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

Remote Sensing

Tiexi Chen¹  A.J. Dolman¹  Xin Chen¹  DanielFiifi Tawia Hagan¹  Shengjie Zhou¹  Chuanzhuang Liang¹  Jun Wang²  Tingting Shi³  Ning Zeng⁴ 

[1] Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disaster, School of Geographical Sciences, Nanjing University of Information Science & Technology, Nanjing 210044, China;International Institute for Earth System Science, Nanjing University, Nanjing 210023, China;School of Applied Meteorology, Nanjing University of Information Science & Technology, Nanjing 210044, China;State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China;

关键词: Sahel;    precipitation;    vegetation;    sea surface temperature;    greening;    wetting;   

DOI  :  10.3390/rs12172723

来源: DOAJ

【 摘 要 】

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.

【 授权许可】

Unknown