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The impact of inefficiency on diversification
Oude Lansink, A.G.J.M. ; Stefanou, S.E. ; Kapelko, M. - \ 2015
Journal of Productivity Analysis 44 (2015)2. - ISSN 0895-562X - p. 189 - 198.
data envelopment analysis - sensitivity-analysis - inputs - dea - technologies - agriculture - efficiency - economies - outputs - demand
Diversification is often seen as a risk management tool, but specialization allows operators to exploit scale economies in single outputs and offers specialized operators more opportunities to fine-tune their skills which can promote a greater degree of technical proficiency. Measuring economies of scope facilitates the assessment of the benefits from output diversification versus specialization for operators and provides a metric for explaining and predicting trends towards specialization or diversification. However, the current literature on economies of scope provides little insight into the potential trade-off between the benefits of diversification and the presence of inefficiency in production and decision making. To remedy this shortcoming, this paper develops a measure of an effective (or behavioral) measure of scope economies which measures the benefits of diversification accounting for the contributions of allocative, congestion and technical efficiency in scaling the perfectly efficient version of scope economies. The application focuses on measuring and explaining economies of scope on Dutch crop farms.
Lumped surface and sub- surface runoff for erosion modeling within a small hilly watershed in northern Vietnam
Bui, Y.T. ; Orange, D. ; Visser, S.M. ; Hoanh, C.T. ; Laissus, M. ; Poortinga, A. ; Tran, D.T. ; Stroosnijder, L. - \ 2014
Hydrological Processes 28 (2014)6. - ISSN 0885-6087 - p. 2961 - 2974.
land-use changes - soil-erosion - sediment transport - steep slopes - sensitivity-analysis - scale - infiltration - catchments - framework - thailand
Developing models to predict on-site soil erosion and off-site sediment transport at the agricultural watershed scale represent an on-going challenge in research today. This study attempts to simulate the daily discharge and sediment loss using a distributed model that combines surface and sub-surface runoffs in a small hilly watershed (<1km(2)). The semi-quantitative model, Predict and Localize Erosion and Runoff (PLER), integrates the Manning-Strickler equation to simulate runoff and the Griffith University Erosion System Template equation to simulate soil detachment, sediment storage and soil loss based on a map resolution of 30m x 30m and over a daily time interval. By using a basic input data set and only two calibration coefficients based, respectively, on water velocity and soil detachment, the PLER model is easily applicable to different agricultural scenarios. The results indicate appropriate model performance and a high correlation between measured and predicted data with both Nash-Sutcliffe efficiency (Ef) and correlation coefficient (r(2)) having values>0.9. With the simple input data needs, PLER model is a useful tool for daily runoff and soil erosion modeling in small hilly watersheds in humid tropical areas.
Methods for uncertainty propagation in life cycle assessment
Groen, E.A. ; Heijungs, R. ; Bokkers, E.A.M. ; Boer, I.J.M. de - \ 2014
Environmental Modelling & Software 62 (2014). - ISSN 1364-8152 - p. 316 - 325.
sensitivity-analysis - decision-making - lca - model - input - simulation - inventory - output
Life cycle assessment (LCA) calculates the environmental impact of a product over its entire life cycle. Uncertainty analysis is an important aspect in LCA, and is usually performed using Monte Carlo sampling. In this study, Monte Carlo sampling, Latin hypercube sampling, quasi Monte Carlo sampling, analytical uncertainty propagation and fuzzy interval arithmetic were compared based on e.g. convergence rate and output statistics. Each method was tested on three LCA case studies, which differed in size and behaviour. Uncertainty propagation in LCA using a sampling method leads to more (directly) usable information compared to fuzzy interval arithmetic or analytical uncertainty propagation. Latin hypercube and quasi Monte Carlo sampling provide more accuracy in determining the sample mean than Monte Carlo sampling and can even converge faster than Monte Carlo sampling for some of the case studies discussed in this paper.
