Staff Publications

Staff Publications

  • external user (warningwarning)
  • Log in as
  • language uk
  • About

    '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.

    We have a manual that explains all the features 

    Current refinement(s):

    Records 1 - 14 / 14

    • help
    • print

      Print search results

    • export

      Export search results

    Check title to add to marked list
    Deriving optimal weather pattern definitions for the representation of precipitation variability over India
    Neal, Robert ; Robbins, Joanne ; Dankers, Rutger ; Mitra, Ashis ; Jayakumar, A. ; Rajagopal, E.N. ; Adamson, George - \ 2020
    International Journal of Climatology 40 (2020)1. - ISSN 0899-8418 - p. 342 - 360.
    cluster analysis - forecasts - India - monsoon - weather patterns

    This study utilizes cluster analysis to produce sets of weather patterns for the Indian subcontinent. These patterns have been developed with future applications in mind; specifically relating to the occurrence of high-impact weather and meteorologically induced hazards such as landslides. The weather patterns are also suited for use within probabilistic medium- to long-range weather pattern forecasting tools driven by ensemble prediction systems. A total of 192 sets of weather patterns have been generated by varying the parameter which is clustered, the spatial domain and the number of weather patterns. Non-hierarchical k-means clustering was applied to daily 1200 UTC ERA-Interim reanalysis data between 1979 and 2016 using pressure at mean sea level (PMSL) and u- and v-component winds at 10-m, 925-hPa and 850-hPa. The resultant weather pattern sets (clusters) were analysed for their ability to represent the main climatic precipitation patterns over India using the explained variation score. Weather patterns generated using 850-hPa winds are among the most representative, with 30 patterns being enough to represent variability within different phases of the Indian climate. For example, several weather pattern variants are evident within the active monsoon, break monsoon and retreating monsoon. There are also several variants of weather patterns susceptible to western disturbances. These weather pattern variants are useful when it comes to identifying periods most susceptible to high-impact weather within a large-scale regime, such as identifying the most flood prone periods within the active monsoon. They hence have potentially many forecasting applications.

