Résumé
Abstract. This paper examines the ability of optical reflectance data assimilation to improve snow depth and snow water equivalent simulations from a chain of models with the SAFRAN meteorological model driving the detailed multilayer snowpack model Crocus now including a two-stream radiative transfer model for snow, TARTES. The direct use of reflectance data, allowed by TARTES, instead of higher level snow products, mitigates uncertainties due to commonly used retrieval algorithms.Data assimilation is performed with an ensemble-based method, the Sequential Importance Resampling Particle filter, to represent simulation uncertainties. In snowpack modeling, uncertainties of simulations are primarily assigned to meteorological forcings. Here, a method of stochastic perturbation based on an autoregressive model is implemented to explicitly simulate the consequences of these uncertainties on the snowpack estimates.Through twin experiments, the assimilation of synthetic spectral reflectances matching the MODerate resolution Imaging Spectroradiometer (MODIS) spectral bands is examined over five seasons at the Col du Lautaret, located in the French Alps. Overall, the assimilation of MODIS-like data reduces by 45% the root mean square errors (RMSE) on snow depth and snow water equivalent. At this study site, the lack of MODIS data on cloudy days does not affect the assimilation performance significantly. The combined assimilation of MODIS-like reflectances and a few snow depth measurements throughout the 2010/2011 season further reduces RMSEs by roughly 70%. This work suggests that the assimilation of optical reflectances has the potential to become an essential component of spatialized snowpack simulation and forecast systems. The assimilation of real MODIS data will be investigated in future works.
Auteurs, date et publication :
Auteurs Luc Charrois , Emmanuel Cosme , Marie Dumont , Matthieu Lafaysse , Samuel Morin , Quentin Libois , Ghislain Picard
Publication : The Cryosphere
Date : 2016
Volume : 10
Issue : 3
Pages : 1021-1038
Catégorie(s)
#CNRS #Lautaret #UGAAuteurs, date et publication :
Auteurs Jean-Pierre Dedieu , Bradley Carlson , Sylvain Bigot , Pascal Sirguey , Vincent Vionnet , Philippe Choler
Publication : Remote Sensing
Date : 2016
Volume : 8
Issue : 6
Pages : 481
Catégorie(s)
#CNRS #Lautaret #UGAAuteurs, date et publication :
Auteurs Cécile H. Albert , Francesco de Bello , Isabelle Boulangeat , Gilles Pellet , Sandra Lavorel , Wilfried Thuiller
Publication : Oikos
Date : 2025
Volume : 121
Issue : 1
Pages : 116-126
Catégorie(s)
#CNRS #Lautaret #UGAAuteurs, date et publication :
Auteurs Timothy E Higham , Tony Gamble , Anthony P Russell
Publication : Biological Journal of the Linnean Society
Date : 2025
Volume : 120
Issue : 3
Pages : 503-517
Catégorie(s)
#CNRS #FORET NouraguesRésumé
The regular monitoring of evapotranspiration from satellites has been limited because of discontinuous temporal coverage, resulting in snapshots at a particular point in space and time. We developed a temporal upscaling scheme using satellite-derived instantaneous estimates of evapotranspiration to produce a daily-sum evapotranspiration averaged over an 8-day interval. We tested this scheme against measured evapotranspiration data from 34 eddy covariance flux towers covering seven plant functional types from boreal to tropical climatic zones. We found that the ratio of a half-hourly-sum of potential solar radiation (extraterrestrial solar irradiance on a plane parallel to the Earth’s surface) between 10:00 hh and 14:00 hh to a daily-sum of potential solar radiation provides a robust scaling factor to convert a half-hourly measured evapotranspiration to an estimate of a daily-sum; the estimated and measured daily sum evapotranspiration showed strong linear relation (r2 = 0.92) and small bias (−2.7%). By comparison, assuming a constant evaporative fraction (the ratio of evapotranspiration to available energy) during the daytime, although commonly used for temporal upscaling, caused 13% underestimation of evapotranspiration on an annual scale. The proposed temporal upscaling scheme requires only latitude, longitude and time as input. Thus it will be useful for developing continuous evapotranspiration estimates in space and time, which will improve continuous monitoring of hydrological cycle from local to global scales.