A global assembly of adult female mosquito mark-release-recapture data to inform the control of mosquito-borne pathogens
Guerra, C.A. ; Reiner Jr, R.C. ; Perkins, T.A. ; Lindsay, S.W. ; Midega, J.T. ; Brady, O.J. ; Barker, C.M. ; Reisen, W.K. ; Harrington, L.C. ; Takken, W. ; Kitron, U. ; Lloyd, A.L. ; Hay, S.I. ; Scott, T.W. ; Smith, D.L. - \ 2014
Parasites & Vectors 7 (2014). - ISSN 1756-3305 - 15 p.
dominant anopheles vectors - plasmodium-falciparum transmission - distribution maps - bionomic precis - human malaria - sensitivity-analysis - population-dynamics - mathematical-model - aedes-aegypti - culicidae
Background Pathogen transmission by mosquitos is known to be highly sensitive to mosquito bionomic parameters. Mosquito mark-release-recapture (MMRR) experiments are a standard method for estimating such parameters including dispersal, population size and density, survival, blood feeding frequency and blood meal host preferences. Methods We assembled a comprehensive database describing adult female MMRR experiments. Bibliographic searches were used to build a digital library of MMRR studies and selected data describing the reported outcomes were extracted. Results The resulting database contained 774 unique adult female MMRR experiments involving 58 vector mosquito species from the three main genera of importance to human health: Aedes, Anopheles and Culex. Crude examination of these data revealed patterns associated with geography as well as mosquito genus, consistent with bionomics varying by species-specific life history and ecological context. Recapture success varied considerably and was significantly different amongst genera, with 8, 4 and 1% of adult females recaptured for Aedes, Anopheles and Culex species, respectively. A large proportion of experiments (59%) investigated dispersal and survival and many allowed disaggregation of the release and recapture data. Geographic coverage was limited to just 143 localities around the world. Conclusions This MMRR database is a substantial contribution to the compilation of global data that can be used to better inform basic research and public health interventions, to identify and fill knowledge gaps and to enrich theory and evidence-based ecological and epidemiological studies of mosquito vectors, pathogen transmission and disease prevention. The database revealed limited geographic coverage and a relative scarcity of information for vector species of substantial public health relevance. It represents, however, a wealth of entomological information not previously compiled and of particular interest for mosquito-borne pathogen transmission models.
Evaluating the hydrological component of the new catchment-scale sediment delivery model LAPSUS-D
Keesstra, S.D. ; Temme, A.J.A.M. ; Schoorl, J.M. ; Visser, S.M. - \ 2014
Geomorphology 212 (2014). - ISSN 0169-555X - p. 97 - 107.
soil-erosion model - land-use change - landscape evolution - mesoscale catchment - sensitivity-analysis - simulation-model - drainage basins - single-event - runoff - water
Physically-based, catchment scale sediment delivery models have become increasingly complex, sophisticated and are suitable for a diverse range of environmental contexts. However, in their attempts to best represent the physical processes of erosion and deposition, these models require large and detailed input datasets. When such data are unavailable, annual sediment yield models are relied upon. However, in this class of models, widely available data such as daily precipitation and discharge are disregarded resulting in a reduction in temporal accuracy. To fill this scientific and management gap, the landscape evolution model LAPSUS was adapted (LAPSUS-D) for a meso-scale catchment to model sediment yield on a daily resolution. The water balance component within the model enables the calibration of the model in terms of water discharge with measured daily discharge at the outlet. This methodology is especially important when modeling sediment yield from catchments which are ungaged catchments in terms of sediment, but where hydrological data are available. As the simulation of sediment yield was the main objective of the study, the calibration focused on peak discharge. The focus on peak discharge provides insight into the capability of the model to generate, route and deliver sediment at the outlet of a meso-scale catchment. LAPSUS-D has daily temporal resolution and requires a 10 to 30 m pixel size DEM, soil map, land-use map and daily hydrological records (precipitation and discharge). In this paper we present the first assessment of the hydrological model performance and an analysis of the sensitivity of the model to input parameters. Our study site is a 23-km2 catchment in Upper Nysa Szalona, southwest Poland with temperate climate. Results show that the model can reliably predict peak discharge, which is expected in future studies to allow reliable estimates of sediment transport capacity, redistribution and yield.
