Evaluating rainwater harvesting systems in arid and semi-arid regions
Ammar, Adham Ali - \ 2017
Wageningen University. Promotor(en): C.J. Ritsema, co-promotor(en): M.J.P.M. Riksen; M. Quessar. - Wageningen : Wageningen University - ISBN 9789463431460 - 207
water harvesting - rain - water - arid zones - semiarid zones - geographical information systems - water management - climatic change - tunisia - iraq - regenwateropvang - regen - water - aride klimaatzones - semi-aride klimaatzones - geografische informatiesystemen - waterbeheer - klimaatverandering - tunesië - irak
Rainwater harvesting (RWH) is an ancient traditional technology practised in many parts of the world, especially in arid and semi-arid regions (ASARs). ASARs represent 40% of the earth’s land surface and are characterised by low average annual rainfall and uneven temporal and spatial distributions of that rainfall. In these regions an efficient use of the limited amount of rainfall available is important, e.g. by collecting and using surface runoff (water harvesting). Lately, access to water for agriculture and domestic use has become worse because of increasing population, higher levels of human activity and the impacts of climate change. The inhabitants of ASARs have developed several RWH techniques to increase the water availability, thus coping with water shortages. RWH is an important mitigation strategy to the impact of climate change on water availability in ASARs.
Four main methodologies of site selection were categorised, ranging from those based only on biophysical criteria to more integrated approaches that include socioeconomic criteria. Our analysis suggests that the integration of multi-criteria analysis (MCA) with a geographic information system (GIS) is the most advanced approach. It offers high potential in data-poor regions; GIS-based hydrological modelling is always recommended for data-rich regions.
The potential for RWH in wadi Horan (western desert of Iraq) was identified using a GIS-based suitability model. The method for selecting suitable sites for RWH was then further developed into an evaluation and decision support tool for assessing the overall performance of existing RWH systems by integrating engineering, biophysical and socioeconomic criteria using MCA supported by GIS. It was tested in the wadi Oum Zessar in southeastern Tunisia.
A simple but generally applicable water harvesting model (WHCatch) was developed to investigate and optimise the performance of the RWH systems under various scenarios of design and management, It was tested in wadi Oum Zessar. The advantages of simulating long-term water balances at the sub-catchment level for improving our understanding of hydrological processes in an RWH system are emphasised. Several solutions for optimising RWH performance in various scenarios are provided.
Finally, the impact of climate change on existing RWH systems in the Oum Zessar watershed under current and future scenarios of climate was investigated. The downscaled maximum and minimum temperatures clearly indicated an increasing trend in the mean monthly temperature and the generated precipitation tended to decrease in the future. It was shown that the combination of changing the flow direction and the spillway height had a large impact on the performance of the RWH systems under current and future conditions. Water management and structural design at the sub-catchment level plays a more important role than climate change in the performance of RWH.
Rainfall over the Netherlands & beyond: a remote sensing perspective
Rí́os Gaona, Manual Felipe - \ 2017
Wageningen University. Promotor(en): R. Uijlenhoet, co-promotor(en): A. Overeem; H. Leijnse. - Wageningen : Wageningen University - ISBN 9789463432009 - 124
rain - remote sensing - satellites - estimation - netherlands - brazil - regen - remote sensing - satellieten - schatting - nederland - brazilië
Earthlings like to measure everything (especially now that we are undergoing the era of big-data revolution) maybe because it is such a nice hobby... although a more serious school of thought believes that when measuring our environment we get to understand physics and ourselves.
This thesis explores the uncertainties in rainfall measurements from state-of-the-art technologies like commercial microwave links (CML) and meteorological satellites. Rainfall has been measured by rain gauges since quite some time ago; and by weather radars since the end of WWII. Here we evaluate the performance of gridded-rainfall products for the land surface of the Netherlands. These gridded-rainfall products are CML-rainfall maps produced by the Royal Netherlands Meteorology Institute (KNMI), and the IMERG product developed by Global Precipitation Measurement mission (GPM).
Overall, this thesis shows that CML-rainfall products are very reliable sources with regards to rainfall estimates for the land surface of the Netherlands... even better than the satellite products for rainfall estimation. We are also confident in the promising potential these technologies hold for places around the world where conventional technologies like gauges or radars are not scarce or not affordable.
