Improving Forecast Skill of Lowland Hydrological Models Using Ensemble Kalman Filter and Unscented Kalman Filter
Sun, Y. ; Bao, W. ; Valk, K. ; Brauer, C.C. ; Sumihar, J. ; Weerts, A.H. - \ 2020
Water Resources Research 56 (2020)8. - ISSN 0043-1397
Kalman filters - lowland hydrology - state updating - streamflow - verification
For operational water management in lowlands and polders (for instance, in the Netherlands), lowland hydrological models are used for flow prediction, often as an input for a real-time control system to steer water with pumps and weirs to keep water levels within acceptable bounds. Therefore, proper initialization of these models is essential. The ensemble Kalman filter (EnKF) has been widely used due to its relative simplicity and robustness, while the unscented Kalman filter (UKF) has received little attention in the operational context. Here, we test both UKF and EnKF using a lowland lumped hydrological model. The results of a reforecast experiment in an operational context using an hourly time step show that when using nine ensemble members, both filters can improve the accuracy of the forecast by updating the state of a lumped hydrological model (Wageningen Lowland Runoff Simulator, WALRUS) based on the observed discharge, while UKF has achieved better performance than EnKF. Additionally, we show that an increase in the ensemble members does not necessarily mean a significant increase in performance. WALRUS model with either UKF or EnKF could be considered for hydrological forecasting for supporting water management of polders and lowlands, with UKF being the computationally leaner option.
How to measure, report and verify soil carbon change to realize the potential of soil carbon sequestration for atmospheric greenhouse gas removal
Smith, Pete ; Soussana, Jean Francois ; Angers, Denis ; Schipper, Louis ; Chenu, Claire ; Rasse, Daniel P. ; Batjes, Niels H. ; Egmond, Fenny van; McNeill, Stephen ; Kuhnert, Matthias ; Arias-Navarro, Cristina ; Olesen, Jorgen E. ; Chirinda, Ngonidzashe ; Fornara, Dario ; Wollenberg, Eva ; Álvaro-Fuentes, Jorge ; Sanz-Cobena, Alberto ; Klumpp, Katja - \ 2020
Global Change Biology 26 (2020)1. - ISSN 1354-1013 - p. 219 - 241.
measurement - monitoring - MRV - reporting - soil organic carbon - soil organic matter - verification
There is growing international interest in better managing soils to increase soil organic carbon (SOC) content to contribute to climate change mitigation, to enhance resilience to climate change and to underpin food security, through initiatives such as international ‘4p1000’ initiative and the FAO's Global assessment of SOC sequestration potential (GSOCseq) programme. Since SOC content of soils cannot be easily measured, a key barrier to implementing programmes to increase SOC at large scale, is the need for credible and reliable measurement/monitoring, reporting and verification (MRV) platforms, both for national reporting and for emissions trading. Without such platforms, investments could be considered risky. In this paper, we review methods and challenges of measuring SOC change directly in soils, before examining some recent novel developments that show promise for quantifying SOC. We describe how repeat soil surveys are used to estimate changes in SOC over time, and how long-term experiments and space-for-time substitution sites can serve as sources of knowledge and can be used to test models, and as potential benchmark sites in global frameworks to estimate SOC change. We briefly consider models that can be used to simulate and project change in SOC and examine the MRV platforms for SOC change already in use in various countries/regions. In the final section, we bring together the various components described in this review, to describe a new vision for a global framework for MRV of SOC change, to support national and international initiatives seeking to effect change in the way we manage our soils.
Fatty acid and triglycerides profiling of retail organic, conventional and pasture milk: Implications for health and authenticity
Capuano, E. ; Gravink, R. ; Boerrigter-Eenling, G.R. ; Ruth, S.M. van - \ 2015
International Dairy Journal 42 (2015). - ISSN 0958-6946 - p. 58 - 63.
conjugated linoleic acids - coronary-heart-disease - fresh grass - dairy-products - cows - verification - metaanalysis - cholesterol - systems
Retail full fat high temperature short time pasteurised conventional, organic and “weidemelk” (Dutch quality label for milk from cows on pasture at least 6 h per day, 120 days per year) milk samples were collected on 2 sampling dates in winter and 4 sampling dates in summer 2013 and analysed for the fatty acid (FA) and the triglyceride (TAG) profile by gas chromatography-flame ionisation detection. FA profile of organic milk was significantly different from that of conventional and “weidemelk” milk both in summer and in winter and the differences between conventional and “weidemelk” milk were less remarkable or negligible. Analogously, the TAG profile of organic milk was different from that of the other two groups but the differences were weaker compared with FA profile. The differences in FA composition of retail full fat milk may have implications for consumers' health and may be used for the authentication of retail organic milk.
