Eleventh International Conference on Climate Change: Impacts & Responses

Abstract

Climate models indicate that climate change is likely to affect carbon (C) cycling in drylands, particularly savannas, but the magnitude and direction of change are not fully understood. In this study, we used the Century model to analyze how net primary productivity (NPP), soil respiration and soil C sequestration would respond to an increase in atmospheric CO2 and soil temperature. We also assessed the coupled effects of precipitation and temperature change on C dynamics under future climatic conditions, as well as the decoupled effects of each of the climate variables under three IPCC climate scenarios; historical, Representative Concentration Pathway 2.6 (RCP2.6) and RCP8.5. An increase in soil temperature results in loss of soil organic C (SOC), whereas doubling atmospheric CO2 concentration causes an increase in SOC. The increase in air temperature causes soil respiration to increase, while it causes NPP to decrease. We calculated the total SOC in the Kalahari savannas to be 0.9 Pg C (1 Pg = 1015 g) in the top meter, and the rate of SOC loss due to anthropogenic climate change to be ~1.1 Tg C yr-1 (1 Tg = 1012 g) and ~2.0 Tg C yr-1 under RCP2.6 and RCP8.5, respectively until the end of this century. If extrapolated to the global extent of savannas, our results imply net SOC loss of at least ~28.4 Tg C y-1 and 64.1 Tg C yr-1 under RCP2.6 and RCP8.5, respectively. Our results support the positive feedback between the SOC and atmospheric C cycles.