Past and future of GHG observations in Africa

Abstract:

Through the projects CarboAfrica before (2006-2010) and Africa-GHG afterwards (2010-2014) the authors have contributed to the development of a flux monitoring network in Sub-Saharan Africa and studied the Africa’s GHG budget using different integrated approaches.

The first GHG flux observatory in an African tropical rainforest was established, based on a 60m eddy covariance flux tower in the Ankasa Conservation Area, Ghana. CO2, water and energy fluxes, as well as atmospheric concentrations of gaseous N compounds and aerosols, were measured continuously throughout the year. Field campaigns were carried out during the wet and dry season to measure CH4 and N2O fluxes. The results showed that the tropical forest was acting as C-sink (6-8 MgC ha-1 yr-1).

Other measurements and results concerned:

• the role of CO2 fertilization by analyzing wood growth rings of long-lived trees, with the longest (≈ 400 years) chronology for tropical forests;

• 14C measurements of soil organic matter age and turnover, showing the critical role that soil may have on the net organic C accumulation in tropical forests;

• the role of soil as CH4 source even in forests not visibly flooded;

• the role of tropical forests as natural source of N2O;

• the application of advanced remote sensing techniques, such as discrete and wave forms LiDAR, to assess tropical forests biomass and biodiversity.

All these data were combined with other modeling and observing efforts to reassess the African continent GHG budget. The results showed that Africa is a small sink of carbon (-0.61±0.58 PgC yr-1), but the emissions of CH4 and N2O turn it into a net source of radiative forcing in CO2 equivalent terms. Uncertainties however are still very high. In order to constrain such uncertainty it is of paramount importance to increase the density of observations in space and time so to cover the complex and dynamic temporal and spatial variability of African ecosystems.