This Open Access volume highlights how tree ring stable isotopes have been used to address a range of environmental issues from paleoclimatology to forest management, and anthropogenic impacts on forest growth. It will further evaluate weaknesses and strengths of isotope applications in tree rings. In contrast to older tree ring studies, which predominantly applied a pure statistical approach this book will focus on physiological mechanisms that influence isotopic signals and reflect environmental impacts. Focusing on connections between physiological responses and drivers of isotope variation will also clarify why environmental impacts are not linearly reflected in isotope ratios and tree ring widths. This volume will be of interest to any researcher and educator who uses tree rings (and other organic matter proxies) to reconstruct paleoclimate as well as to understand contemporary functional processes and anthropogenic influences on native ecosystems. The use of stable isotopes in biogeochemical studies has expanded greatly in recent years, making this volume a valuable resource to a growing and vibrant community of researchers.
About the chapter: In this chapter we introduce the climate signal in stable isotope tree-ring records, with the emphasis on temperate forests. The development of the subdiscipline is recapped followed by an exploration of isotope dendroclimatic records by geography and, broadly, by isotopic species. Whilst there are still questions to be answered around signal strength and age-related effects in different environments and in different species, the proxy is now contributing to palaeoclimatology in a far greater way than in the days of the first hints of ‘isotope tree thermometers’. Due to the greater complexity seen in stable carbon isotope interpretations, we explore response groupings with example references given for each category of proxy response. Finally, we summarize the state of the art in isotope dendroclimatology and discuss possible future directions.

Référence : Gagen M., Battipaglia G., Daux V., Duffy J., Dorado-Linan I., Andreu-Hayles L. et al. Climate signals in stable isotope tree-ring records. Chap. 19, In: Stable Isotopes in tree rings, pp 537-579, Eds: R.T.W. Siegwolf, J.R. Brooks, J. Roden, M. Saurer. Tree Physiology series, Vol 8. Springer Int. Pub. ISBN: 978-3-030-92697-7.

Along the coasts of northern Alaska, in a treeless tundra environment, the primary wood resource for coastal populations is driftwood, a seasonal and exogenous resource carried by the major rivers of western North America. The potential of Alaskan coastal archaeological wood for tree-ring research was first assessed in the 1940s by archaeologist and tree-ring research pioneer J. L. Giddings (Figure 1). Despite his success, the difficulties of dendrochronological studies on driftwood and the development of radiocarbon dating during the 1950s resulted in the near-abandonment of dendrochronology to precisely date archaeological sites and build long sequences using archaeological wood in Alaska. In this study, we explored the possibilities and limitations of standard ring-width dendrochronological methods for dating Alaskan coastal archaeological wood. We focus on the site of Pingusugruk, a late Thule site (15th–17th CE) located at Point Franklin, northern Alaska. The preliminary results have been obtained from the standard dendrochronological analyses of 40 timber cross-sections from two semi-subterranean houses at Pingusugruk (Figure 2). We cross-correlated individual ring-width series and built floating chronologies between houses before cross-dating them with existing regional 1000-year-long master chronologies from the Kobuk and Mackenzie rivers (available on the International Tree-Ring Databank, ITRDB). These preliminary results confirm the potential of dendrochronology for a better understanding of the Thule period on climate and cultural change. Additional work on various dendro-archaeological collections using an interdisciplinary approach (geochemical analyses of oxygen isotopes and radiocarbon dating) will help develop and expand regional tree-ring chronologies and climatic tree-ring sequences in Alaska.

Référence : Taïeb J., Alix C., Juday G.P., Jensen A. M., Daux V. Dating coastal archaeological wood from Pingusugruk (15th-17th CE), Northern Alaska. International Journal of wood culture 2, 1-28.

Hydroclimate variability in tropical South America is strongly regulated by the South American Summer Monsoon (SASM). However, past precipitation changes are poorly constrained due to limited observations and high-resolution paleoproxies. We found that summer precipitation and the El Nino-Southern Oscillation (ENSO) variability are well registered in tree-ring stable oxygen isotopes (δ18OTR) of Polylepis tarapacana in the Chilean and Bolivian Altiplano in the Central Andes (18–22°S, ∼4,500 m a.s.l.) with the northern forests having the strongest climate signal (Figure 1). More enriched δ18OTR values were found at the southern sites likely due to the increasing aridity toward the southwest of the Altiplano. The climate signal of P. tarapacana δ18OTR is the combined result of moisture transported from the Amazon Basin, modulated by the SASM, ENSO, and local evaporation, and emerges as a novel tree-ring climate proxy for the southern tropical Andes.

Référence : Rodriguez-Caton M., Andreu-Hayles L., Daux V., Vuille M., Varuolo-Clarke A., Oelkers R., Christie D.A., D’Arrigo R., Morales M., Rao M.P., Srur A., Vimeux F., Villalba R. Hydroclimate and ENSO Variability recorded by oxygen isotopes from tree rings in the South American Altiplano. Geophys. Res. Lett. 49, e2021GL0958

L’anticipation des effets du changement climatique est désormais un objectif de plus en plus partagé. La révision de cette évolution repose sur deux piliers : la reconstitution des variations climatiques passées et la modélisation des variations futures, basée sur les lois physiques qui régissent le climat. La connaissance du passé permet de séparer les effets imputables à l’homme des effets naturels et de tester la capacité des modèles à décrire le climat.
Nous proposons une vision globale du changement climatique en dressant un large panorama des évolutions climatiques, allant de celles du passé (du mésolithique, environ 9 000 ans avant J.C., au début du XXIe siècle) à celles prédites dans un futur plus ou moins proche. Considérant tout particulièrement l’évolution climatique en France métropolitaine, des reconstitutions et des prédictions solidement acquises sont présentées essentiellement pour les variables climatiques à ce jour les plus étudiées : la température et la pluviométrie.

Référence : Daux V., Garcia de Cortazar-Atauri I. Le climat ses évolutions passées et futures. Chapitre 1, In : Adaptation des productions fruitières au cahngement climatique, Legave J.-M. coord., Editions quaea, Versailles, 19-38. ISBN : 978-2-7592+3251-2.

