STORMFLOW SIMULATION USING A GEOGRAPHICAL INFORMATION SYSTEM WITH A DISTRIBUTED APPROACH1

ABSTRACT: With the increasing availability of digital and remotely sensed data such as land use, soil texture, and digital elevation models (DEMs), geographic information systems (GIS) have become an indispensable tool in preprocessing data sets for watershed hydrologic modeling and post processing simulation results. However, model inputs and outputs must be transferred between the model and the GIS. These transfers can be greatly simplified by incorporating the model itself into the GIS environment. To this end, a simple hydrologic model, which incorporates the curve number method of rainfall‐runoff partitioning, the ground‐water base‐flow routine, and the Muskingum flow routing procedure, was implemented on the GIS. The model interfaces directly with stream network, flow direction, and watershed boundary data generated using standard GIS terrain analysis tools; and while the model is running, various data layers may be viewed at each time step using the full display capabilities. The terrain analysis tools were first used to delineate the drainage basins and stream networks for the Susquehanna River. Then the model was used to simulate the hydrologic response of the Upper West Branch of the Susquehanna to two different storms. The simulated streamflow hydrographs compare well with the observed hydrographs at the basin outlet.     

非洲的土地生态:农业发展的机遇和障碍

与其他大陆地区相比,过去40年来非洲撒哈拉以南地区的经济增长一直比较缓慢.同样,该地区农业的发展也有限,绿色革命几乎没有波及到这里.有关文献提出了这样的问题造成这种发展迟缓的原因,究竟是政策的不力,还是该地恶劣的自然条件所致(也就是说,是人为造成的,还是命中注定的).本文从一个更宽的视角出发,分析了目前非洲地区土地利用对环境条件的适应性,比较了非洲与亚洲的自然资源背景.为此,我们对能够实际促进农业发展的统一性原理进行了探讨.结果表明,由于自然资源背景的一些特殊性,也就是构成主体的基底杂岩土壤的局部均一性和空间异质性,仅仅通过简单的施肥策略不能使该地区的粮食产量提高达到其他地区的水平.     

African land ecology: opportunities and constraints for agricultural development

Compared to other continents, the economic growth performance of Sub-Saharan Africa has been poor over the last four decades. Likewise, progress in agricultural development has been limited and the Green Revolution left Africa almost untouched. The question raised in the literature is whether the poor performance is a question of poor policies or of an unfavorable biophysical environment (policy versus destiny). This paper, with a broad perspective, analyzes adaptation of current land use to environmental conditions in Africa and compares the physical resource base of Africa with Asia. In doing so, we search for unifying principles that can have operational consequences for agricultural development. We argue that some specificities of the natural resource base, namely local homogeneity and spatial diversity of the predominant Basement Complex soils, imply that simple fertilizer strategies may not produce the yield increases obtained elsewhere.