Éditeur(s) : IEEE
Résumé : It is now well understood that data on soil moisture and sea surface salinity (SSS) are required to improve meteorological and climate predictions. These two quantities are not yet available globally or with adequate temporal or spatial sampling. It is recognized that a spaceborne L-band radiometer with a suitable antenna is the most promising way of fulfilling this gap. With these scientific objectives and technical solution at the heart of a proposed mission concept the European Space Agency (ESA) selected the Soil Moisture and Ocean Salinity (SMOS) mission as its second Earth Explorer Opportunity Mission. The development of the SMOS mission was led by ESA in collaboration with the Centre National d'Etudes Spatiales (CNES) in France and the Centro para el Desarrollo Tecnologico Industrial (CDTI) in Spain. SMOS carries a single payload, an L-Band 2-D interferometric radiometer operating in the 1400-1427-MHz protected band [1]. The instrument receives the radiation emitted from Earth's surface, which can then be related to the moisture content in the first few centimeters of soil over land, and to salinity in the surface waters of the oceans. SMOS will achieve an unprecedented maximum spatial resolution of 50 km at L-band over land (43 km on average over the field of view), providing multiangular dual polarized (or fully polarized) brightness temperatures over the globe. SMOS has a revisit time of less than 3 days so as to retrieve soil moisture and ocean salinity data, meeting the mission's science objectives. The caveat in relation to its sampling requirements is that SMOS will have a somewhat reduced sensitivity when compared to conventional radiometers. The SMOS satellite was launched successfully on November 2, 2009.
Proceedings of the IEEE (0018-9219) (IEEE), 2010-05 , Vol. 98 , N. 5 , P. 666-687

Droits : 2010 IEEE – All Rights Reserved
http://archimer.ifremer.fr/doc/00004/11483/8065.pdf
DOI:10.1109/JPROC.2010.2043032
http://archimer.ifremer.fr/doc/00004/11483/

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé :  
Modeling soil water availability for tropical trees is a prerequisite to predicting the future impact of climate change on tropical forests. In this paper we develop a discrete-time deterministic water balance model adapted to tropical rainforest climates, and we validate it on a large dataset that includes micrometeorological and soil parameters along a topographic gradient in a lowland forest of French Guiana. The model computes daily water fluxes (rainfall interception, drainage, tree transpiration and soil plus understorey evapotranspiration) and soil water content using three input variables: daily precipitation, potential evapotranspiration and solar radiation. A novel statistical approach is employed that uses Time Domain Reflectometer (TDR) soil moisture data to estimate water content at permanent wilting point and at field capacity, and root distribution. Inaccuracy of the TDR probes and other sources of uncertainty are taken into account by model calibration through a Bayesian framework. Model daily output includes relative extractable water, REW, i.e. the daily available water standardized by potential available water. The model succeeds in capturing temporal variations in REW regardless of topographic context. The low Root Mean Square Error of Predictions suggests that the model captures the most important drivers of soil water dynamics, i.e. water refilling and root water extraction. Our model thus provides a useful tool to explore the response of tropical forests to climate scenarios of changing rainfall regime and intensity.
ISSN: 0168-1923

hal-01032181
https://hal.archives-ouvertes.fr/hal-01032181
DOI : 10.1016/j.agrformet.2011.04.012

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Seasonal climate forecasts mainly rely on the atmospheric sensitivity to its lower boundary conditions and on their own predictability. Besides sea surface temperature (SST), soil moisture (SM) may be an additional source of climate predictability particularly during boreal summer in the mid-latitudes. In this work, we investigate the role of SM initial conditions on near-surface climate predictability during ten boreal summer seasons using three complementary ensembles of AMIP-type simulations performed with the Arpège-Climat atmospheric general circulation model. First we have conducted an assessment of the SM predictability itself through a comparison of simple empirical SM models with Arpège-Climat. The statistical and dynamical models reveal similar SM prediction skill patterns but the Arpège-Climat reaches higher scores suggesting that it is at least suitable to explore the influence of SM initialization on atmospheric predictability. Then we evaluate the relationships between SM predictability and some near surface atmospheric predictability. While SM initialization obviously improves the predictability of land surface evaporation, it has no systematic influence on the precipitation and near surface temperature skills. Nevertheless, the summer hindcast skill is clearly improved during specific years and over certain regions (mainly north America and eastern Europe in the Arpège-Climat model), when and where the SM forcing is sufficiently widespread and strong. In this case, a significant impact is also found on the occurrence of heat waves and heavy rains, whose predictability at the seasonal timescale is a crucial challenge for years to come.
ISSN: 0930-7575

meteo-00346948
https://hal-meteofrance.archives-ouvertes.fr/meteo-00346948
DOI : 10.1007/s00382-008-0375-9