Notre-Dame de Paris, the so famous Catholic cathedral standing on Ile de la Cité in Paris, was built in 1163, largely completed by 1260, then frequently modified in the following centuries until a major restoration between 1844 and 1864. All these steps of construction and modifications involved the frame, so-called “la forêt” (the forest). So, the woods used throughout the cathedral’s history are samples and memories of the forests of oaks grown in the Paris Basin since the Middle Ages. The unfortunate destruction of the cathedral on 15th April of 2019, which miraculously spared a part of the frame, made these woods accessible to the scientific community. Some scientists are particularly interested in the isotopic composition of wood as memory of past climate and as a clock to the past. On one part, the oxygen and carbon isotopes (d13C and d18O) of tree-ring cellulose will bring light to past climate. Indeed, the isotopic composition of this component is determined by the conditions surrounding the trees during their growth. The variations of d13C and d18O with time, recorded in the successive rings built by the trees year after year, allows reconstructing the evolution of some
environmental or climatic parameters such as temperature or humidity. Isotope dendroclimatology, a
rapidly expanding field of investigation, is applied to old living trees, sub-fossil woods from buildings or even fossil material to reconstruct past climate. This methodological approach will be applied to the cathedral's oak timbers that have escaped severe charring and to contemporaneous unburned woods from other buildings (Figure 1). On the other part, measuring ring by ring the residual content of 14C isotope in cellulose will make it possible to refine the 14C clock which allows to date any material containing carbon. This will be achieved by providing new portions of the global calibration curve for the continental Western Europe from the 12th to the 18th century, from uncharred "forest" of Notre-Dame.

Daux V., Hatté C., duBoisgueheneuc D., Beck L., Richardin P. The ‘forest’ of Notre dame de Paris: a path into medieval climate and time. Journal of Cultural Heritage, In press

Tree-ring width (TRW) chronologies have been widely and long-time used to reconstruct past climate variations in the Andes in South America. The use of tree-ring isotopic chronologies is still not widespread in this region although they have proved to be very efficient climate proxies. Araucaria araucana (Molina) K. Koch is a conifer tree species with some multi-century-old individuals that offers an excellent opportunity to measure stable carbon (δ13C) and oxygen (δ18O) isotopes in cellulose from long tree-ring records. Here, we explore whether current or stored carbohydrates are used for A. araucana radial growth and we assess the potential of a tree-ring isotopic record to study past climate variability. Eleven A. araucana cores from a dry and high-elevation forest at the northern border of Patagonia, Argentina (38â—¦55’S, 70â—¦44’W) were selected for stable isotopes analyses. The strong correlation between the isotopic composition of the first and second parts of the same ring, but also the strong relationships between δ13C and δ18O records with climate parameters of the current growing season such as temperature, show that tree-rings are built mostly with carbohydrates produced during the current growing season with little or no supply from storage or reserves. This finding leads to reconsidering the interpretation of the legacy effect (i.e. ecological memory effects) based on the previously described strong negative correlation between A. araucana TRW chronologies and previous growing season temperature and suggests a dependence of radial tree growth on the level of development of organs. Regarding climate sensitivity, the A. araucana tree-ring δ13C chronology is strongly related to current summer temperature (r = 0.82, p < 0.001), vapour pressure deficit (VPD; r = 0.79, p < 0.001), precipitation (r = -0.53, p < 0.001) and SPEI2 (r = - 0.73, p < 0.001) (Figure 1). These strong relationships support the use of δ13C of A. araucana tree-ring cellulose to reconstruct past temperature variations at regional scale in relation with large-atmospheric drivers of climate variability such as the Southern Annular Mode. The A. araucana tree-ring δ18O chronology is also correlated with temperature (r = 0.42, p < 0.01) and VPD (r = 0.45, p < 0.01) of the winter preceding the growing season. This suggests that trees are using water from precipitation infiltrated in the soil during the previous recharge period (autumn-winter). The weak correlations of δ18O with current summer atmospheric conditions and the decoupling between δ18O and δ13C, may be due to a high rate of oxygen exchange between sugars and xylem water (Pex) during cellulose synthesis, which dampens evaporative isotopic fractionation.

Référence : Penchenat T., Daux V., Mundo I ., Pierre M., Stievenard M., Srur A., Andreu-Hayles L., Villalba R.
Dendrochronologia 74, 2022 125979.

Mardi 27, mercredi 28 et jeudi 29 septembre 2022, Camille Asselin, Edouard Régnier et Jérémy Jacob ont été accueillis par la Division Curage du Service Technique de l'Eau et de l'Assainissement (Direction de l'Eau et de la Propreté) de la Ville de Paris pour visiter les bassins de dessablement du secteur Est du réseau d'assainissement. Nous avons accompagné les équipes d'égoutiers qui procédaient aux relevés des bassins. Il s'agit d'opérations qui visent à évaluer le taux de remplissage des bassins de décantation pour prévoir les opérations de curage quand ceux-ci sont remplis.

Dans le cadre de la thèse de Camille Asselin et du projet ANR EGOUT porté par Jérémy Jacob, les objectifs étaient multiples :

• Mieux comprendre le fonctionnement des bassins de dessablement : leur remplissage, le fonctionnement des bypass qui sont activés lors des opérations de curage pour dévier le flux d'eau et mettre à sec le sédiment, le fonctionnement des collecteurs auto-curants, les modalités d'accès aux ouvrages, etc...
• Evaluer les possibilités de carottage des sédiments. D'un point de vue technique et logistique (accès, mise en place des équipements...) mais aussi au regard de la dynamique de remplissage. A ce titre, les relevés du niveau de sable par les égoutiers constituent des données précieuses.
• Nouer le contact avec les égoutiers, les informer sur le projet EGOUT, être à l'écoute des informations qu'ils peuvent apporter au projet, évaluer ce que nos travaux peuvent leur apporter en retour.

A l'arrivée sur le site de Delesseux, nous avons été entièrement équipés par les services de la Ville de Paris. Bottes, combinaison, masque, autosauveur, lunettes, casque, harnais, détecteur 4 gaz. Nous bénéficions tous les trois d'une formation CATEC.

Nous avons visité 8 bassins de décantation : Vincennes, Allard, Soult, Wattignies, Saint Bernard, Faidherbe, Belleville et Ménilmontant. L'ensemble des objectifs a été atteint.

