Estimation of LAI, fAPAR and fCover of Sahel rangelands (Gourma, Mali)

Mougin, E.; Demarez, Valérie; Diawara, Mamadou Oumar; Hiernaux, Pierre; Soumaguel, Nogmana; Berg, Alexis

doi:10.1016/j.agrformet.2014.08.006

Cited by 48 publications

(47 citation statements)

References 54 publications

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“…The standing mass of annual herbaceous vegetation is characterized by a very rapid increasing and decreasing rate, shown e.g. in a herbaceous growth simulation model in Tracol, Mougin, Hiernaux, and Jarlan (2006) or Leaf Area Index (LAI) measurements in Mougin et al (2014). The recurrent vegetation wilt and die from early September to late October, and remains photosynthetically inactive until the new germination with the onset of the following rainy season.…”

Section: Phenological Behavior Of Sahelian Herbaceous and Woody Vegetmentioning

confidence: 99%

“…The months of the wet season during which herbaceous grow are highlighted in a shaded box. Illustrations of typical herbaceous growing curves can be found in Mougin et al (2014).…”

Section: Phenological Behavior Of Sahelian Herbaceous and Woody Vegetmentioning

confidence: 99%

“…The herbaceous layer is only short lasting green (less than a 4-month period) in the Sahel (de Vries & Djitèye, 1982;Mougin et al, 2014) causing a strong peak in the seasonality of vegetation during the rainy season. Senescence of the annual herbaceous vegetation shortly after flowering is determined by a biological clock, regardless of eventual late rains (photoperiodicity).…”

Section: Phenological Behavior Of Sahelian Herbaceous and Woody Vegetmentioning

confidence: 99%

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Woody plant cover estimation in drylands from Earth Observation based seasonal metrics

Brandt

Hiernaux

Tagesson

et al. 2016

Remote Sensing of Environment

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From in situ measured woody cover we develop a phenology driven model to estimate the canopy cover of woody species in the Sahelian drylands at 1 km scale. The model estimates the total canopy cover of all woody phanerophytes and the concept is based on the significant difference in phenophases of dryland trees, shrubs and bushes as compared to that of the herbaceous plants. Whereas annual herbaceous plants are only green during the rainy season and senescence occurs shortly after flowering towards the last rains, most woody plants remain photosynthetically active over large parts of the year. We use Moderate Resolution Imaging Spectroradiometer (MODIS) and Satellite pour l'Observation de la Terre (SPOT) -VEGETATION (VGT) Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) time series and test 10 metrics representing the annual FAPAR dynamics for their ability to reproduce in situ woody cover at 43 sites (163 observations between 1993 and 2013) in the Sahel. Both multi-year field data and satellite metrics are averaged to produce a steady map. Multiple regression models using the integral of FAPAR from the onset of the dry season to the onset of the rainy season, the start date of the growing season and the rate of decrease of the FAPAR curve achieve a cross validated r 2 /RMSE (in % woody cover) of 0.73/3.0 (MODIS) and 0.70/3.2 (VGT). The extrapolation to Sahel scale shows agreement between VGT and MODIS at an almost nine times higher woody cover than in the global tree cover product MOD44B which only captures trees of a certain minimum size. The derived woody cover map of the Sahel is made publicly available and represents an improvement of existing products and a contribution for future studies of drylands quantifying carbon stocks, climate change assessment, as well as parametrization of vegetation dynamic models.

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Section: Phenological Behavior Of Sahelian Herbaceous and Woody Vegetmentioning

confidence: 99%

“…The months of the wet season during which herbaceous grow are highlighted in a shaded box. Illustrations of typical herbaceous growing curves can be found in Mougin et al (2014).…”

Section: Phenological Behavior Of Sahelian Herbaceous and Woody Vegetmentioning

confidence: 99%

Section: Phenological Behavior Of Sahelian Herbaceous and Woody Vegetmentioning

confidence: 99%

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Woody plant cover estimation in drylands from Earth Observation based seasonal metrics

Brandt

Hiernaux

Tagesson

et al. 2016

Remote Sensing of Environment

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“…The CRF ranges between 1 (no reduction because no vegetation, LAI = 0) and 0.83 (LAI = 1.8 at the most, Mougin et al, 2014). Considering the CRF applied, the maximum quantity of N re-deposited above canopy during the wet months when LAI is at its maximum is negligible compared to the total N input from faecal, herbal and root masses.…”

