Future projections of flood dynamics in the Vietnamese Mekong Delta
Triet, Nguyen Van Khanh ; Dung, Nguyen Viet ; Hoang, Long Phi ; Duy, Nguyen Le ; Tran, Dung Duc ; Anh, Tran Tuan ; Kummu, Matti ; Merz, Bruno ; Apel, Heiko - \ 2020
Science of the Total Environment 742 (2020). - ISSN 0048-9697
Climate change - Hydrodynamic modelling - Hydropower - Land subsidence - Sea-level rise
The annual flood pulse of the Mekong River is crucial to sustain agriculture production, nutrition, and the livelihood of millions of people living in the Vietnamese part of the Mekong Delta (VMD). However, climate change impacts on precipitation, temperature and sea-level combined with land subsidence, upstream hydropower development, and water infrastructures (i.e. high-dykes construction) are altering the hydrological regime of the VMD. This study investigates future changes in flood hazard and agricultural production caused by these different scales of human-induced stresses. A quasi- two-dimensional (quasi-2D) hydrodynamic model was used to simulate eight scenarios representing the individual and compound impacts of these drivers for a baseline (1971–2000) and future (2036–2065) period. The scenarios map the most likely future pathway of climate change (RCP 4.5) combined with the best available Mekong upstream hydropower development, and land subsidence scenarios as well as the current delta development plan. We found that sea-level rise and land subsidence would cause the highest changes in flood hazard and damage to rice crop, followed by hydropower and climate change impacts. Expansion of high-dyke areas in two northernmost delta provinces (An Giang and Dong Thap) would have the smallest impact. The combination of all modelled drivers is projected to increase delta inundation extent by 20%, accompanied with prolonging submergence of 1–2 months, and 2–3 times increase in annual flood damage to rice crops in the flood-prone areas of the VMD. These findings of likely increasing risk of tidal induced flood hazard and damage call for well-planned adaptation and mitigation measures, both structural and non-structural.
Managing the effects of multiple stressors on aquatic ecosystems under water scarcity
Navarro-Ortega, A. ; Acuña, V. ; Bellin, A. ; Burek, P. ; Cassiani, G. ; Choukr-Allah, R. ; Dolédec, S. ; Elosegi, A. ; Ferrari, F. ; Ginebreda, A. ; Grathwohl, P. ; Jones, C. ; Ker Rault, P.A. ; Kok, K. ; Koundouri, P. ; Ludwig, R.P. ; Merz, R. ; Milacic, R. - \ 2015
Science of the Total Environment 503-504 (2015). - ISSN 0048-9697 - p. 3 - 9.
climate-change - fresh-water - mediterranean rivers - southern europe - management - scenarios - quality - systems
Water scarcity is a serious environmental problem in many European regions, and will likely increase in the near future as a consequence of increased abstraction and climate change. Water scarcity exacerbates the effects of multiple stressors, and thus results in decreased water quality. It impacts river ecosystems, threatens the services they provide, and it will force managers and policy-makers to change their current practices. The EU-FP7 project GLOBAQUA aims at identifying the prevalence, interaction and linkages between stressors, and to assess their effects on the chemical and ecological status of freshwater ecosystems in order to improve water management practice and policies. GLOBAQUA assembles a multidisciplinary team of 21 European plus 2 non-European scientific institutions, as well as water authorities and river basin managers. The project includes experts in hydrology, chemistry, biology, geomorphology, modelling, socio-economics, governance science, knowledge brokerage, and policy advocacy. GLOBAQUA studies six river basins (Ebro, Adige, Sava, Evrotas, Anglian and Souss Massa) affected by water scarcity, and aims to answer the following questions: how does water scarcity interact with other existing stressors in the study river basins? How will these interactions change according to the different scenarios of future global change? Which will be the foreseeable consequences for river ecosystems? How will these in turn affect the services the ecosystems provide? How should management and policies be adapted to minimise the ecological, economic and societal consequences? These questions will be approached by combining data-mining, field- and laboratory-based research, and modelling. Here, we outline the general structure of the project and the activities to be conducted within the fourteen work-packages of GLOBAQUA.
