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Juan Puigdefabregas - One of the best experts on this subject based on the ideXlab platform.
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monitoring land degradation risk using aster data the non evaporative fraction as an indicator of ecosystem function
Remote Sensing of Environment, 2008Co-Authors: Monica Garcia, Cecilio Oyonarte, L Villagarcia, Sergio Contreras, F Domingo, Juan PuigdefabregasAbstract:Abstract There is a need to develop operational land degradation indicators for large Regions to prevent losses of biological and economic productivity. Disturbance events press ecosystems beyond resilience and modify the associated hydrological and surface energy balance. Therefore, new indicators for water-limited ecosystems can be based on the partition of the surface energy into latent ( λE ) and sensible heat flux ( H ). In this study, a new methodology for monitoring land degradation risk for Regional scale application is evaluated in a semiarid area of SE Spain. Input data include ASTER surface temperature and reflectance products, and other ancillary data. The methodology employs two land degradation indicators, one related to ecosystem water use derived from the non-evaporative fraction (NEF = H / ( λE + H)), and another related to vegetation greenness derived from the NDVI. The surface energy modeling approach used to estimate the NEF showed errors within the range of similar studies ( R 2 = 0.88; RMSE = 0.18 (22%)). To create quantitative indicators suitable for Regional analysis, the NEF and NDVI were standardized between two possible extremes of ecosystem status: extremely disturbed and undisturbed in each Climatic Region to define the NEFS (NEF Standardized) and NDVIS (NDVI Standardized). The procedure was successful, as it statistically identified ecosystem status extremes for both indicators without supervision. Evaluation of the indicators at disturbed and undisturbed (control) sites, and intermediate surface variables such as albedo or surface temperature, provided insights on the main surface energy status controls following disturbance events. These results suggest that ecosystem functional indicators, such as the NEFS, can provide information related to the surface water deficit, including the role of soil properties.
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monitoring land degradation risk using aster data the non evaporative fraction as an indicator of ecosystem function
Remote Sensing of Environment, 2008Co-Authors: Monica Garcia, Cecilio Oyonarte, L Villagarcia, Sergio Contreras, F Domingo, Juan PuigdefabregasAbstract:Abstract There is a need to develop operational land degradation indicators for large Regions to prevent losses of biological and economic productivity. Disturbance events press ecosystems beyond resilience and modify the associated hydrological and surface energy balance. Therefore, new indicators for water-limited ecosystems can be based on the partition of the surface energy into latent ( λE ) and sensible heat flux ( H ). In this study, a new methodology for monitoring land degradation risk for Regional scale application is evaluated in a semiarid area of SE Spain. Input data include ASTER surface temperature and reflectance products, and other ancillary data. The methodology employs two land degradation indicators, one related to ecosystem water use derived from the non-evaporative fraction (NEF = H / ( λE + H)), and another related to vegetation greenness derived from the NDVI. The surface energy modeling approach used to estimate the NEF showed errors within the range of similar studies ( R 2 = 0.88; RMSE = 0.18 (22%)). To create quantitative indicators suitable for Regional analysis, the NEF and NDVI were standardized between two possible extremes of ecosystem status: extremely disturbed and undisturbed in each Climatic Region to define the NEFS (NEF Standardized) and NDVIS (NDVI Standardized). The procedure was successful, as it statistically identified ecosystem status extremes for both indicators without supervision. Evaluation of the indicators at disturbed and undisturbed (control) sites, and intermediate surface variables such as albedo or surface temperature, provided insights on the main surface energy status controls following disturbance events. These results suggest that ecosystem functional indicators, such as the NEFS, can provide information related to the surface water deficit, including the role of soil properties.
Brian M Chase - One of the best experts on this subject based on the ideXlab platform.
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holocene climate change in southernmost south africa rock hyrax middens record shifts in the southern westerlies
Quaternary Science Reviews, 2013Co-Authors: Brian M Chase, Andrew S Carr, Michael E. Meadows, Arnoud Boom, Paula J ReimerAbstract:Abstract South Africa's southern coastal margin is recognised as being a highly dynamic Climatic Region that plays a critical role in both Regional and global atmospheric and oceanic circulation dynamics. Our understanding of the past dynamics of this system, however, has been limited by the number and nature of datasets available that can be used to infer changes in key Climatic parameters in the Region. In this paper we present new high resolution δ13C and δ15N data from two independently dated rock hyrax (Procavia capensis) middens from Seweweekspoort in South Africa's Groot Swartberg mountains. These data provide information regarding both past vegetation and hydroClimatic change, and allow a Regional integration of available data that explore the long-term dynamics of mid-latitude circulation systems in the African sector of the Southern Hemisphere. Combined, a negative relationship is apparent between temperature and humidity in this area of the southern Cape, and these changes can for the first time be clearly linked to variations in Antarctic sea-ice extent and shifts in the southern westerly storm track. This dynamic is particularly evident between 5 and 7 cal kBP, when a reduction in sea-ice extent and a southward shift of the westerlies are manifested Regionally by increased temperatures and a phase of marked aridity.