‘Force of Nature’ : climate shocks, food crises and conflict in Colonial Africa and Asia, 1880-1960
Papaioannou, Kostadis J. - \ 2017
Wageningen University. Promotor(en): E.H.P. Frankema; E.H. Bulte. - Wageningen : Wageningen University - ISBN 9789463431668 - 238
climatic change - environmental degradation - environmental impact - agricultural development - agriculture - agriculture and environment - historical ecology - history - colonialism - colonization - africa - asia - nigeria - rainfed agriculture - rain - klimaatverandering - milieuafbraak - milieueffect - landbouwontwikkeling - landbouw - landbouw en milieu - historische ecologie - geschiedenis - kolonialisme - kolonisatie - afrika - azië - nigeria - regenafhankelijke landbouw - regen
“Global climate change poses one of the most urgent challenges of our age. The increasing frequency and intensity of weather shocks, such as heat waves, droughts, floods, and hurricanes, are all anticipated to adversely affect conditions of agricultural production, and jeopardize efforts to achieve global food security. In recent years, there has been a rapidly growing body of literature across multiple disciplines aiming to quantify and assess the adverse consequences of climate on relatively poor rural societies. Building entirely on original primary sources, this dissertation provides evidence that weather shocks raised property crime, triggered civil conflict and shaped patterns of human settlement in British colonial Africa and Asia during the first half of the twentieth century (~1880-1960). By merging the theoretical and empirical insights of several strands of literature (e.g. economics, history, geography), this dissertation has both academic and social merit. Its academic merit lies in its promise to disentangle the net effect of climate on societies from the many other contextual factors that may affect them. And its social merit lies in its capacity to reveal key factors that can mitigate the adverse consequences of weather shocks, enabling tailor-made policy interventions. In sum, the present dissertation contributes to a better understanding of long-term agrarian development in tropical Africa and Asia, offering fresh input to academic debates on how to mitigate the effects of weather extremes”
Dynamics of rainwater lenses on upward seeping saline groundwater
Eeman, Sara - \ 2017
Wageningen University. Promotor(en): Sjoerd van der Zee, co-promotor(en): Toon Leijnse. - Wageningen : Wageningen University - ISBN 9789462579330 - 158
seepage - rain - water - groundwater - saline water - vegetation - kwel - regen - water - grondwater - zout water - vegetatie
Fresh water is generally a limited resource in coastal areas which are often densely populated. In low-lying areas, groundwater is mostly saline and both agriculture and freshwater nature depend on a thin lens of rainwater that is formed by precipitation surplus on top of saline, upward seeping groundwater. Understanding the dynamics of such lenses is vital for sustainable food production and development of natural vegetation and biodiversity under changing conditions like sea level rise and climate change. The thickness of the mixing zone between the fresh and saline water is substantial and characteristics of this mixing zone cannot be neglected. In this thesis we have studied the behaviour of these thin rainwater lenses and their mixing zones.
To study the basic relations of such a system, we considered the development of a rainwater lens, starting from initially saline conditions using a numerical model. The ratio of seepage over precipitation, density difference and to a lesser extent the geometry of the flow domain, significantly influence the thickness of the lens and mixing zone. The thickness of the mixing zone is also significantly influenced by dispersion (as the lens grows), diffusion (at steady state) and distance from a drain (caused by convergence). Field observations show that geological layering influences these processes importantly and that head differences often overrule the effects of density difference. Groundwater salinity is furthermore influenced by re-mixing of soil- and rainwater, dual porosity and preferential flow. If there is significant seepage, the thickness of a lens can be estimated by an analytical solution.
The effects of weather and climate variations were numerically studied using sinusoidal and actual net precipitation patterns. The average lens thickness is hardly influenced by weather fluctuations and we can relate minimum and maximum lens thickness to this average thickness. The thickness of the mixing zone can be derived from the “travelled distance” from its center: thickness increases with increasing vertical movement due to alternating precipitation and evaporation. Field observations confirm this, but show concentration of dynamics in the top of the lens. This is not contradictory since the mixing zone for the studied site starts very near the ground water table, so indeed the mixing zone thickness is influenced by precipitation events. Convolution theory can be used to determine the impulse-response function for a thin lens which enables derivation of the delay and amplitude of a lens reaction to changes in climate.
The cation exchange process was investigated using a numerical model based on field data. On the short term, the process is characterized by the salt-shock caused by the large difference in concentration between rainwater and seepage water. The pore water quality changes quickly from saline to relatively fresh and from sodium and magnesium dominated to calcium dominated. On the long term, changes of the soil complex occur. This is a process of several centuries (even for the shallow systems studied), since the amount of cations in the fresh solution is very small compared to the amount of cations adsorbed to the soil. Initially, both calcium and magnesium in the sorption complex increase and later magnesium is outcompeted by calcium. The net flux downward has a much larger effect on the mixing process than short-term variations and the influence of tile drainage. Although the main flow component is horizontal, the water quality and soil complex are only influenced by the vertical flow that causes mixing of water with different composition. Comparison of the numerical model with field data from both study sites in Zeeland confirm our results and show that equilibrium has not yet been reached.
Influence of saline groundwater on vegetation development has been assessed simulating combinations of different vegetation types, soil characteristics and groundwater levels and –salinities for two different climates. We assessed the relative importance of these parameters on the fresh water availability and stress experienced by vegetation and put this in perspective of stress due to drought and lack of oxygen. Soil type and climate are shown to be the most important parameters. Salinity stress is substantial, but small compared to stress caused by lack of oxygen and drought. For areas with groundwater with limited salinity, salt tolerance may be a parameter that can be used to improve sustainability of agriculture. Where groundwater is more saline, soil and ground water management are the most effective tools.