Acceptability of inversely-modelled parameters for non-equilibrium sorption of pesticides in soil
Horst, M.M.S. ter; Boesten, J.J.T.I. ; Beinum, W. van; Beulke, S. - \ 2013
Environmental Modelling & Software 46 (2013). - ISSN 1364-8152 - p. 260 - 270.
sensitivity-analysis - simulation - isoproturon - persistence - lysimeters
Simulation of the increase of sorption in time is one of the options in higher tiers of pesticide regulatory leaching assessments to obtain more realistic leaching estimates. Therefore, accurate estimates of non-equilibrium sorption parameters are required as input for the pesticide leaching scenarios. Usually, non-equilibrium sorption is described with a two-site equilibrium/non-equilibrium model in which the non-equilibrium sorption is described with two parameters (i.e. the desorption rate coefficient of the non-equilibrium site and the Freundlich sorption coefficient of this site). Estimates of these parameters can be obtained with inverse modelling techniques. At the moment, there is little understanding about whether the confidence intervals provided by inverse modelling can be used as measure of the likely accuracy (i.e. how close the estimated value is to the true value) of these estimates. We set up a semi-global inverse modelling exercise for a large number of parameter sets (Le. different pesticides) using simulated datasets. Inverse modelling of non-equilibrium parameters demonstrated decreasing accuracy of the estimates for decreasing values of the non-equilibrium sorption parameters and the equilibrium sorption coefficient. Furthermore, we found a relationship between the accuracy of a parameter estimate and its CV (coefficient of variation) provided by the inverse modelling technique. Using this relationship we calculated the likelihood of rightly or wrongly accepting or rejecting a parameter estimate as a function of this CV. We recommend to use this likelihood as the basis of communication with decision makers on how to decide on accepting or rejecting parameter estimates. (C) 2013 Elsevier Ltd. All rights reserved.
Factors affecting domestic water consumption in rural households upon access to improved water supply: insights from the Wei River Basin, China
Fan, L. ; Liu, G. ; Wang, F. ; Geissen, V. ; Ritsema, C.J. - \ 2013
PLoS One 8 (2013)8. - ISSN 1932-6203 - p. 1 - 9.
path-coefficient analysis - developing-countries - sensitivity-analysis - use patterns - zimbabwe - behavior - disease - storage - home
Comprehensively understanding water consumption behavior is necessary to design efficient and effective water use strategies. Despite global efforts to identify the factors that affect domestic water consumption, those related to domestic water use in rural regions have not been sufficiently studied, particularly in villages that have gained access to improved water supply. To address this gap, we investigated 247 households in eight villages in the Wei River Basin where three types of improved water supply systems are implemented. Results show that domestic water consumption in liters per capita per day was significantly correlated with water supply pattern and vegetable garden area, and significantly negatively correlated with family size and age of household head. Traditional hygiene habits, use of water appliances, and preference for vegetable gardening remain dominant behaviors in the villages with access to improved water supply. Future studies on rural domestic water consumption should pay more attention to user lifestyles (water appliance usage habits, outdoor water use) and cultural backgrounds (age, education).
Managing uncertainty in integrated environmental modelling: The UncertWeb framework.
Bastin, L. ; Cornford, D. ; Jones, R. ; Heuvelink, G.B.M. ; Pebesma, E. ; Stasch, C. ; Nativi, S. ; Mazzetti, P. - \ 2013
Environmental Modelling & Software 39 (2013). - ISSN 1364-8152 - p. 116 - 134.
sensitivity-analysis - parameter-estimation - bayesian-approach - watershed model - climate-change - error - calibration - systems - design - tools
Web-based distributed modelling architectures are gaining increasing recognition as potentially useful tools to build holistic environmental models, combining individual components in complex workflows. However, existing web-based modelling frameworks currently offer no support for managing uncertainty. On the other hand, the rich array of modelling frameworks and simulation tools which support uncertainty propagation in complex and chained models typically lack the benefits of web based solutions such as ready publication, discoverability and easy access. In this article we describe the developments within the UncertWeb project which are designed to provide uncertainty support in the context of the proposed ‘Model Web’. We give an overview of uncertainty in modelling, review uncertainty management in existing modelling frameworks and consider the semantic and interoperability issues raised by integrated modelling. We describe the scope and architecture required to support uncertainty management as developed in UncertWeb. This includes tools which support elicitation, aggregation/disaggregation, visualisation and uncertainty/sensitivity analysis. We conclude by highlighting areas that require further research and development in UncertWeb, such as model calibration and inference within complex environmental models.
