Response of southern African vegetation to climate change at 1.5 and 2.0° global warming above the pre-industrial level

Abstract

Climate change has severely impacted southern African vegetation over the last decades. Recent studies have shown that limiting the global warming level to well below 2 °C above pre-industrial level may reduce the catastrophic effects of anthropogenic climate change. However, there is limited knowledge on the response of vegetation to climate change at different global warming levels. This study examines how southern African vegetation may respond to climate change at 1.5 °C and 2 °C warming. An ensemble of climate projections from the CESM model were analyzed to evaluate the potential changes in timing and magnitude of vegetation index and parameters across southern African biomes for a global warming of 1.5 °C and 2 °C under the RCP8.5 scenario. The results show that the spatial pattern of the Normalized Difference Vegetation Index (NDVI) are well captured by the ensemble mean. However, the model overestimates NDVI over the east coast of South Africa while it underestimates it over Angola. The strong relationship between the NDVI and other vegetation parameters (e.g. net primary production, leaf area cover) over southern Africa, suggests that vegetation productivity is projected to decline over Mozambique, Namibia, Botswana, Zimbabwe and Zambia at 1.5 °C and 2 °C warming. However, vegetation productivity is projected to likely increase over some parts of Madagascar and South Africa. The results further show that there is a similarity in the response of vegetation parameters at 1.5 °C and 2 °C warming. The difference in projected changes of the above ground net primary production, soil carbon and surface run-off is negligible between 1.5 °C and 2 °C warming. While the model ensemble members show a range in the magnitude of changes, they all project an increase in below ground net primary production, soil carbon and photosynthesis over the southern African biomes while projecting a decline in canopy transpiration over all the biomes. Furthermore, the CESM projects an increase in drought intensity as temperature increases over the southern African biomes. The projected changes in the drought intensity appears more pronounced with the Standardized Precipitation Evapotranspiration Index (SPEI) than with the Standardized Precipitation Index (SPI). The results of the study is important in informing policy makers for climate change mitigation and adaptation efforts in southern Africa. For effective mitigation and adaptation strategy, there is a need to translate the results to make them more accessible to inform policy through the use of appropriate engagement platforms such as multi-stakeholder partnerships and workshops.