Flexibility in land and water use for coping with rainfall variability
Siderius, C. - \ 2015
Wageningen University. Promotor(en): Ekko van Ierland; Pavel Kabat, co-promotor(en): Petra Hellegers. - Wageningen : Wageningen University - ISBN 9789462576063 - 222
rain - land use - water use - climatic change - food production - sustainable agriculture - irrigation - rainfed agriculture - regen - landgebruik - watergebruik - klimaatverandering - voedselproductie - duurzame landbouw - irrigatie - regenafhankelijke landbouw
Effect van afstromend regenwater op het watersysteem in de Wieringermeer
Slijkerman, D.M.E. ; Bos, R. - \ 2015
H2O : tijdschrift voor watervoorziening en afvalwaterbehandeling 40 (2015)21. - ISSN 0166-8439 - p. 30 - 32.
riolering - regen - watersystemen - ecosystemen - effecten - waterkwaliteit - hydrologie - stedelijke gebieden - oppervlaktewaterkwaliteit - wieringermeer - sewerage - rain - water systems - ecosystems - effects - water quality - hydrology - urban areas - surface water quality - wieringermeer
Voor een grootschalig afkoppelproject in de gemeente Wieringermeer is onderzoek verricht naar de verontreiniging in het afstromende regenwater en de ecologische effecten op het watersysteem. Dat gebeurde in het kader van NORIS (NO Rainwater in Sewers). Dit project wordt gesubsidieerd vanuit het Interreg IIIb North Sea-programma van de Europse Unie. Het Nederlandse deel van het project is uitgevoerd door TNO-IMARES en het Hoogheemraadschap Hollands Noorderkwartier. Het onderzoek toont aan dat locatiespecifiek chemische effecten kunnen optreden (verzoeting en periodieke overschrijding MTR van zink in water), maar dat dit niet direct leidt tot ecologische gevolgen. Landelijk en regionaal bestaan echter grote verschillen in typen ecosystemen en daarmee ook in de lokale veerkracht en gevoeligheid voor uiteenlopende sturende factoren. Daarom wordt gepleit voor een gebiedsgerichte evaluatie bij emissie van regenwater op oppervlaktewater
Functional traits, drought performance, and the distribution of tree species in tropical forests of Ghana
Amissah, L. - \ 2014
Wageningen University. Promotor(en): Frits Mohren, co-promotor(en): Lourens Poorter; B. Kyereh. - Wageningen : Wageningen University - ISBN 9789462570726 - 196
tropische bossen - bomen - droogteresistentie - plantengeografie - bosecologie - regen - temperatuur - plantenfysiologie - ghana - tropical forests - trees - drought resistance - phytogeography - forest ecology - rain - temperature - plant physiology - ghana
Tropical forests occur along a rainfall gradient where annual amount, the length and intensity of dry season vary and water availability shapes therefore strongly the distribution of tree species. Annual rainfall in West Africa has declined at a rate of 4% per decade, and climate change models predict a further reduction in rainfall and an increase in frequency and intensity of drought. This will have large consequences for the diversity, composition and distribution of tropical tree species. Understanding the factors that shape tree species distribution will help to understand current forest functioning and to predict the potential impact of climate change on forests.
In this thesis, I used a combination of forest inventory data, greenhouse and field experiments to determine the responses of 10-23 species to drought and shade, and analyse the underlying mechanisms. I addressed 4 questions: (1) What is the relative importance of rainfall and temperature on tree species distribution? (2) How do tree species acclimatise to drought and shade in terms of their physiology, morphology, growth and survival? (3) What morphological and physiological traits determine species drought performance and distribution? (4) How do seedling survival, growth and physiology vary between dry and wet forests, and does drought tolerance and growth determine species distribution along the rainfall gradient?
Forest inventory data showed that the distribution of 95% of 20 species was significantly associated with annual rainfall, 60% with rainfall seasonality, 45% with isothermality and 40% with temperature seasonality. Thus, a reduction in annual rainfall, and an increase in frequency and intensity of drought as predicted by climate change models may affect the distribution of many tree species. A greenhouse experiment indicated that shade facilitated the survival of seedlings subjected to drought, rather than reducing it. This contrasts with the trade-off hypothesis that suggests a stronger impact of drought in shade conditions. Across 23 species, I found a trade-off between drought avoidance (by a deciduous leaf habit during drought) and physiological drought tolerance (by having tough and persistent tissues that allow plants to function during drought) strategies. These strategies were closely associated with species’ shade tolerance and growth rates. A suite of functional traits predicted drought survival and tree species position on the rainfall gradient. Across species, drought survival was enhanced by having less biomass allocation to transpiring leaves, a low leaf area per unit plant mass, and by dense and tough leaf and wood tissues that allow plants to function during drought. The field experiment showed that drought survival (and growth) in the dry forest relative to the wet forest correlated negatively with species position on the rainfall gradient. Hence, species that survive and grow relatively well in dry forests are found at the drier end of the rainfall gradient. This suggests that species sensitivity to low water availability determines the distribution of tree species. The predicted increase in drought frequency and intensity may, therefore, cause a shift in the distribution of tree species in tropical forests.
