GPP) data globally at 1 km spatial resolution and 8-day temporal resolution. MOD17A2 estimates GPP according to the light use efficiency (LUE) concept assuming a fixed maximum rate of carbon assimilation per unit photosynthetically active radiation absorbed by the vegetation (emax). Minimum temperature and vapor pressure deficit derived from meteorological data down-regulate emax and constrain carbon assimilation. This data is useful for regional to global studies of the terrestrial carbon budget, climate change and natural resources. In this study we evaluated the MOD17A2 product and its driver data by using in situ measurements of meteorology and eddy covariance GPP for 12 African sites. MOD17A2 agreed well with eddy covariance GPP for wet sites. Overall, seasonality was well captured but MOD17A2 GPP was underestimated for the dry sites located in the Sahel region. Replacing the meteorological driver data derived from coarse resolution reanalysis data with tower measurements reduced MOD17A2 GPP uncertainties, however, the underestimations at the dry sites persisted. Inferred emax calculated from tower data was higher than the emax prescribed in MOD17A2. This, in addition to uncertainties in fraction of absorbed photosynthetically active radiation (FAPAR) explains some of the underestimations. The results suggest that improved quality of driver data, but primarily a readjustment of the parameters in the biome parameter look-up table (BPLUT) may be needed to better estimate GPP for African ecosystems in MOD17A2.
Swiss prealpine Rietholzbach research catchment and lysimeter: 32 year time series and 2003 drought event
Seneviratne, S.I. ; Lehner, I. ; Gurtz, J. ; Teuling, A.J. ; Lang, H. ; Moser, U. ; Grebner, D. ; Menzel, L. ; Schroff, K. ; Vitvar, T. ; Zappa, M. - \ 2012
Water Resources Research 48 (2012)6. - ISSN 0043-1397 - 20 p.
soil-moisture memory - european summer - united-states - heat-wave - groundwater recharge - spatial variability - carbon-dioxide - climate-change - water-vapor - evapotranspiration
The prealpine Rietholzbach research catchment provides long-term continuous hydroclimatological measurements in northeastern Switzerland, including lysimeter evapotranspiration measurements since 1976, and soil moisture measurements since 1994. We analyze here the monthly data record over 32 years (1976–2007), with a focus on the extreme 2003 European drought. In particular, we assess whether the well-established hypothesis that the 2003 event was due to spring precipitation deficits is valid at the site. The Rietholzbach measurements are found to be internally consistent and representative for a larger region in Switzerland. Despite the scale discrepancy (3.14 m2 versus 3.31 km2), the lysimeter seepage and catchment-wide streamflow show similar monthly dynamics. High correlations are further found with other streamflow measurements within the Thur river basin (1750 km2) and—for interannual anomalies—also in most of northern Switzerland. Analyses for 2003 confirm the occurrence of extreme heat and drought conditions at Rietholzbach. However, unlike findings from regional-scale modeling studies, they reveal a late onset of the soil moisture deficit (from June onward), despite large precipitation deficits from mid-February to mid-April. These early spring deficits were mostly compensated for by decreased runoff during this period and excess precipitation in the preceding weeks to months (including in the 2002 fall). Our results show that evapotranspiration excess in June 2003 was the main driver initiating the 2003 summer drought conditions in Rietholzbach, contributing 60% of the June 2003 water storage deficit. Finally, long-lasting drought effects on the lysimeter water storage due to rewetting inhibition were recorded until spring 2004.