    DEB parameter estimation for Saccostrea cucullata (Born), an intertidal rock oyster in the Northern Bay of Bengal
    Chowdhury, Shah ; Wijsman, J.W.M. ; Hossain, M.S. ; Ysebaert, T. ; Smaal, A.C. - \ 2018
    Journal of Sea Research 142 (2018). - ISSN 1385-1101 - p. 180 - 190.
    DEB model - saccostrea-cuccullata - Parameter estimation - monsoon
    Dynamic Energy Budget (DEB) models describe the energy flow in organisms focusing on food assimilation and utilization for maintenance, growth and reproduction. In this paper, specific DEB parameters were obtained for
    the intertidal rock oyster Saccostrea cucullata, which has culture potential and important ecological functions in estuarine and coastal ecosystems along the Bay of Bengal, Bangladesh. Oyster samples were collected from natural oyster beds and used in a starvation experiment for 20 weeks in the laboratory. A sub-sample of starved oyster was used to record respiration rates and depletion of reserves was recorded by fortnightly measurements of flesh weight. Simultaneously, a group of oysters was used for physiological experiments and growth measurements, required for DEB parameter estimation. Consequently, Arrhenius temperature related parameters (i.e. TA, TL, TH, TAL, and TAH), shape coefficient (δM), volume specific maintenance rate ([PM]) and volume specific cost for structure ([EG]) were estimated using data from the respiration and starvation experiments. An iterative co-variation method was used to estimate the specific DEB parameters using the results of the physiological experiments, field observations and additional literature information. Estimated Arrhenius temperature was 5640 K, which applies between 297 and 305 K. Shape coefficient (δM=0.159) was low, compared to other oyster species that characterized the morphology of the oyster. Volume specific maintenance rate ([PM]) was equivalent to 17.99 J cm−3 day−1, while 2377 J cm−3 was estimated as the volume specific cost for structure ([EG]). These efforts provide opportunities to apply the DEB model for better understanding the energetics
    of bivalves under sub-tropical conditions. It is concluded that the hydrometeorological aspects, i.e. a monsoon regime and high turbidity levels, are quite different from temperate regions and drives the physiological traits of shellfish organisms.
    Flexible strategies for coping with rainfall variability : seasonal adjustments in cropped area in the Ganges basin
    Siderius, C. ; Biemans, Hester ; Walsum, P.E.V. van; Ierland, E.C. van; Hellegers, P.J.G.J. - \ 2016
    Wageningen University & Research
    coping strategy - flexibility - rainfall variability - crop production - cropped area - Ganges basin - monsoon - rice-wheat cropping system - climate change - hydroeconomic modelling - WaterWise - adaptation
    One of the main manifestations of climate change is expected to be increased rainfall variability. How to deal with this in agriculture will be a major societal challenge. In this paper we explore flexibility in land use, through deliberate seasonal adjustments in cropped area, as a specific strategy for coping with rainfall variability. Such adjustments are not incorporated in hydro-meteorological crop models commonly used for food security analyses. Our paper contributes to the literature by making a comprehensive model assessment of inter-annual variability in crop production, including both variations in crop yield and cropped area. The Ganges basin is used as a case study. First, we assessed the contribution of cropped area variability to overall variability in rice and wheat production by applying hierarchical partitioning on time-series of agricultural statistics. We then introduced cropped area as an endogenous decision variable in a hydro-economic optimization model (WaterWise), coupled to a hydrology-vegetation model (LPJmL), and analyzed to what extent its performance in the estimation of inter-annual variability in crop production improved. From the statistics, we found that in the period 1999-2009 seasonal adjustment in cropped area can explain almost 50% of variability in wheat production and 40% of variability in rice production in the Indian part of the Ganges basin. Our improved model was well capable of mimicking existing variability at different spatial aggregation levels, especially for wheat. The value of flexibility, i.e. the foregone costs of choosing not to crop in years when water is scarce, was quantified at 4% of gross margin of wheat in the Indian part of the Ganges basin and as high as 34% of gross margin of wheat in the drought-prone state of Rajasthan. We argue that flexibility in land use is an important coping strategy to rainfall variability in water stressed regions.
    Report of the potato mission of the Netherlands industry and knowledge institutions to Myanmar : March 7 - 15, 2015
    Pronk, A.A. ; Haverkort, A.J. ; Veldhuijsen, C. van; Alberts, B. ; Remijn, P. ; Peltjes, J. ; Waes, J. Van; Kooman, P. - \ 2015