Section: Nofluxmentioning

confidence: 99%

“…The herbaceous layer has been monitored using a two-level stratified random sampling design, as described in Hiernaux et al (2009). Total and green vegetation cover (visual and digital photograph estimates in %, Mougin et al, 2014), standing and litter mass (destructive measure, with harvest, air drying and weighing) and species composition (list with visual estimates of contribution to bulk) are assessed in 1 × 1 m plots randomly sampled in each of the vegetated strata along the transect. Aboveground green and dry masses and surface litter mass have been sampled during several years, but only the years 2004, 2005, 2006, 2007 and 2008 are used in this study to evaluate the performance of the model.…”

Section: Meteorological and Vegetation Datamentioning

confidence: 99%

Modelling the effect of soil moisture and organic matter degradation on biogenic NO emissions from soils in Sahel rangeland (Mali)

et al. 2015

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Abstract. This work is an attempt to provide seasonal variation of biogenic NO emission fluxes in a Sahelian rangeland in Mali (Agoufou, 15.34 • N, 1.48 • W) for years 2004, 2005, 2006, 2007 and 2008. Indeed, NO is one of the most important precursors for tropospheric ozone, and previous studies have shown that arid areas potentially display significant NO emissions (due to both biotic and abiotic processes). Previous campaigns in the Sahel suggest that the contribution of this region in emitting NO is no longer considered as negligible. However, very few data are available in this region, therefore this study focuses on model development. The link between NO production in the soil and NO release to the atmosphere is investigated in this modelling study, by taking into account vegetation litter production and degradation, microbial processes in the soil, emission fluxes, and environmental variables influencing these processes, using a coupled vegetation-litter decompositionemission model. This model includes the Sahelian Transpiration Evaporation and Productivity (STEP) model for the simulation of herbaceous, tree leaf and faecal masses, the GENDEC model (GENeral DEComposition) for the simulation of the buried litter decomposition and microbial dynamics, and the NO emission model (NOFlux) for the simulation of the NO release to the atmosphere. Physical parameters (soil moisture and temperature, wind speed, sand percentage) which affect substrate diffusion and oxygen supply in the soil and influence the microbial activity, and biogeochemical parameters (pH and fertilization rate related to N content) are necessary to simulate the NO flux. The reliability of the simulated parameters is checked, in order to assess the robustness of the simulated NO flux. Simulated yearly average of NO flux ranges from 2.09 to 3.04 ng(N) m −2 s −1 (0.66 to 0.96 kg(N) ha −1 yr −1 ), and wet season average ranges from 3.36 to 5.48 ng(N) m −2 s −1 (1.06 to 1.73 kg(N) ha −1 yr −1 ). These results are of the same order as previous measurements made in several sites where the vegetation and the soil are comparable to the ones in Agoufou. This coupled vegetationlitter decomposition-emission model could be generalized at the scale of the Sahel region, and provide information where few data are available.

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The Surface Energy Budget Computed at the Grid‐Scale of a Climate Model Challenged by Station Data in West Africa

Diallo

Hourdin

Rio

et al. 2017

J Adv Model Earth Syst

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In most state‐of‐the‐art climate models, systematic errors persist in the representation of the rainfall seasonality, near surface air temperature, and surface energy budget over West Africa, even during the dry season. Most biases are related to an incorrect latitudinal position of the monsoon structures. To disentangle the role of the large‐scale dynamics from that of the physical processes in these biases, simulations are performed with the LMDZ general circulation model in which the horizontal winds are nudged toward reanalysis. Wind nudging greatly improves the position of the ITCZ as well as the representation of the components of the surface energy budget directly impacted by the water budget and hence facilitates a more systematic analysis of remaining biases associated with the physics in the model. The great potential of wind nudging to compare the energetics of the atmospheric column in climate models at grid cell scale with station observations, even for coarse grid models, is then shown. Despite the improved water advection and rainfall seasonality in the nudged simulations, errors consisting in a cold bias during the dry season over Sahel, an underestimated seasonal variation of surface albedo, and an overestimation of the solar incoming flux remain. The origin of these remaining biases is further investigated by conducting a series of dedicated sensitivity experiments. Results highlight the key role of the soil thermal inertia, the turbulent mixing efficiency, the surface albedo, and the aerosols and clouds radiative effects in the representation of meteorological 2m‐variables and surface energy budget.

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Estimation of LAI, fAPAR and fCover of Sahel rangelands (Gourma, Mali)

Cited by 48 publications

References 54 publications

Woody plant cover estimation in drylands from Earth Observation based seasonal metrics

Woody plant cover estimation in drylands from Earth Observation based seasonal metrics

Modelling the effect of soil moisture and organic matter degradation on biogenic NO emissions from soils in Sahel rangeland (Mali)

The Surface Energy Budget Computed at the Grid‐Scale of a Climate Model Challenged by Station Data in West Africa

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