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.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Ecosystem service change caused by climatological and non-climatological drivers: a Swiss case study
    Braun, Daniela ; Jong, Rogier de; Schaepman, Michael E. ; Furrer, Reinhard ; Hein, Lars ; Kienast, Felix ; Damm, Alexander - \ 2019
    Ecological Applications 29 (2019)4. - ISSN 1051-0761
    climate change - land use change - regulating services - remote sensing - time series - trends

    Understanding the drivers of ecosystem change and their effects on ecosystem services are essential for management decisions and verification of progress towards national and international sustainability policies (e.g., Aichi Biodiversity Targets, Sustainable Development Goals). We aim to disentangle spatially the effect of climatological and non-climatological drivers on ecosystem service supply and trends. Therefore, we explored time series of three ecosystem services in Switzerland between 2004 and 2014: carbon dioxide regulation, soil erosion prevention, and air quality regulation. We applied additive models to describe the spatial variation attributed to climatological (i.e., temperature, precipitation and relative sunshine duration) and non-climatological drivers (i.e., random effects representing other spatially structured processes) that may affect ecosystem service change. Obtained results indicated strong influences of climatological drivers on ecosystem service trends in Switzerland. We identified equal contributions of all three climatological drivers on trends of carbon dioxide regulation and soil erosion prevention, while air quality regulation was more strongly influenced by temperature. Additionally, our results showed that climatological and non-climatological drivers affected ecosystem services both negatively and positively, depending on the regions (in particular lower and higher altitudinal areas), drivers, and services assessed. Our findings highlight stronger effects of climatological compared to non-climatological drivers on ecosystem service change in Switzerland. Furthermore, drivers of ecosystem change display a spatial heterogeneity in their influence on ecosystem service trends. We propose an approach building on an additive model to disentangle the effect of climatological and non-climatological drivers on ecosystem service trends. Such analyses should be extended in the future to ecosystem service flow and demand to complete ecosystem service assessments and to demonstrate and communicate more clearly the benefits of ecosystem services for human well-being.

    Dataset: BioTIME: A database of biodiversity time series for the Anthropocene
    Dornelas, M. ; Antão, L.H. ; Moyes, F. ; Bates, A.E. ; Magurran, Anne E. ; Adam, D. ; Akhmetzhanova, A.A. ; Appeltans, W. ; Arcos, J.M. ; Arnold, H. ; Prins, Herbert - \ 2018
    University of St Andrews
    time series - ecology - biodiversity - Anthropocene - spatial and temporal analysis
    The BioTIME database contains raw data on species identities and abundances in ecological assemblages through time. The database consists of 11 tables; one raw data table plus ten related meta data tables. For further information please see our associated data paper. This data consists of several elements: BioTIMESQL_02_04_2018.sql - an SQL file for the full public version of BioTIME which can be imported into any mySQL database. BioTIMEQuery_02_04_2018.csv - data file, although too large to view in Excel, this can be read into several software applications such as R or various database packages. BioTIMEMetadata_02_04_2018.csv - file containing the meta data for all studies. BioTIMECitations_02_04_2018.csv - file containing the citation list for all studies. BioTIMECitations_02_04_2018.xlsx - file containing the citation list for all studies (some special characters are not supported in the csv format). BioTIMEInteractions_02_04_2018.Rmd - an r markdown page providing a brief overview of how to interact with the database and associated .csv files (this will not work until field paths and database connections have been added/updated).
    Integrated-lts-cbm v1.0.0
    DeVries, B.R. - \ 2016
    landsat - time series - community-based forestry - tropical forest - deforestation - forest degradation
    Meerwaarde van ruimtelijke neerslagdata voor het modelleren van stijghoogtefluctuaties
    Ottow, Bouke Pieter ; Schuurmans, H. ; Steijn, T. van - \ 2015
    Stromingen : vakblad voor hydrologen 24 (2015)4. - ISSN 1382-6069 - p. 43 - 52.
    grondwaterstand - watersystemen - neerslag - grondwater - hydrologie - tijdreeksen - gegevensanalyse - grondwateraanvulling - groundwater level - water systems - precipitation - groundwater - hydrology - time series - data analysis - groundwater recharge
    Om het effect van velerlei processen die van invloed zijn op grondwaterstanden goed te kunnen analyseren, is het belangrijk om goed te weten wat de respons van het grondwatersysteem is op de neerslag. Een methode om dat te modelleren is de PIRFICT tijdreeksanalyse geïmplementeerd in het programma Menyanthes. De meest gebruikte databron voor neerslag is de neerslagstations van het KNMI. Waar de neerslagstations soms 5 à 10 km van een peilbuis af staan, zorgen radargebaseerde neerslagproducten voor vlakdekkende informatie. Hiermee wordt een nauwkeuriger beeld van de lokale neerslag verkregen. De invloed van dit verschil op een tijdreeksanalysemodel is onderzocht voor 77 locaties met 109 peilbuisfilters in de Mariapeel (Noord-Brabant/Limburg). De gemiddelde verklaarde variantie van de modellen ging door gebruik van de Nationale Regenradar omhoog van 69,1% naar 76,9%. Het resultaat van deze case studie geeft aan dat het opportuun is om ook elders ruimtelijke informatie van neerslag te gebruiken voor grondwaterstudies.
    Monitoring tropical forest dynamics using Landsat time series and community-based data
    DeVries, B.R. - \ 2015
    Wageningen University. Promotor(en): Martin Herold, co-promotor(en): Lammert Kooistra; Jan Verbesselt. - Wageningen : Wageningen University - ISBN 9789462574762 - 161
    tropische bossen - bosdynamiek - monitoring - landsat - satellieten - tijdreeksen - remote sensing - tropical forests - forest dynamics - monitoring - landsat - satellites - time series - remote sensing