Quantifying heterogeneous transport of a tracer and a degradable contaminant in the field, with snowmelt and irrigation
Schotanus, D. ; Ploeg, M.J. van der; Zee, S.E.A.T.M. van der - \ 2012
Hydrology and Earth System Sciences 16 (2012). - ISSN 1027-5606 - p. 2871 - 2882.
well-structured soil - solute transport - water-flow - preferential flow - spatial variability - propylene-glycol - unsaturated zone - saturated soil - steady-state - nonequilibrium
To examine the persistence of preferential flow paths in a field soil, and to compare the leaching of a degradable contaminant with the leaching of a tracer, two field experiments were performed using a multi-compartment sampler (MCS). The first experiment was carried out during the snowmelt period in early spring, characterized by high infiltration fluxes from snowmelt. The second experiment was carried out in early summer with irrigation to mimic homogeneous rainfall. During the second experiment, the soil was warmer and degradation of the degradable contaminant was observed. For both experiments, the highest tracer concentrations were found in the same area of the sampler, but the leached tracer masses of the individual locations were not highly correlated. Thus, the preferential flow paths were stable between the two experiments. With a lower infiltration rate, in the second experiment, more isolated peaks in the drainage and the leached masses were found than in the first experiment. Therefore, it is concluded that the soil heterogeneity is mainly caused by local differences in the soil hydraulic properties, and not by macropores. With higher infiltration rates, the high and low leaching cells were more clustered. The leached masses of the degradable contaminant were lower than the leached masses of the tracer, but the masses were highly correlated. The first-order degradation rate and the dispersivity were fitted with CXTFIT; the first-order degradation rate was 0.02 d-1, and the dispersivity varied between 1.9 and 7.1 cm. The persistence of the flow paths during the experiments suggests soil heterogeneity as the driver for heterogeneous flow and solute transport in this soil. At the MCS scale, heterogeneous snowmelt did not seem to have much influence on the flow and solute paths
Evaluation of MSG-derived global radiation estimates for application in a regional crop model
Roerink, G.J. ; Bojanowski, J.S. ; Wit, A.J.W. de; Eerens, H. ; Supit, I. ; Leo, O. ; Boogaard, H.L. - \ 2012
Agricultural and Forest Meteorology 160 (2012). - ISSN 0168-1923 - p. 36 - 47.
incident solar-radiation - satellite data - spatial variability - surface
Crop monitoring systems that rely on agrometeorologic models require estimates of global radiation. These estimates are difficult to obtain due to the limited number of weather stations that measure this variable. In the present study, we validated the global radiation estimates derived from MeteoSat Second Generation (MSG) and evaluated their use in the European Crop Growth Monitoring System (CGMS). A validation with measurements from four CarboEurope flux towers showed that the MSG estimates are accurate and unbiased (standard deviation between 30 and 51 W/m2). Moreover, a comparison with global radiation estimates from about 300 operational weather stations throughout Europe confirmed that the quality of the MSG product is high and spatially uniform. We also made an intercomparison between the MSG product and the ECMWF (ERA-INTERIM) and CGMS products at 25 km resolution, thus demonstrating that the CGMS and ECMWF products generally underestimate radiation. Nevertheless, the CGMS product showed irregular spatial patterns of local over- and underestimation, while the ECMWF product consistently underestimated. A trend analysis using a seasonal Mann-Kendall test between 2005 and 2009 did not reveal any significant monotonic trends in the MSG radiation estimates, except for 1 location out of 15. Finally, when we applied the WOFOST crop model for maize throughout Europe, the simulated potential total biomass increased due to higher estimates of global radiation made by MSG. In contrast, the water-limited simulated total-biomass generally decreased due to a higher reference evapotranspiration, causing faster depletion of soil moisture and increased water stress.
