Clustered land restoration projects increase cloud formation in West African drylands

Land restoration projects are implemented across Africa to combat land degradation and climate change. By changing the vegetation cover, these projects can potentially impact cloud formation through changes in energy and water partitioning between the Earth's surface and the atmosphere. In West Africa, satellite observations have shown an increase in cloud formation over restored areas. However, even though the spatial arrangement of restored areas differs between regreening approaches, such as farmer-managed natural regeneration, area protection or reforestation, it is unknown how the spatial pattern of restoration projects impacts cloud formation. In this study, we use the Weather Research and Forecasting (WRF) mesoscale atmospheric model to determine how land restoration affects cloud formation for a case study at the border of the transnational W-Arly-Pendjari national park complex, with a sharp boundary between forest and grassland. First, we carry out a sensitivity analysis to determine the underlying mechanisms of cloud formation over forest regions, after which we run 27 land restoration scenarios with low (21%), intermediate (43%), and high (85%) forest cover and varying spatial clustering to assess the impact of land restoration patterns on cloud formation. The results highlight that an intermediate forest cover with higher clustering increases cloud formation due to stronger mesoscale circulation. A small scale heterogeneity in forest cover or a high forest cover, on the other hand, inhibits cloud formation. Because clouds play an important role in the Earth's water and energy balance, these results provide important insight into how projects can be designed to increase their climate benefits.