Changes in Sahel Land-Surface Characteristics and Climate Variation

小行星9706403 萨赫勒地区有两种截然不同的水文现象：一是持续干旱，很可能部分是由地表变化造成的;二是地表水平衡出现重大季节性变化。 将进行模拟，将国家环境评估方案的大气环流模式与生物圈模式（SSiB）结合起来，该模式已根据HAPEX和SEBEX数据进行了校准和验证，以调查地表条件对萨赫勒地区水文过程和区域气候变异的影响，特别是土地覆盖对萨赫勒地区长期干旱模式的影响。 这些模拟将利用从实地测量和卫星观测中获得的土地财产数据和土地覆盖物数据，评价在确定降雨量时区域和当地水分来源之间的综合情况。 将探讨植被分布的不均匀性对陆-气相互作用的影响。 随后将制定一种方法，将陆面参数汇总到全球环流模式格网框或次格网框。 该研究将集中在如何土地 条件改变降雨、ET、土壤水和径流的季节性模式。将通过与观测到的降雨量、地表温度、特别是河流流量的变化进行比较来确认结果。 将使用河流路径模型将地面模型在GCM的每个网格单元中产生的径流值转换为流域出口。 将进行诊断分析，以确定萨赫勒降水的来源，以及每种蒸发源对萨赫勒降水及其异常的相对贡献。 还将注意研究陆面过程对AFJ动力学和波传播的影响。 将检验陆面效应对各种土地强迫异常模式的重要性，这些模式包括不同程度的陆面退化和一个GCM格框中不同百分比的植被覆盖变化。

9706403 Xue There are two distinct hydrological phenomena in the Sahel: a persistent drought, which is very likely to have been partially caused by the land surface change, and a significant seasonal variation in the surface water balance. Simulations that couple a NCEP GCM with a biosphere model (SSiB), which has been calibrated and validated against HAPEX and SEBEX data, will be conducted to investigate influences of land-surface conditions on hydrological processes and regional climate variability in the Sahel, especially the impact of land cover on long-term Sahel drought patters. The simulations will use land property data and land cover data from field measurements and satellite observations to evaluate the integration between regional and local moisture sources in determining rainfall. The impacts of heterogeneity of vegetation distribution on land-atmosphere interactions will be explored. It will be followed by the development of a methodology to aggregate land-surface parameters to GCM grid boxes or sub-grid box. The study will focus on how land condition changes seasonal patterns in rainfall, ET, Soil water, and runoff. The results will be confirmed through comparisons with observed changing rainfall, surface temperature, and in particular, the river discharge. A river routing model will be used to convert the runoff values produced by the land surface model in each grid cell of a GCM to the basin outlet. The diagnostic analyses will be made to determine sources of Sahel precipitation, and relative contributions of each evaporation source to the rainfall and its anomalies in the Sahel. Attention will also be paid to study the impacts of land surface processes on AFJ dynamics and wave propagation. The significance of the land surface effects will be tested with respect to various patterns of land forcing anomalies, which include different degrees of land surface degradation and different percentage of vegetation cover changes in one GCM grid box.