Contrasting consequences of the Great Green Wall: Easing aridity while increasing heat extremes

• Published in: One earth (Cambridge, Mass.) Vol. 7; no. 3; pp. 455 - 472
• Main Authors: Ingrosso, Roberto, Pausata, Francesco S.R.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 15.03.2024
• Subjects: Africa; extreme; monsoon; Sahel; Wall; monsoon; Wall; extreme; Sahel; Africa
• ISSN: 2590-3322; 2590-3322
• DOI: 10.1016/j.oneear.2024.01.017

The Great Green Wall (GGW) is a multibillion-dollar African initiative to combat desertification in the Sahel. However, the potential climate impacts of the most recent GGW plan on northern Africa have not yet been adequately evaluated, raising concerns about unforeseen climate ramifications that could affect stability in northern Africa and undermine the goals of the initiative. Using a high-resolution (∼13 km) regional climate model, we evaluate the climate impacts of four GGW scenarios with varying vegetation densities under two extreme emission pathways (low and high). Higher vegetation density GGW scenarios under both emission pathways show enhanced rainfall, reduced drought lengths, and decreased summer temperatures beyond the GGW region relative to the cases with no GGW. However, all GGW scenarios show more extreme hot days and higher heat indices in the pre-monsoonal season. These findings highlight the GGW contrasting climatic effects, emphasizing the need for comprehensive assessments in shaping future policies. [Display omitted] •The GGW effectively reduces drought lengths•While decreasing temperature in summer, the GGW causes warming in the other seasons•The GGW leads to an increase in temperature extremes•While water availability improves, the heat stress on local population worsens Africa’s Great Green Wall (GGW) initiative seeks to plant a wall of trees across the entire Sahel in an effort to hold back the expansion of the Sahara Desert and restore degraded land to the benefit of local communities. Although this geoengineering project has potential advantages, the extent to which the experiment will lead to a noticeable reduction in the intensity of droughts and heatwaves remains unclear. Without a deeper understanding of the potential climate impacts of the project, land restoration goals may not be achieved. Computer modeling that considers different GGW scenarios with different combinations of grasses and tree species, reveals that, while the project could increase rainfall and decrease drought duration, this would be accompanied by more extreme heat events in the pre-monsoonal season. Recognizing these diverse effects is essential for policymakers to align the GGW’s goals with sustainable climate targets and mitigate potential regional repercussions. The Great Green Wall (GGW) initiative in Sahel aims to combat desertification but lacks a thorough understanding of its potential climate impacts. Our study considers multiple vegetation density and global warming scenarios. The GGW generally led to increased rainfall, reduced drought lengths, and cooler summer temperatures beyond its immediate borders. However, all scenarios show more extreme heat events. Understanding these diverse effects is crucial for policymakers to align the GGW goals with sustainable climate targets and mitigate potential regional repercussions.