    Tropical forests cover a significant portion of the earth's surface and provide a range of

    ecosystem services, but are under increasing threat due to human activities. Deforestation

    and forest degradation in the tropics are responsible for a large share of global CO2

    emissions. As a result, there has been increased attention and effort invested in the

    reduction of emission from deforestation and degradation and the protection of remaining

    tropical forests in recent years. Methods for tropical forest monitoring are therefore vital

    to track progress on these goals. Two data streams in particular have the potential to

    play an important role in forest monitoring systems. First, satellite remote sensing is

    recognized as a vital technology in supporting the monitoring of tropical forests, of which

    the Landsat family of satellite sensors has emerged as one of the most important. Owing

    to its open data policy, a large range of methods using dense Landsat time series have

    been developed recently which have the potential to greatly enhance forest monitoring

    in the tropics. Second, community-based monitoring is supported in many developing

    countries as a way to engage forest communities and lower costs of monitoring activities.

    The development of operational monitoring systems will need to consider how these data

    streams can be integrated for the effective monitoring of forest dynamics.

    This thesis is concerned with the monitoring of tropical forest dynamics using a combi-

    nation of dense Landsat time series and community-based monitoring data. The added

    value conferred by these data streams in monitoring deforestation, degradation and re-

    growth in tropical forests is assessed. This goal is approached from two directions. First,

    the application of econometric structural change monitoring methods to Landsat time

    series is explored and the efficacy and accuracy of these methods over several tropical

    forest sites is tested. Second, the integration of community-based monitoring data with

    Landsat time series is explored in an operational setting. Using local expert monitoring

    data, the reliability and consistency of these data against very high resolution optical

    imagery are assessed. A bottom-up approach to characterize forest change in high the-

    matic detail using a priori community-based observations is then developed based on

    these findings.

    Chapter 2 presents a robust data-driven approach to detect small-scale forest disturbances

    driven by small-holder agriculture in a montane forest in southwestern Ethiopia. The

    Breaks For Additive Season and Trend Monitoring (BFAST Monitor) method is applied

    to Landsat NDVI time series using sequentially defined one-year monitoring periods. In

    addition to time series breakpoints, the median magnitude of residuals (expected versus

    observed observations) is used to characterize change. Overall disturbances are mapped

    with producer's and user's accuracies of 73%. Using ordinal logistic regression (OLR)

    models, the extent to which degradation and deforestation can be separately mapped is

    explored. The OLR models fail to distinguish between deforestation and degradation,

    however, owing to the subtle and diffuse nature of forest degradation processes.

    Chapter 3 expands upon the approach presented in Chapter 2 by tracking post-disturbance

    forest regrowth in a lowland tropical forest in southeastern Peru using Landsat Normalized

    Difference Moisture Index (NDMI) time series. Disturbance between 1999 and 2013 are

    mapped using the same sequential monitoring method as in Chapter 2. Pixels where

    disturbances are detected are then monitored for follow-up regrowth using the reverse of

    the method employed in Chapter 2. The time of regrowth onset is recorded based on a

    comparison to defined stable history period. Disturbances are mapped with 91% accuracy,

    while post-disturbance regrowth is mapped with a total accuracy of 61% for disturbances

    before 2006.

    Chapter 4 and 5 explore the integration of community-based forest monitoring data and

    remote sensing data streams. Major advantages conferred by community-based forest dis-

    turbance observations include the ability to report on drivers and other thematic details

    of forest change and the ability to detect low-level forest degradation before these changes

    are visible above the forest canopy. Chapter 5 builds on these findings and presents a

    novel bottom-up approach to characterize forest changes using local expert disturbance

    reports to calibrate and validate forest change models based on Landsat time series. Using

    random forests and a selection of Landsat spectral and temporal metrics, models describ-

    ing forest state variables (deforested, degraded or stable) at a given time are produced.

    As local expert data are continually acquired, the ability of these models to predict forest

    degradation are shown to improve.

    Chapter 6 summarizes the main findings of the thesis and provides a future outlook, given

    the prospect of increasing availability of satellite and in situ data for tropical forest mon-

    itoring. This chapter argues that forest change methods should strive to utilize satellite

    time series and ground data to their maximum potential. As “big data" emerges in the

    field of earth observation, new data streams need to be accommodated in monitoring

    methods. Operational forest monitoring systems that are able to integrate such diverse

    data streams can support broader forest monitoring goals such as quantitative monitoring

    of forest dynamics. Even with a wealth of time series based forest disturbance methods

    developed recently, forest monitoring systems require locally calibrated forest change esti-

    mates with higher spatial, temporal and thematic resolution to support a variety of forest

    monitoring objectives.