    Wageningen : Plant Research International, part of Wageningen UR, Business Unit Agrosystems Research (Report / Plant Research International 611) - 17
    potatoes - seed potatoes - solanum tuberosum - myanmar - monsoon - rainfed agriculture - aardappelen - pootaardappelen - solanum tuberosum - myanmar - moesson - regenafhankelijke landbouw
    This report describes a potato mission of the Netherlands industry and knowledge institutions to Myanmar.
    Tree-ring d18O in African mahogany (Entandrophragma utile) records regional precipitation and can be used for climate reconstructions
    Sleen, J.P. van der; Groenendijk, P. ; Zuidema, P. - \ 2015
    Global and Planetary Change 127 (2015). - ISSN 0921-8181 - p. 58 - 66.
    oxygen-isotope ratios - tropical atlantic - west-africa - monsoon - growth - forest - chronologies - temperature - variability - salinity
    The availability of instrumental climate data in West and Central Africa is very restricted, both in space and time. This limits the understanding of the regional climate system and the monitoring of climate change and causes a need for proxies that allow the reconstruction of paleoclimatic variability. Here we show that oxygen isotope values (d18O) in tree rings of Entandrophragma utile from North-western Cameroon correlate to precipitation on a regional to sub-continental scale (1930–2009). All found correlations were negative, following the proposed recording of the ‘amount effect’ by trees in the tropics. The capacity of E. utile to record the variability of regional precipitation is also confirmed by the significant correlation of tree-ring d18O with river discharge data (1944–1983), outgoing longwave radiation (a proxy for cloud cover; 1974–2011) and sea surface salinity in the Gulf of Guinea (1950–2011). Furthermore, the high values in the d18O chronology from 1970 onwards coincide with the Sahel drought period. Given that E. utile presents clear annual growth rings, has a wide-spread distribution in tropical Africa and is long lived (> 250 years), we argue that the analysis of oxygen isotopes in growth rings of this species is a promising tool for the study of paleoclimatic variability during the last centuries in West and Central Africa.
    Effects of Irrigation in India on the Atmospheric Water Budget
    Tuinenburg, O.A. ; Hutjes, R.W.A. ; Stacke, T. ; Wiltshire, A. ; Lucas-Picher, P. - \ 2014
    Journal of Hydrometeorology 15 (2014)3. - ISSN 1525-755X - p. 1028 - 1050.
    soil-moisture - part i - precipitation - climate - monsoon - scheme - models - cycle - parameterization - representation
    The effect of large-scale irrigation in India on the moisture budget of the atmosphere was investigated using three regional climate models and one global climate model, all of which performed an irrigated run and a natural run without irrigation. Using a common irrigation map, year-round irrigation was represented by adding water to the soil moisture to keep it at 90% of the maximum soil moisture storage capacity, regardless of water availability. For two focus regions, the seasonal cycle of irrigation matched that of the reference dataset, but irrigation application varied between the models by up to 0.8 mm day(-1). Because of the irrigation, evaporation increased in all models, but precipitation decreased because of a strong decrease in atmospheric moisture convergence. A moisture tracking scheme was used to track individual evaporated moisture parcels through the atmosphere to determine where these lead to precipitation. Up to 35% of the evaporation moisture from the Ganges basin is recycling within the river basin. However, because of a decreased moisture convergence into the river basin, the total amount of precipitation in the Ganges basin decreases. Although a significant fraction of the evaporation moisture recycles within the river basin, the changes in large-scale wind patterns due to irrigation shift the precipitation from the eastern parts of India and Nepal to the northern and western parts of India and Pakistan. In these areas where precipitation increases, the relative precipitation increase is larger than the relative decrease in the areas where precipitation decreases. It is concluded 1) that the direct effects of irrigation on precipitation are small and are not uniform across the models; 2) that a fraction of up to 35% of any marginal evaporation increase (for example, due to irrigation) will recycle within the river basin; and 3) that when irrigation is applied on a large scale, the dominant effect will be a change in large-scale atmospheric flow that decreases precipitation in eastern India and increases it in western and northern India.
    Atmospheric effects of irrigation in monsoon climate: the Indian subcontinent
    Tuinenburg, O.A. - \ 2013
    Wageningen University. Promotor(en): Pavel Kabat, co-promotor(en): Ronald Hutjes. - S.l. : s.n. - ISBN 9789461734990 - 166
    irrigatie - atmosfeer - moesson - evaporatie - waterbudget - india - irrigation - atmosphere - monsoon - evaporation - water budget - india

