Variability and recent trends in the African terrestrial carbon balance
Variability and recent trends in the African terrestrial carbon balance
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DOI：
10.5194/bg-6-1935-2009
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发表时间：
2009-01-01
期刊：
影响因子：
4.9
通讯作者：
Chedin, A.
中科院分区：
文献类型：
--
作者：
Ciais, P.;Piao, S. -L.;Chedin, A.
我们模拟了非洲陆地碳平衡在过去的世纪，使用空间分辨过程为基础的植被模型（ORCHIDEE）。该模型是由不断变化的气候和人类引起的土地利用变化所推动的。它包括一个简单的参数化的自然火灾，但自然植被动态被忽略。分析的时间段是1901-2002年。总的来说，我们发现，非洲净陆地碳平衡（净生物群落生产力，NBP）增加了从净CO2源的大气中的0.14 PgC年（-1）在20世纪80年代到净汇的0.15 PgC年（-1）在20世纪90年代。据估计，仅土地利用通量一项，就有0.13 PgC yr（-1）是由毁林造成的。这意味着气候趋势（主要是降水量增加）和CO2增加（施肥效应）正在造成0.28 PgC yr（-1）的汇，抵消了土地利用源。结果表明，NBP的年际变化较大，主要受光合作用的影响。在热带稀树草原，光合作用从一年到下一年的变化与降雨量的变化密切相关（北方非洲的R-2 = 0.77，南部非洲热带稀树草原的R-2=0.42）。在森林中，这样的控制降雨是没有发现的NBP和光合作用/生态系统呼吸通量的年际变化的主要空间格局与ENSO，干燥的条件下，在热带稀树草原在厄尔尼诺和潮湿的条件下，森林。气候引起的火灾排放的变化响应于这种ENSO强迫，但不强烈地决定NBP年际变化。最后，我们的模型，生态系统的呼吸变化（主要是自养呼吸）与光合作用，在年际和十年的时间尺度上，但这一结果是不确定的潜在的驯化自养呼吸过程。
We modeled the African terrestrial carbon balance over the past century using a spatially resolved process based vegetation model (ORCHIDEE). The model is forced by changing climate and by human-induced changes in land use. It includes a simple parameterization of natural fires, but the natural vegetation dynamics was ignored. The period analyzed is 1901-2002. Overall, we found that the African net terrestrial carbon balance (Net Biome Productivity, NBP) increased from a net CO2 source to the atmosphere of 0.14 PgC yr(-1) in the 1980s to a net sink of 0.15 Pg C yr(-1) in the 1990s. The land use flux alone is estimated to be a source of 0.13 PgC yr(-1) caused by deforestation. This implies that climatic trends (mainly increasing precipitation) and CO2 increase (fertilization effect), are causing a sink of 0.28 PgC yr(-1) which offsets the land-use source. We found that the interannual variability of NBP is large, and mostly driven by photosynthesis variability. Over savannas, photosynthesis changes from one year to the next are strongly correlated with rainfall changes (R-2 = 0.77 in northern Africa, and R-2=0.42 in southern African savannas). Over forests, such a control by rainfall is not found. The main spatial pattern of interannual variability in NBP and photosynthesis/ecosystem respiration fluxes is related with ENSO, with dryer conditions prevailing over savannas during El Nino and wetter conditions over forests. Climate induced variations in fire emissions respond to this ENSO forcing, but do not determine strongly the NBP interannual variability. Finally, we model that ecosystem respiration variations (mostly autotrophic respiration) are correlated with those of photosynthesis, on interannual as well as on decadal time scales, but this result is uncertain given the potential for acclimation for autotrophic respiration processes.