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Desertification is the major environmental threat in the arid and semiarid regions. The soil-adjusted vegetation index (SAVI) was used as an indicator to monitor the desertification change in Egypt. A multi-temporal satellite data of moderate-resolution imaging spectroradiometer were used to estimate SAVI and land surface temperature. Also, Global Multi-resolution Terrain Elevation Data 2010 and climatic data were used for the analysis. This research focuses on assessing the trend of the vegetation cover change in the seasons of January, March, June, September, and December for the years 2002, 2005, 2008, and 2011. The magnitude of the vegetation cover change in periods 2002–2005, 2005–2008, and 2008–2011 at ≤100 and >100 m elevation was analyzed. A major increase in the vegetation cover that occurred in the period 2002–2005 was about 3,400 km2, as a result of two national megaprojects (Toshka Project and El-Salam Canal). In contrast, vegetation cover decreased by 5,500 km2 in March during the period 2005–2008, coinciding with the period when the management of the megaprojects failed. Vegetation cover changed again by 1,500 km2 in the period of 2008–2011, and the vegetated areas in the Nile Delta were affected by the sea level rising which was responsible for the soil salinization. Three sites were chosen in this investigation (Kom Ombo, El-Oweinat, and Nile Delta) in order to observe the difference of desertification dynamics and to understand the relationship between the vegetation cover distribution and other environmental variables. Anti-desertification policies and advanced agricultural management are highly required in Egypt to decrease any environmental crises and food shortage. 相似文献
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Amaury?PourteauEmail author Romain?Bousquet Olivier?Vidal Alexis?Plunder Erik?Duesterhoeft Osman?Candan Roland?Oberh?nsli 《Contributions to Mineralogy and Petrology》2014,168(6):1090
We provide new insights into the prograde evolution of HP/LT metasedimentary rocks on the basis of detailed petrologic examination, element-partitioning analysis, and thermodynamic modelling of well-preserved Fe–Mg–carpholite- and Fe–Mg–chloritoid-bearing rocks from the Afyon Zone (Anatolia). We document continuous and discontinuous compositional (ferromagnesian substitution) zoning of carpholite (overall X Mg = 0.27–0.73) and chloritoid (overall X Mg = 0.07–0.30), as well as clear equilibrium and disequilibrium (i.e., reaction-related) textures involving carpholite and chloritoid, which consistently account for the consistent enrichment in Mg of both minerals through time, and the progressive replacement of carpholite by chloritoid. Mg/Fe distribution coefficients calculated between carpholite and chloritoid vary widely within samples (2.2–20.0). Among this range, only values of 7–11 correlate with equilibrium textures, in agreement with data from the literature. Equilibrium phase diagrams for metapelitic compositions are calculated using a newly modified thermodynamic dataset, including most recent data for carpholite, chloritoid, chlorite, and white mica, as well as further refinements for Fe–carpholite, and both chloritoid end-members, as required to reproduce accurately petrologic observations (phase relations, experimental constraints, Mg/Fe partitioning). Modelling reveals that Mg/Fe partitioning between carpholite and chloritoid is greatly sensitive to temperature and calls for a future evaluation of possible use as a thermometer. In addition, calculations show significant effective bulk composition changes during prograde metamorphism due to the fractionation of chloritoid formed at the expense of carpholite. We retrieve P–T conditions for several carpholite and chloritoid growth stages (1) during prograde stages using unfractionated, bulk-rock XRF analyses, and (2) at peak conditions using compositions fractionated for chloritoid. The P–T paths reconstructed for the Kütahya and Afyon areas shed light on contrasting temperature conditions for these areas during prograde and peak stages. 相似文献
