Model results in NetCDF format of North African vegetation-precipitation in early and mid-Holocene climate simulated by CCSM3-DGVM//

The present study analyses the sign, strength, and working mechanism of the vegetation-precipitation feedback over North Africa in middle (6 ka BP) and early Holocene (9 ka BP) simulations using the comprehensive coupled climate-vegetation model CCSM3-DGVM (Community Climate System Model version 3 and a dynamic global vegetation model). The coupled model simulates enhanced summer rainfall and a northward migration of the West African monsoon trough along with an expansion of the vegetation cover for the early and middle Holocene compared to the pre-industrial period. It is shown that dynamic vegetation enhances the orbitally triggered summer precipitation anomaly by approximately 20% in the Sahara-Sahel region (10-25° N, 20° W-30° E) in both the early and mid-Holocene experiments compared to their fixed-vegetation counterparts. The primary vegetation-rainfall feedback identified here operates through surface latent heat flux anomalies by canopy evaporation and transpiration and their effect on the mid-tropospheric African easterly jet, whereas the effects of vegetation changes on surface albedo and local water recycling play a negligible role. Even though CCSM3-DGVM simulates a positive vegetation-precipitation feedback in the North African region, this feedback is not strong enough to produce multiple equilibrium climate-ecosystem states on a regional scale.

本研究采用综合耦合气候-植被模型CCSM3-DGVM（通用气候系统模型第3版（Community Climate System Model version 3）与动态全球植被模型（dynamic global vegetation model）），针对全新世早期（9 ka BP）与中期（6 ka BP）的模拟结果，分析北非地区植被-降水反馈的信号特征、强度及作用机制。相较于前工业化时期，该耦合模型模拟显示，全新世早、中期的夏季降水显著增强，西非季风槽向北迁移，植被覆盖范围亦有所扩张。研究表明，在撒哈拉-萨赫勒地区（10°N~25°N，20°W~30°E），相较于固定植被对照组，动态植被可使全新世早、中期由轨道因子触发的夏季降水异常提升约20%。本研究识别出的核心植被-降水反馈机制，通过冠层蒸发与蒸腾引发的地表潜热通量异常，及其对对流层中层非洲东风急流的影响实现；而植被变化对地表反照率与局地水循环的影响则可忽略不计。尽管CCSM3-DGVM模拟得到北非地区存在正向植被-降水反馈，但该反馈强度不足以在区域尺度上催生多重平衡气候-生态系统状态。