Importance of soil properties for simulating vegetation during the Green Sahara period

During the early to middle Holocene, the Sahara received enhanced precipitation and was covered by steppe-like vegetation. However, most coupled land-atmosphere models underestimate the precipitation and vegetation cover, suggesting that critical atmospheric or land surface processes are lacking in models. Here, we examine in a land surface model five plausible soil-vegetation processes that may modify soil hydraulic properties. We show that these processes have strong positive impacts on vegetation and soil moisture, especially the increase of soil evaporative resistance. After considering all soil feedbacks on vegetation, the model requires precipitation of ~400 mm/yr to reproduce the pollen-inferred vegetation extension in the mid-Holocene Sahara. From the mid-Holocene to pre-industrial period, we infer that terrestrial carbon stocks decrease by ~58 PgC due to the removal of carbon in vegetation, soil and litter pools. We propose it is essential for future model studies to have a better representation of soil processes. These files contain output of our sensitivity simulations with ORCHIDEE-MICT land surface model.在全新世（Holocene）早中期，撒哈拉地区降水显著增多，区域被草原类植被覆盖。然而，多数陆气耦合模式（coupled land-atmosphere models）对该区域降水与植被覆盖度的模拟结果偏低，这表明现有模式中缺失了关键的大气或陆面过程。本研究基于陆面模式（land surface model），对五种可改变土壤水力特性（soil hydraulic properties）的合理土壤-植被过程展开分析。研究结果表明，这些过程对植被与土壤湿度具有显著的正向影响，其中以土壤蒸发阻力（soil evaporative resistance）的提升作用最为突出。在纳入所有土壤对植被的反馈作用后，该模式需要约400毫米/年的降水，才能复现全新世中期撒哈拉地区经孢粉反演（pollen-inferred）得到的植被扩张情况。从全新世中期到工业革命前时期，我们估算得到陆地碳库（terrestrial carbon stocks）因植被、土壤与凋落物库（litter pools）中的碳流失，总量减少了约58拍克碳（PgC）。我们提出，未来的模式研究需更精准地刻画土壤过程，这一点至关重要。本数据集包含我们基于ORCHIDEE-MICT陆面模式开展的敏感性模拟实验的输出结果。