    During the 20th century, an increasing population increased the demand for food. As a consequence, agricultural activity has expanded and become more intense. A part of this intensification is the use of irrigation systems to water crops. Due to this irrigation, dams and channeling systems, water can be made available for agriculture in places or during seasons with limited precipitation. In monsoon climates, such as India, the majority of the precipitation falls in one season. During the rest of the year, water that is stored in dammed reservoirs can be made available to spread the water availability more evenly over the year. Previous studies with large scale hydrological models have shown that as a consequence of human influences (such as dams and irrigation systems), the river flow decreases during the wet monsoon months, but the evaporation of water into the atmosphere increases during the dry months. However, these large scale hydrological models did not take into account the atmospheric effects of a changed land surface. This PhD research studies these atmospheric effects of large scale irrigation in India. Three perspectives are taken to determined the influence of irrigation: (1) the local effects of a moister land-surface on the triggering of precipitation (i.e. does the change in land surface wetness lead to a different amount of precipitation?), (2) the atmospheric fate of evaporation due to irrigation (i.e. where does the evaporation lead to (down-wind) precipitation?), and (3) the effects of a moister land-surface on the large scale (monsoon) moisture transport patterns (i.e. do the monsoon flows change significantly due to large scale irrigation?) In the first part (the first perspective), several land-atmosphere diagnostics are tested globally. The goal of these diagnostics is to determine the influence of the land surface on precipitation, based on surface and atmospheric conditions. Of these diagnostics, the CTP-HIlow framework (Convective Triggering Potential and Humidity Index of the LOWer atmosphere) of Findell and Eltahir (2003a) performed well globally and over the Indian region. The summertime atmospheric conditions were diagnosed using this framework and the presence of a land-atmosphere coupling hot-spot in the Indian peninsula, proposed by previous studies (Koster et al. (2004)), is confirmed. Secondly, the local perspective is taken in the Indian subcontinent. The CTP- HIlow framework is tested in India, using an atmospheric slab model (a simple, one- dimensional model of the atmosphere) combined with atmospheric soundings (balloon measurements of temperature and moisture of an atmospheric profile of up to 30 km). This model is run twice; once with a wet land surface and once with a dry land surface. The results of these model runs can have two outcomes; the land surface does not have an influence on precipitation or it does have an influence. The CTP-HIlow framework proves to be useful to classify the potential influence of the land surface. When the atmosphere is very wet (low values of HIlow ), precipitation will occur regardless of the land surface, when the atmosphere is very dry (high HIlow values) no precipitation will occur, regardless of the land surface. However, for intermediate HIlow values, the effect of the land surface depends on the stability or the amount of convective energy (CTP) in the atmosphere. The stability of the atmosphere is related to how fast a particle will ascend in the atmosphere, which depends mostly on the temperature profile. For positive, but low convective potentials (0200 J/kg), a dry land surface will produce more precipitation. For India, a small adaptation of the framework improved the performance in predicting the influence of the land surface on precipitation triggering. For India, the effect of the land surface on precipitation is seasonal. During the periods two months before the monsoon onset and after the monsoon retreat, precipitation triggering was found to be sensitive to land surface wetness. During those periods, a wet land surface is expected to increase precipitation. The atmospheric conditions under which a wet land surface is expected to decreases precipitation do not occur frequently in India. During the dry winter season, the atmosphere is too dry for the land surface to have an influence on precipitation. During the monsoon period, the atmosphere is too wet for the land surface to have an influence on precipitation, it will occur regardless of the land surface conditions. In the third part of the study, the moisture recycling perspective was taken and the atmospheric moisture budget of the Ganges basin is studied. A three-dimensional moisture tracing model is used to release moisture parcels from the Ganges basin, similarly to a class of school children releasing helium-filled balloons with their address on it. These parcels were transported along the wind patterns. During the trajectory of the parcel through the atmosphere, some moisture will precipitate out of it and contribute to the precipitation at that location. For each location, many parcels were released for every time step of 6 hours. Similar to the balloons of the school children that are hopefully sent back to them, the fate of the released moisture was accounted. The fraction of the evaporated moisture that subsequently falls as precipitation (recycles) within the Ganges basin shows a strong seasonality. During the winter months, practically all evaporation parcels were transported towards the Indian ocean and were lost for the Ganges basin. During the pre-monsoon months, the recycled fraction increased and was between 30-40%. During the monsoon months, the recycling peaks at up to 60%, after which it drops off again. The importance of recycled evaporation to the total precipitation peaks during the pre-monsoon and post-monsoon periods, when it contributes up to 15% of the precipitation. In the last part of the study, the effects from the local and moisture recycling perspectives are compared to those from the large scale perspective. Four atmospheric models were run with and without irrigation to test the large scale effects of irrigation on the Ganges basin atmospheric water budget and the influence on large scale atmospheric moisture transport. The local effects on precipitation were minimal and not uniform across the models. The Ganges river basin evaporation increased, as well as the amount of evaporation recycled within the river basin. However, the large scale wind patterns showed an uniform change across the models. Due to an increased flow in the direction of north-west India, the precipitation in east-India decreased while it increased in north-west India and Pakistan. Therefore, the Ganges basin precipitation decreased slightly. The conclusion of the work is that from the local perspective and the moisture recycling perspective, irrigation will lead to more precipitation in India. A wetter land surface will trigger some additional precipitation (especially just before and after the monsoon season) and a significant fraction of the evaporation will return to the same river basin as precipitation. However, from the large scale perspective, large scale irrigation will shift the wind patterns due to changes in the land-sea temperature contrast; precipitation will decrease slightly in the Ganges basin and be shifted towards the Indus basin and north-west India. The effects of irrigation on precipitation is small compared to the hydrological response of human influences simulated by the large scale hydrological models. Moreover, the spread in response across these hydrological models is large compared to the simulated effects of irrigation by the atmospheric models. Therefore, it is recommended to improve the large scale hydrological models and reduce their uncertainty before including the feedbacks of land use changes on their precipitation input.