The DYNAMO-HIA Model: An Efficient Implementation of a Risk Factor/Chronic Disease Markov Model for Use in Health Impact Assessment (HIA)
Boshuizen, H.C. ; Lhachimi, S.K. ; Baal, P.H.M. van; Hoogenveen, R.T. ; Smit, H.A. ; Mackenbach, J.P. ; Nusselder, W.J. - \ 2012
Demography 49 (2012)4. - ISSN 0070-3370 - p. 1259 - 1283.
sensitivity-analysis - economic-evaluation - life expectancy - population - care - prevalence
In Health Impact Assessment (HIA), or priority-setting for health policy, effects of risk factors (exposures) on health need to be modeled, such as with a Markov model, in which exposure influences mortality and disease incidence rates. Because many risk factors are related to a variety of chronic diseases, these Markov models potentially contain a large number of states (risk factor and disease combinations), providing a challenge both technically (keeping down execution time and memory use) and practically (estimating the model parameters and retaining transparency). To meet this challenge, we propose an approach that combines micro-simulation of the exposure information with macro-simulation of the diseases and survival. This approach allows users to simulate exposure in detail while avoiding the need for large simulated populations because of the relative rareness of chronic disease events. Further efficiency is gained by splitting the disease state space into smaller spaces, each of which contains a cluster of diseases that is independent of the other clusters. The challenge of feasible input data requirements is met by including parameter calculation routines, which use marginal population data to estimate the transitions between states. As an illustration, we present the recently developed model DYNAMO-HIA (DYNAMIC MODEL for Health Impact Assessment) that implements this approach.
Spatially and Financially Explicit Population Viability Analysis of Maculinea alcon in The Netherlands
Radchuk, V. ; Wallis de Vries, M.F. ; Schtickzelle, N. - \ 2012
PLoS One 7 (2012)6. - ISSN 1932-6203
individual-based model - large blue butterflies - habitat quality - ant nests - metapopulation dynamics - sensitivity-analysis - host-specificity - social parasite - conservation - lepidoptera
Background The conservation of species structured in metapopulations involves an important dilemma of resource allocation: should investments be directed at restoring/enlarging habitat patches or increasing connectivity. This is still an open question for Maculinea species despite they are among the best studied and emblematic butterfly species, because none of the population dynamics models developed so far included dispersal. Methodology/Principal Findings We developed the first spatially and financially explicit Population Viability Analysis model for Maculinea alcon, using field data from The Netherlands. Implemented using the RAMAS/GIS platform, the model incorporated both local (contest density dependence, environmental and demographic stochasticities), and regional population dynamics (dispersal rates between habitat patches). We selected four habitat patch networks, contrasting in several basic features (number of habitat patches, their quality, connectivity, and occupancy rate) to test how these features are affecting the ability to enhance population viability of four basic management options, designed to incur the same costs: habitat enlargement, habitat quality improvement, creation of new stepping stone habitat patches, and reintroduction of captive-reared butterflies. The PVA model was validated by the close match between its predictions and independent field observations on the patch occupancy pattern. The four patch networks differed in their sensitivity to model parameters, as well as in the ranking of management options. Overall, the best cost-effective option was enlargement of existing habitat patches, followed by either habitat quality improvement or creation of stepping stones depending on the network features. Reintroduction was predicted to generally be inefficient, except in one specific patch network. Conclusions/Significance Our results underline the importance of spatial and regional aspects (dispersal and connectivity) in determining the impact of conservation actions, even for a species previously considered as sedentary. They also illustrate that failure to account for the cost of management scenarios can lead to very different conclusions.
Uncertainty modelling to evaluate nitrogen balances as a tool to determine N2 and N2O formation in ammonia bioscrubbers
Estelles, F. ; Calvet, S. ; Melse, R.W. ; Ogink, N.W.M. - \ 2012
Environmental Engineering Science 29 (2012)6. - ISSN 1092-8758 - p. 520 - 525.