Propagation of Uncertainties in Soil and Pesticide Properties to Pesticide Leaching
Berg, F. van den; Tiktak, A. ; Heuvelink, G.B.M. ; Burgers, S.L.G.E. ; Brus, D.J. ; Vries, F. de; Stolte, J. ; Kroes, J.G. - \ 2012
Journal of Environmental Quality 41 (2012)1. - ISSN 0047-2425 - p. 253 - 261.
spatial variability - water-flow - groundwater - model - degradation - vulnerability - framework - rates
In the new Dutch decision tree for the evaluation of pesticide leaching to groundwater, spatially distributed soil data are used by the GeoPEARL model to calculate the 90th percentile of the spatial cumulative distribution function of the leaching concentration in the area of potential usage (SP90). Until now it was not known to what extent uncertainties in soil and pesticide properties propagate to spatially aggregated parameters like the SP90. A study was performed to quantify the uncertainties in soil and pesticide properties and to analyze their contribution to the uncertainty in SP90. First, uncertainties in the soil and pesticide properties were quantified. Next, a regular grid sample of points covering the whole of the agricultural area in the Netherlands was randomly selected. At the grid nodes, realizations from the probability distributions of the uncertain inputs were generated and used as input to a Monte Carlo uncertainty propagation analysis. The analysis showed that the uncertainty concerning the SP90 is 10 times smaller than the uncertainty about the leaching concentration at individual point locations. The parameters that contribute most to the uncertainty about the SP90 are, however, the same as the parameters that contribute most to uncertainty about the leaching concentration at individual point locations (e.g., the transformation half-life in soil and the coefficient of sorption on organic matter). Taking uncertainties in soil and pesticide properties into account further leads to a systematic increase of the predicted SP90. The important implication for pesticide regulation is that the leaching concentration is systematically underestimated when these uncertainties are ignored.
Reliability of Carbon Stock Estimates in Imperata Grassland (East Kalimantan, Indonesia), Using Georeferenced Information
Yassir, I. ; Putten, B. van; Buurman, P. - \ 2012
Soil Science 177 (2012)1. - ISSN 0038-075X - p. 22 - 30.
soil organic-carbon - spatial variability - regional-scale - land-use - uncertainty - management - storage - design - belgium - field
Knowledge of the spatial distribution of total carbon is important for understanding the impact of regional land use change on the global carbon cycle. We studied spatial total carbon variability using transect sampling in an Imperata grassland area. Spatial variability was modeled following an isotropic stationary process with spherical and exponential variogram functions. Range and sill were estimated at 100 m and 82.29 ton2 ha-2, respectively. For nugget, sill ratio was estimated at 24%, implying a rather strong spatial dependence. In a subsequent total carbon stock inventory based on the sampling design mentioned above, we applied three types of estimators, namely, “naive average procedure,” “spatial average procedure,” and “spatial optimal procedure.” Estimation of total carbon stock (in ton ha-1) following naive average procedure (which erroneously ignores the spatial dependence) resulted in a considerably too narrow 95% confidence interval of 37.52 to 39.75, whereas the outcomes using spatial average procedure and spatial optimal procedure were 36.54 to 40.73 and 37.14 to 40.78), respectively, using the spherical model, and 36.63 to 40.64 and 37.07 to 40.64, respectively, using the exponential model. Our research indicated that, when total carbon stock estimation is the main goal, random sampling is optimal, whereas wide design sampling (i.e., shortest distance between sampling locations not less than the range) can be preferred in some cases
Natural and fire-induced soil water repellency in a Portugese Shrubland
Stoof, C.R. ; Moore, D. ; Ritsema, C.J. ; Dekker, L.W. - \ 2011
Soil Science Society of America Journal 75 (2011)6. - ISSN 0361-5995 - p. 2283 - 2295.