    Regional projections of North Indian climate for adaptation studies
    Mathison, C. ; Wiltshire, A. ; Dimri, A.P. ; Moors, E.J. ; Siderius, C. ; Ridley, J. - \ 2013
    Science of the Total Environment 468-469 (2013)S1. - ISSN 0048-9697 - p. S4 - S17.
    interannual variability - global precipitation - monsoon - model - heat - representation - uncertainty - irrigation - simulation - prediction
    Adaptation is increasingly important for regions around the world where large changes in climate could have an impact on populations and industry. The Brahmaputra–Ganges catchments have a large population, a main industry of agriculture and a growing hydro-power industry, making the region susceptible to changes in the Indian Summer Monsoon, annually the main water source. The HighNoon project has completed four regional climate model simulations for India and the Himalaya at high resolution (25 km) from 1960 to 2100 to provide an ensemble of simulations for the region. In this paper we have assessed the ensemble for these catchments, comparing the simulations with observations, to give credence that the simulations provide a realistic representation of atmospheric processes and therefore future climate. We have illustrated how these simulations could be used to provide information on potential future climate impacts and therefore aid decision-making using climatology and threshold analysis. The ensemble analysis shows an increase in temperature between the baseline (1970–2000) and the 2050s (2040–2070) of between 2 and 4 °C and an increase in the number of days with maximum temperatures above 28 °C and 35 °C. There is less certainty for precipitation and runoff which show considerable variability, even in this relatively small ensemble, spanning zero. The HighNoon ensemble is the most complete data for the region providing useful information on a wide range of variables for the regional climate of the Brahmaputra–Ganges region, however there are processes not yet included in the models that could have an impact on the simulations of future climate. We have discussed these processes and show that the range from the HighNoon ensemble is similar in magnitude to potential changes in projections where these processes are included. Therefore strategies for adaptation must be robust and flexible allowing for advances in the science and natural environmental changes.
    The fate of evaporated water from the Ganges basin
    Tuinenburg, O.A. ; Hutjes, R.W.A. ; Kabat, P. - \ 2012
    Journal of Geophysical Research: Atmospheres 117 (2012)D1. - ISSN 2169-897X
    hydrologic-cycle - soil-moisture - global energy - part i - precipitation - irrigation - monsoon - model - validation - vapor
    This research studies river basin moisture recycling rates in order to determine the atmospheric part of the water cycle and the influence of the land surface there on. For river basins in India (Ganges and Indus), the fraction of evaporation that falls again as precipitation in the same river basin (the moisture recycling) is determined. Furthermore, the seasonal variance of moisture recycling and the fraction of precipitation that originates from evaporation from the same river basin is quantified. Using a quasi-isentropic moisture tracking scheme, evaporation from land surfaces in India is tracked through the atmosphere until precipitation brings it back to the land surface. This scheme is forced with ERA-Interim reanalysis data from 1990 to 2009. With the information about the atmospheric paths of water vapor, the distance between evaporation and precipitation location is determined. To get an approximation of the influence of land use on the atmospheric moisture budget, the atmospheric paths of water vapor from two bordering areas with different evaporative regimes are compared. Results show a strong annual cycle in the recycling ratio. For the Ganges basin, the recycling ranges from 5% during the winter months (November–March) to 60% during the June–July–August season. The comparison of two focus areas in the Ganges basin with a difference in March–August evaporation shows that during the premonsoon months (March–May), up to 70% of the evaporation difference between the two areas recycles within the Ganges basin. Analysis of the soil moisture nudging terms in ERA-Interim compared to independent irrigation data strongly suggest this evaporation difference can be attributed to large-scale irrigation. The importance of basin moisture recycling for precipitation shows an annual cycle as well. An annual average of 4.5% of Ganges precipitation originates from water evaporating in the Ganges basin. During the dry winter monsoon, any precipitation originates from sources outside the basin. During March–April–May and October–November, 10% of the precipitation originates from evaporation within the basin. During the summer monsoon season, the large influx of moisture from the Indian Ocean dominates the precipitation, and recycling is 5% of precipitation.
