Modelling the location and spatial pattern of a crop boom. A case study from Laos

International audienceCrop booms are phenomena of global environmental change that keep on occurring around the globe and frequently exploit or degrade the local socio-ecological resources (resulting in e.g. loss of biodiversity, soil erosion, indebtedness). While causal mechanisms were identified and summarized in several frameworks, the causal effects of the identified factors remained largely unknown. In this study, we set up a new application of a spatial land system model to examine the causes for the clustered spatial pattern of the maize boom between 2000 and 2016 in Sayaboury Province, Laos. The factors tested included market access (travel time to trader companies), land productivity and total net revenue (proxy for profitability), spatial differences in farm gate price of maize, slope, and soil types. While crop booms are commonly associated with high commodity prices and improved market accessibility, our simulation results suggested that the combination of the geographic and economic factors we tested partially contribute to explain the location and spatial extent of the maize boom, but a full explanation has not been found. Interestingly though, temporal dynamics, such as increases in land productivity and profitability had the largest effect on model performance regarding the size of the maize boom area (experiment 2). Productivity and profitability increased thanks to political economic support for the introduction of a series of techniques (i.e. hybrid maize cultivars, herbicides, mechanical tillage and sowing) that made maize mono-cropping disproportionally competitive over other land management. We outline implications of our findings for governance bodies that are faced with crop booms

Self-confinement of wildfire smoke within long-lived vortices rising in the stratosphere

International audienceThe 2019-2020 Australian wildfires have produced a striking phenomenon in the stratosphere: an ascending disc of smoke contained within an anticyclonic vortex that persisted 3 months, travelled 66000 km and rose from 16 to 36 km. We analyse this exceptional structures and several of its companions with CALIOP data and the ERA5 reanalysis demonstrating its analogy with ellipsoidal free solutions of the quasi-geostrophic equation. A main difference is that here the vortex is maintained and rises due to the heating by the absorbing smoke. In the ERA5, where the wildfire smoke is missing, this forcing is exerted by the assimilation of spaceborne temperature profiles that produces an assimilation increment compensating the fast decay of the free solution. Based on these observations, we discuss the theoretical basis for the self-organisation and the stability of the smoke vortex. We show evidences that similar events, albeit of lesser magnitude, have already occurred, in particular during the Australian 2009 wildfire and the Canadian 2017 widlfire

Self-confinement of wildfire smoke within long-lived vortices rising in the stratosphere

International audienceThe 2019-2020 Australian wildfires have produced a striking phenomenon in the stratosphere: an ascending disc of smoke contained within an anticyclonic vortex that persisted 3 months, travelled 66000 km and rose from 16 to 36 km. We analyse this exceptional structures and several of its companions with CALIOP data and the ERA5 reanalysis demonstrating its analogy with ellipsoidal free solutions of the quasi-geostrophic equation. A main difference is that here the vortex is maintained and rises due to the heating by the absorbing smoke. In the ERA5, where the wildfire smoke is missing, this forcing is exerted by the assimilation of spaceborne temperature profiles that produces an assimilation increment compensating the fast decay of the free solution. Based on these observations, we discuss the theoretical basis for the self-organisation and the stability of the smoke vortex. We show evidences that similar events, albeit of lesser magnitude, have already occurred, in particular during the Australian 2009 wildfire and the Canadian 2017 widlfire

Self-confinement of wildfire smoke within long-lived vortices rising in the stratosphere

International audienceThe 2019-2020 Australian wildfires have produced a striking phenomenon in the stratosphere: an ascending disc of smoke contained within an anticyclonic vortex that persisted 3 months, travelled 66000 km and rose from 16 to 36 km. We analyse this exceptional structures and several of its companions with CALIOP data and the ERA5 reanalysis demonstrating its analogy with ellipsoidal free solutions of the quasi-geostrophic equation. A main difference is that here the vortex is maintained and rises due to the heating by the absorbing smoke. In the ERA5, where the wildfire smoke is missing, this forcing is exerted by the assimilation of spaceborne temperature profiles that produces an assimilation increment compensating the fast decay of the free solution. Based on these observations, we discuss the theoretical basis for the self-organisation and the stability of the smoke vortex. We show evidences that similar events, albeit of lesser magnitude, have already occurred, in particular during the Australian 2009 wildfire and the Canadian 2017 widlfire