Nous avons pu apprécier le professionnalisme des équipes, leur connaissance du milieu et la maîtrise des risques par le respect des consignes de sécurité. Et, bien plus encore, nous avons apprécié l'accueil, les discussions très pointues sur le métier et sur le fonctionnement des égouts.

Site web du projet EGOUT : https://egout.cnrs.fr/

L'objectif de la Journée Thématique était de sensibiliser la communauté de l'archéométrie et de la conservation aux sens. Il s'agissait à la fois de présenter quelques exemples de travaux visant à reconstruire les ambiances sensorielles passées et de questionner l'utilisation des sens dans la caractérisation des objets d'étude en archéométrie. Aussi, la journée s'est déroulée en deux temps. Le matin était dédié à des exposés scientifiques, organisés selon les cinq sens, qui ont présenté des travaux originaux sur les ambiances sensorielles de diverses époques, reconstruites par les techniques de l'archéométrie. L'après-midi était dédiée à des ateliers animés par des experts des sens durant lesquels les participants ont discuté de l'utilisation des sens dans la caractérisation de leurs objets d'étude, de manière à parvenir à des principes et des clés communes de caractérisation. Le déjeuner était en phase avec la thématique de la journée. Anaïs Tondeur, artiste plasticienne œuvrant à la frontière des Sciences et de l'Art, a accompagné cette journée.

En octobre 2021, des chercheures et chercheurs du Laboratoire des Sciences du Climat et de l’Environnement (LSCE, Gif-sur-Yvette), de l’Institut des Sciences de l’Évolution de Montpellier (ISEM) et de l’Université Fédérale du Ceara (Brésil) ont parcouru l’état du Piauí pour prélever des carottes de sédiments lacustres et des échantillons de surface. L’objectif est de reconstruire l’évolution des conditions environnementales (climat, végétation) associées aux premières occupations humaines en Amérique du Sud.

Au retour au laboratoire, les carottes de sédiments ont été datées et analysées avec différents traceurs (pollen, analyses géochimiques, etc…).

Cette mission s’inscrit dans le projet ANR “SESAME” (Human paleoecology, Social and cultural Evolutions among first Settlements in Southern AMErica), porté par Eric Boëda (Archéologies et Sciences de l’Antiquité, Paris).

Au retour de la mission, les prises de vue ont été montées en vidéo par Edouard Régnier (LSCE) sous la forme d'un "roadtrip".

Site web du projet : https://sesame.hypotheses.org

Changes in the climate dynamics have already modified characteristics and impacts of storms in France: the case  study of storm Alex 2020

by Mireia Ginesta

Extratropical cyclones play a key role in modulating the precipitation and wind in mid-latitudes and can be responsible for extreme wet and windy events. With global warming, the dynamics and thermodynamics associated with these atmospheric systems are being affected. However, due to the complexity of modelling the climate system, a challenge arises when evaluating the influence that climate change might have had in specific observed extreme cyclones. An effort towards this direction has been made by Extreme Event Attribution, a recent research field that aims to analize how global warming has modified the characteristics, such as frequency, intensity and duration, of an extreme event. A recent study led by Mireia Ginesta presents a methodology for attributing the changes in the underlying dynamics of extreme extratropical cyclones to ongoing climate change. They illustrate the methodology on storm Alex, a severe storm that affected southwestern Europe at the beginning of October 2020. Southern France and Northern Italy received numerous record-breaking precipitation amounts, such as 630 mm in just 24 hours in Sambughetto. Storm Alex caused more than 20 fatalities and an estimated economic loss of at least 2 and a half billion euros.

The study uses climate observations of the last seven decades to define two different climate periods: a past period from 1950 to 1984, and a more recent period, from 1986 to 2021. The latter represents a climate largely influenced by anthropogenic emissions, while in the former, the human influence on climate is weaker. They first identified 30 storms similar to Alex, which they named analogues, by selecting those that resemble Alex in terms of sea level pressure in each period. They then compared the characteristics of the storms of the past and present periods. They found that Alex-like storms in the more recent period have more meridional atmospheric pressure patterns, and they are more persistent. Storms in the present period become more common in autumn, when Alex took place. In terms of impacts, there is an increase in precipitation and wind gusts in Southern France and Northern Italy, increasing the probability of severe flooding events. Therefore, those changes collectively point to Alex-like storms more impactful and common in a warmer climate.

Reference

Ginesta, M., Yiou, P., Messori, G., Faranda, D. A methodology for attributing severe extratropical cyclones to climate change based on reanalysis data: the case study of storm Alex 2020. Clim Dyn (2022). https://doi.org/10.1007/s00382-022-06565-x 

Can we attribute the intense precipitation event in the Brisbane region in February 2022 to climate change?

This extreme precipitation event was unprecedented in the Brisbane region and very intense with respect to previous historical records in the broader Eastern coast of Australia. To understand to what extent climate change could have influenced this extreme event, researchers employed attribution methods, which aims to quantify the influence of climate change on a meteorological event and to investigate the physical mechanisms that lead to it.

In this paper, the ESTIMR team used two attribution methods: a classical one based on return time statistics and a new one introduced recently by the team and based on the atmospheric circulation. The first method consists in comparing the likelihood of observing an event so intense in the past with respect to the present. If this probability is greater in the present climate, it means climate change made this event more likely.  The second one compares the large air masses and the high and low pressure systems at the time of the rain bomb event. Then it determines if a similar situation had already occurred in the recent (1990-2020) and remote past (1950-1980). The systematic comparison between the recent and remote past allows them to compare the impacts of a similar atmospheric configuration when the influence of climate change on the atmosphere was still weak. 

The climate of Australia is strongly influenced by the natural evolution of the climate, in particular a large atmospheric and oceanic oscillation called El-Niño-Southern-Oscillation (ENSO). ENSO is a phenomenon of the Pacific region that irregularly alternates between two phases. During the event, ENSO was in the La Niña phase, which induces additional air moisture in the south West Pacific and wind circulation patterns that could have played a role in the intensity of the event. They adapt the attribution methods to compare between El Niño and La Niña phases and evaluate how ENSO could have played a role in the intensity of the event.

The statistical attribution shows that this event has a low probability of happening both in the past and present climates (less than one in a century). This first attribution method yields no clear signal of a climate change influence. The second method reaches similar conclusions, with no clear signal of climate change on precipitation for the atmospheric configuration observed. It is likely that the La Niña phase of the ENSO played a significant role in the intensity of the event.