    Effects of soil moisture gradients on the path and the intensity of a West African squall line
    Wolters, D. ; Heerwaarden, C.C. van; Vilà-Guerau de Arellano, J. ; Cappelaere, B. ; Ramier, D. - \ 2010
    Quarterly Journal of the Royal Meteorological Society 136 (2010)653. - ISSN 0035-9009 - p. 2162 - 2175.
    mesoscale convective complexes - land-surface - monsoon - variability - sahel - model - precipitation - dynamics - system - field
    During the West African monsoon season, precipitation is strongly coupled to soil moisture availability. This interaction is generally understood as a positive feedback mechanism, and has been considered on very different spatial and temporal scales. Past research has mainly focused on this feedback in terms of the effects on general precipitation patterns, not on a single convective system. In this research, a single squall line is reproduced using the Weather Research and Forecasting Advanced Research (WRF-ARW) mesoscale weather model. Model results are analyzed and compared with surface and upper-air observations. A sensitivity analysis on the influence of soil moisture on the squall line is performed through five numerical experiments. In four experiments, soil moisture is increased or decreased with respect to a control experiment. This is done in two manners: by affecting soil moisture most strongly in the wetter places in the modelled domain and by affecting soil moisture most strongly in the drier places. Minor deviations occur in the path of the squall line after modifying soil moisture most strongly in the wetter places. Systematic deviations occur in its path after increasing soil moisture most strongly in the drier places. A mechanism is proposed that connects the applied soil moisture modifications to larger-scale flow patterns that determine the path of the squall line. In all five experiments, the precipitation intensity of the squall line strongly declines when the systemmoves towards western areaswith lower soil moisture values. It is concluded that a positive effect of local soil moisture on precipitation intensity in passing squall lines is likely on the considered length-scale of 100 km. Until now, this mechanism has only been shown for much smaller spatial scales.
    Impacts of the Madden-Julian oscillation on Australian rainfall and circulation
    Wheeler, M.C. ; Hendon, H.H. ; Cleland, S. ; Meinke, H.B. ; Donald, A. - \ 2009
    Journal of Climate 22 (2009)6. - ISSN 0894-8755 - p. 1482 - 1498.
    outgoing longwave radiation - tropical-extratropical interaction - northern winter - climate variability - prediction - monsoon - precipitation - temperature - reanalysis - atmosphere
    Impacts of the Madden¿Julian oscillation (MJO) on Australian rainfall and circulation are examined during all four seasons. The authors examine circulation anomalies and a number of different rainfall metrics, each composited contemporaneously for eight MJO phases derived from the real-time multivariate MJO index. Multiple rainfall metrics are examined to allow for greater relevance of the information for applications. The greatest rainfall impact of the MJO occurs in northern Australia in (austral) summer, although in every season rainfall impacts of various magnitude are found in most locations, associated with corresponding circulation anomalies. In northern Australia in all seasons except winter, the rainfall impact is explained by the direct influence of the MJO's tropical convective anomalies, while in winter a weaker and more localized signal in northern Australia appears to result from the modulation of the trade winds as they impinge upon the eastern coasts, especially in the northeast. In extratropical Australia, on the other hand, the occurrence of enhanced (suppressed) rainfall appears to result from induced upward (downward) motion within remotely forced extratropical lows (highs), and from anomalous low-level northerly (southerly) winds that transport moisture from the tropics. Induction of extratropical rainfall anomalies by remotely forced lows and highs appears to operate mostly in winter, whereas anomalous meridional moisture transport appears to operate mainly in the summer, autumn, and to some extent in the spring
    Microscale vegetation-soil feedback boosts hysteresis in a regional vegetation-climate system
    Janssen, R.H.H. ; Meinders, M.B.J. ; Nes, E.H. van; Scheffer, M. - \ 2008
