Jérôme Lopez Saez

University of Geneva | UNIGE · Institute of Environmental Sciences

Debris-flow activity in the Alps is anticipated to undergo pronounced changes in response to a warming climate. Yet, a fundamental challenge in comprehensively assessing changes in process activity is the systematic lack of long-term observational debris-flow records. Here, we reconstruct the longest, continuous time series (1626-2020) of debris fl...

Glacier mass balance reconstructions provide a means of placing relatively short observational records into a longer-term context. Here, we use multiple proxies from Pinus cembra trees from God da Tamangur, combining tree ring anatomy and stable isotope chronologies to reconstruct seasonal glacier mass balance (i.e., winter, summer, and annual mass...

Glacier mass-balance reconstructions provide a means of placing relatively short observational records into a longer-term context. Here, we use multiple proxies from Pinus cembra trees from God da Tamangur combining tree-ring anatomy and stable isotope chronologies to reconstruct seasonal glacier mass balance (i.e. winter, summer and annual mass ba...

Previous attempts to quantify tree abundance at global scale have largely neglected the role of local competition in modulating the influence of climate and soils on tree density. Here, we evaluated whether mean tree size in the world’s natural forests alters the effect of global productivity on tree density. In doing so, we gathered a vast set of...

Mountain ecosystems are particularly sensitive to climate change, which in part causes encroachment of woody plants at the treeline ecotone, with repercussions on treeline advance and ecosystem carbon balance. Yet, studies investigating the long-term trends in radial growth as well as year-to-year response of several tree and shrub species to clima...

Tree rings form the backbone of high-resolution palaeoclimatology and represent one of the most frequently used proxy to reconstruct climate variability of the Common Era. In the European Alps, reconstructions were often based on tree-ring width (TRW) and maximum latewood density (MXD) series, with a focus on European larch. By contrast, only a ver...

In mountainous regions, global warming will likely affect the frequency and magnitude of geomorphic processes. This is also the case for rockfall, one of the most common mass movements on steep slopes. Rainfall, snowmelt, or freeze-thaw cycles are the main drivers of rockfall activity, rockfall hazards are thus generally thought to become more rele...

This paper reports on climate-induced growth changes in relict, low-altitude mountain pines ( Pinus uncinata Mill. ex. Mirb.) from two refugia with cold microclimates located in the Northern French Alps. The P. uncinata stands analyzed grow at the lower bound of their ecological limit and are thus thought to be sensitive indicators of ongoing clima...

The spatial and temporal quantification of rockfall frequency remains a major challenge in mountain environments, especially also in terms of rockfall management. Approaches that have been used traditionally to quantify rockfall frequency include historical records, remote sensing, or in situ monitoring, but have been shown repeatedly to suffer fro...

To overcome the lack of historical archives at active rockfall environments, dendrogeomorphic techniques have been used extensively on forested slopes since the early 2000s and several approaches developed to extract rockfall signals from tree-ring records. Given the unpredictable nature of rockfall, these reconstructions are, in principle, of grea...

In mountain environments, precise rockfall risk evaluation is crucial to reduce death tolls and costs. However, to date, existing rockfall risk assessment procedures remain scarce, as they focus only on existing elements at risk and with the damage expectation as sole risk measure. Here, we propose an approach to evaluate the distribution of damage...

More tree species can increase the carbon storage capacity of forests (here referred to as the more species hypothesis) through increased tree productivity and tree abundance resulting from complementarity, but they can also be the consequence of increased tree abundance through increased available energy (more individuals hypothesis). To test thes...

In mountain environments, precise rockfall risk evaluation is crucial to reduce death tolls and costs. However, to date, existing rockfall risk assessment procedures remain scarce, as they focus only on existing elements at risk and with the damage expectation as sole risk measure. Here, we propose an approach to evaluate the distribution of damage...

Les chutes de blocs représentent un aléa majeur dans les zones montagneuses, menaçant infrastructures collectives, zones urbanisée et vies humaines. Les conséquences de ces événements peuvent être importantes pour les collectivités locales ainsi que les pouvoirs publics, qui restent démunis en matière de méthode de diagnostic et d'analyse du risque...

Depuis deux décennies, de nombreuses publications scientifiques ont mis en évidence les impacts du changement climatique sur la fréquence des chutes de pierres dans les parois englacées de haute altitude. À plus basse altitude, les inventaires rares et incomplets existants n’ont pas permis d’identifier un impact significatif de l’augmentation des t...

Dendrogeomorphic analyses provide long and continuous chronologies of mass movements that are useful for the detection of trends related to climate change. Socio-environmental changes can, however, induce non-stationarities. This study addresses the following questions: (1) How does the evolution of forest cover induce non-stationarities in tree-ri...

Rockfall release is a rather unpredictable process. As a result, the occurrence of rockfall often threatens humans and (infra)structures. The assessment of potential drivers of rockfall activity therefore remains a major challenge, even if the relative influence of rainfall, snowmelt, or freeze–thaw cycles have long been identified in short‐term mo...