Dynamic and Capillary Shear Rheology of Natural Fiber-Reinforced Composites
Moigne, N. Le; Oever, M.J.A. van den; Budtova, T. - \ 2013
Polymer Engineering and Science 53 (2013)12. - ISSN 0032-3888 - p. 2582 - 2593.
An extended dynamic and capillary rheological study of molten flax and sisal polypropylene (PP) composites was performed. Fiber concentration varied from 20 to 50 wt% and shear rate from 0.1 rad s−1 to 10,000 s#142;−1. Maleic anhydride-grafted-PP was used as compatibilizer; it strongly reduces PP and composite viscosity. Composites are yield-stress shear-thinning fluids with solid-like behavior being more pronounced at high fiber content. Composites do not obey Cox–Merz rule, which was explained by different macrostructures of the molten composites in parallel plates and capillary die geometries: random fiber orientation versus strong alignment in the flow direction, respectively. Theories describing the viscosity of suspensions of solid particles were applied to the composites studied and rheological parameters and maximal packing fiber volume fraction were calculated. POLYM. ENG. SCI., 53:2582–2593, 2013. ©2013 Society of Plastics Engineers.
|A new perspective on hydrological drought: a process-based classification into different drought types
Loon, A.F. van; Lanen, H.A.J. van - \ 2012
Almost ten years ago, the well-known flood typology of Merz and Blöschl (2003) was published. Up to now, such a typology does not exist for hydrological drought, while both drought management and research could strongly benefit from a thorough understanding and associated specific description of different drought types. Here, we present a hydrological drought typology based on underlying drought propagation processes. In the proposed hydrological drought typology six drought types are distinguished, i.e. i) classical rainfall deficit drought, ii) rain-to-snow-season drought, iii) wet-to-dry-season drought, iv) cold snow season drought, v) warm snow season drought, and vi) composite drought. The processes underlying these drought types are the result of the interplay of precipitation and temperature at catchment scale in different seasons. The most common drought type in five contrasting European catchments is the classical rainfall deficit drought, caused by an anomaly in precipitation. However, when only the most severe drought events are selected, anomalies in temperature play an increasingly important role in hydrological drought development. For severe hydrological drought events, the most common types are rain-to-snow-season drought (rainfall deficit causes hydrological drought that continues into snow season due to below-zero temperatures) and warm snow season drought (complete melt of snow cover, due to high temperatures, in combination with rainfall deficit causes hydrological drought). The occurrence of hydrological drought types in a specific catchment is based on climate and catchment control, which makes it possible to infer the drought type occurrence from information on climate and catchment characteristics (i.e. response to precipitation) using a general framework. This hydrological drought typology is based upon a thorough analysis of the processes underlying a high number of hydrological drought events in European case study catchments. The typology has a worldwide applicability, because it is based on general drought propagation principles. The proposed typology can be used to improve understanding of drought generating processes and to support the comparison of drought occurrence in different regions, the statistical analysis and prediction of drought, the development of drought indices, and research on the impact of global change on drought. The paper will present the main characteristics of the different drought types, their occurrences in contrasting European catchments, and how this can be translated to catchments around the world using the general framework. With this elaborated hydrological drought typology, river basin management, which in many places needs to balance between the two hydrological extremes flood and drought, gets the appropriate tool to take both extremes into account equally. After ten years, the flood typology of Merz and Blöschl (2003) finally has a successor in the field of drought.