    Combining SAR and optical satellite image time series for tropical forest monitoring
    Reiche, J. - \ 2015
    Wageningen University. Promotor(en): Martin Herold, co-promotor(en): Dirk Hoekman; Jan Verbesselt. - Wageningen : Wageningen University - ISBN 9789462573130 - 151
    satellietbeelden - satellieten - satellietkarteringen - tropische bossen - bosmonitoring - tijdreeksen - satellite imagery - satellites - satellite surveys - tropical forests - forest monitoring - time series

    Tropical forests are the largest of the global forest biomes and play a crucial role in the global carbon, hydrological and biochemical cycles. Increasing demand for resources rapidly increases the pressure on tropical forests. As a result tropical regions have been undergoing rapid changes in forest cover in recent decades. These changes are the second largest contributor of greenhouse gas emissions in the atmosphere. Spatially and timely consistent detection of tropical deforestation and forest degradation is fundamental to reliably estimate greenhouse gas emissions, and to successfully implement climate mechanisms like reducing emissions from deforestation and forest degradation (REDD+).

    To assess historical and future changes in forest cover, satellite remote sensing at medium resolution scale constitutes a powerful tool. Reviewing satellite-based optical and Synthetic Aperture Radar (SAR) efforts for tropical forest monitoring revealed that operationalised optical-based approaches exist, but frequent cloud cover limits their applicability in the tropics. SAR remote sensing has also demonstrated its capability, but the observation frequency of SAR imagery and appropriate time series methods are limited. Research has indicated there is potential for multi-sensor approaches to overcome the limitations of the single-sensors, but so far developments are restricted to mapping approaches. This thesis addressed the need for advancing multi-sensor methods that combine time series imagery from medium resolution SAR and optical satellites to improve tropical forest monitoring. The main scientific contributions include the introduction of three novel SAR-optical approaches, two of them capable of exploiting the full observation density of time series. Furthermore, an approach for multi-model land cover dependent SAR slope correction was proposed.

    Chapter 2 introduced an approach for feature level fusing of multi-temporal L-band SAR and optical forest disturbance information. Using Landsat and ALOS PALSAR imagery from 2007 and 2010, we applied the approach to map forest land cover and to detect deforestation and forest degradation of a persistently cloud covered mining region in Central Guyana. By making use of the complementarities of Landsat and ALOS PALSAR, we demonstrated the reduction of Landsat (cloud cover, Landsat 7 scan line corrector error) and PALSAR data gaps (SAR layover and shadow in mountainous area) to a negligible amount.

    Chapter 3 described a practical approach for multi-model land cover dependent slope correction of SAR images that can handle a wide range of terrain and topographic conditions. We corrected ALOS PALSAR images of two topographically complex sites in Fiji (study site of Chapter 4 and 5) and Brazil and showed that the remaining slope effects for the multi-model case are marginal for all land cover types. Particularly, this improves the detection of forest degradation and biomass changes. Considering the large change in the L-band backscatter signal caused by the removal of forest, however, remaining slope effects are already sufficiently small after applying a single-model approach already.

    Chapter 4 presented a novel multi-sensor time series correlation and fusion (MulTiFuse) approach that was applied to fuse Landsat NDVI and ALOS PALSAR time series. The fused Landsat-PALSAR time series was used in a change detection framework to detect deforestation at a managed forest site in Fiji for the period 01/2008 - 09/2010. We tested the impact of persistent cloud cover in the tropics by increasing the per-pixel missing data percentage of the Landsat time series in a stepwise manner. The results were evaluated against three-monthly reference data that covered the entire study area. For the Landsat-only case, a very strong decrease in spatial and temporal accuracies were observed for increasing Landsat missing data. This highlights the vulnerability of tropical forest monitoring systems that rely only on optical data. In contrast, the results for the fused Landsat-PALSAR case remained high with increasing missing data and were observed to be always above the accuracies for the Landsat- and PALSAR-only cases.

    To address the need for near real-time monitoring systems at medium resolution scale, Chapter 5 introduced a Bayesian change detection approach to combine SAR and optical time series for near real-time deforestation detection. We applied the approach in a simulated near real-time scenario using Landsat NDVI and ALSO PALSAR time series already used in Chapter 4. Once a new image of either of the two time series was available, the probability of deforestation was calculated immediately and deforestation events were indicated. These near real-time capabilities are essential to support timely action against illegal forest activities. Spatial and temporal accuracies for the fused Landsat-PALSAR case were consistently higher than those of the Landsat- and PALSAR-only cases, even for increasing Landsat missing data.

    With these studies we demonstrated the potential of SAR-optical time series approaches to use the historical and upcoming streams of medium resolution optical and SAR satellite image time series for improving forest monitoring in the tropics.

