Interannual persistence effects in vegetation dynamics of semi‐arid Africa

Martiny, Nadège; Richard, Yves; Camberlin, Pierre

doi:10.1029/2005gl024634

Cited by 44 publications

(38 citation statements)

References 18 publications

(18 reference statements)

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“…In the Sahel, the response of vegetation to the first rain pulse is very active. There is a lag-time between these first rains and the first vegetation cover (Jarlan et al, 2005;Martiny et al, 2005). A long time series of space remote sensing products has been developed to estimate the FAPAR for various optical instruments (Gobron et al, 2000(Gobron et al, , 2006(Gobron et al, , 2007 http://fapar.jrc.ec.europa.eu/).…”

Section: Acidic Contributionmentioning

confidence: 99%

“…Sahelian vegetation density depends also upon monsoonal rainfall variability (Jarlan et al, 2005;Martiny et al, 2005). At the same time the population growth (with a 2-fold increase in the last 40 years) and intense land-use enhance desertification processes (Rayanaut, 2001) which partly explains the intensification of dust emissions and increase of dust transport over the tropical north-Atlantic (Moulin and Chiapello, 2006).…”

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confidence: 99%

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Long term precipitation chemistry and wet deposition in a remote dry savanna site in Africa (Niger)

et al. 2009

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Abstract. Long-term precipitation chemistry have been recorded in the rural area of Banizoumbou (Niger), representative of a semi-arid savanna ecosystem. A total of 305 rainfall samples ∼90% of the total annual rainfall) were collected from June 1994 to September 2005. From ionic chromatography, pH major inorganic and organic ions were detected. Rainwater chemistry is controlled by soil/dust emissions associated with terrigeneous elements represented by SO concentrations of 11.6 and 18.1 µeq.l −1 , respectively. This is the signature of ammonia sources from animals and NO x emissions from savannas soil-particles rain-induced. The mean annual NH 3 and NO 2 air concentration are of 6 ppbv and 2.6 ppbv, respectively. The annual VWM precipitation concentration of sodium and chloride are both of 8.7 µeq.l −1 which reflects the marine signature of monsoonal and humid air masses. The median pH value is of 6.05. Acidity is neutralized by mineral dust, mainly carbonates, and/or dissolved gases such NH 3 . High level of organic acidity with 8µeq.l −1 and 5.2 µeq.l −1 of formate and acetate were also found. The analysis of monthly Black Carbon emissions and Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) values show that both biogenic emission from vegetation and biomass burning could explain the Correspondence to: C. Galy-Lacaux (lacc@aero.obs-mip.fr) rainfall organic acidity content. The interannual variability of the VWM concentrations around the mean (1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005) is between ±5% and ±30% and mainly due to variations of sources strength and rainfall spatio-temporal distribution. From 1994 to 2005, the total mean wet deposition flux in the Sahelian region is of 60.1 mmol.m −2 .yr −1 ±25%. Finally, Banizoumbou measurements are compared to other long-term measurements of precipitation chemistry in the wet savanna of Lamto (Côte d'Ivoire) and in the forested zone of Zoétélé (Cameroon). The total chemical loading presents a maximum in the dry savanna and a minimum in the forest (from 143.7, 100.2 to 86.6 µeq.l −1 ), associated with the gradient of terrigeneous sources. The wet deposition fluxes present an opposite trend, with 60.0 mmol.m −2 .yr −1 in Banizoumbou, 108.6 mmol.m −2 .yr −1 in Lamto and 162.9 mmol.m −2 .yr −1 in Zoétélé, controlled by rainfall gradient along the ecosystems transect.

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Section: Acidic Contributionmentioning

confidence: 99%

mentioning

confidence: 99%

Long term precipitation chemistry and wet deposition in a remote dry savanna site in Africa (Niger)

et al. 2009

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“…14,15 Global warming has also caused an increase in precipitation that resulted in vegetation greening in the southern hemisphere, such as African Sahel [16][17][18][19][20][21] and South America, 22 although some areas with a decrease in precipitation markedly reduced vegetation production. 23,24 The Qinghai-Tibetan Plateau is regarded as a typical area for investigating the relationships between vegetation condition and climate variables, because the vegetation remains relatively undisturbed by human activities due to the low population and the plateau is dominated by alpine grasslands that appear to be highly sensitive to global climate change.…”

Section: Introductionmentioning

confidence: 99%

Vegetation greenness trend (2000 to 2009) and the climate controls in the Qinghai-Tibetan Plateau

