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Article

The Greening and Wetting of the Sahel Have Leveled off since about 1999 in Relation to SST

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Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disaster, School of Geographical Sciences, Nanjing University of Information Science & Technology, Nanjing 210044, China
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State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
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Department of Atmospheric and Oceanic Science and Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD 20742, USA
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International Institute for Earth System Science, Nanjing University, Nanjing 210023, China
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School of Applied Meteorology, Nanjing University of Information Science & Technology, Nanjing 210044, China
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Department of Earth Sciences, Free University Amsterdam, 1081 HV Amsterdam, The Netherlands
*
Author to whom correspondence should be addressed.
Remote Sens. 2020, 12(17), 2723; https://doi.org/10.3390/rs12172723
Received: 12 July 2020 / Revised: 19 August 2020 / Accepted: 21 August 2020 / Published: 23 August 2020
The Sahel, a semi-arid climatic zone with highly seasonal and erratic rainfall, experienced severe droughts in the 1970s and 1980s. Based on remote sensing vegetation indices since early 1980, a clear greening trend is found, which can be attributed to the recovery of contemporaneous precipitation. Here, we present an analysis using long-term leaf area index (LAI), precipitation, and sea surface temperature (SST) records to investigate their trends and relationships. LAI and precipitation show a significant positive trend between 1982 and 2016, at 1.72 × 10 −3 yr −1 (p < 0.01) and 4.63 mm yr−1 (p < 0.01), respectively. However, a piecewise linear regression approach indicates that the trends in both LAI and precipitation are not continuous throughout the 35 year period. In fact, both the greening and wetting of the Sahel have been leveled off (pause of rapid growth) since about 1999. The trends of LAI and precipitation between 1982 and 1999 and 1999–2016 are 4.25 × 10 − 3 yr −1 to − 0.27 × 10 −3 yr −1, and 9.72 mm yr −1 to 2.17 mm yr −1, respectively. These declines in trends are further investigated using an SST index, which is composed of the SSTs of the Mediterranean Sea, the subtropical North Atlantic, and the global tropical oceans. Causality analysis based on information flow theory affirms this precipitation stabilization between 2003 and 2014. Our results highlight that both the greening and the wetting of the Sahel have been leveled off, a feature that was previously hidden in the apparent long-lasting greening and wetting records since the extreme low values in the 1980s. View Full-Text
Keywords: Sahel; precipitation; vegetation; sea surface temperature; greening; wetting Sahel; precipitation; vegetation; sea surface temperature; greening; wetting
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MDPI and ACS Style

Chen, T.; Zhou, S.; Liang, C.; Hagan, D.F.T.; Zeng, N.; Wang, J.; Shi, T.; Chen, X.; Dolman, A.J. The Greening and Wetting of the Sahel Have Leveled off since about 1999 in Relation to SST. Remote Sens. 2020, 12, 2723. https://doi.org/10.3390/rs12172723

AMA Style

Chen T, Zhou S, Liang C, Hagan DFT, Zeng N, Wang J, Shi T, Chen X, Dolman AJ. The Greening and Wetting of the Sahel Have Leveled off since about 1999 in Relation to SST. Remote Sensing. 2020; 12(17):2723. https://doi.org/10.3390/rs12172723

Chicago/Turabian Style

Chen, Tiexi, Shengjie Zhou, Chuanzhuang Liang, Daniel Fiifi Tawia Hagan, Ning Zeng, Jun Wang, Tingting Shi, Xin Chen, and A.J. Dolman. 2020. "The Greening and Wetting of the Sahel Have Leveled off since about 1999 in Relation to SST" Remote Sensing 12, no. 17: 2723. https://doi.org/10.3390/rs12172723

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