sensitivity-analysis - biotrickling filter - ventilation rates - waste gases - air - removal - emissions - netherlands - buildings - europe
Biological scrubbers aim at reducing gaseous ammonia emissions by transferring it to a water phase followed by conversion to nitrite and nitrate. A small part of the removed nitrogen may be emitted as N2 and N2O produced as a result of denitrification processes. Due to the large greenhouse warming potential of N2O, even a small emission could be a point of concern. Determining these N losses in form of N2 and N2O via nitrogen balance is an alternative, but little is known about the uncertainty associated to this method. The main aim of this work was to develop an uncertainty model that evaluated N-balances in biological scrubbers in terms of result uncertainty. Secondary objectives were to provide a methodology to determine individual uncertainties involved, and to conduct a sensitivity analysis to identify the main contributors to the final uncertainty. For a defined scenario (biotrickling scrubber, 70% NH3 removal; 5% of inlet N-NH3 lost as N2 and N2O), the standard uncertainty expressed in relative terms of the average was 132% (released N in form of N2 and N2O). Main contributors to the final uncertainty were airflow rate and water volume in the scrubber basin. Uncertainty of the measurements of gaseous NH3 concentrations and N compounds in water had a reduced effect on the final uncertainty. Based on these results, N balances are not recommended to evaluate N2 and N2O formation in biological scrubbers, at least for the conditions considered in this work.
Quantifying water and salt fluxes in a lowland polder catchment dominated by boil seepage: a probabilistic end-member mixing approach
Louw, P.G.B. de; Velde, Y. van der; Zee, S.E.A.T.M. van der - \ 2011
Hydrology and Earth System Sciences 15 (2011)7. - ISSN 1027-5606 - p. 2101 - 2117.
grondwater - zoutwaterindringing - kwel - polders - kustgebieden - groundwater - salt water intrusion - seepage - coastal areas - rhine-meuse delta - sensitivity-analysis - surface-water - groundwater discharge - parameter uncertainty - coastal aquifers - climate-change - model - netherlands - flow
Upward saline groundwater seepage is leading to surface water salinization of deep lying polders in the Netherlands. Identifying measures to reduce the salt content requires a thorough understanding and quantification of the dominant sources of water and salt on a daily basis. However, as in most balance studies, there are large uncertainties in the contribution from groundwater seepage. Taking these into account, we applied a probabilistic (GLUE) end-member mixing approach to simulate two years of daily to weekly observations of discharge, salt loads and salt concentration of water pumped out of an artificially drained polder catchment area. We were then able to assess the contribution from the different sources to the water and salt balance of the polder and uncertainties in their quantification. Our modelling approach demonstrates the need to distinguish preferential from diffuse seepage. Preferential seepage via boils contributes, on average, 66 % to the total salt load and only about 15 % to the total water flux into the polder and therefore forms the main salinization pathway. With the model we were able to calculate the effect of future changes on surface water salinity and to assess the uncertainty in our predictions. Furthermore, we analyzed the parameter sensitivity and uncertainty to determine for which parameter the quality of field measurements should be improved to reduce model input and output uncertainty. High frequency measurements of polder water discharge and weighted concentration at the outlet of the catchment area appear to be essential for obtaining reliable simulations of water and salt fluxes and for allotting these to the different sources.
New challenges in integrated water quality modelling
Rode, M. ; Arhonditsis, G. ; Balin, D. ; Kebede, T. ; Krysanova, V. ; Griensven, A. ; Zee, S.E.A.T.M. van der - \ 2010
Hydrological Processes 24 (2010)24. - ISSN 0885-6087 - p. 3447 - 3461.
chain monte-carlo - stream nitrogen attenuation - hyporheic zone - uncertainty analysis - sensitivity-analysis - catchment models - eutrophication models - bayesian calibration - nutrient losses - organic-matter
There is an increasing pressure for development of integrated water quality models that effectively couple catchment and in-stream biogeochemical processes. This need stems from increasing legislative requirements and emerging demands related to contemporary climate and land use changes. Modelling water quality and nutrient transport is challenging due a number of serious constraints associated with the input data as well as existing knowledge gaps related to the mathematical description of landscape and in-stream biogeochemical processes. The present paper summarizes the discussions held during the workshop on ‘Integrated water quality modelling: future demands and perspectives’ (Magdeburg, Germany, 23–24 June 2008). Our primary focus is placed on the current limitations and future challenges in water quality modelling. In particular, we evaluate the current state of integrated water quality modelling, we highlight major research needs to assess and reduce model uncertainties, and we examine opportunities to enhance model predictive capacity. To better account for the need of upscaling process knowledge, we advocate the adoption of combined process-oriented field and modelling studies at representative sites. In-stream nutrient metabolism investigations at the entire range of stream and river scales will enable the improvement of the mathematical representation of these processes and therefore the articulation level of coupled watershed-receiving waterbody models. Keeping the complexity of integrated water quality models in mind, the development of novel uncertainty analysis techniques for rigorous assessing parameter identification and model credibility is essential. In this regard, we recommend the use of Bayesian calibration frameworks that explicitly accommodate measurement errors, parameter uncertainties, and model structure errors. The Bayesian inference can be used to quantify the information the data contain about model inputs, to offer insights into the covariance structure among parameter estimates, to obtain predictions along with credible intervals for model outputs, and to effectively address the ‘change of support’ problems
A physiologically based biodynamic (PBBD) model for estragole DNA binding in rat liver based on in vitro kinetic data and estragole DNA adduct formation in primary hepatocytes
Paini, A. ; Punt, A. ; Viton, F. ; Scholz, G. ; Delatour, T. ; Marin-Kuan, M. ; Schilter, B. ; Bladeren, P.J. van; Rietjens, I. - \ 2010
Toxicology and Applied Pharmacology 245 (2010)1. - ISSN 0041-008X - p. 57 - 66.
