- Bayreuth, Bavaria, Germany
Cyrus Samimi
University Of Bayreuth, Germany, Geography, Faculty Member
In the past decade, West Asia has witnessed more frequent and intensified dust storms affecting Iran and Persian Gulf countries. Employing a varying threshold that takes into account systematic differences between TOMS and OMI data,... more
In the past decade, West Asia has witnessed more frequent and intensified dust storms affecting Iran and Persian Gulf countries. Employing a varying threshold that takes into account systematic differences between TOMS and OMI data, TOMS-OMI Aerosol Index data are used to identify long-term changes in the horizontal distribution of dust storms in West Asia from 1980 to present. The northwest of Iraq and east of Syria are identified as emerging dusty areas, whereas east of Saudi Arabia and southeast of Iraq are identified as permanent dusty areas, including both dust sources and affected areas. Whereas the frequency of dust events increased slightly in the permanent dusty areas, it increased markedly in the emerging dusty areas. As expected, the frequency of dust events is highest in June and July. The dust source areas are identified as the Iraq-Saudi Arabia boundary region and (recently) the northwest of Iraq, using MODIS deep blue aerosol optical depth data. Subsequently, a lagged correlation was implemented between identified dust sources and whole West Asia to determine the main paths and receptors of intense dust storms. Accordingly, southwest of Iran and Persian Gulf countries were determined as main receptors of summertime dust storms in West Asia. During spring, dust storms mostly hit the northern half of the region and reach to the Caspian Sea. Analyzing atmospheric patterns, Shamal and Frontal patterns were found as dominant atmospheric circulations simultaneous with summertime and springtime dust storms, respectively.
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We analyse various observational data sets in order to assess and to compare th spatio-temporal characteristics and intensity of the Sahel flood in 2007 and the associated rain events. The return times are estimated from daily... more
We analyse various observational data sets in order to assess and to compare th spatio-temporal characteristics and intensity of the Sahel flood in 2007 and the associated rain events. The return times are estimated from daily precipitation time series at high spatial resolution and the potential causes are disclosed in a global and regional context. Finally, future changes in the occurrence of such heavy rain events are simulated by a regional climate model in order to judge the flood risk potential until the middle of the 21st century. Satellite data reveal that the flood was not large-scale but confined to the main river basins in sub-Saharan West Africa. Nonetheless, abundant rainfall prevailed over large parts of western Africa extending north into the western Sahara, particularly during the second half of August and the beginning of September 2007. In detail, the various precipitation data sets differ considerably in terms of the monthly anomalies, demonstrating the difficulty...
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В данной работе изучается связь между практикой содержания скота на пастбищах, потенциала пастбищ и имущественными правами на Восточном Памире Таджикистана через 10 лет после приватизации 1999 года. В ней также приводится обзор... more
В данной работе изучается связь между практикой содержания скота на пастбищах, потенциала пастбищ и имущественными правами на Восточном Памире Таджикистана через 10 лет после приватизации 1999 года. В ней также приводится обзор пространственно-временной вариативности сегодняшнего использования пастбищ и численности поголовья скота. Допущения о потенциале пастбищ пересматриваются в свете потребностей в корме для животных с целью извлечения основанных на полевой работе выводов касательно чрезмерного использования или недоис- пользования в определенных областях. Данные были получены в рамках меж- дисциплинарного исследования постсоветского отгонного животноводства и связанного взаимодействия на уровне « человек-среда ». Мы показываем, что животноводы на Восточном Памире сталкиваются с несколькими проблемами: по мере того как ресурсы почвенно-растительного покрова ограничены и вари- ативны, а сенокосные луга для животного корма редки, подвижность поголовья или внешние вливания корма про...
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Mountains play an important role in the world's sustainable development. Despite the acquired knowledge about their importance the Global Environment Outlook 3 (UNEP 2002) states that most "mountain commons are ecologically... more
Mountains play an important role in the world's sustainable development. Despite the acquired knowledge about their importance the Global Environment Outlook 3 (UNEP 2002) states that most "mountain commons are ecologically under-managed and suffer from the classic 'commons syndrome': while all seek to benefit, stakeholders lack coordination, incentives and instruments for joint care." For the Eastern Pamirs, a dry (< 100 mm/a) and high (3,500-5,500 m asl) mountain plateau in the east of Tajikistan, grazing and fuel-wood are identified as key ecosystem services. Extensive pastoralism is a prime adapted land use strategy. Therefore, the Soviet administration allocated the production of meat on collective and state farms as the region's main task. Elaborate management plans, usually with four seasonal pasture camps, and additional imports of fuel and forage, led to a well-balanced utilization of all pastures. The dissolution of the USSR resulted in signifi...
