First-order uncertainty analysis using AD 2D application

This paper presents an efficient method to quantify uncertainty in morphodynamic models. The FOSM/AD method is applied to a complex 2D test case; the long terms morphodynamic evolution of a tidal inlet. The sensitivity to grain size and bed roughness has been quantified as well as various model parameters including slope effect and secondary currents using the tangent linear model (TLM) of the Sisyphe/Telemac2D model for the 7.0 release

Linking forest cover, soil erosion and mire hydrology to late-Holocene human activity and climate in NW Spain

This article is distributed under the terms of the Creative Commons Attribution-NonCommercial 3.0 License (http://www.creativecommons.org/licenses/by-nc/3.0/) which permits non-commercial use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access page (http://www.uk.sagepub.com/aboutus/openaccess.htm).This article has been made available through the Brunel Open Access Publishing Fund.Forest clearance is one of the main drivers of soil erosion and hydrological changes in mires, although climate may also play a significant role. Because of the wide range of factors involved, understanding these complex links requires long-term multi-proxy approaches and research on the best proxies to focus. A peat core from NW Spain (Cruz do Bocelo mire), spanning the last ~3000 years, has been studied at high resolution by physical (density and loss on ignition (LOI)), geochemical (elemental composition) and palynological (pollen and non-pollen palynomorphs) analyses. Proxies related to mineral matter fluxes from the catchment (lithogenic tracers, Glomus and Entorrhiza), rainfall (Bromine), mire hydrology (HdV-18), human pressure (Cerealia-type, nitrophilous taxa and coprophilous fungi) and forest cover (mesophilous tree taxa) were the most useful to reconstruct the evolution of the mire and its catchment. Forest clearance for farming was one of the main drivers of environmental change from at least the local Iron Age (~2685 cal. yr BP) onwards. The most intense phase of deforestation occurred during Roman and Germanic times and the late Middle Ages. During these phases, the entire catchment was affected, resulting in enhanced soil erosion and severe hydrological modifications of the mire. Climate, especially rainfall, may have also accelerated these processes during wetter periods. However, it is noteworthy that the hydrology of the mire seems to have been insensitive to rainfall variations when mesophilous forest dominated. Abrupt changes were only detected once intense forest clearance commenced during the Iron Age/Roman transition (~2190 cal. yr BP) phase, which represented a tipping point in catchment's ability to buffer impacts. Overall, our findings highlight the importance of studying ecosystems' long-term trajectories and catchment-wide processes when implementing mire habitat protection measures.This work was funded by the projects CGL2010-20672 (Plan Nacional I+D+i, Spanish Ministry of Science and Innovation) and 10PXIB200182PR (General Directorate of I+D, Xunta de Galicia). N Silva-Sánchez and L López-Merino are currently supported by a FPU predoctoral scholarship (AP2010-3264) funded by the Spanish Government and a MINT postdoctoral fellowship funded by the Brunel Institute for the Environment, respectively

Polynomial surrogates for open-channel flows in random steady state

Assessing epistemic uncertainties is considered as a milestone for improving numerical predictions of a dynamical system. In hydrodynamics, uncertainties in input parameters translate into uncertainties in simulated water levels through the shallow water equations. We investigate the ability of generalized polynomial chaos (gPC) surrogate to evaluate the probabilistic features of water level simulated by a 1-D hydraulic model (MASCARET) with the same accuracy as a classical Monte Carlo method but at a reduced computational cost. This study highlights that the water level probability density function and covariance matrix are better estimated with the polynomial surrogate model than with a Monte Carlo approach on the forward model given a limited budget of MASCARET evaluations. The gPC-surrogate performance is first assessed on an idealized channel with uniform geometry and then applied on the more realistic case of the Garonne River (France) for which a global sensitivity analysis using sparse least-angle regression was performed to reduce the size of the stochastic problem. For both cases, Galerkin projection approximation coupled to Gaussian quadrature that involves a limited number of forward model evaluations is compared with least-square regression for computing the coefficients when the surrogate is parameterized with respect to the local friction coefficient and the upstream discharge. The results showed that a gPC-surrogate with total polynomial degree equal to 6 requiring 49 forward model evaluations is sufficient to represent the water level distribution (in the sense of the ℓ2 norm), the probability density function and the water level covariance matrix for further use in the framework of data assimilation. In locations where the flow dynamics is more complex due to bathymetry, a higher polynomial degree is needed to retrieve the water level distribution. The use of a surrogate is thus a promising strategy for uncertainty quantification studies in open-channel flows and should be extended to unsteady flows. It also paves the way toward cost-effective ensemble-based data assimilation for flood forecasting and water resource management