These results are coherent with what the IPCC report states about rainfall over Australia, namely that “Available evidence has not shown an increase or a decrease in heavy precipitation over Australasia as a whole (medium confidence), but heavy precipitation tends to increase over Northern Australia (particularly the north-west) and decrease over the eastern and southern regions.” 

Reference

Cadiou*, C., Noyelle*, R., Malhomme, N., Faranda D.  Challenges in Attributing the 2022 Australian Rain Bomb to Climate Change. Asia-Pac J Atmos Sci (2022). https://doi.org/10.1007/s13143-022-00305-1

*Equal Contributions

Acknowledgments

A weather ensemble forecasting tool based on statistical and probabilistic methods

Ensemble weather forecasts can help to anticipate the risks and probabilities of extreme weather events. Nevertheless, weather forecasting is a complex task due to the chaotic behavior of the atmosphere [1]. This represents a major source of uncertainties in particular for the sub-seasonal lead times (from a few days to one month) [2]. To overcome those uncertainties, a large number of numerical simulations is necessary. 

In this study, we propose a weather ensemble forecasting tool based on statistical and probabilistic methods to generate ensemble weather forecasts [3]. The Analog-SWG is designed to mimic the behavior of climate variables [4] by assuming the relationship between past and future weather and using similarities in atmospheric circulation patterns [5]. We have tested the Analog-SWG to forecast European precipitation at a local scale ( i.e. station level: Berlin, Madrid, Paris and Toulouse) [3]. We assessed the performance of our forecasts against other forecasts from meteorological centers [3]. We found good performance in different regions of Europe for up to 10 days. We confirmed the importance of atmospheric circulation in driving the meteorological parameters. We also identified the influence of high and low pressure on good and bad forecasts [3].  

References

[1] Faranda, D., Messori, G., and Yiou, P.: Dynamical proxies of North Atlantic predictability and extremes. Scientific Reports (2017).

[2] Vitart, F., et al.: The Subseasonal to Seasonal (S2S) Prediction Project Database, Bulletin of the American Meteorological Society. (2017).

[3] Krouma, M., Yiou, P., Déandreis, C., and Thao, S.: Assessment of stochastic weather forecast of precipitation near European cities, based on analogs of circulation, Geosci. Model Dev. (2022).  

[4] Ailliot, P., Allard, D., Monbet, V., and Naveau, P.: Stochastic weather generators: an overview of weather type models, Journal de la Société Française de Statistique. (2015)

[5] Yiou, P. and Déandréis, C.: Stochastic ensemble climate forecast with an analogue model, Geoscientific Model Development. (2019). 

[6] Krouma, M., Silini, R., and Yiou, P.: Ensemble forecast of an index of the Madden Julian Oscillation using a stochastic weather generator based on circulation analogs, EGUsphere [preprint] (2022)

More Resources

Get to know: Meriem Krouma (Aria Technologies, Paris, France)

Ensemble weather forecast with a stochastic weather generator and analogs of the atmospheric circ...

Changes in the climate dynamics have already modified characteristics and impacts of storms in France: the case  study of storm Alex 2020

by Mireia Ginesta

Extratropical cyclones play a key role in modulating the precipitation and wind in mid-latitudes and can be responsible for extreme wet and windy events. With global warming, the dynamics and thermodynamics associated with these atmospheric systems are being affected. However, due to the complexity of modelling the climate system, a challenge arises when evaluating the influence that climate change might have had in specific observed extreme cyclones. An effort towards this direction has been made by Extreme Event Attribution, a recent research field that aims to analize how global warming has modified the characteristics, such as frequency, intensity and duration, of an extreme event. A recent study led by Mireia Ginesta presents a methodology for attributing the changes in the underlying dynamics of extreme extratropical cyclones to ongoing climate change. They illustrate the methodology on storm Alex, a severe storm that affected southwestern Europe at the beginning of October 2020. Southern France and Northern Italy received numerous record-breaking precipitation amounts, such as 630 mm in just 24 hours in Sambughetto. Storm Alex caused more than 20 fatalities and an estimated economic loss of at least 2 and a half billion euros.

The study uses climate observations of the last seven decades to define two different climate periods: a past period from 1950 to 1984, and a more recent period, from 1986 to 2021. The latter represents a climate largely influenced by anthropogenic emissions, while in the former, the human influence on climate is weaker. They first identified 30 storms similar to Alex, which they named analogues, by selecting those that resemble Alex in terms of sea level pressure in each period. They then compared the characteristics of the storms of the past and present periods. They found that Alex-like storms in the more recent period have more meridional atmospheric pressure patterns, and they are more persistent. Storms in the present period become more common in autumn, when Alex took place. In terms of impacts, there is an increase in precipitation and wind gusts in Southern France and Northern Italy, increasing the probability of severe flooding events. Therefore, those changes collectively point to Alex-like storms more impactful and common in a warmer climate.

Reference

Ginesta, M., Yiou, P., Messori, G., Faranda, D. A methodology for attributing severe extratropical cyclones to climate change based on reanalysis data: the case study of storm Alex 2020. Clim Dyn (2022). https://doi.org/10.1007/s00382-022-06565-x 

Can we attribute the intense precipitation event in the Brisbane region in February 2022 to climate change?

This extreme precipitation event was unprecedented in the Brisbane region and very intense with respect to previous historical records in the broader Eastern coast of Australia. To understand to what extent climate change could have influenced this extreme event, researchers employed attribution methods, which aims to quantify the influence of climate change on a meteorological event and to investigate the physical mechanisms that lead to it.

In this paper, the ESTIMR team used two attribution methods: a classical one based on return time statistics and a new one introduced recently by the team and based on the atmospheric circulation. The first method consists in comparing the likelihood of observing an event so intense in the past with respect to the present. If this probability is greater in the present climate, it means climate change made this event more likely.  The second one compares the large air masses and the high and low pressure systems at the time of the rain bomb event. Then it determines if a similar situation had already occurred in the recent (1990-2020) and remote past (1950-1980). The systematic comparison between the recent and remote past allows them to compare the impacts of a similar atmospheric configuration when the influence of climate change on the atmosphere was still weak. 