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : Coarse woody debris (CWD, dead wood sections a parts per thousand yen10 cm diameter) represents a large store of carbon in tropical forests; however, estimates of the flux of carbon from CWD in these forests remain poorly constrained. The objective of this study was to resolve the dry/wet season response of respiration in CWD (R (cwd)), and investigate the importance of biotic and abiotic factors for predicting the seasonal change of R (cwd) at the ecosystem level. This study presents a 4-month time series of R (cwd) measurements conducted on 42 dead trees (26 species) at the Paracou Research Station in French Guiana. R (cwd) measurements were repeated 13 times on each CWD sample from July to November 2011, spanning the transition from wet to dry season, and then from dry season to the following wet season. Seasonal drought caused monthly R (cwd) to drop by 20.5 +/- A 5.1% over the wet-dry transition. Changes in woody tissue moisture content explained 41.9% of the measured seasonal variability in R (cwd), but 60% of the seasonal variability in mean forest R (cwd) rates could be modelled using surface soil water content. We estimate that R (cwd) is approximately 5% of annual ecosystem respiration (R (eco)) and that seasonal variations in R (cwd) contribute appreciably to seasonal variations of R (eco), and should be included in functional models simulating the response of tropical rainforest ecosystems to current and future climate.
ISSN: 1432-9840

hal-01032431
https://hal.archives-ouvertes.fr/hal-01032431
DOI : 10.1007/s10021-013-9684-x

Éditeur(s) : HAL CCSD
Résumé : Diffusion du document : INRA Documentation de Centre, Domaine de Duclos, 97170 Petitt-Bourg (Guadeloupe, France) Diplôme : DEA
il s'agit d'un type de produit dont les métadonnées ne correspondent pas aux métadonnées attendues dans les autres types de produit : DISSERTATION
Because soil respiration representes 80% of ecosystem respiration, it is a major flux between biosphere and atmosphere. We examined the effects of root and litter exclusion on soil CO! efflux (Rsu1) using trenching and litter exclusion in a tropical plantation constituted of trees seedlings installed in 16 mono-specific stands 20 years ago near Kourou, French Guyana. Soil CO2 efflux was measured using an infra red gas analyser (PP System,EGM4 ) at 16 randomly distributed plot in each treatment: control, root exclusion, litter exclusion and both root and litter exclusion. in the plantation. We measured R'1l1during four periods, and we have collected soil samples, litter biomass and measured moisture at 5 cm depth in the soil. Soil CO, efflux varied significantly among species from 2,8±O,7f1mo l. m''. s' (mean ± standard deviation) to 7.4± 1.7fLmol. n'-' . s ' for Qualea rosea and Vochys ia tomentosa, respectively. 1'0 significant correlation was found between RSIlI variability and soil moisture, which is mostly related to soil texture in the experimental site. Soil CO2 efflux was significantly reduced in litter exclusion treatment and root exclusion plots (6 months litter and/or root exclusion) during ail measurements period and for ail species, compared to control plots. The reduction of soil CO, efflux was higher in plot without root than in plot without litter of control plot (42% and 25%, respectively). There was an import ant specific diversity in these reductions . We estimated the contribution of roof respiration (Rr) to total Rso1 by calculating the difference between Rso1 control and Rsn l root exclusion plot corrected for the decomposition of root that were killed following t re n e h in ~. Thus the heterotrophic component of soil carbon efflux accounts for 46% of total carbon efflux (1,9f1 mol. rn" . s•') while root respiration accounts for 54% of soil carbon release (2,3 ~t mo l. m-2 S-I) . Because there was a negative and significant correlation between microbial respiration (Rrn) and C/N of mature leaves it seemed to be possible to predict Rm if we known the mature leaves quality. In addition a good estimate theorical R ~, values from R~, measured in different treatments.
La respiration du sol en représentant une part de 80% de la respiration de l'écosystème apparaît être un flux majeur entre la biosphère et l'atmosphère. Nous avons étudié les effets de l'exclusion racinaire et de la litière sur le flux de CO, du sol (R ~ , ) en utilisant la méthode de " Trench-plots" et de suppression de litière dans une plantation d'arbres tropicaux. Ces arbres, âgés de 20 ans ont été plantés sur un sol uniforme, près de Kourou en Guyane française, en 16 placeaux mono-spécifiques. Pour mesurer les flux de CO2 provenant du sol, nous avons utilisé un analyseur différentiel de gaz infrarouge portable muni d'une chambre. Les mesures ont été faites sur 4 traitements différents tels que : le contrôle, l'exclusion racinaire, l'exclusion de litière et l'exclusion de litière et de racine et ce, répétés sur chacune des 16 placettes mono-spécifiques. Cette étude comporte 4 campagnes de mesures. Nous avons également effectué des prélèvements de sol de litière et nous avons fait des mesures d’humidité de sol à une profondeur de 5 cm. Les flux de C01 du sol varient fortement entre espèces de 2.8±O.7 ~t m o 1. m-2. sol à 7 A± 1. 7 ~t m o l. m•1 sol pour Qua/ev rosea ct Vochysto tomentasa, respectivement. Il n'existe pas de corrélation significative entre les variations de Rw l ct celles de l'humidité du sol (indication sur la texture du sol de la plantation ). Nous avons observé que Rso1 était significativement plus faible dans les placeaux sans racines et/ou sans litière (6 mois après la mise en place de l'expérimentation) pour toutes les campagnes de mesures et pour toutes les espèces que dans les placeaux contrôlés. Cette réduction du flux de CO2 du sol est plus forte dans les "trench-plots " que dans les traitement s d'exclusion de litière avec 42 et 25% respectivement. Un effet "traitement " et un effet "espèce" important expliquent 3 1"/.. ct 13% de la variabilité totale de R~. Nous avons cherché à connaître la contribution des racines dans les valeurs de R""I. en comparant le flux de CO2 provenant du sol sur des "trench -plot s'' au flux de COl provenant du sol dans les placeaux contrôlés . Cette estimation a été corrigée pour prendre en compte la décomposition des racines tuées par les tranchées. Ainsi, la composante appartenant aux micro -organismes représente 46% du flux total de carbone provenant du sol (1.9Jlmo l. m-2 S•I ) alors que la respiration des racines représente 54% du dégagement de carbone (2 ,3~lmol. m ol . 5-La respiration des micro-organismes pourrait être estimée en mesurant le C/N des feuilles matures puisqu'il existe une corrélation significative et négative entre les deux. Enfin les résultats obtenus sur les différents traitements permettent d'obtenir une bonne estimation de la respiration du sol avec un RSIlI théorique corrélé à 66% avec les valeurs réelles mesurées.
https://hal.archives-ouvertes.fr/hal-01189239