    Een tool voor controle van hoogfrequente grondwaterstandsreeksen
    Walvoort, D.J.J. ; Knotters, M. ; Hoogland, T. - \ 2013
    Stromingen : vakblad voor hydrologen 19 (2013)3/4. - ISSN 1382-6069 - p. 49 - 61.
    grondwaterstand - tijdreeksen - monitoring - modellen - gelderse vallei - groundwater level - time series - monitoring - models - gelderse vallei
    Grondwaterstanden en stijghoogten worden steeds vaker gemeten met druksensoren, met hoge frequenties zoals viermaal daags of ieder uur. Het is ondoenlijk al deze metingen visueel te controleren op fouten. Alterra, onderdeel van Wageningen UR, ontwikkelde in opdracht van Eijkelkamp Agrisearch Equipment een tool voor automatische controle van de metingen die worden verzameld in het Regionaal Grondwatermeetnet Vallei en Eem. De tool maakt het mogelijk grote hoeveelheden metingen efficiënt te controleren. De tool is gebaseerd op fuzzy-set-theorie waardoor informatie beter wordt benut. Door robuuste statistieken te gebruiken is de tool toepasbaar voor reeksen met uiteenlopende eigenschappen.
    Validatie van tijdreeksmodellen voor de grondwaterstand
    Knotters, M. - \ 2012
    Stromingen : vakblad voor hydrologen 18 (2012)2. - ISSN 1382-6069 - p. 31 - 42.
    watersystemen - grondwaterstand - tijdreeksen - water systems - groundwater level - time series
    Essentially, all models are wrong, but some are useful’, is een gezegde van de statisticus George E.P. Box, die samen met Gwilym M. Jenkins het bekende boek ‘Time Series Analysis: Forecasting and Control’ schreef. In dit artikel wil ik ingaan op de pragmatische vraag of een tijdreeksmodel bruikbaar is voor een bepaald doel. Ik beperk me tot tijdreeksmodellen voor grondwaterstandsreeksen. Na een korte inleiding over tijdreeksmodellering van grondwaterstandsreeksen zal ik ingaan op de verschillende manieren waarop de kwaliteit van deze modellen wordt uitgedrukt, wat dit zegt over de bruikbaarheid van een model, wanneer je zou kunnen spreken van ‘validatie’ en hoe je met validatie een idee kunt krijgen van de bruikbaarheid van een tijdreeksmodel. Vervolgens zal ik ter illustratie validatieresultaten presenteren voor tijdreeksmodellen die zijn gekalibreerd op vijftien reeksen van grondwaterstanden, om af te sluiten met enkele concluderende opmerkingen.
    A disposition of interpolation techniques
    Knotters, M. ; Heuvelink, G.B.M. - \ 2010
    Wageningen : Wettelijke Onderzoekstaken Natuur & Milieu (WOt-werkdocument 190) - 86
    pesticiden - waterkwaliteit - kriging - tijdreeksen - statistiek - onzekerheid - nauwkeurigheid - natuur - milieu-analyse - geostatistiek - interpolatie - pesticides - water quality - kriging - time series - statistics - uncertainty - accuracy - nature - environmental analysis - geostatistics - interpolation
    A large collection of interpolation techniques is available for application in environmental research. To help environmental scientists in choosing an appropriate technique a disposition is made, based on 1) applicability in space, time and space-time, 2) quantification of accuracy of interpolated values, 3) incorporation of ancillary information, and 4) incorporation of process knowledge. The described methods include inverse distance weighting, nearest neighbour methods, geostatistical interpolation methods, Kalman filter methods, Bayesian Maximum Entropy methods, etc. The applicability of methods in aggregation (upscaling) and disaggregation (downscaling) is discussed. Software for interpolation is described. The application of interpolation techniques is illustrated in two case studies: temporal interpolation of indicators for ecological water quality, and spatio-temporal interpolation and aggregation of pesticide concentrations in Dutch surface waters. A valuable next step will be to construct a decision tree or decision support system, that guides the environmental scientist to easy-to-use software implementations that are appropriate to solve their interpolation problem. Validation studies are needed to assess the quality of interpolated values, and the quality of information on uncertainty provided by the interpolation method.
    Effecten van klimaatverandering op de watervraag in de Nederlandse groene ruimte : analyse van de waterbeschikbaarheid rekeninghoudend met de freatische grondwaterstand
    Gaast, J.W.J. van der; Massop, H.T.L. ; Vroon, H.R.J. - \ 2009
    Wageningen : Alterra (Alterra-rapport 1791) - 116
    neerslag - grondwaterstand - tijdreeksen - landbouw - waterbehoefte - klimaatverandering - platteland - nederland - precipitation - groundwater level - time series - agriculture - water requirements - climatic change - rural areas - netherlands
    In deze studie is onderzoek gedaan naar de veranderingen in de grondwaterstand en daarmee op de waterbeschikbaarheid in het landelijk gebied als gevolg van klimaatverandering. Hiervoor zijn klimaatrepresentatieve meteoreeksen afgeleid. Met tijdreeksmodellen zijn vervolgens grondwaterstandsreeksen berekend voor het huidige klimaat en toekomstige klimaatscenario’s. De tijdreeksmodellen zijn landelijk voor pixels van 25*25 m geparametriseerd op basis van fysische parameters. Met lineaire tijdreeksmodellen zijn landsdekkende berekeningen uitgevoerd, met niet-lineaire modellen zijn berekeningen uitgevoerd voor een proefgebied. De resultaten van de landsdekkende berekeningen zijn gebruikt om landsdekkende GxG-kaarten af te leiden voor de verschillende klimaatscenario’s. Deze kaarten zijn vervolgens gebruikt om het effect van klimaatverandering op het vochtleverend vermogen van de bodem en de hiermee samenhangende veranderingen in de watervraag te bepalen.
    Wat is de kans op neerslag in Wageningen?
    Wesseling, J.G. ; Stoof, C.R. ; Ritsema, C.J. ; Oostindie, K. ; Dekker, L.W. - \ 2007
    Stromingen : vakblad voor hydrologen 13 (2007)3. - ISSN 1382-6069 - p. 5 - 11.
    neerslag - regen - monitoring - tijdreeksen - precipitation - rain - monitoring - time series
    Dit artikel beschrijft de neerslagreeks van 1974-2006 van het meteostation van Wageningen Universiteit (Leerstoelgroep Meteorologie en Luchtkwaliteit). De neerslagreeks wordt grafisch gepresenteerd en er wordt een verdeling gemaakt aan de hand van de jaarlijkse hoeveelheid neerslag. Ook wordt de verdeling van de dagelijkse hoeveelheid neerslag geanalyseerd en wordt per dag gekeken hoe groot de kans op neerslag is
    Een statistische analyse van de invloed van het mestbeleid op de oppervlaktewaterkwaliteit
    Knotters, M. ; Walvoort, D.J.J. ; Leenders, T.P. - \ 2007
    Wageningen : Alterra (Alterra-rapport 1540) - 114
    waterkwaliteit - oppervlaktewater - monitoring - dierlijke meststoffen - voedingsstoffen - nitraten - tijdreeksen - nederland - bodemchemie - geostatistiek - water quality - surface water - monitoring - animal manures - nutrients - nitrates - time series - netherlands - soil chemistry - geostatistics
    Het effect van het mestbeleid op vrachten van N-totaal, N-mineraal, P-totaal en orthofosfaat werd geanalyseerd voor drie stroomgebieden: de Drentse Aa, de Schuitenbeek en de Krimpenerwaard. Met behulp van statistische interventieanalyse werd beoordeeld of de dynamiek van nutriëntenvrachten bij de invoering (1984) of wijziging (1992) van het mestbeleid een verandering te zien geeft die niet kan worden verklaard uit het neerslagoverschot.
    Extreme hydro-meteorological events and their probabilities = Extreme hydro-meteorologische gebeurtenissen en de kans daarop
    Beersma, J.J. - \ 2007
    Wageningen University. Promotor(en): Bert Holtslag, co-promotor(en): T.A. Buishand. - [S.l.] : S.n. - ISBN 9789085046158 - 157
    meteorologie - hydrologie - tijdreeksen - monitoring - waarschijnlijkheidsanalyse - gegevensanalyse - onzekerheid - hoogwaterbeheersing - meteorology - hydrology - time series - monitoring - probability analysis - data analysis - uncertainty - flood control
    Extreme hydro-meteorologische gebeurtenissen hebben vaak een grote maatschappelijke impact. Bescherming tegen de gevolgen van zulke gebeurtenissen, zoals zeer natte periodes, is veelal gebaseerd op extremen, zoals overstromingen, met overschrijdingkansen van slechts eens in de 100 tot eens in de 10.000 jaar. Door gebrek aan lange waarnemingsreeksen worden zulke extremen gewoonlijk geschat door extrapolatie van een aan de waarnemingen gefitte kansverdeling. Nadeel van deze methode is dat de schattingen sterk afhangen van de veronderstelde kansverdeling. De in dit proefschrift gebruikte tijdreeks resampling vormt een aantrekkelijk alternatief omdat geen aannames over de onderliggende kansverdeling nodig zijn. Tijdreeks resampling geeft daarnaast de mogelijkheid om simultaan reeksen voor verschillende meteorologische variabelen en locaties te simuleren waarbij zowel de correlaties tussen de variabelen als de ruimtelijke correlaties automatisch behouden blijven. Resampling maakt het verder mogelijk om veel langere reeksen te simuleren dan de standaard historische reeksen. Zulke zeer lange reeksen bevatten gewoonlijk verschillende niet eerder waargenomen extremen die zeer welkom zijn bij een frequentieanalyse van de extremen omdat ze de statistische onzekerheid van het resultaat reduceren. In dit proefschrift worden, met het oog op hydrologische toepassingen, zulke zeer lange tijdreeksen gesimuleerd om de grootte en de bijbehorende overschrijdingskans te bepalen van zeer natte periodes in het stroomgebied van de Rijn (die tot overstromingen zouden kunnen leiden) en van extreme droogte in Nederland (die economische schade in de landbouw en scheepvaart tot gevolg heeft). Resampling technieken worden tenslotte ook gebruikt om de statistische onzekerheid te kwantificeren
    Sampling for natural resource monitoring
    Gruijter, J.J. de; Brus, D.J. ; Bierkens, M.F.P. ; Knotters, M. - \ 2006
    Berlin (Germany) etc. : Springer - ISBN 9783540224860 - 322
    natuurlijke hulpbronnen - monitoring - bemonsteren - gegevensanalyse - ruimtelijke verdeling - statistiek - methodologie - tijdreeksen - hydrologie - bodemkunde - geostatistiek - natural resources - sampling - data analysis - spatial distribution - statistics - methodology - time series - hydrology - soil science - geostatistics
    The book presents the statistical knowledge and methodology of sampling and data analysis useful for spatial inventory and monitoring of natural resources. The authors omitted all theory not essential for applications or for basic understanding. This presentation is broader than standard statistical texts, as the authors pay much attention to how statistical methodology can be employed and embedded in real-life spatial inventory and monitoring projects. Thus they discuss in detail how efficient sampling schemes and monitoring systems can be designed in view of the aims and constraints of the project.
    Risk, Incentives and Coordination Costs in Agro-Food Chains in the Presence of Futures Markets
    Kuwornu, J.K.M. - \ 2006
    Wageningen University. Promotor(en): Joost Pennings, co-promotor(en): Erno Kuiper. - Wageningen : s.n. - ISBN 9789085043560 - 193
    voedselketens - risico - stimulansen - termijnhandel - marketingkanalen - aardappelen - solanum tuberosum - nederland - tijdreeksen - agro-industriële ketens - marketing channels - food chains - risk - incentives - futures trading - potatoes - solanum tuberosum - netherlands - time series - agro-industrial chains
    This thesis focuses on developing conceptual models to examine the role of futures markets for risk-shifting, incentives and coordination costs in the context of commodity marketing channels. The empirical analysis is conducted for different marketing channel structures (two-stage and three-stage marketing channels) and for different situations regarding the availability of a futures market ( i.e ., with and without futures markets). The conceptual models have been applied to the Dutch potato marketing channel.