Merging validation and evaluation of ecological models to evaluation': a review of terminology and a practical approach
Augusiak, J.A. ; Brink, P.J. van den; Grimm, V. - \ 2014
Ecological Modelling 280 (2014). - ISSN 0304-3800 - p. 117 - 128.
individual-based models - risk-assessment - environmental-models - quality-assurance - simulation-model - complex-systems - beech forests - assessments - verification - uncertainty
Confusion about model validation is one of the main challenges in using ecological models for decision support, such as the regulation of pesticides. Decision makers need to know whether a model is a sufficiently good representation of its real counterpart and what criteria can be used to answer this question. Unclear terminology is one of the main obstacles to a good understanding of what model validation is, how it works, and what it can deliver. Therefore, we performed a literature review and derived a standard set of terms. ‘Validation’ was identified as a catch-all term, which is thus useless for any practical purpose. We introduce the term ‘evaludation’, a fusion of ‘evaluation’ and ‘validation’, to describe the entire process of assessing a model's quality and reliability. Considering the iterative nature of model development, the modelling cycle, we identified six essential elements of evaludation: (i) ‘data evaluation’ for scrutinising the quality of numerical and qualitative data used for model development and testing; (ii) ‘conceptual model evaluation’ for examining the simplifying assumptions underlying a model's design; (iii) ‘implementation verification’ for testing the model's implementation in equations and as a computer programme; (iv) ‘model output verification’ for comparing model output to data and patterns that guided model design and were possibly used for calibration; (v) ‘model analysis’ for exploring the model's sensitivity to changes in parameters and process formulations to make sure that the mechanistic basis of main behaviours of the model has been well understood; and (vi) ‘model output corroboration’ for comparing model output to new data and patterns that were not used for model development and parameterisation. Currently, most decision makers require ‘validating’ a model by testing its predictions with new experiments or data. Despite being desirable, this is neither sufficient nor necessary for a model to be useful for decision support. We believe that the proposed set of terms and its relation to the modelling cycle can help to make quality assessments and reality checks of ecological models more comprehensive and transparent. Keywords Model validation; Terminology; Decision support; Documentation; Ecological models; Risk assessment
Spatial patterns of infauna, epifauna and demersal fish communities in the North Sea.
Reiss, H. ; Degraer, S. ; Duineveld, G.C.A. ; Craeymeersch, J.A.M. - \ 2010
ICES Journal of Marine Science 67 (2010). - ISSN 1054-3139 - p. 278 - 293.
species-diversity - sampling effort - irish sea - classification - circulation - model - assemblages - density - biodiversity - verification
Understanding the structure and interrelationships of North Sea benthic invertebrate and fish communities and their underlying environmental drivers is an important prerequisite for conservation and spatial ecosystem management on scales relevant to ecological processes. Datasets of North Sea infauna, epifauna, and demersal fish (1999–2002) were compiled and analysed to (i) identify and compare spatial patterns in community structure, and (ii) relate these to environmental variables. The multivariate analyses revealed significantly similar large-scale patterns in all three components with major distinctions between a southern community (Oyster Ground and German Bight), an eastern Channel and southern coastal community, and at least one northern community (>50 m deep). In contrast, species diversity patterns differed between the components with a diversity gradient for infauna and epifauna decreasing from north to south, and diversity hotspots of demersal fish, e.g. near the major inflows of Atlantic water. The large-scale hydrodynamic variables were the main drivers for the structuring of communities, whereas sediment characteristics appeared to be less influential, even for the infauna communities. The delineation of ecologically meaningful ecosystem management units in the North Sea might be based on the structure of the main faunal ecosystem components
Real-Time Water Vapor Maps from a GPS Surface Network: Construction, Validation, and Applications
Haan, S. de; Holleman, I. ; Holtslag, A.A.M. - \ 2009
Journal of Applied Meteorology and Climatology 48 (2009)7. - ISSN 1558-8424 - p. 1302 - 1316.