In the current context of anthropogenic global warming, one of the purposes of dendrogeomorphic analyses is to provide long and continuous chronologies of mass movements, so as to detect potential trends or shift related to increasing temperatures. However, on documented slopes, the comparison between historical archives and tree-ring records sugge...

The rockfall phenomenon is deined as a rock block that detaches from a vertical or sub-vertical clif and travels down the slope in rapid motions. Every year, some rockfalls reach urbanized areas, causing damage to structures and injuring people. In this context, a precise rockfall risk analysis has become essential for authorities and stakeholders....

Due to intense urban sprawl in rockfall-prone areas, a precise rockfall risk assessment has become a crucial issue for public authorities and stakeholders. In this context, quantitative risk analysis (QRA) procedures, accounting for the specificities of the rockfall process, have been developed. For the last few decades, several studies have examin...

En région de montagne, les chutes de blocs représentent un aléa majeur qu’il convient de caractériser par le biais de sa fréquence, de son intensité (énergie) et de sa propagation (distance d’arrêt). Bien que particulièrement complexe, en raison du caractère diffus de cet aléa et des lacunes existant dans les archives historiques, cette caractérisa...

The medium-high mountain ranges of Western Europe are undergoing rapid socio-environmental changes. The aim of this study is to show that their landscape can be strongly shaped by the actions of avalanche activity, humans and climate. The study area is the Rothenbachkopf-Rainkopf complex, a site representative of avalanche-prone areas of the Vosges...

Expected runout distances and related return periods are the most important parameters needed for zoning in terrain prone to snow avalanching. Hazard mapping procedures usually allocate areas of land to zones with a different degree of danger based on return periods estimated for given snow volumes in the starting zone or with statistical/dynamical...

Sea cliffs represent 80% of the world's coasts and can be found virtually in all types of morphogenetic environments. Most studies on rocky environments focused on the impacts of modern sea level rise on cliff stability derived from sequential surveys, direct measurements or erosional features in anthropogenic structures. In this study, we explore...

One of the most important issues of current landslide research is related to the dating of their reactivations, both in spatial and in temporal terms. Landslide chronologies thus play a key role because they provide very essential information on past activity and thereby contribute substantially to hazard assessment, in particular in areas with int...

The purpose of dendrogeomorphic analyses is to amplify the signal related to the geomorphic process under investigation, and to minimize the noise induced by other signals in the tree-ring series. Yet, to date, no study accounts specifically for interferences induced by climate conditions or exogenous disturbances and which can, potentially, affect...

Determination of spatial and temporal patterns of rockfall events remains a serious challenge in most mountain areas and especially when it comes to quantitative hazard assessments, because of the scarcity and incompleteness of long-Term records. his lack of reliable baseline data is particularly problematic in urbanized areas where rockfall risk t...

Cold microclimatic conditions provide exceptional microhabitats to Pinus uncinata stands occurring at abnormally low altitudes in seven relict stands of the northern French Alps. Here, P. uncinata is located at the lower bounds of its ecological limits and therefore expected to provide a sensitive indicator of climate change processes. We used dend...

Dans les Alpes, les glissements de terrain font partie des processus géomorphologiques les plus répandus et sont à l'origine de nombreux dommages socio-économiques (Hil-ker et al., 2009). La détermination des facteurs déclenchants de ces mouvements de masse et leur cartographie constituent des enjeux majeurs pour les scientifiques mais également po...

In this contribution, past process activity is reconstructed on seven landslide bodies of the Riou Bourdoux catchment (southeastern French Alps). Based on an unusually dense data set of 3036 tree-ring series extracted from 759 conifers, we provide evidence for 61 landslide reactivations since A.D. 1898. Based on logistic regressions and threshold a...

Probability maps of landslide reactivation are presented for the Aiguettes landslide located in the southern French Alps based on results obtained with dendrogeomorphic analysis. Spatio-temporal activity was derived from tree-ring series of 223 disturbed trees. 355 growth disturbances were identified in the samples indicating 14 reactivation phases...

This study is a first attempt to specify the geodynamic processes leading to the erosion of detrital quaternary cliffs on the island of Porquerolles, and to quantify the rate of erosion by means of dendrogeomorphology. The island is located in the Mediterranean Sea, off the coast of Provence (France). This method identifies the roots of Aleppo pine...

This study is a first attempt to specify the geodynamic processes leading to the erosion of detrital quaternary cliffs on the island of Porquerolles, and to quantify the rate of erosion by means of dendrogeomorphology. The island is located in the Mediterranean Sea, off the coast of Provence (France). This method identifies the roots of Aleppo pine...

Dendrogeomorphology relies on the capacity of ligneous vegetation to react to external stresses induced by changes in the environment and to register these impacts in the form of either characteristic annual rings or morphological anomalies. By analyzing the radial growth of trees (in the form of one or several abnormally narrow or wide tree rings)...

In snow-rich areas, snow avalanches endanger settlements and cause heavy damage to infrastructure or transportation routes. In wooded avalanche paths, dendrogeomorphology has been used extensively to reconstruct snow avalanche histories or to complement existing archival records. Several authors noted (i) that avalanche chronologies reconstructed f...