Population densities of eastern black rhinoceros : unravelling the controls
Ouma, B.O. - \ 2014
Wageningen University. Promotor(en): Herbert Prins, co-promotor(en): Ignas Heitkonig; Sip van Wieren. - Wageningen : Wageningen University - ISBN 9789461739599 - 158
rhinoceros - populatiedichtheid - populatie-ecologie - savannen - afgrazen - voedingsstoffenbeschikbaarheid - regen - temperatuur - kenya - rhinoceros - population density - population ecology - savannas - browsing - nutrient availability - rain - temperature - kenya
Key words: black rhinoceros, browser, corticosterone, diet, density dependence, minerals, moisture, physiological stress, savanna, soil nutrients, woody cover.
Understanding the forces that cause variability in population sizes is a central theme in ecology. The limiting factor in populations of large mammals which are not controlled top‐down by predation is food, i.e., such populations are controlled by bottom‐up processes. However, there is little evidence of density dependence in large‐ to mega-herbivores. Yet, conservationists have managed Critically Endangered mega‐herbivores like rhinoceros as if their population growth were density dependent, i.e., following a logistic growth curve, focusing on large growth at population densities presumed to be at half‐carrying capacity (K/2). This would enable them to translocate animals at presumed half‐carrying capacity to retain local population densities and to create new populations in areas of suitable habitat, where animals are considered safe against poaching. This study focused on one such mega‐herbivore, the eastern black rhinoceros (Diceros bicornis michaeli) to re‐consider the density dependence population regulation in a mega‐herbivore and uses the findings to contribute to possible solutions towards conservation challenges facing this species. The expectations were that increases in population density would result in a decrease in reproductive performance, and that physiological stress levels in animals in populations of high density would be higher than in animals in populations of low densities. Nine populations of black rhinoceros across Kenya were studied, with variation in their respective densities, Plant Available Moisture (‘PAM’ i.e., ‘soil moisture’) and Plant Available Nutrients (‘PAN’ i.e., ‘soil fertility’). Data from available records (1993‐2010) were used to assess reproductive performance. Dietary quality and levels of corticosterone were estimated through faecal analysis from animals sampled in the field and from data on feeding trials of black rhinoceroses in zoos (dietary analysis only). Woody cover estimates were used to assess available browse for black rhinoceros. Two measures of density were used, i.e., absolute density (animals/km2) and relative density, i.e., absolute density as a ratio to the estimated maximum stocking density or ‘carrying capacity’. The effects of PAM and PAN, and subsets of PAM (rainfall and temperature) were incorporated and controlled in testing expectations. No evidence for density dependence was found. Reproductive performances tended to be better where PAM was high, PAN was low and woody cover was sparse. PAM was found to be directly correlated with quality of dietary browse. Black rhinoceros populations appeared controlled more by bottom‐up processes through key resources, even though their densities were perhaps too low to fully support this alternative view. It was apparent that the density dependence concept still requires more investigation. Deliberate efforts should be made to secure high PAM – low PAN – sparse woody cover areas for conservation of black rhinoceros. Conservation managers are advised to consider set percentage translocations, as opposed to the current translocation of black rhinoceros on the basis of an imaginary ‘carrying capacity’ and density dependence.
Modelling rainfall-runoff processes in lowland catchments
Brauer, C.C. - \ 2014
Wageningen University. Promotor(en): Remko Uijlenhoet, co-promotor(en): Ryan Teuling. - Wageningen : Wageningen University - ISBN 9789461738547 - 93
hydrologie - hydrologie van stroomgebieden - regen - afvloeiingswater - laaglandgebieden - modelleren - nederland - hydrology - catchment hydrology - rain - runoff water - lowland areas - modeling - netherlands
Lowland catchments can be divided into mildly sloping, freely draining catchments and flat areas with managed surface water levels. In this thesis, data from two Dutch field sites are used. The mildly sloping, freely draining Hupsel Brook catchment is located in the east of The Netherlands, with elevations ranging from 22 to 35 m above sea level. This catchment has been an experimental catchment since the 1960s. The flat Cabauw polder is located in the west of The Netherlands at an “elevation” of 1 meter below sea level. This area is part of the Cabauw Experimental Site for Atmospheric Research (CESAR).
