Emissões de gases do efeito estufa e estoque de carbono no solo em cenários de mudanças climáticas e uso da terra na bacia estendida do Rio São Francisco.

Abstract

Greenhouse gas (GHG) emissions are the main agents of climate change and come mainly from activities associated with the use of fossil fuels, agriculture and livestock and land use change. Thus, the soil, as the main terrestrial reservoir of organic carbon, has become na important base for research as it can act as a sink or source of atmospheric C. Studies that carry out estimates of GHG emissions and C changes in the soil are of fundamental importance to efficiently assist land use. The objective of this work was to evaluate the dynamics of agricultural activities and estimate greenhouse gas emissions in the period 2005 to 2017, as well as in climate change scenarios for the periods 2021-2030, 2031-40 and 2041- 2050; in addition to estimating area changes in land use and changes in soil C stocks due to land use changes over the period 1985 to 2017 in the Extended São Francisco River Basin (BESF). The estimates of GHG emissions for the agricultural sector at BESF for the period 2005 to 2017 were based on the methodologies employed in the Guide for National Greenhouse Gas Inventories of the International Panel on Climate Change and in the Reference Reports of the Fourth National Communication of the Brazil to the United Nations Framework Convention on Climate Change, using data obtained from the IBGE System of Automatic Recovery, which were used as indicators of agriculture at BESF. In addition, emission estimates in future periods were performed with future productivity data estimated from the determination of future impacts on the climate using the ETA HadGEM2-ES CMIP5 climatological model for the simulations. Estimates of changes in soil C stocks for the periods 1985 to 2005, 1997 to 2017 and 1985 to 2017 were performed considering the association between the BESF region and the classes aggregated by land use and management system based on the described methodology by the IPCC, through geoprocessing techniques using the combination of reference carbon data, land use classes and specific emission factors of the management systems. The animal population at BESF in 2017 was 106.06 million heads and total production of the main crops analyzed was 33.64 million tons. Emissions from the agricultural sector totaled 36,946.26 Gg CO2eq in 2017, with the largest contribution attributed to the Enteric Fermentation subsector with an estimated emission of 21,714.63 Gg CO2eq in 2017. For the period 2041-50, an estimated emission of 44,906.98 Gg CO2eq from the agricultural sector in the BESF region, making it the period with the highest amount of GHG emitted. The use and coverage of land by human activities and water bodies occupy 41.1% of BESF's total area. Changes in soil organic carbon stocks in BESF during the entire period analyzed, from 1985 to 2017, resulted in an increase of 0.72 Mt C yr-1 , with an average rate of 0.12 t C ha-1 yr-1 . Agricultural activity at BESF grew during the period 2005 to 2017, as did GHG emissions, with a trend towards changes in the animal population and in the average productivity gain of agricultural crops in view of future climate change scenarios, with a worrying increase in emissions GHG, requiring practices and management of water resources that minimize the impacts caused by climate change, with the soil being a potential C mitigation system through the adoption of conservation management. Key words: Agriculture, Global Warming, Caatinga, Cerrado, Atlantic Forest.