Changes in Sahel Land-Surface Characteristics and Climate Variation

[405431薛]自20世纪60年代末以来，非洲萨赫勒地区的气候一直以干旱为主。许多研究表明，撒哈拉以南地区的地表-大气相互作用非常强，地表反馈可能在萨赫勒干旱中发挥了作用。然而，在这些研究中，大多数只使用了简单的地表模型，结果从未与观测数据进行验证。在过去五年中，在萨赫勒地区进行了两次综合地面场测量（HAPEX-Sahel和SEBEX）。这些数据集将用于验证简单生物圈模型（SSiB）的简化版本，并为GCM边界条件创建植被数据集。在定标研究中，将特别关注共存植被覆盖的真实模拟，这是地表非均质性的表现之一。研究了地表方案对植被和土壤参数值的敏感性。这一校准将有助于我们改进对水文循环和地表能量收支的模拟。生物圈-大气耦合模式将用于研究地表过程和大气动力学在确定萨赫勒地区气候和水文变化中的作用。为了理解地表反馈的机制，我们将植被和土壤参数分为几组。每个组及其组合对模拟的萨赫勒气候异常的影响将被检查。异质性的影响也将被研究。根据上述建议的研究结果，将进行两次多年数值积分。长期整合将允许对结果进行更严格的统计显著性检验。控制运行的结果将用于分析撒哈拉以南地区水和能量平衡年循环的模拟。萨赫勒的陆地表面被指定为沙漠化地区的异常运行将被用来评估沙漠化在所有季节对区域和全球气候和水文的影响。由于这项1994年7月25日的敏感性研究是以全面的观测数据为基础的，它的成功完成将有助于我们现实地评估区域和全球气候中沙漠化的后果，特别是萨赫勒干旱。

9405431 Xue The climate in the Sahel area of Africa has been dominated by drought since the late 1960's. A number of studies have shown that the land surface-atmosphere interaction in the sub-Sahara region is very strong and that the land surface feedback may have played a role in the Sahel drought. However, in most of these studies only simple surface models were used and the results were never verified against observational data. Two comprehensive surface field measurements (HAPEX-Sahel and SEBEX) were conducted in the Sahel during the past five years. These data sets will be used to validate a simplified version of the Simple Biosphere Model (SSiB) and to create vegetation data sets for GCM boundary conditions. In the calibration study, special attention will be given to the realistic simulation of co-existing vegetation covers, which is one of the manifestations of surface heterogeneity. The sensitivity of the land-surface scheme to vegetation and soil parameter values will be investigated. This calibration will help us to improve the simulation of the hydrological cycle and the surface energy budget. The coupled biosphere-atmosphere model will be used to study the roles of the surface processes and atmospheric dynamics in determining the variation in the climate and hydrology of the Sahel. To understand the mechanisms of land surface feedback, we will divide the vegetation and soil parameters into several groups. The effects of each group and their combination on the simulated climate anomaly in the Sahel will be examined. The effect of heterogeneity will also be investigated. Based on the results of the above proposed studies, two multi-year numerical integrations will be conducted. The long term integration will allow more stringent statistical significance testing of the results. The results from the control run will be used to analyze The simulation of the annual cycle of water and energy balances in the sub-Sahara area. the anomaly run, in which the land surface in the Sahel is assigned as a desertification area, will be used to assess the effects of the desertification on the regional and global climate and hydrology during all seasons. Since this July 25, 1994 sensitivity study is based upon comprehensive observational data, its successful completion will help us in realistically assessing the consequences of the desertification in the regional as well as the global climate, in particular the Sahel drought.