Rainfall estimation for hydrology using volumetric weather radar
Hazenberg, P. - \ 2013
Wageningen University. Promotor(en): Remko Uijlenhoet, co-promotor(en): Hidde Leijnse; G. Delrieu. - S.l. : s.n. - ISBN 9789461736307 - 232
regen - schatting - radar - hydrologie - meting - fouten - neerslag - rain - estimation - radar - hydrology - measurement - errors - precipitation
This thesis focuses specifically on weather radar rainfall measurements in strati form precipitation. In North-Western Europe this type of precipitation is most dominant in winter and leads to the largest hydro logical response of catchments. Unfortunately, the quality of uncorrected radar rainfall estimates starts decreasing at relatively close range from the radar for this type of precipitation. Therefore, as a first approach, a number of previously proposed radar error correction algorithms were applied in this thesis. The implementation of these methods shows a positive impact on the quality of the obtained precipitation measurements as compared to rain gauges. However, the traditional approach of applying a uniform Eulerian based algorithm for the entire radar umbrella to correct for VPR, limits its impact to improve the corrected weather radar precipitation measurements
Rainfall variability in the Netherlands from radars, rain gauges, and disdrometers
Beek, R. van de - \ 2013
Wageningen University. Promotor(en): Remko Uijlenhoet, co-promotor(en): Hidde Leijnse. - S.l. : s.n. - ISBN 9789461736437 - 128
regen - neerslag - radar - regenmeters - hydrologie - meteorologie - schattingen - schatting - meettechnieken - meetsystemen - nederland - rain - precipitation - radar - rain gauges - hydrology - meteorology - estimates - estimation - measurement techniques - measurement systems - netherlands
Chapter 1. This thesis presents studies on the variability of precipitation in the Netherlands from datasets collected by radars, rain gauges and disdrometers. Accurate rainfall estimates are highly relevant in hydrology, meteorology and climatology as precipitation has a large impact on society. Precipitation has been studied extensively in the past, although it is impossible to describe all processes and behavior involved. This thesis attempts to add to the knowledge on precipitation. In the first chapter a short overview of rainfall variability at different scales is presented together with the most common instruments for measuring precipitation.
Chapter 2. The spatial variability of daily rainfall accumulations is studied. Ninety-day averaged semi-variograms are created based on a 30-year data set gathered by automatic stations operated by the Royal Netherlands Meteorological Institute (KNMI). This is complemented by a one-year dataset of 10 gauges within a 5 km radius around CESAR (Cabauw Experimental Site for Atmospheric Research) in the center of the Netherlands. It is shown that it is possible to derive an average semi-variogram that describes the climatology of daily precipitation for each day of the year.
Chapter 3. The study of chapter 2 is extended by investigating accumulation intervals shorter than daily scales. These are at 12, 8, 6, 4, 3, 2 and 1-hour accumulation intervals. It is shown that at shorter temporal scales the behavior of semi-variograms of precipitation still shows a clear seasonal trend. At hourly and two-hourly accumulation intervals the signal of the range becomes fairly constant during the summer due to the limited accumulation period, the frequent occurrence of convective precipitation, and measurement errors. This illustrates the lower limit of using cosine functions to describe variogram parameters. By fitting a power-law function through the different cosine parameters it is possible to describe the semi-variance of precipitation at scales between 1 and 24 hours using a limited set of equations.
Chapter 4. Different sources of error affecting rainfall estimates by weather radar are identified. By focussing on precipitation near a C-band radar some of these sources are reduced, which allows to focus on a limited set of error sources. These are radar calibration, ground clutter, wet radome attenuation and variations in rain drop size distribution. An event that caused high precipitation amounts in a band along the center of the Netherlands and more than 50~mm near the radar between the 25th and the 27th of August 2010 is studied. Without any correction and by applying a standard Marshall-Palmer Z-R relation the radar is found to underestimate by approximately 50% with respect to the rain gauge measurements. Using the sun for calibration a correction of 1 dB is applied. Clutter is corrected by subtracting a clear sky clutter map as this proves to provide better results than the standard doppler filter. Wet-radome attenuation is corrected by looking at the amount of attenuation at a known strong clutter pixel near the radar. Disdrometer data near the radar are used to derive accurate Z-R relations specific to the precipitation of the event. These corrections combined provide very promising results with a slight overestimation of the quantitative precipitation estimates (QPE) from the radar by 5 to 8%.
Chapter 5. An extensive dataset of 195 precipitation events measured by an X-band radar (SOLIDAR) is used to study precipitation at a high spatial resolution of 120 m and a high temporal resolution of 16 s. This study shows the benefit of using such high resolution X-band radars over flat terrain. The errors in the radar measurements are first assessed and corrected as well as possible by considering different techniques. These errors are calibration, ground clutter and attenuation. Finally, five strongly different precipitation events are studied in detail to illustrate the strengths and weaknesses of the X-band weather radar.
Chapter 6. The variability and possible measurement methods of precipitation have been studied. It was shown that precipitation spatial and temporal variability has a clear statistical signal by analyzing variograms for different accumulation intervals. Weather radars were also shown to be able to give good estimates of precipitation at ground level as well as detailed information on the spatial variability. Some recommendations are given to perform follow up studies. For chapters 2 & 3 it is recommended to use a larger and more detailed dataset, which also incorporates Belgian and German data. This would allow the study of anisotropy in the semi-variograms as well as extending the analysis to accumulation times shorter than 1 hour and longer than 24 hours. For chapter 4 it is recommended to study pixels located further away from the radar. While other error sources would become more pronounced it would be possible to study the applicability of the proposed corrections at longer ranges. Studying the wet-radome attenuation with several strong clutter pixels near the radar would allow the study of wind-effects on wet-radome attenuation, possibly allowing corrections using measurements of (Doppler) wind-speed and direction. Finally, in chapter 5 it is recommended to study the successor of SOLIDAR, IDRA, which is currently operational at CESAR. This radar is a polarimetric radar, allowing a more detailed study of precipitation together with the data from other instruments at this location and the C-band radar of KNMI, which is located close to this location at approximately 23 km.