    We model and empirically examine incentives, coordination costs, and risk-shifting in the Dutch ware potato marketing channel that includes producers and marketing firms ( e.g. , retailers), when these marketing channel members (MCMs) are allowed to trade on spot markets only. We apply the classic agency model to investigate risk shifting in the Dutch ware potato marketing channel, using time-series analysis. We show that, if the principal (marketing firm) is risk neutral and the agent (producer) is risk averse instead of risk neutral, a linear contract can still be optimal if the fixed payment is negative. The empirical results over the period 1946 - 2003 indicate that, while fixed payments to farmers (agents) have decreased over time since the 1980s to become more and more negative, the incentive intensity has approximately doubled, and the risk premium that farmers demand has remained considerable. Moreover, since the mid 1960s, risk has shifted from retailers to farmers. We argue that this shift could be the consequence of chain reversal, i.e ., the transformation of the traditional supply chain into a demand-oriented chain. From the mid 1980s on, potato growers have had to pay an increasing amount of fixed compensation to the marketing firms. As a percentage of output value at consumer prices, as received by the marketing firms, this compensation has increased from -43% in 1948 to 23% in 1998. This value, however, decreased to 15% in 2003. Nevertheless, together with the rise in the output-value sharing rate ( i.e ., incentive intensity), farmers became less risk averse. Furthermore, the empirical results reveal that as a consequence of increases in incentives to producers, the coordination costs of the marketing channel decreased considerably.