The climate of Australia is strongly influenced by the natural evolution of the climate, in particular a large atmospheric and oceanic oscillation called El-Niño-Southern-Oscillation (ENSO). ENSO is a phenomenon of the Pacific region that irregularly alternates between two phases. During the event, ENSO was in the La Niña phase, which induces additional air moisture in the south West Pacific and wind circulation patterns that could have played a role in the intensity of the event. They adapt the attribution methods to compare between El Niño and La Niña phases and evaluate how ENSO could have played a role in the intensity of the event.

The statistical attribution shows that this event has a low probability of happening both in the past and present climates (less than one in a century). This first attribution method yields no clear signal of a climate change influence. The second method reaches similar conclusions, with no clear signal of climate change on precipitation for the atmospheric configuration observed. It is likely that the La Niña phase of the ENSO played a significant role in the intensity of the event.

These results are coherent with what the IPCC report states about rainfall over Australia, namely that “Available evidence has not shown an increase or a decrease in heavy precipitation over Australasia as a whole (medium confidence), but heavy precipitation tends to increase over Northern Australia (particularly the north-west) and decrease over the eastern and southern regions.” 

Reference

Cadiou*, C., Noyelle*, R., Malhomme, N., Faranda D.  Challenges in Attributing the 2022 Australian Rain Bomb to Climate Change. Asia-Pac J Atmos Sci (2022). https://doi.org/10.1007/s13143-022-00305-1

*Equal Contributions

Acknowledgments

A weather ensemble forecasting tool based on statistical and probabilistic methods

Ensemble weather forecasts can help to anticipate the risks and probabilities of extreme weather events. Nevertheless, weather forecasting is a complex task due to the chaotic behavior of the atmosphere [1]. This represents a major source of uncertainties in particular for the sub-seasonal lead times (from a few days to one month) [2]. To overcome those uncertainties, a large number of numerical simulations is necessary. 

In this study, we propose a weather ensemble forecasting tool based on statistical and probabilistic methods to generate ensemble weather forecasts [3]. The Analog-SWG is designed to mimic the behavior of climate variables [4] by assuming the relationship between past and future weather and using similarities in atmospheric circulation patterns [5]. We have tested the Analog-SWG to forecast European precipitation at a local scale ( i.e. station level: Berlin, Madrid, Paris and Toulouse) [3]. We assessed the performance of our forecasts against other forecasts from meteorological centers [3]. We found good performance in different regions of Europe for up to 10 days. We confirmed the importance of atmospheric circulation in driving the meteorological parameters. We also identified the influence of high and low pressure on good and bad forecasts [3].  

References

[1] Faranda, D., Messori, G., and Yiou, P.: Dynamical proxies of North Atlantic predictability and extremes. Scientific Reports (2017).

[2] Vitart, F., et al.: The Subseasonal to Seasonal (S2S) Prediction Project Database, Bulletin of the American Meteorological Society. (2017).

[3] Krouma, M., Yiou, P., Déandreis, C., and Thao, S.: Assessment of stochastic weather forecast of precipitation near European cities, based on analogs of circulation, Geosci. Model Dev. (2022).  

[4] Ailliot, P., Allard, D., Monbet, V., and Naveau, P.: Stochastic weather generators: an overview of weather type models, Journal de la Société Française de Statistique. (2015)

[5] Yiou, P. and Déandréis, C.: Stochastic ensemble climate forecast with an analogue model, Geoscientific Model Development. (2019). 

[6] Krouma, M., Silini, R., and Yiou, P.: Ensemble forecast of an index of the Madden Julian Oscillation using a stochastic weather generator based on circulation analogs, EGUsphere [preprint] (2022)

More Resources

Get to know: Meriem Krouma (Aria Technologies, Paris, France)

Ensemble weather forecast with a stochastic weather generator and analogs of the atmospheric circ...

Attributing Extreme Events to Climate Change using Observations and taking into account the Atmospheric Circulation

When extreme events are very rare, it is often difficult to prove that their probability of occurrence has changed due to climate change. Thus a new way of doing things has appeared to study the link between climate change and extreme events. This no longer attempts to compare frequencies of occurrence, but rather to understand how climate change influences the climatic parameters at the origin of extreme phenomena. This line of research seeks to establish the mechanisms that produce these extreme events. In this way, researchers can explain how global warming modifies the power, the duration or even the geographical extension of natural disasters.

This new current of research of the ESTIMR team, coordinated by Davide Faranda, is presented in the article “A climate-change attribution retrospective of some impactful weather extremes of 2021” which has just been published in the journal Weather and climate dynamics. the ESTIMR team has indeed proposed a new method for attributing extreme events to climate change without climate models, using only current and past meteorological observations.

For this, the ESTIMR team used the two-step method. First step: establish, using a map of atmospheric pressures, what were the large air masses and the high and low pressure systems at the time of the storm. Second step, determine if a similar situation had already occurred before climate change began to weigh on the atmosphere. For this, Faranda and his team used ERA 5, an European database that provides meteorological parameters for the atmosphere, land surface and sea since 1950. 

They looked in this archive for configurations similar to that of the extreme events analyzed over a period between 1950 and 1979, that is to say, when the effects of climate change were still weak, even imperceptible, and in the period 1992-2021 that is in the actual climate, affected by climate change.   The method also evaluates the role of internal variability of the climate system such as El Nino or the Atlantic Meridional overturning circulation.

The LSCE team used this method on a series of climate events that occurred in 2021. Among them, Cyclone Ida in the United States, the April cold wave in France, the tornadoes over the Po Valley in Italy, the winter storm Filomena in Spain and the Mediterranean cyclone Apollo. In most cases, they found a very clear link to climate change. However, Filomena and Apollo appear as peculiar events. Indeed, researchers have found no equivalent in historical records to the atmospheric configuration at the time of these events. "As we have not found a similar configuration, we are unable to determine the role of climate change in their occurrence", regrets Davide Faranda, in an interview for the CNRS journal. "However, this is not necesseraly a negative feature of the methodology that, on the contrary, is able to highlight unprecedented events", continue Faranda.

This method has been already applied to determine the role of climate change in enhnacing the impacts of the Corsica thunderstorm occured the 18 August 2022. The report of this study can be found here.  This method has already received the attention of the attribution community, as the journal Science dedicated a perspective article to this technique, among others. 