Differences in leaf litter, ascospore production and infection of pear scab (Venturia pirina) in Dutch organic orchards
Timmermans, B.G.H. ; Jansonius, P.J. - \ 2012
In: Eco-fruit : 15th international conference on cultivation technique and phytopathological problems in organic fruit-growing and viticulture, 20-22 February 2012, Hohenheim. - Weinsberg : Foerdergemeinschaft Oekologischer Obstbau e.V. - p. 253 - 259.
venturia pyrina - peren - fruitteelt - epidemiologie - plantenziekteverwekkende schimmels - schimmelziekten - plantenziekten - biologische landbouw - analyse - ziektebestrijdende teeltmaatregelen - regen - ascosporen - venturia pyrina - pears - fruit growing - epidemiology - plant pathogenic fungi - fungal diseases - plant diseases - organic farming - analysis - cultural control - rain - ascospores
In 2010 and 2011 the amounts of leaf litter and ascospore production per unit of leaf litter area in 7 organic pear orchards throughout the Netherlands were measured. In one of the orchards, adapted managements strategies were implemented, being grass/clover that is grown as ground cover on the tree-strip, and organic cattle-manure that replaces chicken manure pellets, in order to stimulate the earthworm population and change the palatability of the leaf litter. First results indicate large differences between orchards in percentage of ground covered by dead leaves at the time of major ascospore infections, but also in number of ascospores per cm2 leaf litter and in resulting potential ascospore dose. These data, together with weather data (temperature, rainfall), were used in a simple multivariate analysis to gain insight in the dynamics of the system. The first results show that, to a limited degree, leaf litter was indeed important for the scab epidemic in 2011, whereas in 2010 the high amount of rainfall in the second part of the growing season must have led to a high conidial infection pressure. Surprisingly, in both years ascospore number per unit leaf area was of more importance than leaf litter area or potential ascospore dose.
Statistiek van extreme gebiedsneerslag in Nederland
Overeem, A. ; Buishand, A. ; Holleman, I. ; Uijlenhoet, R. - \ 2012
H2O : tijdschrift voor watervoorziening en afvalwaterbehandeling 44 (2012)12. - ISSN 0166-8439 - p. 29 - 31.
hoogwaterbeheersing - neerslag - regen - regenmeters - meting - kwantitatieve methoden - gebiedsgericht beleid - kansverdelingen - meteorologische waarnemingen - statistische gegevens - flood control - precipitation - rain - rain gauges - measurement - quantitative methods - integrated spatial planning policy - probability distributions - meteorological observations - statistical data
Kansverdelingen van extreme neerslag zijn doorgaans afgeleid van puntmetingen van regenmeternetwerken en gelden voor een locatie. In het waterbeheer is echter vaak de extreme gebiedsneerslag van belang. Die is voor een bepaalde herhalingstijd lager dan de extreme neerslag op een locatie in dat gebied voor dezelfde herhalingstijd. Door deze gebiedsreductie leiden de gangbare neerslagstatistieken tot een onderschatting van de herhalingstijd voor extreme gebiedsneerslag. Daarom is het noodzakelijk om de kansverdeling van extreme gebiedsneerslag te bestuderen. Dit is maar beperkt mogelijk met de netwerken van regenmeters in Nederland. Recent hebben het Koninklijk Nederlands Meteorologisch Instituut (KNMI) en de leerstoelgroep Hydrologie en Kwantitatief Waterbeheer van Wageningen Universiteit een elfjarige radardataset van neerslaghoeveelheden geanalyseerd. Hierdoor zijn nu neerslagwaarnemingen met een hoge resolutie in tijd en ruimte beschikbaar voor heel Nederland. Met behulp van deze dataset zijn kansverdelingen van extreme gebiedsneerslag afgeleid.
Ziek en Zeer : Oorzaak vroege bloemverdroging 'Bridal Crown' nog niet helemaal duidelijk
Vink, P. - \ 2012
BloembollenVisie 2012 (2012)248. - ISSN 1571-5558 - p. 23 - 23.
narcissus pseudonarcissus - bloembollen - verdroging - cultivars - weersbeïnvloeding - regen - schade - landbouwkundig onderzoek - narcissus pseudonarcissus - ornamental bulbs - desiccation - cultivars - weather control - rain - damage - agricultural research
Bij de bollenteelt van narcissen van met name 'BridalCrown' bleek in de zomer van 2011 dat soms sprake was van vroege bloemverdroging. Middels een enquête bij gededupeerde bollentelers is nageggaan wat een mogelijke oorzaak zou kunnen zijn geweest. Het aanvankelijke idee dat het warme en droge voorjaar er debet aan zou kunnen zijn geweest is echter niet bevestigd. Wel zijn aanwijzingen verkregen dat de extreme regenval in juli 2011 op sommige percelen een rol heeft gespeeld bij het vroeg verdrogen van de bloemen.
