Pôle de Recherche pour l'Organisation et la Diffusion de l'Information Géographique

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[1] This work provides an initial overview of climate features and their related hydrological impacts during the recent extreme droughts (1995, 1998, 2005 and 2010) in the upper Solimões River (western Amazon), using comprehensive in situ discharge and rainfall datasets. The droughts are generally associated with positive SST anomalies in the tropical North Atlantic and weak trade winds and water vapor transport toward the upper Solimões, which, in association with increased subsidence over central and southern Amazon, explain the lack of rainfall and very low discharge values. But in 1998, toward the end of the 1997–98 El Niño event, the drought is more likely related to an anomalous divergence of water vapor in the western Amazon that is characteristic of a warm event in the Pacific. During the austral spring and winter of 2010, the most severe drought since the seventies has been registered in the upper Solimões. Its intensity and its length, when compared to the 2005 drought, can be explained by the addition of an El Niño in austral summer and a very warm episode in the Atlantic in boreal spring and summer. As in 2005, the lack of water in 2010 was more important in the southern tropical tributaries of the upper Solimões than in the northern ones.

Abstract. In Europe, river floods have been increasing in frequency and severity. These circumstances require the management of flood risk by integrating new concepts like urban resilience. Nevertheless, urban resilience seems to have no accurate meanings. That is why researchers are primarily concerned with defining resilience. Nevertheless, focus on research object seems to be more important than focus on conceptual debate (Resilience of what? Rather than what is resilience?). Thus the methodology designed here is focused on urban considerations. In fact, a system approach emphasizes technical networks' importance concerning urban resilience. Principles and assumptions applied in this research finally lead to the analysis of how urban networks are able to face natural hazards. In this context, a Web-GIS has been developed for analyzing resistance capacity, absorption capacity and recovery capacity of different technical networks. A first application has been carried out on a French agglomeration in order to analyze road network absorption capacity. This application is very specific but, thanks to this example, it is already possible to highlight the methodology's usefulness.

Abstract Monsoon rainfall is central to the climate of West Africa, and understanding its variability is a challenge for which satellite rainfall products could be well suited to contribute to. Their quality in this region has received less attention than elsewhere. The focus is set on the scales associated with atmospheric variability, and a meteorological benchmark is set up with ground-based observations from the African Monsoon Multidisciplinary Analysis (AMMA) program. The investigation is performed at various scales of accumulation using four gauge networks. The seasonal cycle is analyzed using 10-day-averaged products, the synoptic-scale variability is analyzed using daily means, and the diurnal cycle of rainfall is analyzed at the seasonal scale using a composite and at the diurnal scale using 3-hourly accumulations. A novel methodology is introduced that accounts for the errors associated with the areal–time rainfall averages. The errors from both satellite and ground rainfall data are computed using dedicated techniques that come down to an estimation of the sampling errors associated to these measurements. The results show that the new generation of combined infrared–microwave (IR–MW) satellite products is describing the rain variability similarly to ground measurements. At the 10-day scale, all products reveal high regional and seasonal skills. The day-to-day comparison indicates that some products perform better than others, whereas all of them exhibit high skills when the spectral band of African easterly waves is considered. The seasonal variability of the diurnal scale as well as its relative daily importance is only captured by some products. Plans for future extensive intercomparison exercises are briefly discussed.