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MODIS (MCD12Q1) or Globcover are often the only available global land-cover products, however ground-truthing in the Sahel of Senegal has shown that most classes do have any agreement with actual land-cover making those products unusable... more
MODIS (MCD12Q1) or Globcover are often the only available global land-cover products, however ground-truthing in the Sahel of Senegal has shown that most classes do have any agreement with actual land-cover making those products unusable in any local application. We suggest a methodology, which models local Wolof land- and soil-types in an area in the Senegalese Ferlo around Linguère at different scales. In a first step, interviews with the local population were conducted to ascertain the local denotation of soil units, as well as their agricultural use and woody vegetation mainly growing on them. "Ndjor" are soft sand soils with mainly Combretum glutinosum trees. They are suitable for groundnuts and beans while millet is grown on hard sand soils ("Bardjen") dominated by Balanites aegyptiaca and Acacia tortilis. "Xur" are clayey depressions with a high diversity of tree species. Lateritic pasture sites with dense woody vegetation (mostly Pterocarpus luc...
In the 20th century, the West African Sahel has been a hot-spot of climatic changes. After severe drought-events in the 1970s and 1980s which were followed by a significant drop in annual precipitation, rainfall seems to increase again... more
In the 20th century, the West African Sahel has been a hot-spot of climatic changes. After severe drought-events in the 1970s and 1980s which were followed by a significant drop in annual precipitation, rainfall seems to increase again during the past years. Most studies are based on monthly or yearly datasets. However, many processes and events which are important for the local population depending on rainfall are not related to monthly or annual precipitation but are related to intra-annual, often daily scales. During this study, interviews with farmers and herders were conducted in the Senegalese Sahel. The results show, that wet months with unsuitably distributed precipitation can cause more harm than bringing benefits - depending on the phenological stage of the plants. Agricultural crops for example need rainfall breaks. On the other hand, natural herbaceous vegetation tolerates longer wet periods. So, a wet season can still hide dry spells that alter crops and vegetation deve...
The Sahel region has been acclaimed as one of the "hot spots" of global environmental change in the last decades. The degradation of the environmental conditions was accelerated by prolonged droughts in the region during the... more
The Sahel region has been acclaimed as one of the "hot spots" of global environmental change in the last decades. The degradation of the environmental conditions was accelerated by prolonged droughts in the region during the 1970s and 1980s and an overall decrease in annual precipitation. The resulting loss of woody vegetation cover was often considered as irreversible desertification. Recent findings, based on small-scaled analyses of satellite images, show an increase of vegetation greenness over most parts of the Sahel since the mid-1980s. However, due to a lack of detailed regional studies, it remains largely unclear if this is a return to pre-drought conditions or a transformation of land cover to a new equilibrium state. This study intends to use remote sensing techniques, supplemented by ground truth data to compare the pre-drought woody vegetation and land cover with the current situation. High resolution panchromatic Corona imagery of 1967 and multispectral RapidE...
Climatic changes and population pressure have caused major environmental change in the Sahel during the last fifty years. Many studies use coarse resolution NDVI time series such as GIMMS to detect environmental trends; however... more
Climatic changes and population pressure have caused major environmental change in the Sahel during the last fifty years. Many studies use coarse resolution NDVI time series such as GIMMS to detect environmental trends; however explanations for these trends remain largely unknown. We suggest a five-step methodology for the validation of trends with a case study on the Dogon Plateau, Mali. The first step is to monitor long-term trends with coarse scale time series. Instead of GIMMS, we use a combination of LTDR (derived from AVHRR) and SPOT VGT NDVI data, covering the period from 1982-today with a temporal resolution of 10 days and a spatial resolution of 5.6 km. Areas with significant trends are further analysed in a second step. Here we use a decomposed MODIS time series with a spatial resolution of 250 m. Due to the large scaled MODIS dataset, trends can be identified at a local scale / village level. Using very high resolution imagery (e.g. SPOT, Quickbird) areas of interest can ...
During the rainy season 2007 international institutions (e.g. WFP) and news agencies reported floods in the Sahel. Especially in August and September some news gave the impression that the whole Sahel was flooded, in contrast to the... more
During the rainy season 2007 international institutions (e.g. WFP) and news agencies reported floods in the Sahel. Especially in August and September some news gave the impression that the whole Sahel was flooded, in contrast to the droughts more frequently reported for that region. But it is well known that the precipitation patterns in the Sahel are characterized by a
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Western Africa has been discussed as a hot spot of environmental change. In the 1970ies and 80ies a drastic decrease in precipitation and severe droughts occurred in the Sahel. The degradation of the vegetation led to the desertification... more
Western Africa has been discussed as a hot spot of environmental change. In the 1970ies and 80ies a drastic decrease in precipitation and severe droughts occurred in the Sahel. The degradation of the vegetation led to the desertification paradigm. But also in wetter regions south of the Sahel vegetation changes, mainly forest losses nhave happened. Since the 90ies the precipitation stabilized somewhat and a greening trend can be observed. Both paradigms, desertification and greening, tend to neglect regional and local differences. These differences are often decoupled from rainfall and are linked to land use practices. The article gives an overview about regional trends of vegetation and climate change and emphasize on decoupling precipitation and vegetation. Local examples show how land use leads to diverse vegetation developments.