Revealing the last 13,500 years of environmental history from the multiproxy record of a mountain lake (Lago Enol, northern Iberian Peninsula)

This is the author's accepted manuscript. The final publication is available at Springer via http://dx.doi.org/10.1007/s10933-009-9387-7.We present the Holocene sequence from Lago Enol (43°16′N, 4°59′W, 1,070 m a.s.l.), Cantabrian Mountains, northern Spain. A multiproxy analysis provided comprehensive information about regional humidity and temperature changes. The analysis included sedimentological descriptions, physical properties, organic carbon and carbonate content, mineralogy and geochemical composition together with biological proxies including diatom and ostracod assemblages. A detailed pollen study enabled reconstruction of variations in vegetation cover, which were interpreted in the context of climate changes and human impact. Four distinct stages were recognized for the last 13,500 years: (1) a cold and dry episode that includes the Younger Dryas event (13,500–11,600 cal. year BP); (2) a humid and warmer period characterizing the onset of the Holocene (11,600–8,700 cal. year BP); (3) a tendency toward a drier climate during the middle Holocene (8,700–4,650 cal. year BP); and (4) a return to humid conditions following landscape modification by human activity (pastoral activities, deforestation) in the late Holocene (4,650–2,200 cal. year BP). Superimposed on relatively stable landscape conditions (e.g. maintenance of well established forests), the typical environmental variability of the southern European region is observed at this site.The Spanish Inter-Ministry Commission of Science and Technology (CICYT), the Spanish National Parks agency, the European Commission, the Spanish Ministry of Science, and the European Social Fund

Revealing the last 13,500 years of environmental history from the multiproxy record of a mountain lake (Lago Enol, northern Iberian Peninsula)

This is the author's accepted manuscript. The final publication is available at Springer via http://dx.doi.org/10.1007/s10933-009-9387-7.We present the Holocene sequence from Lago Enol (43°16′N, 4°59′W, 1,070 m a.s.l.), Cantabrian Mountains, northern Spain. A multiproxy analysis provided comprehensive information about regional humidity and temperature changes. The analysis included sedimentological descriptions, physical properties, organic carbon and carbonate content, mineralogy and geochemical composition together with biological proxies including diatom and ostracod assemblages. A detailed pollen study enabled reconstruction of variations in vegetation cover, which were interpreted in the context of climate changes and human impact. Four distinct stages were recognized for the last 13,500 years: (1) a cold and dry episode that includes the Younger Dryas event (13,500–11,600 cal. year BP); (2) a humid and warmer period characterizing the onset of the Holocene (11,600–8,700 cal. year BP); (3) a tendency toward a drier climate during the middle Holocene (8,700–4,650 cal. year BP); and (4) a return to humid conditions following landscape modification by human activity (pastoral activities, deforestation) in the late Holocene (4,650–2,200 cal. year BP). Superimposed on relatively stable landscape conditions (e.g. maintenance of well established forests), the typical environmental variability of the southern European region is observed at this site.The Spanish Inter-Ministry Commission of Science and Technology (CICYT), the Spanish National Parks agency, the European Commission, the Spanish Ministry of Science, and the European Social Fund

Pollution fluorée et croissance radiale des conifères en Maurienne (Savoie, France)