F Domingo - One of the best experts on this subject based on the ideXlab platform.
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monitoring land degradation risk using aster data the non evaporative fraction as an indicator of ecosystem function
Remote Sensing of Environment, 2008Co-Authors: Monica Garcia, Cecilio Oyonarte, L Villagarcia, Sergio Contreras, F Domingo, Juan PuigdefabregasAbstract:Abstract There is a need to develop operational land degradation indicators for large Regions to prevent losses of biological and economic productivity. Disturbance events press ecosystems beyond resilience and modify the associated hydrological and surface energy balance. Therefore, new indicators for water-limited ecosystems can be based on the partition of the surface energy into latent ( λE ) and sensible heat flux ( H ). In this study, a new methodology for monitoring land degradation risk for Regional scale application is evaluated in a semiarid area of SE Spain. Input data include ASTER surface temperature and reflectance products, and other ancillary data. The methodology employs two land degradation indicators, one related to ecosystem water use derived from the non-evaporative fraction (NEF = H / ( λE + H)), and another related to vegetation greenness derived from the NDVI. The surface energy modeling approach used to estimate the NEF showed errors within the range of similar studies ( R 2 = 0.88; RMSE = 0.18 (22%)). To create quantitative indicators suitable for Regional analysis, the NEF and NDVI were standardized between two possible extremes of ecosystem status: extremely disturbed and undisturbed in each Climatic Region to define the NEFS (NEF Standardized) and NDVIS (NDVI Standardized). The procedure was successful, as it statistically identified ecosystem status extremes for both indicators without supervision. Evaluation of the indicators at disturbed and undisturbed (control) sites, and intermediate surface variables such as albedo or surface temperature, provided insights on the main surface energy status controls following disturbance events. These results suggest that ecosystem functional indicators, such as the NEFS, can provide information related to the surface water deficit, including the role of soil properties.
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monitoring land degradation risk using aster data the non evaporative fraction as an indicator of ecosystem function
Remote Sensing of Environment, 2008Co-Authors: Monica Garcia, Cecilio Oyonarte, L Villagarcia, Sergio Contreras, F Domingo, Juan PuigdefabregasAbstract:Abstract There is a need to develop operational land degradation indicators for large Regions to prevent losses of biological and economic productivity. Disturbance events press ecosystems beyond resilience and modify the associated hydrological and surface energy balance. Therefore, new indicators for water-limited ecosystems can be based on the partition of the surface energy into latent ( λE ) and sensible heat flux ( H ). In this study, a new methodology for monitoring land degradation risk for Regional scale application is evaluated in a semiarid area of SE Spain. Input data include ASTER surface temperature and reflectance products, and other ancillary data. The methodology employs two land degradation indicators, one related to ecosystem water use derived from the non-evaporative fraction (NEF = H / ( λE + H)), and another related to vegetation greenness derived from the NDVI. The surface energy modeling approach used to estimate the NEF showed errors within the range of similar studies ( R 2 = 0.88; RMSE = 0.18 (22%)). To create quantitative indicators suitable for Regional analysis, the NEF and NDVI were standardized between two possible extremes of ecosystem status: extremely disturbed and undisturbed in each Climatic Region to define the NEFS (NEF Standardized) and NDVIS (NDVI Standardized). The procedure was successful, as it statistically identified ecosystem status extremes for both indicators without supervision. Evaluation of the indicators at disturbed and undisturbed (control) sites, and intermediate surface variables such as albedo or surface temperature, provided insights on the main surface energy status controls following disturbance events. These results suggest that ecosystem functional indicators, such as the NEFS, can provide information related to the surface water deficit, including the role of soil properties.
Basharat Jamil - One of the best experts on this subject based on the ideXlab platform.
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statistical analysis of sunshine based global solar radiation gsr models for tropical wet and dry Climatic Region in nagpur india a case study
Renewable & Sustainable Energy Reviews, 2018Co-Authors: Rahul G Makade, Basharat JamilAbstract:Abstract In literature, numerous models are available to predict Global Solar Radiation (GSR) on a horizontal surface, which is predominantly a site-specific characteristic. Hence, a comparative study is required to predict GSR using a correct model for a particular site. The principal aim of the present work is to analyze the most precise model for estimation of monthly average daily global solar radiation (MADGSR) on a horizontal surface for the Region of interest. In the current work, the performance of 300 existing sunshine based GSR models are compared using 15-year meteorological data for Tropical wet and dry Climatic Region of India. The accuracy of each model is tested using ten different statistical error tests. Further, the Global Performance Indicator (GPI) is used to rank the selected GSR models. According to results, the Ampratwum Model (Model 274, proposed for Marmul, Oman) has shown the best capability to estimate the GSR on a horizontal surface followed by Srivastava (Model 26, proposed for Kolkata, India) and Rensheng model (Model 282, proposed for China). The results of the present study are valuable for the developing countries and remote areas where very few metrological stations are available since the technological expenses are very high.
