Global and Sahel Regional Biophysical Processes, Vegetation Dynamics, and Climate Interactions
Global and Sahel Regional Biophysical Processes, Vegetation Dynamics, and Climate Interactions
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全球和萨赫勒区域生物物理过程、植被动态和气候相互作用
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发表时间：
2013
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通讯作者：
G. Song
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作者：
G. Song
Author（s）：宋国琼|顾问：薛永康|摘要：这项研究的目的是更好地了解全球和区域尺度上的生物物理过程、植被动态和气候相互作用。萨赫勒是这项研究的主要重点地区。我们的方法是基于观测分析，以及模拟的国家环境预测中心（NCEP）大气环流模型（AGCM）加上简化的简单生物圈模型版本2（SSiB 2）和离线版本的SSiB 4加上动态全球植被模型（DGVM）自上而下的交互式树叶和植物群，包括动态（TRIFFID）。本文首先从长时间尺度的角度研究了植被生物物理过程（VBP）对气候的影响，特别是利用NCEP AGCM结合SSiB 2和双层土壤模式两种不同的陆面参数化，研究了近60年来年际和年代际气候变率。在年际时间尺度上，VBP的模拟使均方根误差降低了约65%。此外，在年代际时间尺度上，VBP通过改变地表能量平衡、地表潜热通量和感热通量的分配以及大气环流和水汽通量的辐合来校正西非、南非、亚马逊和东亚地区的干湿偏差。并确定控制气候响应LULCC的机制，通过使用最新的LULCC数据在一个“理想化的，但现实的”方式在过去的六十年。土地利用、土地利用变化和气候变化导致蒸发量增加和蒸发量减少。热带效应（冷却）和蒸发效应（变暖）相互竞争，导致热带地区的地表温度较高，而中纬度地区的地表温度较低。在全球陆地上，LULCC放大了地表变暖（全球陆地为0.11K，退化地区为0.43K）。LULCC导致全球降水减少（全球陆地为-0.15 mm/天，退化地区为-0.35 mm/天），季风区的信号最强，这是由于蒸发减少和季风辐合区的辐合减少。最后，通过不同尺度下的生物物理和光合作用过程，系统地研究了西非气候变异和异常对该区域陆地生态系统的影响，包括植物功能类型（PFT）和其他植被特征的空间分布和时间变化。本研究中使用了离线SSiB 4/TRIFFID模型。结果表明，模拟的PFT的空间分布和总叶面积指数（LAI）与气候变率有很好的对应关系，与卫星反演的植被状况相一致。模拟的植被状况的年代际变化与1970年代和1980年代萨赫勒干旱以及1990年代和2000年代的部分恢复是一致的。SSiB 4/TRIFFID模拟的植被特征主要响应于气温、土壤湿度和辐射通量。
Author(s): Song, Guoqiong | Advisor(s): Xue, Yongkang | Abstract: The objective of this research is to gain a better understanding of the biophysical processes, vegetation dynamics, and climate interactions on global and regional scales. Sahel is the major focus region for this research. Our methodology is based on the analysis of observations, as well as simulations by the National Centers for Environmental Prediction (NCEP) Atmospheric General Circulation Model (AGCM) coupled with the Simplified Simple Biosphere model version 2 (SSiB2) and an offline version of the SSiB4 coupled with a Dynamic Global Vegetation Model (DGVM) Top-down Representation of Interactive Foliage and Flora Including Dynamics (TRIFFID). We first examine the impact of vegetation biophysical processes (VBP) on climate from a long temporal scale point of view, specifically, the climate variability on inter-annual and inter-decadal time scales in the past six decades by using the NCEP AGCM coupled with two different land surface parameterizations: SSiB2 and the two-layer soil model. At the inter-annual time scale, the simulation with VBP decreases the root mean squared error by about 65%. Moreover, on inter-decadal time scale, VBP corrects the wet or dry biases over West Africa, South Africa, Amazon, and East Asia, through changing surface energy balances and the partitioning of surface latent and sensible heat fluxes, as well as changing atmospheric circulation and moisture flux convergence.In the second part, we systematically investigate the climate impact of large-scale land use land cover change (LULCC), and identify the mechanisms that control the response of climate to LULCC, by using the most recent LULCC data in an "idealized but realistic" way for the past six decades. LULCC leads to an increase in albedo and decrease in evaporation. The albedo effect (cooling) and evaporation effect (warming) compete with each other, resulting in warmer surface temperatures at tropics, and cooler surface temperatures at middle latitude. Over global land, the LULCC amplifies surface warming (0.11K over global land and 0.43K over degraded area respectively). LULCC cause a precipitation reduction globally (-0.15mm/day over global land and -0.35mm/day over degraded areas), with strongest signals over monsoon regions, resulting from evaporation reduction and less convergence from monsoon convergence zones. Finally, I systematically investigate how climate variability and anomalies in West Africa affect the regional terrestrial ecosystem, including spatial distribution and temporal variations of plant functional types' (PFT) and other vegetation characteristics, though biophysical and photosynthesis processes at different scales. The offline SSiB4/TRIFFID model is used in this study. The results show that the simulated PFT's spatial distribution and total leaf area index (LAI) correspond well to climate variability and are consistent with satellite derived vegetation conditions. The simulated inter-decadal variability in vegetation conditions is consistent with the Sahel drought in the 1970s and the 1980s and partial recovery in the 1990s and the 2000s. The vegetation characteristics simulated by SSiB4/TRIFFID responds primarily to air temperature, soil moisture and radiative fluxes.