Abstract. The aim of this study is to evaluate the ability of the ORCHIDEE land surface model to simulate streamflows over each sub-basin of the Amazon River basin. For this purpose, simulations are performed with a routing module including the influence of floodplains and swamps on river discharge and validated against on-site hydrological measurements collected within the HYBAM observatory over the 1980–2000 period. When forced by the NCC global meteorological dataset, the initial version of ORCHIDEE shows discrepancies with ORE HYBAM measurements with underestimation by 15% of the annual mean streamflow at Óbidos hydrological station. Consequently, several improvements are incrementally added to the initial simulation in order to reduce those discrepancies. First, values of NCC precipitation are substituted by ORE HYBAM daily in-situ rainfall observations from the meteorological services of Amazonian countries, interpolated over the basin. It highly improves the simulated streamflow over the northern and western parts of the basin, whereas streamflow over southern regions becomes overestimated, probably due to the extension of rainy spots that may be exaggerated by our interpolation method, or to an underestimation of simulated evapotranspiration when compared to flux tower measurements. Second, the initial map of maximal fractions of floodplains and swamps which largely underestimates floodplains areas over the main stem of the Amazon River and over the region of Llanos de Moxos in Bolivia, is substituted by a new one with a better agreement with different estimates over the basin. Simulated monthly water height is consequently better represented in ORCHIDEE when compared to Topex/Poseidon measurements over the main stem of the Amazon. Finally, a calibration of the time constant of the floodplain reservoir is performed to adjust the mean simulated seasonal peak flow at Óbidos in agreement with the observations.

Abstract The Laurichard active rock glacier is the permafrost‐related landform with the longest record of monitoring in France, including an annual geodetic survey, repeated geoelectrical campaigns from 1979 onwards and continuous recording of ground temperature since 2003. These data were used to examine changes in creep rates and internal structure from 1986 to 2006. The control that climatic variables exert on rock glacier kinematics was investigated over three time scales. Between the 1980s and the early 2000s, the main observed changes were a general increase in surface velocity and a decrease in internal resistivity. At a multi‐year scale, the high correlation between surface movement and snow thickness in the preceding December appears to confirm the importance of snow cover conditions in early winter through their influence on the ground thermal regime. A comparison of surface velocities, regional climatic datasets and ground sub‐surface temperatures over six years suggests a strong relation between rock glacier deformation and ground temperature, as well as a role for liquid water due to melt of thick snow cover. Finally, unusual surface lowering that accompanied peak velocities in 2004 may be due to a general thaw of the top of the permafrost, probably caused both by two successive snowy winters and by high energy inputs during the warm summer of 2003. Copyright © 2009 John Wiley & Sons, Ltd.

Geomorphic footprints of past large Himalayan earthquakes are elusive, although they are urgently needed for gauging and predicting recovery times of seismically perturbed mountain landscapes. We present evidence of catastrophic valley infill following at least three medieval earthquakes in the Nepal Himalaya. Radiocarbon dates from peat beds, plant macrofossils, and humic silts in fine-grained tributary sediments near Pokhara, Nepal's second-largest city, match the timing of nearby M > 8 earthquakes in ~1100, 1255, and 1344 C.E. The upstream dip of tributary valley fills and x-ray fluorescence spectrometry of their provenance rule out local sources. Instead, geomorphic and sedimentary evidence is consistent with catastrophic fluvial aggradation and debris flows that had plugged several tributaries with tens of meters of calcareous sediment from a Higher Himalayan source >60 kilometers away.

International audience

BACKGROUND: Every year, West Africa is afflicted with Meningococcal Meningitis (MCM) disease outbreaks. Although the seasonal and spatial patterns of disease cases have been shown to be linked to climate, the mechanisms responsible for these patterns are still not well identified. RESULTS: A statistical analysis of annual incidence of MCM and climatic variables has been performed to highlight the relationships between climate and MCM for two highly afflicted countries: Niger and Burkina Faso. We found that disease resurgence in Niger and in Burkina Faso is likely to be partly controlled by the winter climate through enhanced Harmattan winds. Statistical models based only on climate indexes work well in Niger showing that 25% of the disease variance from year-to-year in this country can be explained by the winter climate but fail to represent accurately the disease dynamics in Burkina Faso. CONCLUSION: This study is an exploratory attempt to predict meningitis incidence by using only climate information. Although it points out significant statistical results it also stresses the difficulty of relating climate to interannual variability in meningitis outbreaks.