Seasonal oxygen isotope variations in freshwater bivalve shells as recorders of Amazonian rivers hydrogeochemistry

Freshwater bivalve shell oxygen isotope values (δ 18 OS) may act as a recorder of river δ 18 O variations that can then be interpreted in terms of hydrology (e.g. precipitation-evaporation balance, precipitation and river discharge patterns). We investigated the potential of this proxy measured across the hinge of South American unionid shells: Anodontites elongatus collected in Peru and A. trapesialis in Brazil. The isotopic signatures were reproducible between individuals of the same species. A. trapesialis clearly showed a strong δ 18 OS cyclicity in accordance with its growth patterns while A. elongatus presented less clear δ 18 OS with lower amplitude. We confirm that the deposition of successive growth lines and increments is annual, with growth line corresponding to the wet season. Also, we suggest that low amplitude of δ 18 OS in the A. elongatus shells indicates a habitat close to the river while large amplitude of δ 18 O cycles observed in A. trapesialis shells would reflect a floodplain lake habitat, seasonally disconnected from the river and thus subjected to higher seasonal fluctuations in water δ 18 O. Considering these promising first results, future studies could be directed towards the use of fossil shells to reconstruct the past and present hydrological and geochemical conditions of the Amazon

Guide méthodologique pour la planification territoriale concertée

Ce guide méthodologique pour la planification territoriale concertée a été élaboré par le CIRAD et ses partenaires de recherche et d'enseignement supérieur (IRSTEA, INAT, INRGREF) pour la Direction Générale de l'Aménagement et de la Conservation des Terres Agricoles (DG/ACTA) du Ministère de l'Agriculture et des Ressources Hydrauliques et de la Pêche (MARHP) tunisien. Il a été écrit à l'intention des agents de développement territorial travaillant directement avec les communautés locales. Il s'adresse plus particulièrement aux Chargés d'Appui au Développement Rural (CADR) du MARHP qui interviendront dans le Programme PACTE (Programme d'Adaptation au changement Climatique des Territoires vulnérables de Tunisie, 2018-2024), mais également de manière plus large à toutes les personnes (par exemple : agents de terrain, membres des communautés, consultants, vulgarisateurs) souhaitant s'investir dans des actions de planification participative du développement à l'échelle du territoire. Ce guide se veut opérationnel et facilement accessible. Il est fait pour accompagner l'agent sur le terrain, et aménage des espaces pour que le lecteur puisse annoter le document et l'adapter à ses besoins spécifiques. On y trouvera des éléments de cadrage sur les conditions de mise en place d'une démarche de planification territoriale concertée et, notamment, sur les enjeux de la participation et de l'engagement d'acteurs aux identités multiples dans un dispositif multi-niveaux de production et de partage de connaissances, de débat citoyen, de planification et mise en oeuvre d'actions et de suivi-évaluation. Le guide détaille également les étapes clés de la démarche de planification concertée ainsi que la structure et le fonctionnement du dispositif « plateforme de concertation territoriale ». Cette méthode a été conçue pour pouvoir intervenir dans des territoires vulnérables en Tunisie afin d'y mener des actions de planification participative pour une utilisation durable des ressources naturelles en vue du développement durable des communautés et de leurs territoires. Il est le produit de différentes expériences pratiques menées par les UMR G-eau et TETIS (CIRAD et IRSTEA) et leurs partenaires de recherche et de développement. Cette approche n'est pas la seule existante et s'appuie fortement sur différents cadres méthodologiques dont les références sont données dans le texte. Elle est le fruit d'une confrontation des auteurs à différentes questions et problématiques de terrain. Elle a été conduite dans des cadres divers de recherche, de recherche-action et de développement, dans les pays du Sud comme du Nord