Reference

Faranda, D., Bourdin, S., Ginesta, M., Krouma, M., Noyelle, R., Pons, F., Yiou, P., and Messori, G.: A climate-change attribution retrospective of some impactful weather extremes of 2021, Weather Clim. Dynam., 3, 1311–1340, https://doi.org/10.5194/wcd-3-1311-2022, 2022.

Notre-Dame de Paris, the so famous Catholic cathedral standing on Ile de la Cité in Paris, was built in 1163, largely completed by 1260, then frequently modified in the following centuries until a major restoration between 1844 and 1864. All these steps of construction and modifications involved the frame, so-called “la forêt” (the forest). So, the woods used throughout the cathedral’s history are samples and memories of the forests of oaks grown in the Paris Basin since the Middle Ages. The unfortunate destruction of the cathedral on 15th April of 2019, which miraculously spared a part of the frame, made these woods accessible to the scientific community. Some scientists are particularly interested in the isotopic composition of wood as memory of past climate and as a clock to the past. On one part, the oxygen and carbon isotopes (d13C and d18O) of tree-ring cellulose will bring light to past climate. Indeed, the isotopic composition of this component is determined by the conditions surrounding the trees during their growth. The variations of d13C and d18O with time, recorded in the successive rings built by the trees year after year, allows reconstructing the evolution of some
environmental or climatic parameters such as temperature or humidity. Isotope dendroclimatology, a
rapidly expanding field of investigation, is applied to old living trees, sub-fossil woods from buildings or even fossil material to reconstruct past climate. This methodological approach will be applied to the cathedral's oak timbers that have escaped severe charring and to contemporaneous unburned woods from other buildings (Figure 1). On the other part, measuring ring by ring the residual content of 14C isotope in cellulose will make it possible to refine the 14C clock which allows to date any material containing carbon. This will be achieved by providing new portions of the global calibration curve for the continental Western Europe from the 12th to the 18th century, from uncharred "forest" of Notre-Dame.

Daux V., Hatté C., duBoisgueheneuc D., Beck L., Richardin P. The ‘forest’ of Notre dame de Paris: a path into medieval climate and time. Journal of Cultural Heritage, In press

L’anticipation des effets du changement climatique est désormais un objectif de plus en plus partagé. La révision de cette évolution repose sur deux piliers : la reconstitution des variations climatiques passées et la modélisation des variations futures, basée sur les lois physiques qui régissent le climat. La connaissance du passé permet de séparer les effets imputables à l’homme des effets naturels et de tester la capacité des modèles à décrire le climat.
Nous proposons une vision globale du changement climatique en dressant un large panorama des évolutions climatiques, allant de celles du passé (du mésolithique, environ 9 000 ans avant J.C., au début du XXIe siècle) à celles prédites dans un futur plus ou moins proche. Considérant tout particulièrement l’évolution climatique en France métropolitaine, des reconstitutions et des prédictions solidement acquises sont présentées essentiellement pour les variables climatiques à ce jour les plus étudiées : la température et la pluviométrie.

Référence : Daux V., Garcia de Cortazar-Atauri I. Le climat ses évolutions passées et futures. Chapitre 1, In : Adaptation des productions fruitières au cahngement climatique, Legave J.-M. coord., Editions quaea, Versailles, 19-38. ISBN : 978-2-7592+3251-2.

Hydroclimate variability in tropical South America is strongly regulated by the South American Summer Monsoon (SASM). However, past precipitation changes are poorly constrained due to limited observations and high-resolution paleoproxies. We found that summer precipitation and the El Nino-Southern Oscillation (ENSO) variability are well registered in tree-ring stable oxygen isotopes (δ18OTR) of Polylepis tarapacana in the Chilean and Bolivian Altiplano in the Central Andes (18–22°S, ∼4,500 m a.s.l.) with the northern forests having the strongest climate signal (Figure 1). More enriched δ18OTR values were found at the southern sites likely due to the increasing aridity toward the southwest of the Altiplano. The climate signal of P. tarapacana δ18OTR is the combined result of moisture transported from the Amazon Basin, modulated by the SASM, ENSO, and local evaporation, and emerges as a novel tree-ring climate proxy for the southern tropical Andes.

Référence : Rodriguez-Caton M., Andreu-Hayles L., Daux V., Vuille M., Varuolo-Clarke A., Oelkers R., Christie D.A., D’Arrigo R., Morales M., Rao M.P., Srur A., Vimeux F., Villalba R. Hydroclimate and ENSO Variability recorded by oxygen isotopes from tree rings in the South American Altiplano. Geophys. Res. Lett. 49, e2021GL0958

Along the coasts of northern Alaska, in a treeless tundra environment, the primary wood resource for coastal populations is driftwood, a seasonal and exogenous resource carried by the major rivers of western North America. The potential of Alaskan coastal archaeological wood for tree-ring research was first assessed in the 1940s by archaeologist and tree-ring research pioneer J. L. Giddings (Figure 1). Despite his success, the difficulties of dendrochronological studies on driftwood and the development of radiocarbon dating during the 1950s resulted in the near-abandonment of dendrochronology to precisely date archaeological sites and build long sequences using archaeological wood in Alaska. In this study, we explored the possibilities and limitations of standard ring-width dendrochronological methods for dating Alaskan coastal archaeological wood. We focus on the site of Pingusugruk, a late Thule site (15th–17th CE) located at Point Franklin, northern Alaska. The preliminary results have been obtained from the standard dendrochronological analyses of 40 timber cross-sections from two semi-subterranean houses at Pingusugruk (Figure 2). We cross-correlated individual ring-width series and built floating chronologies between houses before cross-dating them with existing regional 1000-year-long master chronologies from the Kobuk and Mackenzie rivers (available on the International Tree-Ring Databank, ITRDB). These preliminary results confirm the potential of dendrochronology for a better understanding of the Thule period on climate and cultural change. Additional work on various dendro-archaeological collections using an interdisciplinary approach (geochemical analyses of oxygen isotopes and radiocarbon dating) will help develop and expand regional tree-ring chronologies and climatic tree-ring sequences in Alaska.

Référence : Taïeb J., Alix C., Juday G.P., Jensen A. M., Daux V. Dating coastal archaeological wood from Pingusugruk (15th-17th CE), Northern Alaska. International Journal of wood culture 2, 1-28.