Purpose The purpose of this paper is to analyze the root causes of disaster vulnerability in Jakarta, to highlight the strategies and implications of official policies, and to consider alternatives for vulnerability mitigation. The February 2007 floods which struck Jakarta emphasized the extreme vulnerability of informal poor communities and the inefficiency of the disaster management policy set up by the Indonesian government. Design/methodology/approach Detailed field investigations were undertaken before, during and after the February 2007 flood event in several informal districts of Jakarta to collect secondary data and conduct interviews with the population and some stakeholders of the disaster management scene. Findings Human factors are dominant in explaining the magnitude of the 2007 flooding episode. Urbanization is partially responsible for the extent of the flooding by waterproofing the soils. Yet floods do not strike the inhabitants of formal and informal settlements in the same way. People from the poor illegal areas are the most affected. Their behaviour and coping strategies during the crisis are not due to a low perception of risk, but rather to some daily and non‐hazard‐related constraints which are not taken into account by the government. Practical implications To prevent increasing vulnerability among these communities, it is essential to refocus disaster management strategies on a daily pattern and to integrate them within a global development framework, to de‐marginalize them in terms of access to resources (public services, economic values), and to favoir empowerment. Originality/value It is imperative to focus on poverty reduction and to develop economic projects aimed at treating the causes of vulnerability.

In this work we document and analyze the hydrological annual cycles characterized by a rapid transition between low and high flows in the Amazonas River (Peruvian Amazon) and we show how these events, which may impact vulnerable riverside residents, are related to regional climate variability. Our analysis is based on comprehensive discharge, rainfall and average suspended sediment data sets. Particular attention is paid to the 2010–11 hydrological year, when an unprecedented abrupt transition from the extreme September 2010 drought (8300 m3 s−1) to one of the four highest discharges in April 2011 (49 500 m3 s−1) was recorded at Tamshiyacu (Amazonas River). This unusual transition is also observed in average suspended sediments. Years with a rapid increase in discharge are characterized by negative sea surface temperature anomalies in the central equatorial Pacific during austral summer, corresponding to a La Niña-like mode. It originates a geopotential height wave train over the subtropical South Pacific and southeastern South America, with a negative anomaly along the southern Amazon and the southeastern South Atlantic convergence zone region. As a consequence, the monsoon flux is retained over the Amazon and a strong convergence of humidity occurs in the Peruvian Amazon basin, favoring high rainfall and discharge. These features are also reported during the 2010–11 austral summer, when an intense La Niña event characterized the equatorial Pacific.

Abstract Sedimentological and geomorphological studies of terraces around Lake Van (1647 m) provided a preliminary framework for lake‐level variations. The elevations of terraces and past lake level were measured with a differential global positioning system. A chronology is developed using 234 U/ 230 Th dating of travertines, 39 Ar/ 40 Ar dating of pyroclastites and 14 C dating of organic matter. Facies and stratigraphic correlations identify four transgressions (C1′, C1″, C2′ and C2″), each followed by a regression which ended with low lake levels that caused river incision and terrace formation. Evidence of the oldest transgression (C1′) is found in the uppermost reaches of valleys up to 1755 m, an altitude higher than the present lake threshold (1736 m). This C1′ transgression may be related to pyroclastic flows which dammed an outlet located in the western part of the lake basin and which is dated to before 105 ka. After 100 ka, a second transgression (C1″) reached 1730/1735 m, possibly related to a younger ignimbrite flow, in association with high water inflow (warm and/or wetter conditions). The two younger transgressions reached 1700–1705 m. The first one (C2′) is dated to 26–24.5 cal. ka BP and the second one (C2″) to 21–20 cal. ka BP. Available data suggest that the long‐term lake‐level changes responded mainly to climate oscillations. Additional events such as river captures caused by volcanic falls filling valleys, tectonism, erosion and karstic diversion may have impacted these long‐term lake‐level changes. Copyright © 2010 John Wiley & Sons, Ltd.