La recherche de l'impact de la pollution fluorée sur la croissance en diamètre des résineux de la Maurienne (vallée de l'Arc), est menée sur 27 populations des 4 espèces principales [Picea abies (L) Karst, Pinus silvestris L, Abies alba Mill, Larix decidua Mill] échantillonnées en fonction de l'éloignement des sources de pollution, l'exposition et l'altitude. L'étude porte exclusivement sur les variations de l'épaisseur des cernes du bois sur la période 1900-1983 partagée en 2 chronoséquences (1900-1941 et 1942-1983), la première période, de moindre pollution, étant prise comme période de référence. Les différentes chronologies maîtresses de cernes obtenues à partir de 10 arbres (3 carottes par arbre), pour chaque population, sont d'abord comparées sur quelques paramètres statistiques (moyenne et écart type, coefficient d'autocorrélation, sensibilité moyenne) et les courbes de variation de l'épaisseur des cernes. Ensuite, à partir d'une modélisation ARMA de la croissance et du calcul des relations cerne climat sur la période de référence, une croissance théorique est calculée sur l'ensemble de la période 1900-1983. Pour chaque population, le décalage de la courbe des épaisseurs de cernes mesurées par rapport à la courbe des épaisseurs théoriques, lorsqu'il correspond à un déficit, est attribué à la pollution. Ainsi l'indifférence au facteur pollution du mélèze est rapportée au caractère caducifolié de l'essence et au jeu des phénomènes de concurrence. Pour presque toutes les populations des autres espèces, la croissance observée est significativement inférieure au potentiel calculé. II faut donc admettre, à ce stade de l'analyse, que l'impact des effluents fluorés se fait ressentir sur l'ensemble de la vallée, l'éloignement des sources n'expliquant pas l'apparente indifférence de certaines populations.Fluoride pollution and radial growth of conifers in Maurienne (Savoy, France). A study was made on the impact of fluoride pollution (fig 2) on the radial growth of conifers in Maurienne (Arc Valley, fig 1) on the basis of 27 populations of the main species [Picea abies (L) Karst, Pinus silvestris L, Abies alba Mill, Larix decidua Mill]. The trees were sampled, taking into account exposure, altitude and their distance from the pollution sources (tables / and II). The study is exclusively concerned with ring-width variations over the period 1900-1983, divided into 2 chronosequences (1900-1941 and 1942-1983). The first period, during which pollution was less was taken as a reference period. Master tree-ring chronologies, derived from 10 trees (3 cores per tree) in each population, were built. Mean and standard deviation, autocorrelation coefficient, mean sensitivity (table III) and the variation curves of ring-width are used to compare these chronologies (fig 5). Over the reference period, time series models were fitted to the annual ring-widths and the ring-width to climate relationships were established. On these bases, theoretical growth was calculated for the entire period 1900-1983. For each population, the deviation of the measured ring-width curve from the predicted one, when corresponding to a deficit, is ascribed to pollution (figs 4 and 5, table IV). Thus, the non sensitivity of larch to pollution is explained both by the deciduous nature of the tree and by the action of concurrence phenomena. In almost all the other species populations, the actual growth is significantly lower than that forecast and, considering that the insensitivity of some populations cannot be correlated with their distance from the pollution sources, one must presume that fluoride pollution affects the whole valley

Dynamique des formations végétales en limite supérieure de l'étage montagnard sur matériaux volcaniques dans le Massif Central : origine de l'asylvatisme, potentialités évolutives actuelles et dans l'hypothèse d'une remontée climatique de 2°c

The two aims of this study were :1- asylvatism origin in areas located at an altitude superior to 1450 m in the Massif du Sancy 2- vegetation potentialities at this altitude : at present and in case of a 2°C thermic raise Presence of european beech- silver fir forest posterior to the decline of an atlantic oak forest was testified by pollen analysis at altitudes not reached at present by such stands (1600m). Present asylvatism could be therefore explained by anthropic activity that started at the suboreal period. Forest recolonization of such areas can occur in the present climatic conditions but this process will probably be blocked by Calluna bushes that invaded these areas during the second half of this century. On the contrary a biomass increase of these heathlands will probably occur because of a better mineralization of organic matter supply but their functioning modified : slowing down of the layering and of the germination process. With regard to this latter question not only Calluna could be concerned but also herbaceous an ligneous species (Scots pine and silver birch). Silver birch stands located at present at 1450 m height would not seen to be able to colonize further heathlands even if their growth will be enhanced.Les travaux engagés cherchent à répondre à un double objectif : 1- l'origine de l'asylvatisme actuel dans les zones supérieures à 1450 m dans le Massif du Sancy 2- les potentialités de la végétation à cette altitude : actuelles et dans l'hypothèse d'une remontée climatique de 2°c. Les analyses palynologiques attestent de la présence d'une hêtraie sapinière postérieure au recul d'une chênaie atlantique à des altitudes que ne connaissent pas ces formations actuellement (1600m). L'actuel asylvatisme trouverait son origine dans l'action anthropique commençant au suboréal. La reconquête forestière de ces zones possible dans le contexte climatique actuel et donc à fortiori dans le cadre d'une éventuelle remontée des températures se heurte néanmoins aux callunaies qui ont envahi ces espaces au cours de la deuxième moitié de ce siècle. Une densification de ces landes est même à prévoir en cas de remontée thermique consécutivement à une meilleure minéralisation des stocks de matière organique. Leur fonctionnement serait toutefois modifié : ralentissement du processus de marcottage et diminution des possibilités de germination de cette espèce ainsi que des herbacées et des ligneux(pin sylvestre et bouleau verruqueux). Les peuplements de bouleaux actuellement en place vers 1450m ne sembleraient donc pas pouvoir étendre leur emprise même si leur croissance progressera