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Variability of African farming systemsfrom phenological analysis of NDVI time series

机译：从NDVI时间序列的物候分析看非洲农业系统的变异性

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Food security exists when people have access to sufficient, safe and nutritious food at all times to meet their dietary needs. The natural resource base is one of the many factors affecting food security. Its variability and decline creates problems for local food production. In this study we characterize for sub-Saharan Africa vegetation phenology and assess variability and trends of phenological indicators based on NDVI time series from 1982 to 2006. We focus on cumulated NDVI over the season (cumNDVI) which is a proxy for net primary productivity. Results are aggregated at the level of major farming systems, while determining also spatial variability within farming systems. High temporal variability of cumNDVI occurs in semiarid and subhumid regions. The results show a large area of positive cumNDVI trends between Senegal and South Sudan. These correspond to positive CRU rainfall trends found and relate to recovery after the 1980's droughts. We find significant negative cumNDVI trends near the south-coast of West Africa (Guinea coast) and in Tanzania. For each farming system, causes of change and variability are discussed based on available literature (Appendix A). Although food security comprises more than the local natural resource base, ourresults can perform an input for food security analysis by identifying zones of high variability or downward trends.
机译：当人们随时获得充足，安全和营养的食物以满足其饮食需求时，就存在粮食安全。自然资源基础是影响粮食安全的众多因素之一。其多变性和下降为当地粮食生产带来了问题。在这项研究中，我们表征了撒哈拉以南非洲的植被物候，并根据1982年至2006年的NDVI时间序列评估了物候指标的变化和趋势。我们专注于整个季节的累积NDVI（cumNDVI），这是净初级生产力的代表。在主要耕作系统层面汇总结果，同时确定耕作系统内的空间变异性。 cumNDVI的高时变性发生在半干旱和半湿润地区。结果表明，塞内加尔和南苏丹之间有很大的cumNDVI积极趋势。这些与发现的CRU降雨趋势呈正相关，并与1980年代干旱后的恢复有关。我们在西非东南部（几内亚海岸）和坦桑尼亚发现显着的cumNDVI负趋势。对于每种耕作系统，根据现有文献讨论了变化和变异的原因（附录A）。尽管粮食安全不仅仅包括当地的自然资源，但我们的结果可以通过识别高度变化或下降趋势的区域来进行粮食安全分析。

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