Hzami Abderraouf, Heggy Essam, Amrouni Oula, Mahé Gil, Maanan Mohamed, Abdeljaouad Saâdi
Faculty of Sciences of Tunis, University of Tunis El Manar, Tunis, Tunisia.
Viterbi School of Engineering, University of Southern California (USC), 3737 Watt Way, Powell Hall of Engineering, Office 502, Los Angeles, CA, 90089-1112, USA.
Sci Rep. 2021 Jan 27;11(1):2320. doi: 10.1038/s41598-020-77926-x.
The arid coasts of North Africa, extending over 4633 km from the Gulf of Tunis to the Nile Delta, are undergoing pronounced shoreline retreats and coastal floodings that are reported as a consequence of the ongoing sea level rise resulting from global warming. Of particular interest are the abnormal shoreline dynamics for deltaic and sandy beaches, which are severely impacted by abrupt decadal variabilities in both climatic and anthropogenic drivers resulting in their increased vulnerability to disturbances from coastal hazards. Unfortunately, the evolution, distribution and impacts of these drivers remain largely unquantified, let alone understood, for these extensive arid coasts that harbor the major portion of North Africa's population as well as unique and fragile marine ecosystems. To address this deficiency, we use GIS-based multi-criteria approaches combined with analytic hierarchy process to map the Coastal Vulnerability Index and the Socioeconomic Vulnerability Index along these coasts to investigate the amplitude and extent of shoreline deterioration resulting from sudden fluctuations in sediment transport to the coastline. We use the western bay of the Gulf of Tunis, the coasts of Tripoli and the Nile Delta as three validation sites for our vulnerability assessment. The statistical Integrated Coastal Vulnerability Index map reveals that 47% of arid North African coasts are characterized by high to very high vulnerability. In particular, we observe that the densely populated deltaic coasts in both Tunisia and Egypt are 70% more vulnerable than any others coast in the eastern Mediterranean Basin. These abnormally high-vulnerability extensive areas are also correlated with significant deterioration of coastal aquifers and hence in crop production, compromising local food security and resulting in increasing outflow migration trends. Both Tunisia and Egypt observed dramatic increases in the net population outflow migration by respectively 62% and 248% between 2000 and 2016, mostly from coastal areas. Our source analysis of the amplitude and extent of these high coastal vulnerabilities suggests that they result from the anthropogenic drivers of damming and rapid urban growth over the last few decades rather than the effects of global warming.
北非干旱海岸从突尼斯湾延伸至尼罗河三角洲，绵延4633公里，正经历着显著的海岸线退缩和沿海洪水，据报道这是全球变暖导致海平面持续上升的结果。特别值得关注的是三角洲和沙滩的异常海岸线动态，气候和人为驱动因素的十年间突然变化对其造成了严重影响，导致它们更容易受到沿海灾害干扰。不幸的是，对于这些承载着北非大部分人口以及独特而脆弱的海洋生态系统的广阔干旱海岸，这些驱动因素的演变、分布和影响在很大程度上仍未得到量化，更不用说被理解了。为了弥补这一不足，我们采用基于地理信息系统的多标准方法，并结合层次分析法，绘制这些海岸的海岸脆弱性指数和社会经济脆弱性指数，以研究由于输沙量突然波动至海岸线而导致的海岸线恶化的幅度和范围。我们将突尼斯湾西部海湾、的黎波里海岸和尼罗河三角洲作为脆弱性评估的三个验证地点。统计得出的综合海岸脆弱性指数地图显示，47%的北非干旱海岸具有高至非常高的脆弱性。特别是，我们观察到，突尼斯和埃及人口密集的三角洲海岸比东地中海盆地的任何其他海岸脆弱70%。这些异常高脆弱性的广阔地区还与沿海含水层的显著恶化相关，进而影响作物产量，危及当地粮食安全，并导致外流移民趋势增加。突尼斯和埃及在2000年至2016年间净人口外流移民分别急剧增加了62%和248%，大部分来自沿海地区。我们对这些高海岸脆弱性的幅度和范围的来源分析表明，它们是过去几十年人为的筑坝和快速城市发展驱动因素造成的，而非全球变暖的影响。