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comparative analysis of diffuse solar radiation models based on sky clearness index and sunshine period for humid subtropical Climatic Region of india a case study
Renewable & Sustainable Energy Reviews, 2017Co-Authors: Basharat Jamil, Naiem AkhtarAbstract:Abstract In the present work, long-term solar radiation assessment was performed for three years (September 2013 to August 2016) in Humid-Subtropical Climatic Region of India for the city of Aligarh (27.88°N, 78.08°E). Annual average global, beam and diffuse solar radiation values for Aligarh were observed as 21.01 MJ/m2-day, 13.40 MJ/m2-day and 7.61 MJ/m2-day. Annual average sky-clearness index, diffuse fraction and diffusion coefficient were found to be 0.66, 0.37 and 0.24 respectively. Ground based global solar radiation measurements were compared with the available satellite data of the closest coordinate location (27.50°N, 78.50°N). Strong association was found between the ground measurements and satellite data. Further, empirical models for estimation of monthly mean diffuse solar radiation were developed using ground-based measured data. Diffuse solar radiation was modelled in terms of single and two input variables (namely sky-clearness index and relative sunshine period). A total of 42 new models in six different categories were developed. Proposed models were also compared with well-established models from literature. Models were assessed for performance in terms of ten most frequently used statistical indicators. Subsequently, proposed models were ranked in order of suitability of estimation within their respective category as well as among the group of all the developed models using Global Performance Index (GPI). Overall GPI of developed models was found in the range of −1.2677 to 5.5596 with the highest value representing the best model. It was inferred that two input variable models perform much better in comparison to single variable input models. Among the two variable models, diffuse fraction model in terms of sky-clearness index and relative sunshine period (each in order one) was found to be the most accurate. Excellent agreement was affirmed between estimated and measured values from two variable models. The use of single variable models was also suggested within reasonable accuracy.
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comparison of empirical models to estimate monthly mean diffuse solar radiation from measured data case study for humid subtropical Climatic Region of india
Renewable & Sustainable Energy Reviews, 2017Co-Authors: Basharat Jamil, Naiem AkhtarAbstract:Abstract This study demonstrates the performance comparison of the models to estimate monthly mean diffuse solar radiation on a horizontal surface for Humid-Subtropical Climatic Region of India. Meteorological data (global and diffuse solar radiation) were observed for the city of Aligarh (27.89°N, 78.08°E) at the Heat Transfer and Solar Energy Laboratory, Department of Mechanical Engineering, Aligarh Muslim University, Aligarh. The mean global, beam and diffuse solar radiation values for Aligarh were observed as 22.12 MJ/m2-day, 14.20 MJ/m2-day and 7.92 MJ/m2-day respectively. The mean values of sky-clearness index, diffuse fraction and diffusion coefficient were found to be 0.69, 0.37 and 0.25, respectively. The Region exhibits abundant potential for solar energy utilization with favorable sky conditions. Diffuse solar radiation models with single input parameter (in the form of global solar radiation) were analyzed for suitability of estimation. 100 typical models were selected from the literature which correlated diffuse fraction (ratio of horizontal diffuse to global solar radiation) to sky-clearness index (ratio of global to extraterrestrial solar radiation). The objective here was to find the most precise model which is suitable to assess diffuse solar radiation in the Region considered. Distinctive statistical evaluation of the models was performed in terms of well-known statistical indicators. Further, the scaled values of statistical indicators were used to calculate Global Performance Indicator (GPI). GPI of the selected models lied in the range of from −4.2987 to 2.6606 with the highest value representing the best performing model. Models were subsequently ranked in order of descending GPI. This study helps to recognize the significance of diffuse solar radiation models where the absence of required equipment as well as high cost of operation and maintenance represents a critical barrier for measurement. The outcomes of the present study are valuable for locations within the developing countries and remote areas with similar Climatic conditions.