International audience

ABSTRACT Long‐term and well‐managed marine protected areas (MPAs) can, under the right circumstances, contribute to biodiversity conservation and fisheries management, thus contributing to food security and sustainable livelihoods. This article emphasizes (1) the potential utility of MPAs as a fisheries management tool, (2) the costs and benefits of MPAs for fishing communities, and (3) the foundations of good governance and management processes for creating effective MPAs with a dual fisheries and conservation mandate. This article highlights case studies from numerous regions of the world that demonstrate practical and often successful solutions in bridging the divide between MPA management and fisheries sustainability, with a focus on small‐scale coastal fisheries in order to emphasize lessons learned. To be an effective fisheries management tool, MPAs should be embedded in broader fisheries management and conservation plans. MPAs are unlikely to generate benefits if implemented in isolation. The spatial and temporal distribution of benefits and costs needs to be taken into account since proximal fishery‐dependent communities may experience higher fishing costs over the short and long‐term while the fisheries benefits from MPAs may only accrue over the long‐term. Key lessons for effectively bridging the divide between biodiversity conservation and fisheries sustainability goals in the context of MPAs include: creating spaces and processes for engagement, incorporating fisheries in MPA design and MPAs into fisheries management, engaging fishers in management, recognizing rights and tenure, coordinating between agencies and clarifying roles, combining no‐take‐areas with other fisheries management actions, addressing the balance of costs and benefits to fishers, making a long‐term commitment, creating a collaborative network of stakeholders, taking multiple pressures into account, managing adaptively, recognizing and addressing trade‐offs, and matching good governance with effective management and enforcement. © 2014 The Authors. Aquatic Conservation: Marine and Freshwater Ecosystems published by John Wiley & Sons, Ltd.

Because of climate change, much attention is drawn to the Amazon River basin, whose hydrology has already been strongly affected by extreme events during the past 20 years. Hydrological annual extreme variations (i.e. low/high flows) associated with precipitation (and evapotranspiration) changes are investigated over the Amazon River sub-basins using the land surface model ORCHIDEE and a multimodel approach. Climate change scenarios from up to eight AR4 Global Climate Models based on three emission scenarios were used to build future hydrological projections in the region, for two periods of the 21st century. For the middle of the century under the SRESA1B scenario, no change is found in high flow on the main stem of the Amazon River (Obidos station), but a systematic discharge decrease is simulated during the recession period, leading to a 10% low-flow decrease. Contrasting discharge variations are pointed out depending on the location in the basin. In the western upper part of the basin, which undergoes an annual persistent increase in precipitation, high flow shows a 7% relative increase for the middle of the 21st century and the signal is enhanced for the end of the century (12%). By contrast, simulated precipitation decreases during the dry seasons over the southern, eastern and northern parts of the basin lead to significant low-flow decrease at several stations, especially in the Xingu River, where it reaches −50%, associated with a 9% reduction in the runoff coefficient. A 18% high-flow decrease is also found in this river. In the north, the low-flow decrease becomes higher toward the east: a 55% significant decrease in the eastern Branco River is associated with a 13% reduction in the runoff coefficient. The estimation of the streamflow elasticity to precipitation indicates that southern sub-basins (except for the mountainous Beni River), that have low runoff coefficients, will become more responsive to precipitation change (with a 5 to near 35% increase in elasticity) than the western sub-basins, experiencing high runoff coefficient and no change in streamflow elasticity to precipitation. These projections raise important issues for populations living near the rivers whose activity is regulated by the present annual cycle of waters. The question of their adaptability has already arisen.

This paper describes a methodology to use the passive microwave measurements of the 6.9 GHz bandwidth of the AMSR‐E sensor which is the most sensitive to surface soil moisture, to constrain satellite‐based rainfall estimates over a semi arid region in West‐Africa. The paper focuses on the aptitude of AMSR‐E measurements to inform if rain occurs or not. The study was conducted over a 125 × 100 km 2 region located in Niger where a dense recording raingauge network is available to build an accurate ground‐based 3‐hour rainfall product at the 25 × 20 km 2 resolution. A satellite‐based rainfall product (EPSAT‐SG), based on both infrared and microwave measurements, was compared to the ground‐based rainfall product. It was shown that EPSAT‐SG overestimates by about 30% the total number of rain events during the 2004 and 2006 rainy seasons. A simple methodology based on the AMSR‐E polarization ratio variations related to the surface soil moisture leaded to suppress a large amount of the wrong rain events.