This Open Access volume highlights how tree ring stable isotopes have been used to address a range of environmental issues from paleoclimatology to forest management, and anthropogenic impacts on forest growth. It will further evaluate weaknesses and strengths of isotope applications in tree rings. In contrast to older tree ring studies, which predominantly applied a pure statistical approach this book will focus on physiological mechanisms that influence isotopic signals and reflect environmental impacts. Focusing on connections between physiological responses and drivers of isotope variation will also clarify why environmental impacts are not linearly reflected in isotope ratios and tree ring widths. This volume will be of interest to any researcher and educator who uses tree rings (and other organic matter proxies) to reconstruct paleoclimate as well as to understand contemporary functional processes and anthropogenic influences on native ecosystems. The use of stable isotopes in biogeochemical studies has expanded greatly in recent years, making this volume a valuable resource to a growing and vibrant community of researchers.
About the chapter: In this chapter we introduce the climate signal in stable isotope tree-ring records, with the emphasis on temperate forests. The development of the subdiscipline is recapped followed by an exploration of isotope dendroclimatic records by geography and, broadly, by isotopic species. Whilst there are still questions to be answered around signal strength and age-related effects in different environments and in different species, the proxy is now contributing to palaeoclimatology in a far greater way than in the days of the first hints of ‘isotope tree thermometers’. Due to the greater complexity seen in stable carbon isotope interpretations, we explore response groupings with example references given for each category of proxy response. Finally, we summarize the state of the art in isotope dendroclimatology and discuss possible future directions.

Référence : Gagen M., Battipaglia G., Daux V., Duffy J., Dorado-Linan I., Andreu-Hayles L. et al. Climate signals in stable isotope tree-ring records. Chap. 19, In: Stable Isotopes in tree rings, pp 537-579, Eds: R.T.W. Siegwolf, J.R. Brooks, J. Roden, M. Saurer. Tree Physiology series, Vol 8. Springer Int. Pub. ISBN: 978-3-030-92697-7.

Tree-ring width (TRW) chronologies have been widely and long-time used to reconstruct past climate variations in the Andes in South America. The use of tree-ring isotopic chronologies is still not widespread in this region although they have proved to be very efficient climate proxies. Araucaria araucana (Molina) K. Koch is a conifer tree species with some multi-century-old individuals that offers an excellent opportunity to measure stable carbon (δ13C) and oxygen (δ18O) isotopes in cellulose from long tree-ring records. Here, we explore whether current or stored carbohydrates are used for A. araucana radial growth and we assess the potential of a tree-ring isotopic record to study past climate variability. Eleven A. araucana cores from a dry and high-elevation forest at the northern border of Patagonia, Argentina (38â—¦55’S, 70â—¦44’W) were selected for stable isotopes analyses. The strong correlation between the isotopic composition of the first and second parts of the same ring, but also the strong relationships between δ13C and δ18O records with climate parameters of the current growing season such as temperature, show that tree-rings are built mostly with carbohydrates produced during the current growing season with little or no supply from storage or reserves. This finding leads to reconsidering the interpretation of the legacy effect (i.e. ecological memory effects) based on the previously described strong negative correlation between A. araucana TRW chronologies and previous growing season temperature and suggests a dependence of radial tree growth on the level of development of organs. Regarding climate sensitivity, the A. araucana tree-ring δ13C chronology is strongly related to current summer temperature (r = 0.82, p < 0.001), vapour pressure deficit (VPD; r = 0.79, p < 0.001), precipitation (r = -0.53, p < 0.001) and SPEI2 (r = - 0.73, p < 0.001) (Figure 1). These strong relationships support the use of δ13C of A. araucana tree-ring cellulose to reconstruct past temperature variations at regional scale in relation with large-atmospheric drivers of climate variability such as the Southern Annular Mode. The A. araucana tree-ring δ18O chronology is also correlated with temperature (r = 0.42, p < 0.01) and VPD (r = 0.45, p < 0.01) of the winter preceding the growing season. This suggests that trees are using water from precipitation infiltrated in the soil during the previous recharge period (autumn-winter). The weak correlations of δ18O with current summer atmospheric conditions and the decoupling between δ18O and δ13C, may be due to a high rate of oxygen exchange between sugars and xylem water (Pex) during cellulose synthesis, which dampens evaporative isotopic fractionation.

Référence : Penchenat T., Daux V., Mundo I ., Pierre M., Stievenard M., Srur A., Andreu-Hayles L., Villalba R.
Dendrochronologia 74, 2022 125979.

Mardi 27, mercredi 28 et jeudi 29 septembre 2022, Camille Asselin, Edouard Régnier et Jérémy Jacob ont été accueillis par la Division Curage du Service Technique de l'Eau et de l'Assainissement (Direction de l'Eau et de la Propreté) de la Ville de Paris pour visiter les bassins de dessablement du secteur Est du réseau d'assainissement. Nous avons accompagné les équipes d'égoutiers qui procédaient aux relevés des bassins. Il s'agit d'opérations qui visent à évaluer le taux de remplissage des bassins de décantation pour prévoir les opérations de curage quand ceux-ci sont remplis.

Dans le cadre de la thèse de Camille Asselin et du projet ANR EGOUT porté par Jérémy Jacob, les objectifs étaient multiples :

• Mieux comprendre le fonctionnement des bassins de dessablement : leur remplissage, le fonctionnement des bypass qui sont activés lors des opérations de curage pour dévier le flux d'eau et mettre à sec le sédiment, le fonctionnement des collecteurs auto-curants, les modalités d'accès aux ouvrages, etc...
• Evaluer les possibilités de carottage des sédiments. D'un point de vue technique et logistique (accès, mise en place des équipements...) mais aussi au regard de la dynamique de remplissage. A ce titre, les relevés du niveau de sable par les égoutiers constituent des données précieuses.
• Nouer le contact avec les égoutiers, les informer sur le projet EGOUT, être à l'écoute des informations qu'ils peuvent apporter au projet, évaluer ce que nos travaux peuvent leur apporter en retour.

A l'arrivée sur le site de Delesseux, nous avons été entièrement équipés par les services de la Ville de Paris. Bottes, combinaison, masque, autosauveur, lunettes, casque, harnais, détecteur 4 gaz. Nous bénéficions tous les trois d'une formation CATEC.