sensitivity-analysis - risk-assessment - mouse-liver - 1'-hydroxyestragole - safrole - humans - bioactivation - toxicity - 1'-hydroxysafrole - carcinogenicity
Estragole has been shown to be hepatocarcinogenic in rodent species at high-dose levels. Translation of these results into the likelihood of formation of DNA adducts, mutation, and ultimately cancer upon more realistic low-dose exposures remains a challenge. Recently we have developed physiologically based biokinetic (PBBK) models for rat and human predicting bioactivation of estragole. These PBBK models, however, predict only kinetic characteristics. The present study describes the extension of the PBBK model to a so-called physiologically based biodynamic (PBBD) model predicting in vivo DNA adduct formation of estragole in rat liver. This PBBD model was developed using in vitro data on DNA adduct formation in rat primary hepatocytes exposed to 1'-hydroxyestragole. The model was extended by linking the area under the curve for 1'-hydroxyestragole formation predicted by the PBBK model to the area under the curve for 1'-hydroxyestragole in the in vitro experiments. The outcome of the PBBD model revealed a linear increase in DNA adduct formation with increasing estragole doses up to 100 mg/kg bw. Although DNA adduct formation of genotoxic carcinogens is generally seen as a biomarker of exposure rather than a biomarker of response, the PBBD model now developed is one step closer to the ultimate toxic effect of estragole than the PBBK model described previously. Comparison of the PBBD model outcome to available data showed that the model adequately predicts the dose-dependent level of DNA adduct formation. The PBBD model predicts DNA adduct formation at low levels of exposure up to a dose level showing to cause cancer in rodent bioassays, providing a proof of principle for modeling a toxicodynamic in vivo endpoint on the basis of solely in vitro experimental data.
Effects of woody elements on simulated canopy reflectance: implications for forest chlorophyll content retrieval
Verrelst, J. ; Schaepman, M.E. ; Malenovsky, Z. ; Clevers, J.G.P.W. - \ 2010
Remote Sensing of Environment 114 (2010)3. - ISSN 0034-4257 - p. 647 - 656.
leaf optical-properties - light-use efficiency - resolution satellite imagery - radiative-transfer models - high-spatial-resolution - spectral reflectance - imaging spectroscopy - vegetation indexes - hyperspectral reflectance - sensitivity-analysis
An important bio-indicator of actual plant health status, the foliar content of chlorophyll a and b (Cab), can be estimated using imaging spectroscopy. For forest canopies, however, the relationship between the spectral response and leaf chemistry is confounded by factors such as background (e.g. understory), canopy structure, and the presence of non-photosynthetic vegetation (NPV, e.g. woody elements)—particularly the appreciable amounts of standing and fallen dead wood found in older forests. We present a sensitivity analysis for the estimation of chlorophyll content in woody coniferous canopies using radiative transfer modeling, and use the modeled top-of-canopy reflectance data to analyze the contribution of woody elements, leaf area index (LAI), and crown cover (CC) to the retrieval of foliar Cab content. The radiative transfer model used comprises two linked submodels: one at leaf level (PROSPECT) and one at canopy level (FLIGHT). This generated bidirectional reflectance data according to the band settings of the Compact High Resolution Imaging Spectrometer (CHRIS) from which chlorophyll indices were calculated. Most of the chlorophyll indices outperformed single wavelengths in predicting Cab content at canopy level, with best results obtained by the Maccioni index ([R780 - R710] / [R780 - R680]). We demonstrate the performance of this index with respect to structural information on three distinct coniferous forest types (young, early mature and old-growth stands). The modeling results suggest that the spectral variation due to variation in canopy chlorophyll content is best captured for stands with medium dense canopies. However, the strength of the up-scaled Cab signal weakens with increasing crown NPV scattering elements, especially when crown cover exceeds 30%. LAI exerts the least perturbations. We conclude that the spectral influence of woody elements is an important variable that should be considered in radiative transfer approaches when retrieving foliar pigment estimates in heterogeneous stands, particularly if the stands are partly defoliated or long-lived
Gaining local accuracy while not losing generality – extending the range of gap model applications
Didion, M.P. ; Kupferschmid, A.D. ; Zingg, A. ; Fahse, L. ; Bugmann, H. - \ 2009
Canadian Journal of Forest Research 39 (2009)6. - ISSN 0045-5067 - p. 1092 - 1107.