AbstractMineral dust emissions from arid regions are influenced by the surface features encountered in the source regions. These surface features control both the erosion threshold and the intensity of the dust flux. Recently, a soil-derived dust emission scheme has been designed in order to provide an explicit representation of the mineral dust accounting for the influence of the surface features on the dust emissions. This physical scheme has been validated with micro-scale field measurements. Its large scale application has required the development of additional relations to estimate the input parameters from more accessible data: the mean height and the covering rate of the roughness elements and the min-eralogical soil type. The determination of these surface data has been based on a geomorphologic approach which describes the surface features of arid areas in a 1 × l° grid. Inside each square degree, up to five different areas characterised by different surface features have been distinguished. However, these areas have not been located inside the square degree. Each area can be constituted by several combined surface features, including roughness, vegetation, granulometry. Five main types of landscapes and eight main types of surface features have been distinguished. This approach is based on the combination of various data, mainly topographical, geological maps and climatological analysis. In addition to the problem of scale transfer, the main constraints to obtain a quantitative assessment are the confidence level of the existing data and the number of parameters to document. On the opposite, with this method, the fine scale required by the dust modelling can be separated from the scale accessible by the mapping approach, of the order of the square degree. This method can also be easily improved by aggregating new data and can be extended to other deserts. An example of application is given for the north-west of the Algerian Sahara where the method has been elaborated. The data provided by the modelling of the surface have been used to simulate dust emissions for 1990, 1991 and 1992 over the central and western Sahara. Over these three years, the mean annual dust emission is about 760 Mt-year−1 Although a significant interannual variability exists (mainly due to changes in the wind pattern), the most intensive emissions remain quite constant in terms of location. The percentage of agreement with satellite observations higher than 0.7 is 74 %, but only 32 % when using a model having a single threshold function for dust emission (i.e. the same surface feature for the whole Sahara) (cf. later Marticorena et al., 1997). © 2000 Éditions scientifiques et médicales Elsevier SASRésuméLes émissions d'aérosols désertiques à partir des régions arides sont fortement influencées par les caractéristiques de la surface des sols en zone source, aussi bien en ce qui concerne les seuils d'érosion que l'intensité des flux de poussières émis. Récemment, un modèle physique a été développé permettant de rendre compte de l'influence des caractéristiques de surface sur les émissions de poussières. Ce modèle a été validé à partir de mesures de terrain à micro-échelle. Son application à plus grande échelle a nécessité le développement de relations supplémentaires permettant d'estimer les paramètres d'entrée du modèle à partir de données plus accessibles : la hauteur moyenne et le taux de couverture des obstacles présents à la surface et le type minéralogique de la couche superficielle du sol. Ces données de surface ont été déterminées au travers d'une modélisation, à partir d'une approche géomorphologique, de la surface des zones arides en secteurs d'un degré carré. Cinq types principaux de paysages et huit types principaux d'états de surface ont été distingués. L'approche est fondée sur l'utilisation de données variées, essentiellement les cartes topographiques, géologiques et les données climatologiques. L'utilisation de « points de calage » (observations de terrain, photographies aériennes, images satellites) permet une approche quantitative d'autant plus fiable que l'on est proche des points de calage. À l'intérieur d'un degré carré, il a été distingué jusqu'à cinq aires différentes, sans qu'elles soient spatialement localisée dans celui-ci. Chaque aire peut elle-même être constituée de plusieurs états de surface combinés, incluant rugosité, végétation et granulométrie. En dehors du transfert d'échelle, les contraintes principales sont la fiabilité des données et le nombre de points à documenter quantitativement. Les apports sont la différence de nature entre les échelles de dimension inférieures au degré carré – du domaine de la seule modélisation – et les échelles supérieures, plus proches de la cartographie, la facilité d'amélioration et de généralisation de la méthode à d'autres déserts. Un exemple de modélisation de la région où elle a été mise au point, au NW du Sahara algérien, est décrit. Les données issues de la modélisation des états de surface sur le Sahara ont été utilisées pour simuler les émissions d'aérosols désertiques pour 1990, 1991 et 1992. En moyenne, ces émissions sont de l'ordre de 760 Mt-an−1. Bien qu'elles présentent une forte variabilité interannuelle liée à des variations des régimes de vents, les zone d'émissions les plus intenses restent relativement constantes en terme de localisation. © 2000 Éditions scientifiques et médicales Elsevier SASKeywordsmodellinggeomorphologyarid environmentsdust emissionsSaharaKeywordsmodélisationgéomorphologiemilieux aridesaérosols désertiquesSahara