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基于四川区域地震台网记录的波形资料,利用CAP波形反演方法,同时获取了2013年4月20日芦山M7.0级地震序列中88个M≥3.0级地震的震源机制解、震源矩心深度与矩震级,进而利用应变花（strain rosette）和面应变（areal strain）As值,分析了芦山地震序列震源机制和震源区构造运动与变形特征.获得的主要结果有：（1）芦山M7.0级主震破裂面参数为走向219°/倾角43°/滑动角101°,矩震级为MW6.55,震源矩心深度15 km.芦山地震余震区沿龙门山断裂带走向长约37 km、垂直断裂带走向宽约16 km.主震两侧余震呈不对称分布,主震南西侧余震区长约27 km、北东侧长约10 km.余震分布在7~22 km深度区间,优势分布深度为9~14 km,序列平均深度约13 km,多数余震分布在主震上部.粗略估计的芦山地震震源体体积为37 km×16 km×16 km.（2）面应变As值统计显示,芦山地震序列以逆冲型地震占绝对优势,所占比例超过93%.序列主要受倾向NW、倾角约45°的近NE-SW向逆冲断层控制;部分余震发生在与上述主发震断层近乎垂直的倾向SE的反冲断层上;龙门山断裂带前山断裂可能参与了部分余震活动.P轴近水平且优势方位单一,呈NW-SE向,与龙门山断裂带南段所处区域构造应力场方向一致,反映芦山地震震源区主要受区域构造应力场控制,芦山地震是近NE-SW向断层在近水平的NW-SE向主压应力挤压作用下发生逆冲运动的结果.序列中6次非逆冲型地震均发生在主震震中附近,且主震震中附近P轴仰角变化明显,表明主震对其震中附近局部区域存在明显的应力扰动.（3）序列整体及不同震级段的应变花均呈NW向挤压白瓣形态,显示芦山地震震源区深部构造呈逆冲运动、NW向纯挤压变形.各震级段的应变花方位与形状一致,具有震级自相似性特征,揭示震源区深部构造运动和变形模式与震级无关.（4）不同深度的应变花形态以NW-NWW向挤压白瓣为优势,显示震源区构造无论是总体还是分段均以NW-NWW向挤压变形为特征.但应变花方位与形状随深度仍具有较明显的变化,可能反映了震源区构造变形在深度方向上存在分段差异.（5）芦山地震震源体尺度较小,且主震未发生在龙门山断裂带南段主干断裂上,南段长期积累的应变能未能得到充分释放,南段仍存在发生强震的危险. 相似文献
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Gully cut‐and‐fill cycles as related to agro‐management: a historical curve number simulation in the Tigray Highlands 
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下载免费PDF全文 Sil Lanckriet Amaury Frankl Gebrekidan Mesfin Katrien Descheemaeker Jan Nyssen 《地球表面变化过程与地形》2015,40(6):796-808
Gully cut‐and‐fill dynamics are often thought to be driven by climate and/or deforestation related to population pressure. However, in this case‐study of nine representative catchments in the Northern Ethiopian Highlands, we find that neither climate changes nor deforestation can explain gully morphology changes over the twentieth century. Firstly, by using a Monte Carlo simulation to estimate historical catchment‐wide curve numbers, we show that the landscape was already heavily degraded in the nineteenth and early twentieth century – a period with low population density. The mean catchment‐wide curve number (> 80) one century ago was, under the regional climatic conditions, already resulting in considerable simulated historical runoff responses. Secondly, twentieth century land‐cover and runoff coefficient changes were confronted with twentieth century changing gully morphologies. As the results show, large‐scale land‐cover changes and deforestation cannot explain the observed processes. The study therefore invokes interactions between authigenic factors, small‐scale plot boundary changes, cropland management and sociopolitical forces to explain the gully cut processes. Finally, semi‐structured interviews and sedistratigraphic analysis of three filled gullies confirm the dominant impact of (crop)land management (tillage, check dams in gullies and channel diversions) on gully cut‐and‐fill processes. Since agricultural land management – including land tenure and land distribution – has been commonly neglected in earlier related research, we argue therefore that it can be a very strong driver of twentieth century gully morphodynamics. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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Biadgilgn Demissie Jan Nyssen Paolo Billi Mitiku Haile Veerle Vaneetvelde Amaury Frankl 《自然地理学》2019,40(1):71-90
This paper investigates land-use/cover changes related to river dynamics in northern Ethiopia. Aerial photographs from 1965 to 1986, and SPOT images of 2007 and 2014 were used to extract land units. Land-use/cover changes took place in 48% of the entire landscape around the river across the last five decades. Changes related to swap accounted for 37%, whereas net changes accounted for 11%. The most systematic transitions in terms of gain were from shrubland to farmland, alluvial deposit to settlement, and alluvial deposit to active channel and settlement. Most of these transitions were related to the river dynamics and depict cyclic transitions: farmland → active channel → alluvial deposits → grassland/shrubland → farmland. Human interventions and natural vegetation succession were also very important. The study concludes that river systems have considerable impact on livelihood and need attention in land management undertakings in graben bottoms. 相似文献
17.