coarse-textured soils - forest soils - pine forests - hydrological behavior - eucalyptus-globulus - spatial variability - prescribed fire - sandy soil - hydrophobicity - moisture
Post-fire land degradation is often attributed to fire-induced soil water repellency, despite the fact that soil water repellency is a natural phenomenon in many soils and is therefore not necessarily caused by fire. To improve our understanding of the role of soil water repellency in causing fire-induced land degradation, a long-term monitoring study was performed in which the temporal variation of topsoil water repellency (0–2.5-cm depth) was captured in a Portuguese shrubland before and after fire between November 2007 and March 2010. In addition, similarities and dissimilarities between changes following burning and clipping were assessed in a plot experiment. Soil water repellency appeared to be the rule rather than the exception, both before and after fire, and was strongly related to soil moisture and organic matter content. Surprisingly, despite the low soil temperatures during the fire (60°C) and the lack of direct soil moisture changes, fire significantly increased the persistence of soil water repellency (the water drop penetration time). Vegetation removal by burning and clipping played a key role in determining post-fire water repellency in litter and at the soil surface and considerably reduced the time needed to both develop and eliminate water repellency of the litter and surface soil. Where pre-fire (or “natural”) soil water repellency is abundant, an increase in erosion after fire cannot be solely caused by soil water repellency. Nevertheless, fire-induced removal of the protective canopy cover may increase the hydrologic significance of soil water repellency in burned landscapes
Tillage and vegetative barrier effects on soil conservation and short-term economic benefits in the Central Kenya highlands
Guto, S.N. ; Pypers, P. ; Vanlauwe, B. ; Ridder, N. de; Giller, K.E. - \ 2011
Field Crops Research 122 (2011)2. - ISSN 0378-4290 - p. 85 - 94.
contour hedgerow systems - water conservation - napier grass - andes region - leucaena-leucocephala - management-practices - spatial variability - physical-properties - northern thailand - intercrop system
Minimum tillage and vegetative barriers can conserve soil and water resources in the steep-sloping highlands of East Africa but there has been little adoption by smallholder farmers. Soil conservation efficiency and short-term economic benefits provided by tillage and vegetative barriers were assessed over four cropping seasons to understand performance under local farming conditions. Minimum tillage was compared with regular tillage and vegetative barriers (leucaena and Napier) with no barriers. Maize and soybean yields were greater with than without vegetative barriers, except with Napier barriers when minimum tillage was practiced where strong root competition occured. Cumulatively for the four cropping seasons, Napier barriers with regular tillage conserved most soil (72%) followed by Napier with minimum tillage (53%). The least soil (1%) was conserved for minimum tillage without barriers and leucaena barriers were intermediate in decreasing soil erosion. The highest positive marginal rate of returns (MRRs) were realized under leucaena barriers with regular tillage (2.09) followed by Napier with regular tillage (1.32). Minimum tillage without barriers had the lowest positive MRRs (0.08). Future increase in the price of key inputs would have greater depressive effect on the MRRs of Napier barriers with regular tillage than leucaena barriers with regular tillage. Minimum tillage without barriers was inefficient in soil conservation particularly when rainfall was intense and had poor MRRs. Leucaena barriers conserved less soil than Napier barriers but were more economically attractive, demonstrating a clear trade-off between soil erosion that is likely to impact crop yields in the long-term and short-term economic benefits. Napier barriers with regular tillage present a win–win scenario due to efficient soil conservation and attractive economic returns provided future prices of labour and Napier cuttings remain stable.
Climatology of daily rainfall semi-variance in The Netherlands
Beek, C.Z. van de; Leijnse, H. ; Torfs, P.J.J.F. ; Uijlenhoet, R. - \ 2011
Hydrology and Earth System Sciences 15 (2011)1. - ISSN 1027-5606 - p. 171 - 183.
spatial variability - daily precipitation - gauge measurements - extreme rainfall - united-states - radar - calibration - resolution - hydrology - sensitivity
Rain gauges can offer high quality rainfall measurements at their locations. Networks of rain gauges can offer better insight into the space-time variability of rainfall, but they tend to be too widely spaced for accurate estimates between points. While remote sensing systems, such as radars and networks of microwave links, can offer good insight in the spatial variability of rainfall they tend to have more problems in identifying the correct rain amounts at the ground. A way to estimate the variability of rainfall between gauge points is to interpolate between them using fitted variograms. If a dense rain gauge network is lacking it is difficult to estimate variograms accurately. In this paper a 30-year dataset of daily rain accumulations gathered at 29 automatic weather stations operated by KNMI (Royal Netherlands Meteorological Institute) and a one-year dataset of 10 gauges in a network with a radius of 5 km around CESAR (Cabauw Experimental Site for Atmospheric Research) are employed to estimate variograms. Fitted variogram parameters are shown to vary according to season, following simple cosine functions. Semi-variances at short ranges during winter and spring tend to be underestimated, but semi-variances during summer and autumn are well predicted.