hal-01189239
https://hal.archives-ouvertes.fr/hal-01189239
PRODINRA : 18212

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : Climate models predict a range of changes in tropical forest regions, including increased average temperatures, decreased total precipitation, reduced soil moisture and alterations in seasonal climate variations. These changes are directly related to the increase in anthropogenic greenhouse gas concentrations, primarily CO2. Assessing seasonal forest growth responses to climate is of utmost importance because woody tissues, produced by photosynthesis from atmospheric CO2, water and light, constitute the main component of carbon sequestration in the forest ecosystem. In this paper, we combine intra-annual tree growth measurements from published tree growth data and the corresponding monthly climate data for 25 pan-tropical forest sites. This meta-analysis is designed to find the shared climate drivers of tree growth and their relative importance across pan-tropical forests in order to improve carbon uptake models in a global change context. Tree growth reveals significant intra-annual seasonality at seasonally dry sites or in wet tropical forests. Of the overall variation in tree growth, 28.7% was explained by the site effect, i.e. the tree growth average per site. The best predictive model included four climate variables: precipitation, solar radiation (estimated with extrasolar radiation reaching the atmosphere), temperature amplitude and relative soil water content. This model explained more than 50% of the tree growth variations across tropical forests. Precipitation and solar radiation are the main seasonal drivers of tree growth, causing 19.8% and 16.3% of the tree growth variations. Both have a significant positive association with tree growth. These findings suggest that forest productivity due to tropical tree growth will be reduced in the future if climate extremes, such as droughts, become more frequent.
ISSN: 1932-6203

hal-01268529
https://hal.archives-ouvertes.fr/hal-01268529
https://hal.archives-ouvertes.fr/hal-01268529/document
https://hal.archives-ouvertes.fr/hal-01268529/file/journal.pone.0092337.PDF
DOI : 10.1371/journal.pone.0092337