Statistiek van extreme gebiedsneerslag in Nederland
Overeem, A. ; Buishand, A. - \ 2012
De Bilt : KNMI (Technical report / Koninklijk Nederlands Meteorologisch Instituut TR-332) - 48
neerslag - regen - meteorologische waarnemingen - meting - statistische gegevens - precipitation - rain - meteorological observations - measurement - statistical data
Kansverdelingen van extreme neerslag zijn doorgaans afgeleid uit puntmetingen van regenmeternetwerken en gelden voor een locatie. Echter, in het waterbeheer is vaak de extreme gebiedsneerslag van belang. Indien daarvoor de gangbare neerslagstatistieken worden gebruikt treedt een onderschatting op van de herhalingstijd. Daarom is het wenselijk om een statistiek van extreme gebiedsneerslag af te leiden. Het KNMI heeft in samenwerking met de Leerstoelgroep Hydrologie en KwantitatiefWaterbeheer van Wageningen Universiteit een klimatologische radardataset van de periode 1998-2008 opgebouwd en geanalyseerd.
Mind the gap: modelling event-based and millennial-scale landscape dynamics
Baartman, J.E.M. - \ 2012
Wageningen University. Promotor(en): Tom Veldkamp; Coen Ritsema, co-promotor(en): Jeroen Schoorl. - S.l. : s.n. - ISBN 9789461732668 - 216
geomorfologie - erosie - sedimentatie - dynamica - tijdschalen - landschapsanalyse - modelleren - rivieren - regen - menselijke invloed - landschap - ontwikkeling - spanje - pleistoceen - holoceen - geomorphology - erosion - sedimentation - dynamics - time scales - landscape analysis - modeling - rivers - rain - human impact - landscape - development - spain - pleistocene - holocene
This research looks at landscape dynamics – erosion and deposition – from two different perspectives: long-term landscape evolution over millennial timescales on the one hand and short-term event-based erosion and deposition at the other hand. For the first, landscape evolution models (LEMs) are often used, which describe landscape forming processes by geomorphic transport laws, usually on annual temporal resolutions. LEM LAPSUS is used in this research to evaluate the landscape dynamics in a study area in south-east Spain: the Guadalentín Basin. The model is calibrated on dated river terrace levels, which show an erosion – deposition – erosion sequence that the model could reproduce. Annual precipitation in this dryland area shows large inter-annual variability and erosion is supposed to be mainly the results of low-frequency, high magnitude rainfall events. Therefore, in this research, landscape dynamics are also assessed using the event-based erosion model OpenLISEM. Eventually, the role of extreme events in long-term landscape evolution are explored by comparing the two models and by incorporating annual rainfall variability into LEM LAPSUS. Another issue that is being addressed in this study is the relative influence of humans as compared to erosion as a natural process. A conceptual model, derived on the basis of dated sediment archives, is tentatively correlated to periods of human impact on the land. Using LAPSUS, the potential influence of historical tillage erosion is simulated, showing that the relatively slow process of tillage erosion added to floodplain aggradation over thousands of years.
Robust assessment of future changes in extreme precipitation over the Rhine basin using a GCM
Kew, S.F. ; Selten, F.M. ; Lenderink, G. ; Hazeleger, W. - \ 2011
Hydrology and Earth System Sciences 15 (2011). - ISSN 1027-5606 - p. 1157 - 1166.
klimaatverandering - neerslag - regen - meteorologische factoren - simulatiemodellen - toekomst - watersystemen - waterstand - rivieren - hydrologie van stroomgebieden - rijn - climatic change - precipitation - rain - meteorological factors - simulation models - future - water systems - water level - rivers - catchment hydrology - river rhine - regional climate model - storm track - simulations - europe - shift - temperature - netherlands - projections - scenarios
Estimates of future changes in extremes of multiday precipitation sums are critical for estimates of future discharge extremes of large river basins. Here we use a large ensemble of global climate model SRES A1b scenario simulations to estimate changes in extremes of 1–20 day precipitation sums over the Rhine basin, projected for the period 2071–2100 with reference to 1961–1990. We find that in winter, an increase of order 10%, for the 99th percentile precipitation sum, is approximately fixed across the selected range of multiday sums, whereas in summer, the changes become increasingly negative as the summation time lengthens. Explanations for these results are presented that have implications for simple scaling methods for creating time series of a future climate. We show that the dependence of quantile changes on summation time is sensitive to the ensemble size and indicate that currently available discharge estimates from previous studies are based on insufficiently long time series.