Landscape graphs are increasingly used in ecology, conservation, and landscape planning for modeling habitat connectivity of wildlife species. We present here the follow-up of Graphab, a software application for modeling habitat networks. This application has been recently enhanced by advanced functions of spatial analysis, command-line facilities, and connections with other software applications. It has been used in many studies, first in ecological studies for analyzing the role of landscape connectivity on biological responses measured in the field, second for supporting decisions concerning biodiversity preservation. Future improvements could be made to make the links more realistic with respect to ecological processes.

Abstract Despite recent advances in land surface modeling and remote sensing, estimates of the global water budget are still fairly uncertain. This study aims to evaluate the water budget of the Amazon basin based on several state-of-the-art land surface model (LSM) outputs. Water budget variables (terrestrial water storage TWS, evapotranspiration ET, surface runoff R, and base flow B) are evaluated at the basin scale using both remote sensing and in situ data. Meteorological forcings at a 3-hourly time step and 1° spatial resolution were used to run 14 LSMs. Precipitation datasets that have been rescaled to match monthly Global Precipitation Climatology Project (GPCP) and Global Precipitation Climatology Centre (GPCC) datasets and the daily Hydrologie du Bassin de l’Amazone (HYBAM) dataset were used to perform three experiments. The Hydrological Modeling and Analysis Platform (HyMAP) river routing scheme was forced with R and B and simulated discharges are compared against observations at 165 gauges. Simulated ET and TWS are compared against FLUXNET and MOD16A2 evapotranspiration datasets and Gravity Recovery and Climate Experiment (GRACE) TWS estimates in two subcatchments of main tributaries (Madeira and Negro Rivers). At the basin scale, simulated ET ranges from 2.39 to 3.26 mm day−1 and a low spatial correlation between ET and precipitation indicates that evapotranspiration does not depend on water availability over most of the basin. Results also show that other simulated water budget components vary significantly as a function of both the LSM and precipitation dataset, but simulated TWS generally agrees with GRACE estimates at the basin scale. The best water budget simulations resulted from experiments using HYBAM, mostly explained by a denser rainfall gauge network and the rescaling at a finer temporal scale.

ABSTRACT In de‐glaciated areas, para‐glaciation (i.e. the conditioning of landscapes by prior glaciation) has often been considered a major predisposing factor in landslide occurrence; its consequences have been particularly well identified at a fine scale (especially on bedrock jointing). Hitherto, the relative impacts of para‐glaciation on hillslope dynamics at a regional scale had nevertheless not been quantified statistically. We examine Skagafjörður area (northern Iceland) where landslides are widespread (at least 108 were mapped in an area of c . 3000 km 2 ). We compare the role of para‐glaciation (debuttressing, influence of post‐glacial rebound) with that of classic factors (topography, lithology, etc.) in landslide occurrence and location, using a spatial analysis based on a chi‐square test. On the one hand, the results highlight that landslides are over‐represented in areas where post‐glacial rebound was at its maximum, with a stronger concentration of landslides in the northern part of the fjord. On the other hand, the distribution of landslides did not show any clear relationship with the pattern of glacial debuttressing. Tschuprow coefficient highlights that the influence of post‐glacial rebound on landslide location is higher than the combined influence of slope gradient, curvature or geological structure. This result is supported by our initial evidence for the timing of landslides in the area: most landslides occurred during the first half of the Holocene, and a period of hillslope instability was initiated when the post‐glacial uplift was at its maximum. Finally, the mechanisms that link post‐glacial rebound and landsliding as well as the geomorphic impacts of landslides, are discussed. Copyright © 2013 John Wiley & Sons, Ltd.