    Next, we model the contractual relationships in the Dutch ware potato marketing channel, while allowing risk-averse producers to use futures contracts in order to manage their increasing income risk. The principal-agent model is extended to include a futures market, in order to assess risk shifting between the principal (retailers) and the agent (producers). We compare the case with a futures market for the risk-averse producers to the case without futures trade. The empirical results show that risk shifted from retailers to farmers, possibly as a consequence of chain reversal, and that this risk can be managed by farmers if they use futures contracts. This demonstrates the hedging role of futures contracts (futures markets) as a risk-shifting, mediating market institution. Furthermore, as a result of increases in incentives from retailers to producers, the coordination costs of the marketing channel have decreased considerably, both with and without producers' futures trade. The  coordination costs are much lower in the scenario with futures use than without futures trade, showing the price-discovery (informational) role of the futures markets. Having obtained the results that producers can manage their increasing income risk by hedging in the futures market, the level of hedging becomes of interest. Therefore, we also model and empirically estimate the optimal time-varying hedge ratio for these risk-averse producers. We use the classic agency model to derive a time-varying optimal hedge ratio for low-frequency, time-series data: the type of data used by crop farmers when deciding about their production and about their hedging strategy. Rooted in the classic agency framework, the proposed hedge ratio reflects the context of both the producer's decision and the producer's contractual relationships in the marketing channel. The empirical illustration for the Dutch ware potato sector and its futures market in Amsterdam over the period 1971 - 2003 reveals that the time-varying optimal hedge ratio decreased from 0.21 in 1971 to 0.15 in 2003. On average these optimal ratios led to a risk reduction through hedging of 39%.