global positioning system - precipitable water - model - verification - netherlands - meteorology - radiosonde - radiometer - errors - delay
In this paper the construction of real-time integrated water vapor (IWV) maps from a surface network of global positioning system (GPS) receivers is presented. The IWV maps are constructed using a twodimensional variational technique with a persistence background that is 15 min old. The background error covariances are determined using a novel two-step method, which is based on the Hollingsworth¿Lonnberg method. The quality of these maps is assessed by comparison with radiosonde observations and IWV maps from a numerical weather prediction (NWP) model. The analyzed GPS IWV maps have no bias against radiosonde observations and a small bias against NWP analysis and forecasts up to 9 h. The standard deviation with radiosonde observations is around 2 kg m-2, and the standard deviation with NWP increases with increasing forecast length (from 2 kg m-2 for the NWP analysis to 4 kg m-2 for a forecast length of 48 h). To illustrate the additional value of these real-time products for nowcasting, three thunderstorm cases are discussed. The constructed GPS IWV maps are combined with data from the weather radar, a lightning detection network, and surface wind observations. All cases show that the location of developing thunderstorms can be identified 2 h prior to initiation in the convergence of moist air.
Understanding heat transfer in 2D channel flows including recirculation
Dirkse, M.H. ; Loon, W.K.P. van; Stigter, J.D. ; Bot, G.P.A. - \ 2007
International Journal of Thermal Sciences 46 (2007)7. - ISSN 1290-0729 - p. 682 - 691.
comprehensive approach - cfd simulations - verification - validation - convection
Inviscid, irrotational two-dimensional flows can be modelled using the Schwarz¿Christoffel integral. Although bounded flows including boundary layer separation and recirculation are not irrotational, a model is presented that uses the Schwarz¿Christoffel integral to model these flows. The model separates the flow domain in the main flow area, where irrotational flow is assumed, and recirculation areas, which are modelled as monopolar vortices. The model has unknown parameters, which are geometric characteristics of the velocity field. The method is demonstrated on a channel with alternating baffles. Many variations of this system were modelled using CFD modelling, and the flow was a typical combination of main flow and recirculation. The CFD results were used as reference to calibrate the parameters of the Schwarz¿Christoffel model. Many parameters appeared to be constant, and calibrating only three variable parameters yielded about 22% error for most velocity fields. After this, heat transfer was added to the CFD models, and the heat flux was analysed using the three variable parameters representing the velocity field. This way, a new model is found for the heat flux from a wall bounding a vortex, which has an error of 7%. Finally, we have calibrated the parameters using a limited number of given velocity vectors, demonstrating that the parameters can be calibrated against a real set of measurements.
Extension of anaerobic digestion model no. 1 with the processes of sulphate reduction
Fedorovich, V. ; Lens, P.N.L. ; Kalyuzhnyi, S. - \ 2003
Applied Biochemistry and Biotechnology 109 (2003)1-3. - ISSN 0273-2289 - p. 33 - 46.
granular sludge reactor - uasb reactor - methanogenesis - verification - competition - inhibition - velocity - hydrogen - biomass - glucose
In the present work, the Anaerobic Digestion Model No. 1 (ADM1) for computer simulation of anaerobic processes was extended to the processes of sulfate reduction. The upgrade maintained the structure of ADM1 and included additional blocks describing sulfate-reducing processes (multiple reaction stoichiometry, microbial growth kinetics, conventional material balances for ideally mixed reactor, liquid-gas interactions, and liquid-phase equilibrium chemistry). The extended model was applied to describe a longterm experiment on sulfate reduction in a volatile fatty acid-fed upflow anaerobic sludge bed reactor and was generally able to predict the outcome of competition among acetogenic bacteria, methanogenic archaea, and sulfate- reducing bacteria for these substrates. The computer simulations also showed that when the upward liquid velocity in the reactor exceeds 1 m/d, the structure of the sludge becomes essential owing to bacterial detachment.