forest patch model - species composition - sensitivity-analysis - population biology - mountain forests - growth - stand - dynamics - simulation - succession
For the study of long-term processes in forests, gap models generally sacrifice accuracy (i.e., simulating system behavior in a quantitatively accurate manner) for generality (i.e., representing a broad range of systems' behaviors with the same model). We selected the gap model ForClim to evaluate whether the local accuracy of forest succession models can be increased based on a parsimonious modeling approach that avoids the additional complexity of a 3D crown model, thus keeping parameter requirements low. We improved the representation of tree crowns by introducing feedbacks between (i) light availability and leaf area per tree and (ii) leaf area per tree and diameter growth rate to account for the self-pruning in real stands. The local accuracy of the new model, ForClim v2.9.5, was considerably improved in simulations at three long-term forest research sites in the Swiss Alps, while its generality was maintained as shown in simulations of potential natural vegetation along a broad environmental gradient in Central Europe. We conclude that the predictive ability of a model does not depend on its complexity, but on the reproduction of patterns. Most importantly, model complexity should be consistent with the objectives of the study and the level of system understanding.
The Influence of Rain Sensible Heat and Subsurface Energy Transport on the Energy Balance at the Land Surface
Kollet, S.J. ; Cvijanovic, I. ; Schüttemeyer, D. ; Maxwell, R.M. ; Moene, A.F. ; Bayer, P. - \ 2009
Vadose Zone Journal 8 (2009). - ISSN 1539-1663 - p. 846 - 857.
atmosphere coupling experiment - soil-moisture - sensitivity-analysis - porous-media - model - temperature - water - flow - evaporation - flux
In land surface models, which account for the energy balance at the land surface, subsurface heat transport is an important component that reciprocally influences ground, sensible, and latent heat fluxes and net radiation. In most models, subsurface heat transport parameterizations are commonly simplified for computational efficiency. A simplification made in all models is to disregard the sensible heat of rain, Hl, and convective subsurface heat flow, qcv, i.e., the convective transport of heat through moisture redistribution. These simplifications act to decouple heat transport from moisture transport at the land surface and in the subsurface, which is not realistic. The influence of Hl and qcv on the energy balance was studied using a coupled model that integrates a subsurface moisture and energy transport model with a land surface model of the land surface energy balance, showing that all components of the land surface energy balance depend on Hl. The strength of the dependence is related to the rainfall rate and the temperature difference between the rain water and the soil surface. The rain water temperature is a parameter rarely measured in the field that introduces uncertainty in the calculations and was approximated using the either air or wet bulb temperatures in different simulations. In addition, it was shown that the lower boundary condition for closing the problem of subsurface heat transport, including convection, has strong implications on the energy balance under dynamic equilibrium conditions. Comparison with measured data from the Meteostation Haarweg, Wageningen, the Netherlands, shows good agreement and further underscores the importance of a more tightly coupled subsurface hydrology–energy balance formulation in land surface models
Integration of Probabilistic Exposure Assessment and Probabilistic Hazard Characterization
Voet, H. van der; Slob, W. - \ 2007
Risk Analysis 27 (2007)2. - ISSN 0272-4332 - p. 351 - 371.
