Drylands cover around 40% of the land surface on Earth and are inhabited by more than 2 billion people, who are directly dependent on these lands. Drylands are characterized by a highly variable rainfall regime and inherent vegetation-climate feedbacks that can enhance the resilience of the system, but also can amplify disturbances. In that way, the system may get locked into two alternate stable states: one relatively wet and vegetated, and the other dry and barren. The resilience of dryland ecosystems derives from a number of adaptive mechanisms by which the vegetation copes with prolonged water stress, such as hydraulic redistribution. The stochastic nature of both the vegetation dynamics and the rainfall regime is a key characteristic of these systems and affects its management in relation to the feedbacks. How the ecohydrology of the African drylands will change in the future depends on further changes in climate, human disturbances, land use, and the socioeconomic system.
A. Johannes Dolman, Luis U. Vilasa-Abad, and Thomas A. J. Janssen
Biomass burning is widespread in sub-Saharan Africa, which harbors more than half of global biomass burning activity. These African open fires are mostly induced by humans for various purposes, ranging from agricultural land clearing and residue burning to deforestation. They affect a wide variety of land ecosystems, including forests, woodlands, shrublands, savannas, grasslands, and croplands. Satellite observations show that fires are distributed almost equally between the northern and southern hemispheres of sub-Saharan Africa, with a dipole-type annual distribution pattern, peaking during the dry (winter) season of either hemisphere. The widespread nature of African biomass burning and the tremendous amounts of particulate and gas-phase emissions the fires produce have been shown to affect a variety of processes that ultimately impact the earth’s atmospheric composition and chemistry, air quality, water cycle, and climate in a significant manner. However, there is still a high level of uncertainty in the quantitative characterization of biomass burning, and its emissions and impacts in Africa and globally. These uncertainties can be potentially alleviated through improvements in the spatial and temporal resolutions of satellite observations, numerical modeling and data assimilation, complemented by occasional field campaigns. In addition, there is great need for the general public, policy makers, and funding organizations within Africa to recognize the seriousness of uncontrolled biomass burning and its potential consequences, in order to bring the necessary human and financial resources to bear on essential policies and scientific research activities that can effectively address the threats posed by the combined adverse influences of the changing climate, biomass burning, and other environmental challenges in sub-Saharan Africa.