Desertification in the Sahel: a reinterpretation of a reinterpretation

Prince, Stephen D.; Wessels, Konrad J; Tucker, Compton J.; Nicholson, Sharon E.

doi:10.1111/j.1365-2486.2007.01356.x

Cited by 151 publications

(121 citation statements)

References 32 publications

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“…The existence and nature of Sahelian regreening following the 1980s drought has been greatly debated, with considerable polarization between camps arguing the desertification and recovery narratives (20)(21)(22)(25)(26)(27)(28)(29). A few studies have examined the specific role of long-term changes in woody and herbaceous components (e.g., refs.…”

Section: Trend Assessments Using Changes In Decadal and Interannual Rmentioning

confidence: 99%

“…In the last 20 y, remote-sensing studies have documented an apparent increase in vegetation productivity in the Sahel using satellite measurements of vegetation greenness (i.e., normalized difference vegetation index, NDVI) as a proxy for NPP (20)(21)(22). Independent studies have also documented farmer strategies to restore landscape-scale function, in particular through planting of trees and soil conservation actions (23,24).…”

mentioning

confidence: 99%

“…In this situation, changing RUE can be used directly to diagnose changes in vegetation, reflecting long-term degradation or recovery (20,21). Meanwhile, based on physical and physiological logic, others argue for an underlying nonlinear relationship between NPP and rainfall, with NPP initially increasing with rainfall before saturating at higher rainfall as light or nutrients become limiting (25,27).…”

mentioning

confidence: 99%

“…Annual integrals of NDVI during the growing season (from June to October) are used as a proxy for NPP (20)(21)(22) over 260 watersheds located in four regions of Senegal, Mali, and Niger (Fig. S1).…”

mentioning

confidence: 99%

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On regreening and degradation in Sahelian watersheds

Kaptué

Prihodko

Hanan

2015

Proc. Natl. Acad. Sci. U.S.A.

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Over many decades our understanding of the impacts of intermittent drought in water-limited environments like the West African Sahel has been influenced by a narrative of overgrazing and human-induced desertification. The desertification narrative has persisted in both scientific and popular conception, such that recent regional-scale recovery ("regreening") and local success stories (community-led conservation efforts) in the Sahel, following the severe droughts of the 1970s-1980s, are sometimes ignored. Here we report a study of watershed-scale vegetation dynamics in 260 watersheds, sampled in four regions of Senegal, Mali, and Niger from 1983-2012, using satellite-derived vegetation indices as a proxy for net primary production. In response to earlier controversy, we first examine the shape of the rainfall-net primary production relationship and how it impacts conclusions regarding greening or degradation. We conclude that the choice of functional relationship has little quantitative impact on our ability to infer greening or degradation trends. We then present an approach to analyze changes in long-term (decade-scale) average rain-use efficiency (an indicator of slowly responding vegetation structural changes) relative to changes in interannual-scale rainfall sensitivity (an indicator of landscape ability to respond rapidly to rainfall variability) to infer trends in greening/degradation of the watersheds in our sample regions. The predominance of increasing rain-use efficiency in our data supports earlier reports of a "greening" trend across the Sahel. However, there are strong regional differences in the extent and direction of change, and in the apparent role of changing woody and herbaceous components in driving those temporal trends.Sahel | desertification | rain-use efficiency | drylands | West Africa

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Section: Trend Assessments Using Changes In Decadal and Interannual Rmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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On regreening and degradation in Sahelian watersheds

Kaptué

Prihodko

Hanan

2015

Proc. Natl. Acad. Sci. U.S.A.

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“…Increases in vegetation greenness are attributed to increased temperatures during spring in midlatitudes [Keeling et al, 1996;Menzel and Fabian, 1999;Myneni et al, 1997], to variations in downwelling solar radiation in the tropics [Nemani et al, 2003], and to variations in the fraction of diffuse radiation [Lucht et al, 2002;Mercado et al, 2009]. Locally, increased vegetation is linked to increased precipitation, e.g., vegetation in the Sahel has partially recovered since the largest drought of the 20th century in 1984 Prince et al, 2007].…”

Section: Introductionmentioning

confidence: 99%

Analysis of trends in fused AVHRR and MODIS NDVI data for 1982–2006: Indication for a CO₂ fertilization effect in global vegetation