Complexity in quantitative food webs
Banasek-Richter, C. ; Bersier, L.F. ; Cattin, M.F. ; Baltensperger, R. ; Gabriel, J.P. ; Merz, Y. ; Ulanowicz, R.E. ; Tavares, A.F. ; Williams, D.D. ; Ruiter, P.C. de; Winemiller, K.O. ; Naisbit, R.E. - \ 2009
Ecology 90 (2009)6. - ISSN 0012-9658 - p. 1470 - 1477.
trophic interactions - community stability - sampling effort - scale - networks - descriptors - connectance - adaptation - ecosystems - patterns
Food webs depict who eats whom in communities. Ecologists have examined statistical metrics and other properties of food webs, but mainly due to the uneven quality of the data, the results have proved controversial. The qualitative data on which those efforts rested treat trophic interactions as present or absent and disregard potentially huge variation in their magnitude, an approach similar to analyzing traffic without differentiating between highways and side roads. More appropriate data are now available and were used here to analyze the relationship between trophic complexity and diversity in 59 quantitative food webs from seven studies (14-202 species) based on recently developed quantitative descriptors. Our results shed new light on food-web structure. First, webs are much simpler when considered quantitatively, and link density exhibits scale invariance or weak dependence on food-web size. Second, the "constant connectance'' hypothesis is not supported: connectance decreases with web size in both qualitative and quantitative data. Complexity has occupied a central role in the discussion of food-web stability, and we explore the implications for this debate. Our findings indicate that larger webs are more richly endowed with the weak trophic interactions that recent theories show to be responsible for food-web stability.
Flow-induced correlation effects within a linear chain in a polymer melt
Stepanyan, R. ; Slot, J.J.M. ; Molenaar, J. ; Tchesnokov, M.A. - \ 2005
Physical Review. E, Statistical nonlinear, and soft matter physics 72 (2005)5. - ISSN 1539-3755 - p. 051807 - 051818.
convective constraint release - cox-merz rule - microscopic theory - molecular theory - constitutive equation - entangled polymers - tube model - stretch - reptation - dynamics
A framework for a consistent description of the flow-induced correlation effects within a linear polymer chain in a melt is proposed. The formalism shows how correlations between chain segments in the flow can be incorporated into a hierarchy of distribution functions for tangent vectors. The present model allows one to take into account all the major relaxation mechanisms. Special cases of the derived set of equations are shown to yield existing models and shed some light on the connection between them. Consequences of several assumptions widely used in the literature are analyzed within the developed framework
A constitutive model with moderate chain stretch for linear polymer melts
Tchesnokov, M.A. ; Molenaar, J. ; Slot, J.J.M. ; Stepanyan, R. - \ 2004
Journal of Non-Newtonian Fluid Mechanics 123 (2004)2-3. - ISSN 0377-0257 - p. 185 - 199.
convective constraint release - cox-merz rule - entangled polymers - microscopic theory - polystyrene solutions - molecular theory - fast flows - shear - reptation - predictions
In our previous publication, we presented a molecular model to describe the dynamics of the interfacial layer between a flowing polymer melt and a die wall. We showed that the ensemble-averaged behavior of polymer molecules adsorbed on the wall could be successfully described in terms of the so-called bond vector probability distribution function (BVPDF). The BVPDF couples the chain orientation and chain stretch on the level of single segment, and thus is an extension of the orientation distribution function of Doi and Edwards introduced for inextensible chains. In this paper, the developed formalism is extended to molecules in the polymer bulk. We show how the well-known Doi and Edwards theory (DE) for inextensible chains based on the orientation distribution function can be naturally extended to include chain stretch and (convective) constraint release (CCR). The final constitutive equation accounts for such mechanisms on polymer chains as reptation, retraction, convection, contour length fluctuations, and (convective) constraint release. It is valid for both linear and non-linear flow regimes. The proposed theory is quantitative, and contains the same input parameters as the original DE model. As an application of the full theory, a simple equation of motion for the stress tensor is derived. Despite the simplicity, its predictions are found to be in good agreement with available experimental data over a wide range of flow regimes and histories.
|An effect of sulphur dioxide on the odour of mustard paste
Griffiths, N.M. ; Mather, A.M. ; Fenwick, G.R. ; Frijters, J.E.R. ; Merz, J.H. - \ 1980
Chemistry & Industry 2 (1980). - ISSN 0009-3068 - p. 239 - 240.