The population of Africa is predicted to double over the next 40 years, driving exceptionally high urban expansion rates that will induce significant socio-economic, environmental and health changes. In order to prepare for these changes, it is important to better understand urban growth dynamics in Africa and better predict the spatial pattern of rural-urban conversions. Previous work on urban expansion has been carried out at the city level or at the global level with a relatively coarse 5-10 km resolution. The main objective of the present paper was to develop a modelling approach at an intermediate scale in order to identify factors that influence spatial patterns of urban expansion in Africa. Boosted Regression Tree models were developed to predict the spatial pattern of rural-urban conversions in every large African city. Urban change data between circa 1990 and circa 2000 available for 20 large cities across Africa were used as training data. Results showed that the urban land in a 1 km neighbourhood and the accessibility to the city centre were the most influential variables. Results obtained were generally more accurate than results obtained using a distance-based urban expansion model and showed that the spatial pattern of small, compact and fast growing cities were easier to simulate than cities with lower population densities and a lower growth rate. The simulation method developed here will allow the production of spatially detailed urban expansion forecasts for 2020 and 2025 for Africa, data that are increasingly required by global change modellers.

中文翻译：

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非洲城市增长的空间模式建模

预计未来 40 年非洲人口将增加一倍，推动城市扩张速度异常加快，从而引发重大的社会经济、环境和健康变化。为了为这些变化做好准备，更好地了解非洲的城市增长动态并更好地预测城乡转变的空间格局非常重要。此前关于城市扩张的工作都是在城市层面或全球层面进行的，分辨率相对较粗，为5-10公里。本文的主要目标是开发一种中等规模的建模方法，以确定影响非洲城市扩张空间格局的因素。开发增强回归树模型是为了预测每个非洲大城市城乡转变的空间模式。非洲 20 个大城市的 1990 年左右至 2000 年左右的城市变化数据被用作训练数据。结果表明，1公里范围内的城市土地和通往市中心的可达性是影响最大的变量。获得的结果通常比使用基于距离的城市扩张模型获得的结果更准确，并且表明小型、紧凑和快速增长的城市的空间格局比人口密度较低和增长率较低的城市更容易模拟。这里开发的模拟方法将能够生成非洲 2020 年和 2025 年空间详细的城市扩张预测，全球变化建模者越来越需要这些数据。结果表明，1公里范围内的城市土地和通往市中心的可达性是影响最大的变量。获得的结果通常比使用基于距离的城市扩张模型获得的结果更准确，并且表明小型、紧凑和快速增长的城市的空间格局比人口密度较低和增长率较低的城市更容易模拟。这里开发的模拟方法将能够生成非洲 2020 年和 2025 年空间详细的城市扩张预测，全球变化建模者越来越需要这些数据。结果表明，1公里范围内的城市土地和通往市中心的可达性是影响最大的变量。获得的结果通常比使用基于距离的城市扩张模型获得的结果更准确，并且表明小型、紧凑和快速增长的城市的空间格局比人口密度较低和增长率较低的城市更容易模拟。这里开发的模拟方法将能够生成非洲 2020 年和 2025 年空间详细的城市扩张预测，全球变化建模者越来越需要这些数据。获得的结果通常比使用基于距离的城市扩张模型获得的结果更准确，并且表明小型、紧凑和快速增长的城市的空间格局比人口密度较低和增长率较低的城市更容易模拟。这里开发的模拟方法将能够生成非洲 2020 年和 2025 年空间详细的城市扩张预测，全球变化建模者越来越需要这些数据。获得的结果通常比使用基于距离的城市扩张模型获得的结果更准确，并且表明小型、紧凑和快速增长的城市的空间格局比人口密度较低和增长率较低的城市更容易模拟。这里开发的模拟方法将能够生成非洲 2020 年和 2025 年空间详细的城市扩张预测，全球变化建模者越来越需要这些数据。