Nous avons visité 8 bassins de décantation : Vincennes, Allard, Soult, Wattignies, Saint Bernard, Faidherbe, Belleville et Ménilmontant. L'ensemble des objectifs a été atteint.

Nous avons pu apprécier le professionnalisme des équipes, leur connaissance du milieu et la maîtrise des risques par le respect des consignes de sécurité. Et, bien plus encore, nous avons apprécié l'accueil, les discussions très pointues sur le métier et sur le fonctionnement des égouts.

Site web du projet EGOUT : https://egout.cnrs.fr/

L'objectif de la Journée Thématique était de sensibiliser la communauté de l'archéométrie et de la conservation aux sens. Il s'agissait à la fois de présenter quelques exemples de travaux visant à reconstruire les ambiances sensorielles passées et de questionner l'utilisation des sens dans la caractérisation des objets d'étude en archéométrie. Aussi, la journée s'est déroulée en deux temps. Le matin était dédié à des exposés scientifiques, organisés selon les cinq sens, qui ont présenté des travaux originaux sur les ambiances sensorielles de diverses époques, reconstruites par les techniques de l'archéométrie. L'après-midi était dédiée à des ateliers animés par des experts des sens durant lesquels les participants ont discuté de l'utilisation des sens dans la caractérisation de leurs objets d'étude, de manière à parvenir à des principes et des clés communes de caractérisation. Le déjeuner était en phase avec la thématique de la journée. Anaïs Tondeur, artiste plasticienne œuvrant à la frontière des Sciences et de l'Art, a accompagné cette journée.

En octobre 2021, des chercheures et chercheurs du Laboratoire des Sciences du Climat et de l’Environnement (LSCE, Gif-sur-Yvette), de l’Institut des Sciences de l’Évolution de Montpellier (ISEM) et de l’Université Fédérale du Ceara (Brésil) ont parcouru l’état du Piauí pour prélever des carottes de sédiments lacustres et des échantillons de surface. L’objectif est de reconstruire l’évolution des conditions environnementales (climat, végétation) associées aux premières occupations humaines en Amérique du Sud.

Au retour au laboratoire, les carottes de sédiments ont été datées et analysées avec différents traceurs (pollen, analyses géochimiques, etc…).

Cette mission s’inscrit dans le projet ANR “SESAME” (Human paleoecology, Social and cultural Evolutions among first Settlements in Southern AMErica), porté par Eric Boëda (Archéologies et Sciences de l’Antiquité, Paris).

Au retour de la mission, les prises de vue ont été montées en vidéo par Edouard Régnier (LSCE) sous la forme d'un "roadtrip".

Site web du projet : https://sesame.hypotheses.org

Une collaboration menée par le LSCE (CEA-CNRS-UVSQ) applique pour la première fois une technique d'apprentissage automatique utilisée en linguistique à des bulletins météorologiques quotidiens couvrant 70 années. La voie est désormais ouverte à des analyses climatologiques hors d'atteinte pour les experts humains !  

Comment « lire » l'évolution du climat dans une masse de bulletins météo quotidiens ?

Voulant relever ce défi, les chercheurs en sciences de l'atmosphère utilisent des algorithmes (Empirical Orthogonal Functions ou k-means) pour réduire la complexité des champs de pressions. Ils obtiennent ainsi un petit nombre d'éléments de base qui peuvent cependant se révéler difficiles à interpréter ou bien, qui combinent des objets intriqués et donc impossibles à étudier séparément, comme les cyclones et les anticyclones.  

Des climatologues du LSCE ont mis en œuvre l'algorithme de machine learning LDA (Latent Dirichlet Allocation) qui, lui, conduit à isoler des structures à grande échelle (cyclones et anticyclones) qu'ils peuvent analyser individuellement. Un atout précieux pour étudier des événements comme les vague de froid ou les tempêtes extratropicales !

La LDA est capable d'analyser des milliers de documents en peu de temps et de mettre en exergue des éléments importants, des récurrences et des anomalies. Il est en particulier utilisé en linguistique pour étudier le langage naturel : son analyse des mots révèle le ou les thèmes d'un document, chaque thème étant identifié par un vocabulaire spécifique ou plus exactement, par une distribution statistique particulière de la fréquence des mots.

Dans l'usage que font les climatologues de la LDA, le document devient une carte météo quotidienne et le mot, un pixel de la carte. Le thème avec son corpus de mots peut devenir un cyclone ou un anticyclone, et plus généralement, un « motif ».

L'intelligence artificielle cherche des corrélations à la fois entre différents lieux sur une même carte, et entre les cartes successives au cours du temps. En quelque sorte, elle « remarque » que tel lieu est souvent corrélé avec tel autre lieu, de façon récurrente sur l'ensemble de la base de données, et cet ensemble de lieux corrélés constitue un « motif ».

L'algorithme effectue des analyses statistiques à deux niveaux distincts :

• à l'échelle du mot ou du pixel de la carte, la LDA définit un thème ou « motif », en attribuant un certain poids à chaque pixel, et définit ainsi la forme et la position du « motif » ;
• la LDA décompose une carte météo quotidienne sur l'ensemble de ces « motifs », qui se voient attribuer, chacun, un certain poids.

Concrètement, les données de base sont les cartes journalières de pression au niveau de la mer entre 1948 et 2018 sur l'Atlantique Nord. La LDA identifie 28 « motifs » définis dans l'espace (parmi lesquels, l'anticyclone des Açores, la dépression de Gênes ou l'anticyclone de Scandinavie) qui permettent de décrire toutes les cartes.

Ces « motifs » et les analyses statistiques qui leur sont associées permettent aux chercheurs d'étudier aussi bien des phénomènes météorologiques tels que des évènements extrêmes, que des tendances climatiques de plus long terme et éventuellement de comprendre leurs mécanismes pour mieux les prévoir à terme.

====================================================

The preprint of the study is available as:
Lucas Fery, Berengere Dubrulle, Berengere Podvin, Flavio Pons, Davide Faranda. Learning a weather dictionary of atmospheric patterns using Latent Dirichlet Allocation. 2021. ⟨hal-03258523)
https://hal-enpc.archives-ouvertes.fr/X-DEP-MECA/hal-03258523v1

Contact

Davide Faranda, LSCE-IPSL • davide.faranda@lsce.ipsl.fr