    The modelling and the empirical investigations in the previous studies in this thesis include only producers and retailers. The intermediary in this marketing channel, i.e ., the wholesaler has been ignored so far. Hence, we model and empirically examine a three-stage, principal-agent, marketing-channel model that includes producers, wholesalers, and retailers. We assess incentives, coordination costs, and risk shifting when the MCMs ( i.e ., producers, wholesalers, and retailers) trade on the spot market only. The empirical application shows that during the period 1961 - 2002, the retailers were able to provide more incentives to the wholesalers and producers, and, as a consequence, the costs of coordination in the supply chain decreased considerably. This study provides insight into the role of incentives in reducing the coordination costs of the marketing channel. Furthermore, it provides insight into the role of the wholesaler regarding risk shifting in the marketing channel. Moreover, the concentration of retailers in food marketing channels and the resulting bargaining power imbalance is evident here, as risks are shifted from retailers to producers and wholesalers.

    To obtain more insight into the results, we specify a three-stage, principal-agent, supply-chain model that includes producers, wholesalers, and retailers, as well as a futures market. We compare the situation with and without a futures market. The empirical results for the Dutch ware potato marketing channel over 1971 - 2003 reveal that the coordination costs of the marketing channel decreased considerably as a result of increased incentives to producers and wholesalers, both with and without futures trade. The coordination costs of the marketing channel are lower in the scenario with futures markets than without futures, demonstrating the informational ( i.e ., price discovery) role of the futures markets. The futures market enables producers and wholesalers to manage the increasing variability in their incomes, thus demonstrating its role as a price-risk management instrument. Furthermore, as a consequence of the decreasing degree of risk aversion among producers and wholesalers, the optimal dynamic hedge ratio for wholesalers decreased from 14% in 1971 to 10% in 2003, while that of producers decreased from 38% in 1982 to 18% in 2002. 