Sensitivity of LISEM predicted catchment discharge to initial soil moisture content of soil profile
Sheikh, V. ; Loon, E. van; Hessel, R. ; Jetten, V.G. - \ 2010
Journal of Hydrology 393 (2010)3-4. - ISSN 0022-1694 - p. 174 - 185.
spatial variability - sequential assimilation - surface evaporation - runoff generation - model - parameters - simulation - schemes - scale - uncertainty
This study conducts a broad sensitivity analysis, taking into account the influence of initial soil moisture content in two soil layers, layer depths, event properties, and two infiltration models. A distributed hydrology and soil erosion model (LISEM) is used. Using the terrain data from the Catsop research catchment and two different rainfall events, the sensitivity of discharge is investigated for a range of pre-event soil moisture contents (0.1-0.40 cm(3) cm(-3)) in two-layers for a two-layer Green-Ampt as well as Richards infiltration model. The sensitivity of the predicted discharge to the initial condition of soil moisture appears to depend highly on all factors: infiltration model, event properties, topsoil/subsoil depth configuration and the level of the initial condition itself. There are interaction effects between all the factors. However, the effect of the different infiltration models is most pronounced. The Green-Ampt model shows less sensitivity to moisture content variation of both top and subsoil. Top/subsoil depth configuration rarely influences the results of the Green-Ampt model. The Richards model shows a highly variable discharge - initial soil moisture relation with changing rainfall intensity and topsoil/subsoil depth configurations. Two methods of sensitivity analysis, relative sensitivity and One factor-At-a Time sensitivity, have been used. The two methods gave comparable results. Depending on the other parameter values, 1% changes in topsoil moisture content resulted into 0.8-1.81% and 0.03-3.5% changes in total discharge predicted by the Green-Ampt and Richards models, respectively.
On Design and Statistical Analysis in Soil Treatment Experiments
Putten, B. van; Knippers, T.S. ; Buurman, P. - \ 2010
Soil Science 175 (2010)11. - ISSN 0038-075X - p. 519 - 529.
spatial variability - geostatistical methods - sampling strategies - field experiments - organic-carbon - resources - landscape - inference - erosion - impact
In the comparison of treatments in soil science experiments, a well-chosen experimental design is of crucial importance for making appropriate (optimal) statistical inference at low (lowest) costs. In the very common case that several observations from each plot are obtained, one should be aware that measurement units are not equivalent to so-called statistical experimental units. We illustrate the severe consequences of misinterpretations in some very commonly used experimental designs. Appropriate methodology is developed, which entails the aggregation of observations at the plot level based on the tools of spatial statistics, followed by a classical statistical analysis on the plot aggregated data. The model-based approach, in contrast to the design-based approach, appears to be a natural setting for comparison of treatments in soil-based experiments. Consequences for the planning of the experimental design are discussed, and recommendations are given
Climate control of terrestrial carbon exchange across biomes and continents
Yi, C. ; Jacobs, C.M.J. ; Moors, E.J. ; Elbers, J.A. - \ 2010
Environmental Research Letters 5 (2010)3. - ISSN 1748-9326 - 10 p.