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estimation of diffuse solar radiation in humid subtropical Climatic Region of india comparison of diffuse fraction and diffusion coefficient models
Energy, 2017Co-Authors: Basharat Jamil, Naiem AkhtarAbstract:In this study, measured data of solar radiation were utilized to develop sixteen empirical models for estimation of monthly mean diffuse solar radiation with single input predictor as clearness index. Global and diffuse solar radiations were measured for three complete years in ‘Humid subtropical Climatic Region’ of India. Equipment consisting of secondary standard pyranometers and continuous datalogging facility were used to observe solar radiation at ground level in the city of Aligarh (27.89°N, 78.08°E). Two categories of models were defined (i.e. diffuse fraction and diffusion coefficient) with eight models under each category. Total solar radiation dataset was divided into two parts where ‘Training dataset’ was used to develop the models while the ‘Validation dataset’ was used to test the models. Accuracy of models was analyzed in terms of some commonly used statistical indicators. Developed models were also compared with well-established models from literature. Models were arranged in order of suitability of estimation using Global Performance Indicator within the respective category as well as among the overall group of developed models. Reasonable agreement was found between estimated values from the developed models and measured data. Developed models can conveniently be utilized to evaluate diffuse solar radiation in the Region considered.
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estimation of solar radiation and optimum tilt angles for south facing surfaces in humid subtropical Climatic Region of india
Engineering Science and Technology an International Journal, 2016Co-Authors: Basharat Jamil, Abid T Siddiqui, Naiem AkhtarAbstract:Abstract In the present work, availability of solar radiation for south-facing flat surfaces in Humid Subtropical Climatic Region of India has been estimated. Measurements of global and diffuse solar radiation for Aligarh (27.89°N, 78.08°E) which lies in the Humid Subtropical Climatic Region were performed for over a period of three years. Monthly, seasonal and annual optimum tilt angles were estimated. Comparison of total incident solar radiation was performed between Aligarh and New Delhi (Capital of India, 28.61°N, 77.20°E). Annual optimum tilt angle for Aligarh and New Delhi was found as 27.62° and 27.95° respectively (close to the latitude of the respective location). Estimated gains in annual average solar radiation (based on monthly, seasonal and annual optimum tilt angles) in comparison to a horizontal surface were 12.92%, 11.61% and 6.51% (for Aligarh) and 13.13%, 11.80% and 7.58% (for New Delhi) respectively. A loss of 1.16% and 5.68% energy (for Aligarh) and 1.18% and 4.91% (for New Delhi) were estimated with surface at seasonal and annual optimum tilt angles respectively compared to a surface at monthly optimum tilt angle. Based on the study, it was recommended that the inclined surface must be tilted on monthly or seasonal optimum tilt angle for better utilization of solar energy.
Birk Kraas - One of the best experts on this subject based on the ideXlab platform.
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solar resource assessment study for pakistan
Renewable & Sustainable Energy Reviews, 2016Co-Authors: Steffen Stokler, Christoph Schillings, Birk KraasAbstract:Solar resource assessment becomes a very important factor for planners of Photovoltaic (PV) and Concentrated Solar Power (CSP) systems. Choice between nearby locations can make a difference if a plant is profitable or not, especially in a Climatic Region with complex topography as can be found in Pakistan. Nevertheless, Pakistan’s geographic location and climate offers a very high potential for solar energy applications. The solar resource assessment study presented in this article describes the approach and set-up required by the World Bank’s Energy Sector Management Assistance Program (ESMAP).11Further details are available at https://www.esmap.org/ and http://www.esmap.org/RE_Mapping (02/2015). The project aims to create a validated solar atlas for Pakistan based on a combination of satellite data and ground measurements to support country-driven efforts to improve renewable energy resource awareness and exploitation. There are several country-specific, ESMAP-funded projects conducted by the World Bank Group (WBG) that cover comprehensive mapping and geospatial planning, including ground-based data collection. The solar resource estimation of Pakistan was one of the first projects to be approved within the program.The final and validated dataset ultimately will be published in the International Renewable Energy Agencies’ (IRENA) global atlas for renewable energy.22Further details are available at https://www.irena.org/ and http://www.irena.org/globalatlas/ (02/2015).
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solar resource assessment study for pakistan
Renewable & Sustainable Energy Reviews, 2016Co-Authors: Steffen Stokler, Christoph Schillings, Birk KraasAbstract:Abstract Solar resource assessment becomes a very important factor for planners of Photovoltaic (PV) and Concentrated Solar Power (CSP) systems. Choice between nearby locations can make a difference if a plant is profitable or not, especially in a Climatic Region with complex topography as can be found in Pakistan. Nevertheless, Pakistan’s geographic location and climate offers a very high potential for solar energy applications. The solar resource assessment study presented in this article describes the approach and set-up required by the World Bank’s Energy Sector Management Assistance Program (ESMAP). 1 The project aims to create a validated solar atlas for Pakistan based on a combination of satellite data and ground measurements to support country-driven efforts to improve renewable energy resource awareness and exploitation. There are several country-specific, ESMAP-funded projects conducted by the World Bank Group (WBG) that cover comprehensive mapping and geospatial planning, including ground-based data collection. The solar resource estimation of Pakistan was one of the first projects to be approved within the program.The final and validated dataset ultimately will be published in the International Renewable Energy Agencies’ (IRENA) global atlas for renewable energy. 2