Los

2013

Global Biogeochemical Cycles

102

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[1] Recent studies report an increase in vegetation greenness in mid-to-high northern latitudes. This increase is observed in leaf-out data in Europe and North America since the 1950s and in satellite data since the 1980s. Increased vegetation greenness is potentially a factor contributing to a land CO 2 sink. Various causes for increased vegetation greenness are suggested, but their relative importance is uncertain. In the present study, the effect of climate and CO 2 fertilization on increased vegetation greenness and the land CO 2 sink are investigated. The study is organized as follows: (1) (2) Residuals between RVI and NDVI are analyzed for associations with variations in downwelling solar radiation, nitrogen deposition, satellite-related artifacts, and CO 2 fertilization. CO 2 fertilization was the only factor that improved RVI modeling. (3) The effect of climate variations and CO 2 fertilization on the land CO 2 sink, as manifested in the RVI, is explored with the Carnegie Ames Stanford Assimilation (CASA) model. Climate (temperature and precipitation) and CO 2 fertilization each explain approximately 40% of the observed global trend in NDVI for 1982-2006 . For 1901-2006, estimated trends in NDVI related to CO 2 fertilization are four to five times larger than climate-related trends. CASA simulations indicate that the CO 2 fertilization effect on vegetation greenness contributes about 0.7 Pg C per year to the recent land CO 2 sink. This is a conservative estimate and is likely larger. This effect of CO 2 fertilization would be a large component of the land carbon sink. In the supporting information the RVI is used as a common standard to fuse MODIS and advanced very high resolution radiometer (AVHRR) NDVI data. This fusion compares well with SeaWiFS data.

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Spatial and temporal variations in ecosystem response to monsoon precipitation variability in southwestern North America

et al. 2014

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Due to its marked vegetation phenology and precipitation gradients, the North American Monsoon Region (NAMR) is a useful domain for studying ecosystem responses to climate variability and change. To this end, we analyze long-term dynamics in monsoon precipitation (Pr), time-integrated Normalized Difference Vegetation Index (TINDVI) used as proxy of net primary productivity, and rain-use efficiency (RUE). The analysis focuses on six ecoregions, spanning from desert environments to tropical dry forests, to investigate (1) how net primary productivity and rain-use efficiency vary along a precipitation gradient, (2) if interannual variability in net primary productivity is linked to the interannual variability in precipitation, and (3) if there is evidence of a long-term signal imposed on the interannual variability in rain-use efficiency. Variations in TINDVI and RUE with Pr along the NAMR precipitation gradient differ among ecoregions exhibiting intensive or extensive water use strategies. We explain the nonlinear behaviors along the precipitation gradient as resulting from different physiological responses to climatological means and the impact of topographic effects. Statistical analysis indicates that the interannual variability in vegetation response is significantly related to the interannual variability in Pr, but their correlation declines with time. A long-term positive signal in RUE imposed on its interannual variability is identified and results from a constant TINDVI under negative long-term trends of Pr. This important finding suggests the combined long-term effects of ecosystem acclimation to reduced water availability and increasing CO 2 concentration across the varied ecosystems of the North American Monsoon Region.

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Desertification in the Sahel: a reinterpretation of a reinterpretation

Cited by 151 publications

References 32 publications

On regreening and degradation in Sahelian watersheds

On regreening and degradation in Sahelian watersheds

Analysis of trends in fused AVHRR and MODIS NDVI data for 1982–2006: Indication for a CO₂ fertilization effect in global vegetation

Spatial and temporal variations in ecosystem response to monsoon precipitation variability in southwestern North America

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Desertification in the Sahel: a reinterpretation of a reinterpretation

Cited by 151 publications

References 32 publications

On regreening and degradation in Sahelian watersheds

On regreening and degradation in Sahelian watersheds

Analysis of trends in fused AVHRR and MODIS NDVI data for 1982–2006: Indication for a CO2 fertilization effect in global vegetation

Spatial and temporal variations in ecosystem response to monsoon precipitation variability in southwestern North America

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Analysis of trends in fused AVHRR and MODIS NDVI data for 1982–2006: Indication for a CO₂ fertilization effect in global vegetation