Desertification and Re-Greening of the Sahel
Desertification and Re-Greening of the Sahel
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DOI：
10.1093/acrefore/9780190228620.013.553
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发表时间：
2017-10
期刊：
影响因子：
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通讯作者：
R. Fensholt;C. Mbow;M. Brandt;K. Rasmussen
中科院分区：
文献类型：
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作者：
R. Fensholt;C. Mbow;M. Brandt;K. Rasmussen
在过去50年中，人类活动和气候多变性在半干旱的萨赫勒地区造成了重大的环境变化，荒漠化/可耕地退化是生计和粮食安全的主要关切。在20世纪70年代初和80年代的萨赫勒干旱之后，联合国于1976年在内罗毕组织了联合国荒漠化问题会议（UNCOD），重点关注荒漠化问题。这促使人们大量增加了对荒漠化的通常危言耸听的描述，也促使人们在科学上努力了解有关的机制。全球对这一问题的关注导致将荒漠化问题指定为三项国际环境公约之一的协调中心：1992年里约会议产生的《联合国防治荒漠化公约》。这意味着为量化荒漠化的程度和了解其原因作出了巨大努力。荒漠化是一种复杂和多方面的现象，它加剧了贫困，既可以被视为土地资源枯竭的原因，也可以被视为其后果。正如《防治荒漠化公约》通过的定义所反映的那样，荒漠化是“由各种因素，包括气候变化和人类活动造成的干旱、半干旱和亚湿润干旱地区的土地退化”（联合国，1992年）。虽然荒漠化被视为与全球旱地有关的现象，但萨赫勒-苏丹地区仍然是一个特别受关注的地区，已投入大量的科学努力，以提供对所涉气候和人为因素的有经验支持的理解。尽管对萨赫勒地区的人类-环境系统进行了数十年的深入研究，但对荒漠化的严重性没有达成总体共识，科学文献的特点是对该地区环境状况的一系列相互矛盾的观察和解释。地球观测研究总体上表明，过去几十年来，萨赫勒大部分地区的降雨量和植被绿化率呈积极趋势，这被解释为生物量增加，与人类过度使用和气候变化造成广泛退化的恶性循环说法相矛盾。尽管从地球观测卫星数据中观察到的植被绿度的增加可以得到地面观测的证实，但在更精细的空间尺度上对生物多样性的长期评估在几项研究中突出显示了物种多样性的负面趋势，总体而言，尚不清楚所观察到的积极趋势是否带来了环境改善，对人民的生计产生了积极影响。
In the past 50 years, human activities and climatic variability have caused major environmental changes in the semi-arid Sahelian zone and desertification/degradation of arable lands is of major concern for livelihoods and food security. In the wake of the Sahel droughts in the early 1970s and 1980s, the UN focused on the problem of desertification by organizing the UN Conference on Desertification (UNCOD) in Nairobi in 1976. This fuelled a significant increase in the often alarmist popular accounts of desertification as well as scientific efforts in providing an understanding of the mechanisms involved. The global interest in the subject led to the nomination of desertification as focal point for one of three international environmental conventions: the UN Convention to Combat Desertification (UNCCD), emerging from the Rio conference in 1992. This implied that substantial efforts were made to quantify the extent of desertification and to understand its causes. Desertification is a complex and multi-faceted phenomenon aggravating poverty that can be seen as both a cause and a consequence of land resource depletion. As reflected in its definition adopted by the UNCCD, desertification is “land degradation in arid, semi-arid [,] and dry sub-humid areas resulting from various factors, including climate variation and human activities”(UN, 1992). While desertification was seen as a phenomenon of relevance to drylands globally, the Sahel-Sudan region remained a region of specific interest and a significant amount of scientific efforts have been invested to provide an empirically supported understanding of both climatic and anthropogenic factors involved. Despite decades of intensive research on human–environmental systems in the Sahel, there is no overall consensus about the severity of desertification and the scientific literature is characterized by a range of conflicting observations and interpretations of the environmental conditions in the region. Earth Observation (EO) studies generally show a positive trend in rainfall and vegetation greenness over the last decades for the majority of the Sahel and this has been interpreted as an increase in biomass and contradicts narratives of a vicious cycle of widespread degradation caused by human overuse and climate change. Even though an increase in vegetation greenness, as observed from EO data, can be confirmed by ground observations, long-term assessments of biodiversity at finer spatial scales highlight a negative trend in species diversity in several studies and overall it remains unclear if the observed positive trends provide an environmental improvement with positive effects on people’s livelihood.