The purpose of this study was to reconstruct spatio-temporal patterns of past landslide reactivation and the possible occurrence of future events in a forested area of the Barcelonnette basin (Southeastern French Alps). Analysis of past events on the Aiguettes landslide was based on growth-ring series from 223 heavily affected Mountain pine (Pinus...

Probability maps of landslide reactivation are presented for the Pra Bellon landslide located in the southern French Alps based on results obtained with dendrogeomorphic analysis. Spatiotemporal patterns of past landslide activity was derived from tree-ring series of 403 disturbed mountain pine trees growing in the landslide body. In total, 704 gro...

The purpose of this study was to reconstruct spatiotemporal patterns of avalanche events in a forested avalanche path of the Queyras massif (Echalp avalanche path, southeast French Alps). Analysis of past events was based on tree-ring series from 163 heavily affected multicentennial larch trees (Larix decidua Mill.) growing near or next to the aval...

Les glissements de terrain sont à l’origine de la destruction de nombreuses infrastructures routières, de bâtiments et causent la perte de vies humaines. L’observation des glissements de terrain est limitée par l’absence d’archives historiques précises. Sur les glissements de terrain superficiels forestiers, la dendrogéomorphologie permet de recons...

Landslides constitute a common mass movement process and a widespread hazard in mountain where they cause damage and destruction to settlements, transportation corridors, or even lead to the loss of life. A major obstacle for the knowledge of past landslide activity is the lack of historical data with satisfying spatial resolution over medium to lo...

Black marls form very extensive outcrops in the Alps and constitute some of the most eroded terrains, thus causing major problems of sedimentation in artificial storage systems (e.g. reservoirs) and river systems. In the experimental catchments near Draix (France), soil erosion rates have been measured in the past at the plot scale through a detail...

The purpose of this study was to reconstruct spatiotemporal patterns of past landslide reactivation in a forested area of the Barcelonnette Basin (Bois Noir landslide, Southern French Alps). Analysis of past events was based on tree ring series from 79 heavily affected Mountain pine (Pinus uncinata Mill. ex Mirb) trees growing near or next to the l...

Hydrogeomorphic processes are a major threat in many parts of the Alps, where they periodically damage infrastructure, disrupt transportation corridors or even cause loss of life. Nonetheless, past torrential activity and the analysis of areas affected during particular events remain often imprecise. It was therefore the purpose of this study to re...

Extensive areas of the French Alps are underlain by Jurassic black marls. Wherever these so-called ‘terres noires’ crop out they are subject to intense erosion, causing major sedimentation in regional reservoirs and river systems. In the badlands near Draix (Alpes de Haute-Provence, France), measured sediment yield obtained by surface elevation cha...

Extensive areas of the French Alps are underlain by Jurassic black marls. Wherever these “terres noires” crop out they become subject to intense erosion, causing major sedimentation in regional reservoirs and river systems. In the badlands near Draix (Alpes de Haute-Provence, France), measured sediment rates were obtained at the plot scale by surfa...

Dendrogeomorphology relies on the capacity of ligneous vegetation to react to external stresses induced by changes in the environment and to register these impacts in the form of either characteristic annual rings or morphological anomalies. By analyzing the radial growth of trees (in the form of one or several abnormally narrow or wide tree rings)...

Extensive areas of the French Alps are underlain by Jurassic black marls. Wherever these so-called 'terres noires' crop out they are subject to intense erosion, causing major sedimentation in regional reservoirs and river systems.the badlands near Draix (Alpes de Haute-Provence, France), measured sediment yield obtained by surface elevation change-...

Snow avalanches are a major threat in many parts of the Alps, where they periodically damage infrastructure, disrupt transportation corridors or even cause loss of life. Nonetheless, the spatial behavior of past avalanche activity and the analysis of areas affected during particular events remain often imprecise. It was therefore the purpose of thi...

Les avalanches constituent l'un des principaux aléas naturels pour les hommes et les activités humaines dans les pays alpins. La prédétermination de l'aléa avalancheux, en termes de probabilité d'occurrence et d'intensité, s'appuie sur des chroniques d'événements passés, souvent lacunaires et imprécises sur le plan spatial. La communication présent...

The resistograph device measures the drill resistance of a fine needle as it penetrates wood. It wa investigated for rapid assessment of relative wood density of particular tree-rings used in dendrogeomorphology. Ring width and resistographic measurements were performed on 15 disc stems (cross sections) of Larix decidua from an avalanche talus. 11...

Trees produce reaction wood when they are exposed to geomorphological and hydrolocical processes like snow avalanches, floods or landslides that lead to changes of the tree position, of the growth conditions or to direct mechanical damage. This wood has a different cell structure that is clearly visible when extracted from a tree. In this way trees...

Unlike avalanche or flood, for example, identifying and recording historical landslides are very sketchy. However, several methods exist such as radiocarbon dating, lichnometry and dendrogeomorphology which offer dating landslides. For the latter, the potential for the analysis of tree rings in the interpretation of geomorphologic processes were de...