Assessing woody vegetation trends in Sahelian drylands using MODIS based seasonal metrics

Brandt, Martin; Hiernaux, Pierre; Rasmussen, Kjeld; Mbow, Cheikh; Kergoat, Laurent; Tagesson, Torbern; Ibrahim, Yahaya; Wélé, Alassane; Tucker, Compton J.; Fensholt, Rasmus

doi:10.1016/j.rse.2016.05.027

Cited by 94 publications

(104 citation statements)

References 46 publications

(2 reference statements)

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“…All study areas cited in this paper with a reported re-greening trend, such as Senegal (e.g. Herrmann and Tappan, 2013;Brandt et al, 2014aBrandt et al, , b, 2015Herrmann and Sop, 2016), Mali and Burkina Faso (Hiernaux et al, 2009a, b;Dardel et al, 2014a, b;Rasmussen et al, 2014;Brandt et al, 2016b), and Niger (Hiernaux et al, 2009a, b;Boubacar, 2016), are situated on the sandy soils of the Quaternary dune systems. Krings (1980).…”

Section: Contributions Of Other Authorsmentioning

confidence: 80%

Desertification, resilience, and re-greening in the African Sahel – a matter of the observation period?

Kusserow

2017

Earth Syst. Dynam.

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Abstract. Since the turn of the millennium various scientific publications have been discussing a re-greening of the Sahel after the 1980s drought mainly based on coarse-resolution satellite data. However, the author's own field studies suggest that the situation is far more complex and that both paradigms, the "encroaching Sahara" and the "re-greening Sahel", need to be questioned. This paper discusses the concepts of desertification, resilience, and re-greening by addressing four main aspects: (i) the relevance of edaphic factors for a vegetation re-greening, (ii-iii) the importance of the selected observation period in the debate on Sahel greening or browning, and (iv) modifications in the vegetation pattern as possible indicators of ecosystem changes (shift from originally diffuse to contracted vegetation patterns).The data referred to in this paper cover a time period of more than 150 years and include the author's own research results from the early 1980s until today. A special emphasis, apart from fieldwork data and remote sensing data, is laid on the historical documents.The key findings summarised at the end show the following: (i) vegetation recovery predominantly depends on soil types; (ii) when discussing Sahel greening vs. Sahel browning, the majority of research papers only focus on post-drought conditions. Taking pre-drought conditions (before the 1980s) into account, however, is essential to fully understand the situation. Botanical investigations and remote-sensing-based time series clearly show a substantial decline in woody species diversity and cover density compared to pre-drought conditions; iii) the self-organised patchiness of vegetation is considered to be an important indicator of ecosystem changes.

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Section: Contributions Of Other Authorsmentioning

confidence: 80%

Desertification, resilience, and re-greening in the African Sahel – a matter of the observation period?

Kusserow

2017

Earth Syst. Dynam.

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“…Brandt et al [89] confirmed an overall positive trend of woody cover dynamics across the entire Sahel in recent decades. This demonstrates the resilience of Sahelian ecosystems, although this trend is generally observed in places with low human pressure.…”

Section: Evaluation Of Global Vegetation Evolution Through Remote Senmentioning

confidence: 87%

Evolution of Surface Hydrology in the Sahelo-Sudanian Strip: An Updated Review

Descroix

Guichard

Grippa

et al. 2018

Water

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Abstract:In the West African Sahel, two paradoxical hydrological behaviors have occurred during the last five decades. The first paradox was observed during the 1968-1990s 'Great Drought' period, during which runoff significantly increased. The second paradox appeared during the subsequent period of rainfall recovery (i.e., since the 1990s), during which the runoff coefficient continued to increase despite the general re-greening of the Sahel. This paper reviews and synthesizes the literature on the drivers of these paradoxical behaviors, focusing on recent works in the West African Sahelo/Sudanian strip, and upscaling the hydrological processes through an analysis of recent data from two representative areas of this region. This paper helps better determine the respective roles played by Land Use/Land Cover Changes (LULCC), the evolution of rainfall intensity and the occurrence of extreme rainfall events in these hydrological paradoxes. Both the literature review and recent data converge in indicating that the first Sahelian hydrological paradox was mostly driven by LULCC, while the second paradox has been caused by both LULCC and climate evolution, mainly the recent increase in rainfall intensity.

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“…Trend analysis of vegetation is commonly used to assess land degradation or changes in vegetation productivity (de Jong et al 2011, Brandt et al 2016. Usually, trends are established using linear regression at annual (Bai et al 2008) or seasonal intervals (Eklundh and Olsson 2003).…”

Section: Methodsmentioning

confidence: 99%

“…To estimate the average amount of vegetation change per year, we used the Theil-Sen slope, which calculates the median of all slope estimates between all potential pairs of points (Hoaglin et al 1983, Fensholt andProud 2012). The Theil-Sen slope is a nonparametric test especially suitable for time series of vegetation indices, as they often do not meet parametric assumptions of normality and heteroscedasticity (Hoaglin et al 1983, Alcaraz-Segura et al 2010, Fensholt and Proud 2012, Brandt et al 2016. Furthermore, the Theil-Sen procedure is especially suitable for short or noisy time series due to its robustness against outliers.…”

Section: Methodsmentioning

confidence: 99%

Differences in resource management affects drought vulnerability across the borders between Iraq, Syria, and Turkey

Eklund¹,

Thompson²

2017

E&S

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ABSTRACT. Much discussion has taken place exploring a potential connection between the 2007-2009 Fertile Crescent drought and Syria's uprising-turned civil war beginning in 2011. This study takes an integrated perspective on the 2007-2009 drought in the border region of Iraq, Syria, and Turkey by looking at the meteorological, agricultural, and socioeconomic aspects of drought vulnerability. Satellite-based precipitation and vegetation data help outline the drought's spatial and temporal properties. In order to understand the context in which this drought happened, we also look at the trends in vegetation productivity between 2001 and 2015, as well as each country's different politico-economic factors affecting land and water resource management leading up to the drought. The findings show that, although the drought was severe in Syria, it was not the only country affected, nor necessarily the worst hit meteorologically. The agricultural drought lasted 2 yr in most affected areas on the Iraqi and Syrian sides, however, only 1 yr in the affected areas on the Turkish side. The vegetation trend analysis shows a striking difference between the Syrian and Turkish sides of the border. Turkey experienced a general improvement in land productivity between 2001 and 2015, whereas Iraq and Syria show a generally negative productivity trend. The fact that the decline in rainfall had different effects on crops in each of the three countries highlights the role government and private sector resource management and infrastructure play in reducing drought vulnerability. The findings of this study highlight the need for an integrated approach to research that investigates the interconnection between climate and conflict.

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Assessing woody vegetation trends in Sahelian drylands using MODIS based seasonal metrics

Abstract: Document Version Peer reviewed version

Cited by 94 publications

References 46 publications

Desertification, resilience, and re-greening in the African Sahel – a matter of the observation period?

Desertification, resilience, and re-greening in the African Sahel – a matter of the observation period?

Evolution of Surface Hydrology in the Sahelo-Sudanian Strip: An Updated Review

Differences in resource management affects drought vulnerability across the borders between Iraq, Syria, and Turkey

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