Amaury Pourteau Erik E. Scherer Simon Schorn Rebecca Bast Alexander Schmidt Lisa Ebert 《地学前缘(英文版)》2019,10(1):127-148
The thermal structure of subduction zones exerts a major influence on deep-seated mechanical and chemical processes controlling arc magmatism, seismicity, and global element cycles. Accretionary complexes exposed inland may comprise tectonic blocks with contrasting pressure–temperature (P–T) histories, making it possible to investigate the dynamics and thermal evolution of former subduction interfaces. With this aim, we present new Lu–Hf geochronological results for mafic rocks of the Halilba?? Complex (Anatolia) that evolved along different thermal gradients. Samples include a lawsonite–epidote blueschist, a lawsonite–epidote eclogite, and an epidote eclogite (all with counter-clockwise P–T paths), a prograde lawsonite blueschist with a “hairpin”-type P–T path, and a garnet amphibolite from the overlying sub-ophiolitic metamorphic sole. Equilibrium phase diagrams suggest that the garnet amphibolite formed at ～0.6–0.7 GPa and 800–850 °C, whereas the prograde lawsonite blueschist records burial from 2.1 GPa and 420 °C to 2.6 GPa and 520 °C. Well-defined Lu–Hf isochrons were obtained for the epidote eclogite (92.38 ± 0.22 Ma) and the lawsonite–epidote blueschist (90.19 ± 0.54 Ma), suggesting rapid garnet growth. The lawsonite–epidote eclogite (87.30 ± 0.39 Ma) and the prograde lawsonite blueschist (ca. 86 Ma) are younger, whereas the garnet amphibolite (104.5 ± 3.5 Ma) is older. Our data reveal a consistent trend of progressively decreasing geothermal gradient from granulite-facies conditions at ～104 Ma to the epidote-eclogite facies around 92 Ma, and the lawsonite blueschist-facies between 90 Ma and 86 Ma. Three Lu–Hf garnet dates (between 92 Ma and 87 Ma) weighted toward the growth of post-peak rims (as indicated by Lu distribution in garnet) suggest that the HP/LT rocks were exhumed continuously and not episodically. We infer that HP/LT metamorphic rocks within the Halilba?? Complex were subjected to continuous return flow, with “warm” rocks being exhumed during the tectonic burial of “cold” ones. Our results, combined with regional geological constraints, allow us to speculate that subduction started at a transform fault near a mid-oceanic spreading centre. Following its formation, this ancient subduction interface evolved thermally over more than 15 Myr, most likely as a result of heat dissipation rather than crustal underplating. 相似文献
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Wouter Lannoeye Cornelis Stal Etefa Guyassa Amanuel Zenebe Jan Nyssen Amaury Frankl 《自然地理学》2016,37(6):430-451
AbstractWith the recent technological advances offered by SfM-photogrammetry, we now have the possibility to study gully erosion at very high spatial and temporal scales from multi-temporal DEMs, and thus to enhance our understanding of both gully erosion processes and controls. Here, we examine gully degradation and aggradation at a gully headcut and at four re-incisions along a gully reach in Northern Ethiopia. Environmental controls recorded are topography rainfall, runoff, land use and cover, land management, and soil characteristics. The overall vulnerability of the catchment to erosion is low as calculated from the RUSLE (average 11.83 t ha?1 y?1). This reflects the successful land management of the past years. The runoff coefficient was on average 7.3% (maximum 18.2%). Runoff events caused most geomorphic change in the gully, but slumping of the gully bank also occurred on dry days. Most geomorphic change was caused by one major rainfall event of 54.8 mm d?1, and smaller runoff events caused both degradation and aggradation, often asynchronous between studied sites. Although most research focuses on gully heads alone, re-incisions at lower locations can still cause important gully degradation, which ultimately will reach the gully head and cause instability. 相似文献
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Revisiting lake sediment budgets: How the calculation of lake lifetime is strongly data and method dependent 下载免费PDF全文
下载免费PDF全文 Hanibal Lemma Teshager Admasu Mekete Dessie Derbew Fentie Jozef Deckers Amaury Frankl Jean Poesen Enyew Adgo Jan Nyssen 《地球表面变化过程与地形》2018,43(3):593-607
Lake sedimentation has a fundamental impact on lake lifetime. In this paper, we show how sensitive calculation of the latter is to the quality of data available and assumptions made during analysis. Based on the collection of a large new dataset, we quantify the sediment masses (1) mobilized on the hillslopes draining towards Lake Tana (Ethiopia), (2) stored in the floodplains, (3) transported into the lake, (4) deposited in the lake and (5) delivered out from the lake so as to establish a sediment budget. In 2012–2013, suspended sediment concentration (SSC) and discharge measurements were made at 13 monitoring stations, including two lake outlets. Altogether, 4635 SSC samples were collected and sediment rating curves that account for land cover conditions and rainfall seasonality were established for the 11 river stations, and mean monthly SSC was calculated for the outlets. Effects of the floodplain on rivers' sediment yield (SY) were investigated using measurements at both sides of the floodplains. SY from ungauged rivers was assessed using a model that includes catchment area and rainfall, whereas bedload and direct sediment input from lake shores were estimated. As a result, the gross annual SY was c. 39.55 (± 0.15) Mt, dominantly from Gilgel Abay and Gumara Rivers. The 2.57 (± 0.17) Mt sediment deposited in floodplains indicate that the floodplains serve as an important sediment sink. Moreover, annually c. 1.09 Mt of sediment leaves the lake through the two outlets. Annual sediment deposition in the lake was c. 36.97 (± 0.22) Mt and organic matter accumulation was 2.15 Mt, with a mean sediment trapping efficiency of 97%. Furthermore, SSC and SY are generally higher at the beginning of the rainy season because soils in cultivated fields are bare and loose due to frequent ploughing and seedbed preparation. Later in the season, increased crop and vegetation cover lead to a decrease in sediment production. Based on the established sediment budget with average rainfall, the lifetime of Lake Tana was estimated as 764 to 1032 years, which is shorter than what was anticipated in earlier studies. The sedimentation rate of Lake Tana (11.7 ± 0.1 kg m?2 yr?1) is in line with the sedimentation rates of larger lakes in the world, like Lake Dongting and Lake Kivu. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献