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In situ measurements of leaf area index (LAI) were taken in two semi-deciduous rainforests in East Africa. Based on field data and optical high resolution satellite images, transfer functions were established that helped to produce high... more
In situ measurements of leaf area index (LAI) were taken in two semi-deciduous rainforests in East Africa. Based on field data and optical high resolution satellite images, transfer functions were established that helped to produce high resolution LAI maps of both areas. In a further step, these maps were used to validate the spatial accuracy of the MODIS LAI product for the two test sites. The temporal consistency of the product was investigated based on a time series for the years 2000-2005. Results show that both spatially and temporally the MODIS LAI product represented the test sites' LAI with satisfying accuracy. Yet temporal interpolation should be applied to bad data quality pixels before MODIS LAI time series are used for further applications.
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Research Interests: Earth Sciences, Arid environments, Temporal dynamics, Plant Diversity, Biological Sciences, and 11 moreBeta diversity, Seasonality, Environmental Sciences, Species Richness, Sustainable Use, Sustainable Management, Management Strategy, Plant Community, Vegetation Cover, Systematic sampling, and Conservation strategies
Time series of Normalized Difference Vegetation Index (NDVI) from the Advanced Very High Resolution Radiometer (AVHRR) were used to capture plant phenology in Etosha National Park, a dry savannah environment in Namibia. Data from two... more
Time series of Normalized Difference Vegetation Index (NDVI) from the Advanced Very High Resolution Radiometer (AVHRR) were used to capture plant phenology in Etosha National Park, a dry savannah environment in Namibia. Data from two consecutive growing periods with different precipitation conditions were included to study impacts of inter‐seasonal rainfall variations on a highly water‐limited ecosystem. Additionally, a contemporary reference
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Operational standard products of biophysical variables, such as leaf area index (LAI) derived from satellite observations (e.g. Moderate Resolution Imaging Spectroradiometer (MODIS), Medium Resolution Imaging Spectrometer (MERIS) or... more
Operational standard products of biophysical variables, such as leaf area index (LAI) derived from satellite observations (e.g. Moderate Resolution Imaging Spectroradiometer (MODIS), Medium Resolution Imaging Spectrometer (MERIS) or VEGETATION), serve the need for adequate input data for quantitative modelling of ecosystem dynamics on regional to global scales. For the validation of those products and for local applications, higher resolution LAI
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... Please follow the link if you wish to visit the database now. International Journal of Remote Sensing. Deforestation in the Miombo woodlands: a pixel-based semi-automated change detection method. ... 199830. Nielsen, AA, Conradsen, K.... more
... Please follow the link if you wish to visit the database now. International Journal of Remote Sensing. Deforestation in the Miombo woodlands: a pixel-based semi-automated change detection method. ... 199830. Nielsen, AA, Conradsen, K. and Simpson, JJ 1998. ...
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ABSTRACT Savannahs are characterized by a co-existence of grasses and trees. Nowadays, these ecosystems arc considerably affected by human impact, as they are used for various types of agriculture and support a major part of the... more
ABSTRACT Savannahs are characterized by a co-existence of grasses and trees. Nowadays, these ecosystems arc considerably affected by human impact, as they are used for various types of agriculture and support a major part of the population within the tropics. E.g., it is widely accepted that in many regions of Southern Africa, livestock farming with inadequate stocking rates has facilitated bush encroachment and strongly alters vegetation structure and composition in these environments. Similar observations are reported from national parks, especially if fences confine the natural mobility of animals. In this study, an approach is developed to model woody vegetation coverage from coarse resolution multitemporal NDVI data by making use of the different phenological characteristics of grasses and trees. A second order polynomial is used to describe NDVI curvature and to quantify phenological metrics. For model calibration and result validation, a reference map is initially generated based on extensive field work and medium resolution Landsat ETM data. The results suggest. a close relationship between woody cover and dry season Curvature and minimum, which are considered to be suitable phenological metrics for a modelling approach. Thus, spatial differences in woody vegetation cover were successfully measured on a regional scale by means of multitemporal NDVI data. The results clearly highlight the potentials of phenological parameters for mapping woody cover.
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... were collected during a study about grazing capacity, whereas the South African data were gathered during field studies under SAFARI 2000. ... Tanja Kraus and Cyrus Samimi: Biomass estimation for land use management and fire... more
... were collected during a study about grazing capacity, whereas the South African data were gathered during field studies under SAFARI 2000. ... Tanja Kraus and Cyrus Samimi: Biomass estimation for land use management and fire management using Landsat-TM and -ETM+ 131 ...