    Hence, the overall results are the following. Incentives reduce the coordination costs in food marketing channels, but at the cost of increasing the risk for those MCMs who obtain these incentives. Consequently, the MCM who provides the incentives faces a trade-off between giving more incentives ( i.e. , lower coordination costs) on the one hand and having to pay a higher risk-premium to the risk-averse MCMs who receive the incentives. The futures market, however, provides the risk-averse MCMs a risk-management instrument so that they can manage more risk and hence, are able to deal with more incentives than without a futures market. What we observe is that income risks shifted from retailers to producers and wholesalers, and we argue that this risk shift could be the consequence of chain reversal ( i.e ., the transformation of traditional supply-oriented chains into demand-oriented chains). The futures market enables MCMs to reduce their increasing income risks so that they can handle more incentives for market orientation.
    Drought in groundwater-drought distribution and performance indicators
    Peters, E. ; Lanen, H.A.J. van; Torfs, P.J.J.F. ; Bier, G. - \ 2005
    Journal of Hydrology 306 (2005)1-4. - ISSN 0022-1694 - p. 302 - 317.
    droogte - grondwateraanvulling - tijdreeksen - meteorologie - grondwater - watersystemen - bodemwaterbalans - klimaat - drought - groundwater recharge - time series - meteorology - groundwater - water systems - soil water balance - climate - vulnerability - reliability - precipitation - resilience - simulation - frequency - reservoir - series
    In order to investigate how droughts are changed by the groundwater system and to analyse the performance of groundwater during drought, 10 time series of 1000 years of recharge and groundwater discharge were generated. The 10×1000 years of synthetic daily data were generated using Nearest Neighbour resampling based on 37 years of observed daily meteorological data. The root zone was simulated by a non-linear water balance model and the groundwater system by a linear reservoir model. The size and thus the response time of the reservoir was characterised by a reservoir coefficient. Subsequently, the deficit and duration of the droughts were derived from the time series of recharge and groundwater discharge using the threshold level approach. An analysis of the distribution of these droughts shows that for droughts with small return periods, the deficit in the groundwater discharge is smaller than in the recharge. For droughts with large return periods, the deficit in the groundwater discharge is larger than in the recharge. The performance of groundwater systems with respect to droughts was evaluated using three classical performance indicators (reliability, resilience and vulnerability), a combination of these three indicators (Loucks' sustainability index) and three newly defined overall performance indicators. The newly defined indicators combine the severity and frequency of the droughts, instead of analysing these separately in reliability and vulnerability. The performance is estimated for the groundwater recharge and for the discharge of groundwater systems with three different values of the reservoir coefficient. Of all the performance indicators used, one of the newly introduced overall performance indicators with a strong emphasis on droughts with a high return period appeared to characterise the groundwater droughts best. This indicator shows a more or less constant performance for low and medium high reservoir coefficients and an increasing performance for higher reservoir coefficients
    Omslagpunten in het functioneren van aquatische ecosystemen?
    Vlek, H.E. ; Diepen, L.T.A. van; Verdonschot, P.F.M. - \ 2005
    Wageningen : Alterra (Alterra-rapport 1178) - 135
    watersystemen - waterorganismen - oppervlaktewater - tijdreeksen - waterkwaliteit - nederland - milieueffect - milieufactoren - zoetwaterecologie - herstel - aquatische ecosystemen - macrofauna - water systems - aquatic organisms - surface water - time series - water quality - netherlands - environmental impact - environmental factors - freshwater ecology - rehabilitation - aquatic ecosystems - macrofauna
    Het doel van deze studie is aanwijzingen te vinden voor het bestaan van `omslagpunten¿ in de toestand van aquatische ecosystemen in Nederland. Het rapport beschrijft de ontwikkeling van een methodiek om snel inzicht te krijgen in het optreden van mogelijk abrupte veranderingen binnen een macrofauna gemeenschap. Daarnaast is een methode opgesteld om objectief te kunnen vaststellen of een abrupte verandering in de samenstelling van de levensgemeenschap is opgetreden. Langjarige macrofauna tijdreeksen van 31 locaties (sloten, kanalen, beken en rivieren) zijn geanalyseerd met behulp van de ontwikkelde methodieken. Het betrof bestaande tijdreeksen afkomstig van verschillende waterbeheerders. De relatie tussen de macrofauna en milieuvariabelen is onderzocht om tot uitspraken te kunnen komen over het optreden van `omslagpunten¿ in sloten, kanalen, beken en rivieren. Op slechts drie van de 31 onderzochte locaties is mogelijk sprake geweest van een `omslag¿. Het is niet mogelijk gebleken om op basis van velddata definitieve uitspraken te doen over het optreden van `omslagpunten¿ in de onderzochte aquatische ecosystemen. Reden hiervoor is dat een aantal milieuvariabelen sturend voor de samenstelling van de macrofauna levensgemeenschap, zoals stroming, permanentie en piekafvoeren, niet of onvoldoende zijn gemeten op de onderzochte locaties. De resultaten van deze studie sluiten niet uit dat `omslagen¿ kunnen optreden, maar maken het optreden van `omslagpunten¿ ook niet erg aannemelijk.
    Hoe de kartering van de grondwaterstand (nog) beter kan
    Hoogland, T. ; Brus, D.J. ; Heuvelink, G.B.M. ; Knotters, M. - \ 2004
    Wageningen : Alterra (Alterra-rapport 1032) - 88
    bodemwater - grondwaterspiegel - monitoring - bemonsteren - tijdreeksen - ondergrondse drainage - soil water - water table - subsurface drainage - monitoring - sampling - time series
    De afgelopen jaren ontwikkelde Alterra een methode voor kartering van grondwaterstandskarakteristieken (de Gd-karteringsmethode). Deze methode, die met behulp van tijdreeksanalyse, lineaire regressie en geostatistische interpolatie ruimtelijke beelden van grondwaterstandskarakteristieken produceert, is de ontwikkelfase inmiddels ontstegen en al een aantal keren in de praktijk toegepast. Op onderdelen is aanpassing, verfijning, correctie en verbetering van de methode mogelijk. Daarom is in dit project de Gd-methodiek grondig onder de loep genomen en is een uitgebreide lijst gemaakt van mogelijke verbeterpunten. Op basis hiervan zijn belangrijke en kansrijke verbeterpunten onderzocht in drie deelonderzoeken. Het eerste deelonderzoek, naar tijdreeksmodellering van grondwaterstandsreeksen voor de predictie van klimaatsrepresentatieve GxG (GHG, GVG en GLG), gaf geen aanleiding de Gd-methode aan te passen. Op het gebied van zowel stambuisregressie voor de omzetting van gemeten grondwaterstanden naar klimaatsrepresentatieve GxG als van vlakdekkende predictie van klimaatsrepresentatieve GxG zijn echter wel mogelijke verbeteringen gevonden. De voorstellen betreffen vooral kleine veranderingen die relatief eenvoudig te implementeren zijn en die de uitgangspunten en globale werkwijze van de Gd-methode intact laten.
    De dynamiek van vennen in schijnspiegelsystemen
    Bakker, D. ; Aggenbach, C. ; Asmuth, J.R. von; Witte, J.P.M. - \ 2004
    Stromingen : vakblad voor hydrologen 10 (2004)4. - ISSN 1382-6069 - p. 5 - 12.
    zwampen - meren - hydrologie - ecologie - tijdreeksen - modellen - waterstand - limburg - swamps - lakes - hydrology - ecology - time series - models - water level - limburg
    Op verscheidene plaatsen in Nederland wordt getracht verdroging van vennen tegen te gaan door verwijdering van veel verdampende bomen. Het effect van deze maatregel op de levensgemeenschap in het ven is echter sterk afhankelijk van de ligging van slecht doorlatende lagen en de grootte van het schijnspiegelsysteem, die op hun beurt de reactie van het venpeil op neerslag beïnvloeden. Meer inzicht in de hydrologie van vennen is verkregen via het tijdreeksmodel PIRFICT, met als onderzoekslocatie Beegderheide
    Hydrological data
    Rees, G. ; Marsh, T.J. ; Roald, L. ; Demuth, S. ; Lanen, H.A.J. van; Kasparek, L. - \ 2004
    In: Hydrological drought. Processes and estimation methods for streamflow and groundwater / Tallaksen, L.M., van Lanen, H.A.J., Amsterdam : Elsevier (Developments in Water Science 48) - ISBN 9780444516886 - p. 99 - 138.
    hydrologische gegevens - tijdreeksen - droogte - hydrological data - time series - drought
    The objective of this chapter is to provide an overview of the hydrological data that are typically available for the analysis of hydrological drought and the procedures that ought to be applied to ensure that this data is of good quality
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