chemical risk-assessment - dietary exposure - sensitivity-analysis - benchmark approach - health-risks - variability - uncertainty - food - distributions - consumption
A method is proposed for integrated probabilistic risk assessment where exposure assessment and hazard characterization are both included in a probabilistic way. The aim is to specify the probability that a random individual from a defined (sub)population will have an exposure high enough to cause a particular health effect of a predefined magnitude, the critical effect size (CES). The exposure level that results in exactly that CES in a particular person is that person's individual critical effect dose (ICED). Individuals in a population typically show variation, both in their individual exposure (IEXP) and in their ICED. Both the variation in IEXP and the variation in ICED are quantified in the form of probability distributions. Assuming independence between both distributions, they are combined (by Monte Carlo) into a distribution of the individual margin of exposure (IMoE). The proportion of the IMoE distribution below unity is the probability of critical exposure (PoCE) in the particular (sub)population. Uncertainties involved in the overall risk assessment (i.e., both regarding exposure and effect assessment) are quantified using Monte Carlo and bootstrap methods. This results in an uncertainty distribution for any statistic of interest, such as the probability of critical exposure (PoCE). The method is illustrated based on data for the case of dietary exposure to the organophosphate acephate. We present plots that concisely summarize the probabilistic results, retaining the distinction between variability and uncertainty. We show how the relative contributions from the various sources of uncertainty involved may be quantified.
Improving efficiency of uncertainty analysis in complex Integrated Assessment models: The case of the RAINS emission module
Gabbert, S.G.M. - \ 2006
Environmental Monitoring and Assessment 119 (2006)1-3. - ISSN 0167-6369 - p. 507 - 526.
sensitivity-analysis - policy models - europe - strategies
Ever since the Regional Acidification Information and Simulation Model (RAINS) has been constructed, the treatment of uncertainty has remained an issue of major interest. In a recent review of the model performed for the Clean Air for Europe (CAFE) programme of the European Commission, a more systematic and structured uncertainty analysis has been recommended. This paper aims at contributing to the scientific debate how this can be achieved. Because of its complex structure on the one hand and limited research resources (time, computational capacities) on the other hand a full-blown uncertainty analysis in RAINS is hardly feasible. Therefore, all types of uncertainty require more efficient ways for uncertainty analysis. With respect to parameter uncertainty, we propose to focus research efforts for uncertainty analysis on key parameters. Among different approaches to select key parameters that have been discussed in the literature screening methods seem to be particularly appropriate for complex, deterministic Integrated Assessment models such as RAINS. Surprisingly, in Integrated Assessment modelling for air pollution problems of screening design have not been taken up so far. As a case study we consider the emission module of RAINS. We show that its structure allows for a straightforward and effective screening procedure
State-of-the-Art Review : a user's guide to the brave new world of designing simulation experiments
Kleijnen, J.P.C. - \ 2005
INFORMS journal on computing 17 (2005)3. - ISSN 1091-9856 - p. 263 - 289.
computer experiments - sensitivity-analysis - sampling criteria - robust design - output - model - optimization - methodology - metamodels - management
Many simulation practitioners can get more from their analyses by using the statistical theory on design of experiments (DOE) developed specifically for exploring computer models. We discuss a toolkit of designs for simulators with limited DOE expertise who want to select a design and an appropriate analysis for their experiments. Furthermore, we provide a research agenda listing problems in the design of simulation experiments¿as opposed to real-world experiments¿that require more investigation. We consider three types of practical problems: (1) developing a basic understanding of a particular simulation model or system, (2) finding robust decisions or policies as opposed to so-called optimal solutions, and (3) comparing the merits of various decisions or policies. Our discussion emphasizes aspects that are typical for simulation, such as having many more factors than in real-world experiments, and the sequential nature of the data collection. Because the same problem type may be addressed through different design types, we discuss quality attributes of designs, such as the ease of design construction, the flexibility for analysis, and efficiency considerations. Moreover, the selection of the design type depends on the metamodel (response surface) that the analysts tentatively assume; for example, complicated metamodels require more simulation runs. We present several procedures to validate the metamodel estimated from a specific design, and we summarize a case study illustrating several of our major themes. We conclude with a discussion of areas that merit more work to achieve the potential benefits¿either via new research or incorporation into standard simulation or statistical packages.