Anatomy of extraordinary rainfall and flash flood in a Dutch lowland catchment
Brauer, C.C. ; Teuling, R. ; Overeem, A. ; Velde, Y. van der; Hazenberg, P. ; Warmerdam, P.M.M. ; Uijlenhoet, R. - \ 2011
Hydrology and Earth System Sciences 15 (2011). - ISSN 1027-5606 - p. 1991 - 2005.
neerslag - regen - waterstand - waterbergend vermogen - wateropslag - waterverzadiging - waterbeheer - laaglandgebieden - precipitation - rain - water level - water holding capacity - water storage - waterlogging - water management - lowland areas - route contributions - groundwater - france - event - south - soil
On 26 August 2010 the eastern part of The Netherlands and the bordering part of Germany were struck by a series of rainfall events lasting for more than a day. Over an area of 740 km2 more than 120 mm of rainfall were observed in 24 h. This extreme event resulted in local flooding of city centres, highways and agricultural fields, and considerable financial loss. In this paper we report on the unprecedented flash flood triggered by this exceptionally heavy rainfall event in the 6.5 km2 Hupsel Brook catchment, which has been the experimental watershed employed by Wageningen University since the 1960s. This study aims to improve our understanding of the dynamics of such lowland flash floods. We present a detailed hydrometeorological analysis of this extreme event, focusing on its synoptic meteorological characteristics, its space-time rainfall dynamics as observed with rain gauges, weather radar and a microwave link, as well as the measured soil moisture, groundwater and discharge response of the catchment. At the Hupsel Brook catchment 160 mm of rainfall was observed in 24 h, corresponding to an estimated return period of well over 1000 years. As a result, discharge at the catchment outlet increased from 4.4 × 10-3 to nearly 5 m3 s-1. Within 7 h discharge rose from 5 × 10-2 to 4.5 m3 s-1. The catchment response can be divided into four phases: (1) soil moisture reservoir filling, (2) groundwater response, (3) surface depression filling and surface runoff and (4) backwater feedback. The first 35 mm of rainfall were stored in the soil without a significant increase in discharge. Relatively dry initial conditions (in comparison to those for past discharge extremes) prevented an even faster and more extreme hydrological response.
Coping with drought for food security in Tigray, Ethiopia
Berhe, A.A. - \ 2011
Wageningen University. Promotor(en): Leo Stroosnijder, co-promotor(en): Saskia Keesstra. - [S.l.] : S.n. - ISBN 9789085859253 - 173
landbouwklimatologie - droogte - waterstress - irrigatie - regen - gewassen - hordeum vulgare - gerst - eragrostis tef - mulches - opbrengsten - ethiopië - agroclimatology - drought - water stress - irrigation - rain - crops - hordeum vulgare - barley - eragrostis tef - mulches - yields - ethiopia
Agricultural production in drylands suffers from drought and in sub-Saharan Africa, only about 15% of the terrestrial rainwater is used by plants for food, fodder and fiber. Drought was the major cause of crop failure and food insecurity for the last three decades in the semi-arid northern Ethiopia. Information from field experiments, farmers and FAO’s AquaCrop model were used to understand and evaluate characteristics of the local climate in relation to drought and its mitigation. Farmers often have a different perception of drought than scientists. This gap was solved with an improved analysis of rainfall data that focuses on drought. Drought in semi-arid north Ethiopia can be due to (1) a too short growing season due to late start and/or early cessation of rains, (2) a too long dry spell at critical growth stage or (3) due to total failure of rain. Different types of drought have different coping strategies. Coping strategies for drought are adaption of sowing date, in-situ water conservation and water harvesting for deficient irrigation. Physical water conservation structures need to account for extreme variations in rainfall typical for most drylands. Ridging is most promising while mulching is no longer promoted. Agronomic measures such as the use of quick maturing and drought resistant crops are often more attainable than adoption of water conservation practices. Crop failure is often more due to water scarcity than to lack of fertility. However, when agricultural production increases, water and nutrients often alternate as production limiting factors. The strong water-nutrient synergy in drylands requires precision fertilization and plant density adjustment. Farmers also have a different opinion about climate change; farmers’ climate change has more to do with desertification. Experimental results showed that drought alleviation strategies have the potential to reduce the risk of crop failure and drought in the semi-arid northern Ethiopia.
Buienradar brengt kans op extreme regenval in kaart
Overeem, A. - \ 2010
Het weer magazine : magazine voor de weerliefhebber 2010 (2010)4. - ISSN 1568-1629 - p. 31 - 33.
neerslag - regen - weersvoorspelling - radar - internet - meteorologische waarnemingen - riolering - pompstations - precipitation - rain - weather forecasting - meteorological observations - sewerage - pumping stations
De KNMI-neerslagradars maken elke vijf minuten scans over heel Nederland, waarna vrijwel gelijk de neerslagintensiteitsbeelden kunnen worden bekeken op internet. Aangetoond is dat deze buienradars ook geschikt zijn om de kans op extreme hoeveelheden neerslag te bepalen. Handige informatie voor de ontwerpers van rioleringen en gemalen.