eddy-covariance measurements - long-term - interannual variability - spatial variability - soil respiration - deciduous forest - water-vapor - fluxes - dioxide - uncertainty
Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predict future levels of atmospheric carbon dioxide because of the potential accelerating effects of positive climate–carbon cycle feedbacks. However, directly observed relationships between climate and terrestrial CO2 exchange with the atmosphere across biomes and continents are lacking. Here we present data describing the relationships between net ecosystem exchange of carbon (NEE) and climate factors as measured using the eddy covariance method at 125 unique sites in various ecosystems over six continents with a total of 559 site-years. We find that NEE observed at eddy covariance sites is (1) a strong function of mean annual temperature at mid- and high-latitudes, (2) a strong function of dryness at mid- and low-latitudes, and (3) a function of both temperature and dryness around the mid-latitudinal belt (45°N). The sensitivity of NEE to mean annual temperature breaks down at ~ 16 °C (a threshold value of mean annual temperature), above which no further increase of CO2 uptake with temperature was observed and dryness influence overrules temperature influence
Variable-suction multicompartment samplers to measure spatiotemporal unsaturated water and solute fluxes
Bloem, E. ; Hogervorst, F.A.N. ; Rooij, G. de; Stagnitti, F. - \ 2010
Vadose Zone Journal 9 (2010)1. - ISSN 1539-1663 - p. 148 - 159.
porous ceramic cups - soil solution sampler - vadose zone - numerical-analysis - spatial variability - fiberglass wicks - moisture flow - field-scale - transport - extraction
To better understand the movement of water and solutes in soils, and the risk of groundwater contamination, we need water and solute flux observations distributed in space and time. We designed a new variable-suction multicompartment percolation sampler that can be buried below an undisturbed soil volume in the field. The instrument collects percolate from 100 cells within a 32.5- by 32.5-cm area. Drop counters record the number of drops falling into the sample collectors of all cells. The cells are covered by a porous material to which suction is applied in accordance with nearby tensiometer readings. The collected water can be repeatedly extracted in situ, allowing the breakthrough curve of each cell to be measured. This temporal and spatial resolution greatly helps to quantify heterogeneous flow at scales between that of the individual sampling cell and the entire sampler. Three prototypes were tested in different laboratory (under a soil monolith) and field experiments (buried in situ) in Australia and the Netherlands. One sampler was covered with a nylon mesh, another with sintered porous stainless steel plates, and a third with a polyamide membrane. Water was uniformly applied at the soil surface by irrigation (laboratory) or natural rainfall (field). Suction could be controlled once the covers were saturated, blocking the inflow of air. The instruments operated continuously for several months. The membrane and metal covers worked best. The wealth of data obtained from a single experiment provides considerable insight in water and solute transport processes in undisturbed soils
Correlation between annual runoff in the Heihe river to the vegetation cover in the Ejina oasis (China)
Jin, X. ; Schaepman, M.E. ; Clevers, J.G.P.W. ; Su, Z. ; Hu, G. - \ 2010
Arid Land Research and Management 24 (2010)1. - ISSN 1532-4982 - p. 31 - 41.
monitoring land-cover - spatial variability - taklamakan desert - semiarid regions - northwest china - water-use - data sets - index - environments - calibration
In arid regions, an oasis plays an important role. It is nearly the only support of living and economic development for the local people. In recent years, the recession of the oasis areas appeared to be significant in Northwest China. It caused a series of environmental problems and part of the area even became the source of sandstorms. In this article, the long-term vegetation change of the Ejina Oasis, which is located in the downstream area of the Heihe River basin, was analyzed based on remote sensing data. The quantitative relationship between the runoff of the Heihe River and the vegetation change of the Ejina Oasis from 1989 to 2006 was established using Advanced Very High Resolution Radiometer (AVHRR) time-series. The vegetation growth of the Ejina Oasis depends on the runoff of the Heihe River. The time lag of the impact of the runoff on the vegetation of the Ejina Oasis is 1 year. The smallest water amount that can sustain the demand of the eco-environment of the Ejina area was estimated. The result can serve as a reference for decision-making processes at the government level, finally allowing for a better allocation of water resources in the Heihe River basin.
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