Analysis of the diurnal cycles for a better understanding of the mean annual cycle of forests greenness in Central Africa

Philippon, Nathalie; Lapparent, B. de; Gond, Valéry; Sèze, Geneviève; Martiny, Nadège; Camberlin, Pierre; Cornu, Guillaume; Morel, Béatrice; Moron, Vincent; Bigot, Sylvain; Brou, Yao Télesphore; Dubreuil, Vincent

doi:10.1016/j.agrformet.2016.04.005

Cited by 21 publications

(21 citation statements)

References 42 publications

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“…the highest photosynthesis levels are recorded during the luminous dry season (Huete et al 2006, Myneni et al 2007, Bi et al 2015, Wagner et al 2017, in Central Africa, the two seasons of highest (lowest) photosynthesis, i.e. March-May and September-November (December-February and June-August), are concomitant with the two rainy (dry) seasons (Gond et al 2013, Philippon et al 2016. Indeed, below 2000 mm yr −1 on average, the water stored during both rainy seasons is not expected to meet the main dry season water demand and to maintain evergreen forest.…”

Section: Introductionmentioning

confidence: 98%

The light-deficient climates of western Central African evergreen forests

Philippon

Cornu

Monteil

et al. 2019

Environ. Res. Lett.

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Rainfall thresholds under which forests grow in Central Africa are lower than those of Amazonia and southeast Asia. Attention is thus regularly paid to rainfall whose seasonality and interannual variability has been shown to control Central African forests' water balance and photosynthetic activity. Nonetheless, light availability is also recognized as a key factor to tropical forests. Therefore this study aims to explore the light conditions prevailing across Central Africa, and their potential impact on forests' traits. Using satellite estimates of hourly irradiance, we find first that the four main types of diurnal cycles of irradiance extracted translate into different levels of rainfall, evapotranspiration, direct and diffuse light. Then accounting for scale interactions between the diurnal and annual cycles, we show that the daily quantity and quality of light considerably vary across Central African forests during the annual cycle: the uniqueness of western Central Africa and Gabon in particular, with strongly lightdeficient climates especially during the main dry season, points out. Lastly, using an original map of terra firme forests, we also show that most of the evergreen forests are located in western Central Africa and Gabon. We postulate that despite mean annual precipitation below 2000 mm yr −1 , the lightdeficient climates of western Central Africa can harbour evergreen forests because of an extensive lowlevel cloudiness developing during the June-September main dry season, which strongly reduces the water demand and enhances the quality of light available for tree photosynthesis. These findings pave the way for further analyses of the past and future changes in the light-deficient climates of western Central Africa and the vulnerability of evergreen forests to these changes.

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Section: Introductionmentioning

confidence: 98%

The light-deficient climates of western Central African evergreen forests

Philippon

Cornu

Monteil

et al. 2019

Environ. Res. Lett.

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“…With S2 optical data, cloud cover limits the data available and unlike other regions the dry season in Africa does not mean an absence of clouds [25]. However, changes in reflectance can be captured for a few months, depending on the pace of vegetation regrowth.…”

Section: Potential Of Sentinel 1 and Sentinel 2 For Burnt Areas Monitmentioning

confidence: 99%

“…However, the Congo Basin region has extensive cloud cover at various times of the year [25] limiting the use of optical sensors. Observations from S1 can complement S2 optical acquisitions due to the high sensitivity to structural properties of vegetation and day and night The Level 1C S2 images are contaminated with cloud and aerosols which need to be masked out before further processing.…”

Section: Sentinelmentioning

confidence: 99%

“…With a temporal resolution of 10 days, S2 images should allow a precise mapping of the timing and extent of fire event. However, the Congo Basin region has extensive cloud cover at various times of the year [25] limiting the use of optical sensors. Observations from S1 can complement S2 optical acquisitions due to the high sensitivity to structural properties of vegetation and day and night observing capabilities of the radar sensor.…”

Section: Sentinelmentioning

confidence: 99%

“…The climate across the study area is tropical humid characterized by an annual precipitation of 1600-2000 mm per year, with two dry seasons, one in June to August and a stronger one from December through to February [23][24][25]. The area is dominated by forests, which cover over 95% of the region.…”

Section: Study Areamentioning

confidence: 99%

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The Potential of Sentinel Satellites for Burnt Area Mapping and Monitoring in the Congo Basin Forests

et al. 2016

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Abstract:In this study, the recently launched Sentinel-2 (S2) optical satellite and the active radar Sentinel-1 (S1) satellite supported by active fire data from the MODIS sensor were used to detect and monitor forest fires in the Congo Basin. In the context of a very strong El Niño event, an unprecedented outbreak of fires was observed during the first months of 2016 in open forests formations in the north of the Republic of Congo. The anomalies of the recent fires and meteorological situation compared to historical data show the severity of the drought. Burnt areas mapped by the S1 SAR and S2 Multi Spectral Instrument (MSI) sensors highlight that the fires occurred mainly in Marantaceae forests, characterized by open tree canopy cover and an extensive tall herbaceous layer. The maps show that the origin of the fires correlates with accessibility to the forest, suggesting an anthropogenic origin. The combined use of the two independent and fundamentally different satellite systems of S2 and S1 captured an extent of 36,000 ha of burnt areas, with each sensor compensating for the weakness (cloud perturbations for S2, and sensitivity to ground moisture for S1) of the other.

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Diurnal to interannual variability of low‐level cloud cover over western equatorial Africa in May–October

Moron

Camberlin

Aellig

et al. 2023

Intl Journal of Climatology

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This study examines the diurnal to interannual variations of the stratiform cloud cover in May–October (1971–2019) from a 3‐hourly station database and from ERA5 reanalyses over western equatorial Africa (WEA). The main diurnal variations of the local‐scale fraction and genus of stratiform clouds are synthesized into three canonical diurnal types (i.e., “clear,” “clear afternoon,” “cloudy” days). The interannual variations of frequencies of the three diurnal types during the cloudiest months (JJAS) are mostly associated with two main mechanisms: a meridional shallow overturning cell associating more “cloudy” and less “clear” and “clear afternoon” days to anomalous southerlies below 900 hPa over and around WEA, anomalous ascent around 5°–7°N, anomalous northerlies between 875 and 700 hPa, and anomalous subsidence over the equatorial Atlantic. This circulation is strongly related to interannual variations of the equatorial Atlantic upwelling (i.e., more clouds when the upwelling is strong) associated with a meridional shift of the Intertropical Convergence Zone over the Tropical Atlantic and adjacent continents. The second mechanism operates mostly in the zonal direction and involves again the coupled ocean–atmosphere system over the equatorial Atlantic, but also the remote El Niño–Southern Oscillation (ENSO). An anomalously cold equatorial Atlantic drives increased low‐level westerlies toward the Congo Basin. Warm ENSO events promote broad warm and easterly anomalies in the middle and upper troposphere, which increase the local static stability, and thus the local stratiform cloud cover over WEA. The present study suggests new mechanisms responsible for interannual variations of stratiform clouds in WEA, thus providing avenues of future research regarding the stability of the stratiform cloud deck under the ongoing differential warming of tropical ocean and land masses.

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Analysis of the diurnal cycles for a better understanding of the mean annual cycle of forests greenness in Central Africa

Cited by 21 publications

References 42 publications

The light-deficient climates of western Central African evergreen forests

The light-deficient climates of western Central African evergreen forests

The Potential of Sentinel Satellites for Burnt Area Mapping and Monitoring in the Congo Basin Forests

Diurnal to interannual variability of low‐level cloud cover over western equatorial Africa in May–October

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