Zhang

Guo

Ji³

et al. 2013

J. Appl. Remote Sens

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Abstract. The Qinghai-Tibetan Plateau has been experiencing a distinct warming trend, and climate warming has a direct and quick impact on the alpine grassland ecosystem. We detected the greenness trend of the grasslands in the plateau using Moderate Resolution Imaging Spectroradiometer data from 2000 to 2009. Weather station data were used to explore the climatic drivers for vegetation greenness variations. The results demonstrated that the region-wide averaged normalized difference vegetation index (NDVI) increased at a rate of 0.036 yr −1 . Approximately 20% of the vegetation areas, which were primarily located in the northeastern plateau, exhibited significant NDVI increase trend (p-value <0.05). Only 4% of the vegetated area showed significant decrease trends, which were mostly in the central and southwestern plateau. A strong positive relationship between NDVI and precipitation, especially in the northeastern plateau, suggested that precipitation was a favorable factor for the grassland NDVI. Negative correlations between NDVI and temperature, especially in the southern plateau, indicated that higher temperature adversely affected the grassland growth. Although a warming climate was expected to be beneficial to the vegetation growth in cold regions, the grasslands in the central and southwestern plateau showed a decrease in trends influenced by increased temperature coupled with decreased precipitation.

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“…Pixels with at least one 10-day value below 0.11 were flagged. Below this value, NDVI is no longer representative of vegetated areas (Martiny et al, 2005). In addition, we computed a regional index (Sahelian NDVI index) which is the spatial average of the 8-km pixels correlated at 0.4 with the Sahelian index computed in a previous study by Philippon et al (2007), using an older version of the GIMMS NDVI dataset.…”

Section: Normalized Difference Vegetation Indexmentioning

confidence: 99%

“…However, for a given rainfall amount, the strength of the relationship significantly varies with the vegetation type: open grassland and cropland areas exhibit the highest NDVI/rainfall correlations . Memory effects from one year to another have also been recently evoked by Martiny et al (2005) and Philippon et al (2007) to explain the persistence of marked NDVI anomalies after very wet or very dry years (e.g. 1984).…”

Section: Introductionmentioning

confidence: 99%

Forecasting the vegetation photosynthetic activity over the Sahel: a Model Output Statistics approach

Philippon

Martiny

Camberlin

2008

Intl Journal of Climatology

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ABSTRACT:The predictability of the mean August-September photosynthetic activity of vegetation over the Sahel for the period 1982-2002 is explored through a Model Output Statistics approach using ECHAM4.5 retrospective forecasts. Given the poor ability of Atmospheric General Circulation Models (AGCMs) to correctly simulate rainfall over the Sahel, the stress is put on using atmospheric dynamics alone. The mean July-September predicted fields of zonal wind at 600 hPa, and humidity flux at 850 hPa, are selected because of their key role in the West African Monsoon system and their consistency in AGCMs. Coupled modes of NDVI/atmospheric dynamics are extracted using Canonical Correlation Analyses performed in leave-one-out cross-validation. The most relevant modes (using NCEP/DOE 2 or ECHAM4.5 atmospheric dynamics) associate enhanced greenness to a weakened African Easterly Jet displaced northward, and strengthened moisture fluxes from the Guinean Gulf. They are linked with increased rainfall over the Sahel and positive (negative) SST anomalies over the Mediterranean (the eastern equatorial Pacific).Used as predictors in a Multiple Linear Regression (MLR) model, the third cross-validated canonical coefficient (CC) derived from ECHAM4.5 simulations added to the August-September NDVI value of the previous year enable to explain 30% of the variance of a Sahelian regional index with a 2-month lead time. Applied at an 8-km spatial resolution, the statistical model possesses a usable skill (>.5) for 24% of the pixels analysed. The NDVI of pixels covered by open grassland appears as the most predictable.

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Interannual persistence effects in vegetation dynamics of semi‐arid Africa

Cited by 44 publications

References 18 publications

Long term precipitation chemistry and wet deposition in a remote dry savanna site in Africa (Niger)

Long term precipitation chemistry and wet deposition in a remote dry savanna site in Africa (Niger)

Vegetation greenness trend (2000 to 2009) and the climate controls in the Qinghai-Tibetan Plateau

Forecasting the vegetation photosynthetic activity over the Sahel: a Model Output Statistics approach

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