Auteurs, date et publication :
Auteurs Youngryel Ryu
Publication : Agricultural and Forest Meteorology
Date : 2025
Pages : 11
Catégorie(s)
#CNRS #FORET PuechabonAuteurs, date et publication :
Auteurs Jérémy Lemaire , Olivier Marquis
Date : 2025
Catégorie(s)
#CNRS #FORET NouraguesAuteurs, date et publication :
Auteurs Olivier Marquis , Nicolas Mathevon , Thierry Aubin , Philippe Gaucher , Jérémy Lemaire
Publication : Herpetology Notes
Date : 2025
Volume : 13
Pages : 513-516
Catégorie(s)
#⛔ No DOI found #CNRS #FORET NouraguesRésumé
We combined imagery from multiple sources (MODIS, Landsat-5, 7, 8) with land cover data to test for long-term (1984–2015) greening or browning trends of vegetation in a temperate alpine area, the Ecrins National Park, in the context of recent climate change and domestic grazing practices. We showed that over half (56%) of the Ecrins National Park displayed significant increases in peak normalized difference vegetation index (NDVImax) over the last 16 years (2000–2015). Importantly, the highest proportional increases in NDVImax occurred in rocky habitats at high elevations (> 2500 m a.s.l.). While spatial agreement in the direction of change in NDVImax as detected by MODIS and Landsat was high (76% overlap), correlations between log-response ratio values were of moderate strength (approx. 0.3). In the context of above treeline habitats, we found that proportional increases in NDVImax were higher between 1984 and 2000 than between 2000 and 2015, suggesting a slowing of greening dynamics during the recent decade. The timing of accelerated greening prior to 2000 coincided with a pronounced increase in the amount of snow-free growing degree-days that occurred during the 1980s and 1990s. In the case of grasslands and low-shrub habitats, we did not find evidence for a negative effect of grazing on greening trends, possibly due to the low grazing intensity typically found in the study area. We propose that the emergence of a longer and warmer growing season enabled high-elevation plant communities to produce more biomass, and also allowed for plant colonization of habitats previously characterized by long-lasting snow cover. Increasing plant productivity in an alpine context has potential implications for biodiversity trajectories and for ecosystem services in mountain landscapes. The presented evidence for long-term greening trends in a representative region of the European Alps provides the basis for further research on mechanisms of greening in alpine landscapes.
Auteurs, date et publication :
Auteurs Bradley Z Carlson , Monica C Corona , Cédric Dentant , Richard Bonet , Wilfried Thuiller , Philippe Choler
Publication : Environmental Research Letters
Date : 2017
Volume : 12
Issue : 11
Pages : 114006
Catégorie(s)
#CNRS #Lautaret #UGARésumé
Animals constantly need to evaluate available external and internal information to make appropriate decisions. Identifying, assessing, and acting on relevant cues in contexts such as mate choice, intra-sexual competition, and parental care is particularly important for optimizing individual reproductive success. Several factors can influence decision-making, such as external environmental cues and the animal’s own internal state, yet, we have limited knowledge on how animals integrate available information. Here, we used an entire island population (57 males, 53 females, and 1,109 tadpoles) of the neotropical brilliant-thighed poison frog Allobates femoralis to investigate how 2 factors (olfactory cues and personality traits) influence the ability of males to find and use new resources for tadpole deposition. We experimentally manipulated the location of tadpole deposition sites and their associated olfactory cues, and repeatedly measured exploration and boldness in adult males. We further reconstructed tadpole deposition choices via inferred parent–offspring relationships of adult frogs and tadpoles deposited in our experimental pools using molecular parentage analysis. We found that the discovery and use of new rearing sites were heavily influenced by olfactory cues; however, we did not find an effect of the measured behavioral traits on resource discovery and use. We conclude that in highly dynamic environments such as tropical rainforests, reliable external cues likely take priority over personality traits, helping individuals to discover and make use of reproductive resources.
Auteurs, date et publication :
Auteurs Mélissa Peignier , Max Ringler , Eva Ringler , Vedrana Šlipogor
Publication : Current Zoology
Date : 2023
Pages : zoad042
Catégorie(s)
#CNRS #FORET NouraguesRésumé
Soil fauna is a key control of the decomposition rate of leaf litter, yet its interactions with litter quality and the soil environment remain elusive. We conducted a litter decomposition experiment across different topographic levels within the landscape replicated in two rainforest sites providing natural gradients in soil fertility to test the hypothesis that low nutrient availability in litter and soil increases the strength of fauna control over litter decomposition. We crossed these data with a large dataset of 44 variables characterizing the biotic and abiotic microenvironment of each sampling point and found that microbe-driven carbon (C) and nitrogen (N) losses from leaf litter were 10.1 and 17.9% lower, respectively, in the nutrient-poorest site, but this among-site difference was equalized when meso- and macrofauna had access to the litterbags. Further, on average, soil fauna enhanced the rate of litter decomposition by 22.6%, and this contribution consistently increased as nutrient availability in the microenvironment declined. Our results indicate that nutrient scarcity increases the importance of soil fauna on C and N cycling in tropical rainforests. Further, soil fauna is able to equalize differences in microbial decomposition potential, thus buffering to a remarkable extent nutrient shortages at an ecosystem level.
Auteurs, date et publication :
Auteurs Guille Peguero , Jordi Sardans , Dolores Asensio , Marcos Fernández-Martínez , Albert Gargallo-Garriga , Oriol Grau , Joan Llusià , Olga Margalef , Laura Márquez , Romà Ogaya , Ifigenia Urbina , Elodie A. Courtois , Clément Stahl , Leandro Van Langenhove , Lore T. Verryckt , Andreas Richter , Ivan A. Janssens , Josep Peñuelas
Publication : Proceedings of the Royal Society B: Biological Sciences
Date : 2019
Volume : 286
Issue : 1910
Pages : 20191300