    Global Change Biology 14 (2008)5. - ISSN 1354-1013 - p. 1104 - 1112.
    semiarid grazing systems - northern africa - spatial heterogeneity - arabian peninsula - arid ecosystems - regime shifts - biome model - midholocene - sahel - monsoon
    It has been hypothesized that a positive feedback between vegetation cover and monsoon circulation may lead to the existence of two alternative stable states in the Sahara region: a vegetated state with moderate precipitation and a desert state with low precipitation. This could explain the sudden onset of desertification in the region about 5000 years ago. However, other models suggest that the effect of vegetation on the precipitation may be insufficient to produce this behavior. Here, we show that inclusion of the microscale feedback between soil and vegetation in the model greatly amplifies the nonlinearity, causing alternative stable states and considerable hysteresis even if the effect of vegetation on precipitation is moderate. On the other hand, our analysis suggests that self-organized vegetation patterns known from models that only focus at the microscale plant¿soil feedback will be limited to a narrower range of conditions due to the regional scale climate-feedback. This implies that in monsoon areas such as the Western Sahara self-organized
    Exploring optimal fishing scenarios for the multispecies artisanal fisheries of Eritrea using a trophic model
    Tsehaye, I.W. ; Nagelkerke, L.A.J. - \ 2008
    Ecological Modelling 212 (2008)3-4. - ISSN 0304-3800 - p. 319 - 333.
    coral-reef ecosystems - red-sea - ecopath - biomass - monsoon - communities - temperature - populations - management - mortality
    This study represents the first attempt to assess the potential for fisheries in the artisanal Red Sea reef fisheries of Eritrea in an ecosystem context. We used an Ecopath with Ecosim model to integrate known aspects of the ecosystem and its inhabitants into a single framework, with the aim to gain a better insight into the structure and functioning of the ecosystem and to assess the impacts of fishing in these data-limited fisheries. Model outputs indicate that most of the primary productivity in the system is recycled through a detritus-based food web, implying a bottom-up energy flow control. Ecotrophic efficiencies were nevertheless higher at higher trophic levels, suggesting that top-down control mechanisms are also ecologically important. Notwithstanding a high degree of primary productivity, the fishery yields estimated for the coral reef ecosystem were relatively low, apparently because of lower ecotrophic efficiencies at the lower trophic levels. A retrospective simulation of trends in these fisheries using Ecosim showed that, given the existing fishing intensity as suggested by official statistics (0.114 tonnes km¿2 year¿1), fishery-induced decline in abundance and yield of reef-associated demersals of the magnitude (ca. 25%) suggested by a previous study are unlikely. However, the decline in yield observed in these fisheries could be reproduced in the simulation when the existing fishing level was assumed to be five-fold the official estimate, as suggested by anecdotal evidence on unreported catches. The simulation results show that an optimal fishing strategy could be achieved through a slight reduction in the annual catch of reef-associated fish (to 0.32 tonnes km¿2 year¿1) and an increase in the capture of near-reef pelagics and large pelagics (to 0.19 and 0.39 tonnes km¿2 year¿1, respectively) from the putative levels. We explored optimal fishing scenarios in view of both direct effects of fishing on target species and indirect effects of fishing on non-target organisms. Finally, this study demonstrates that, even if modeling is no substitute for rigorous assessment of individual fish stocks with more detailed data, it could improve our understanding of the impacts of fishing on the structure and functioning of coral reef ecosystems in such newly developing fisheries, particularly on groups that would otherwise be difficult to monitor.
    Soil tillage in the tropics and subtropics
    Krause, R. ; Lorenz, F. ; Hoogmoed, W.B. - \ 1984
    Eschborn : Deutsche Gesellschaft fuer Technische Zusammenarbeit - ISBN 9783880852006 - 320
    klimaat - cultivators - uitrusting - erosie - gebergten - zeeklimaat - zaaibedbereiding - bodem - subtropen - grondbewerking - gereedschappen - tropen - types - continent - moesson - machines - climate - equipment - erosion - mountains - oceanic climate - seedbed preparation - soil - subtropics - tillage - tools - tropics - monsoon
    Check title to add to marked list

    Show 20 50 100 records per page

     
    Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.