The Experts below are selected from a list of 8418 Experts worldwide ranked by ideXlab platform
Morio Iijima - One of the best experts on this subject based on the ideXlab platform.
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ridge formation with strip tillage alleviates excess moisture stress for drought tolerant crops
Soil & Tillage Research, 2019Co-Authors: Yoshihiro Hirooka, Yasuhiro Izumi, Koichi Shoji, Yoshinori Watanabe, Simon K Awala, Morio IijimaAbstract:Abstract The impact of climate change is expected to be more severe in semi-arid and arid ecosystems. Seasonal and high-rainfall floods have recently become a common occurrence in semi-arid sub-Saharan countries in southwestern Africa, where ridging is becoming an important method to alleviate flooding stress in drought-tolerant crops. The objective of this study was to propose a feasible tillage method and compare its agronomical effects to those of conventional tillage practices in northern Namibia in sub-Saharan Africa. Pearl millet and cowpea were grown in the field using different tillage methods in Seasonal Wetlands in this area. We investigated crop yield, growth parameters, soil moisture content, and the shape of the ridge. Soil tillage using a newly proposed disc ridger for two-wheel tractors resulted in higher yield and growth rate in both crops than using the other tillage methods i.e. single mouldboard ploughing with animals and/or disc harrowing with four-wheel tractor. Ridge formation with strip tillage (partial pulverization) using the disc ridger resulted in significantly lower soil moisture content after irrigation because of the higher aspect ratio of the ridge. It is likely that large undisturbed portion remained therewith prevented the ridge from collapsing because of the irrigation water that imitated natural rainfall in this region. Therefore, ridge formation with strip tillage leads to good drainage, and as a result, proper drying of soil prevents flooding stresses thus enhancing early growth and yield of pearl millet and cowpea.
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development and evaluation of a lookup table based approach to data fusion for Seasonal Wetlands monitoring an integrated use of amsr series modis and landsat
Remote Sensing of Environment, 2017Co-Authors: Hiroki Mizuochi, Tetsuya Hiyama, Jack R Kambatuku, Yuichiro Fujioka, Morio Iijima, Takeshi Ohta, Kenlo Nishida NasaharaAbstract:Abstract Broad scale monitoring of inland waters is essential to research on carbon and water cycles, and for application in the monitoring of disasters including floods and droughts on various spatial and temporal scales. Satellite remote sensing using spatiotemporal data fusion (STF) has recently attracted attention as a way of simultaneously describing spatial heterogeneity and tracking the temporal variability of inland waters. However, existing STF approaches have limitations in describing abrupt temporal changes, integrating “dissimilar” datasets (i.e., fusions between microwave and optical data), and compiling long-term, frequent STF datasets. To overcome these limitations, in this study we developed and evaluated a lookup table (LUT)-based STF, termed database unmixing (DBUX), using multiple types of satellite data (AMSR series, MODIS, and Landsat), and applied it to semi-arid Seasonal Wetlands in Namibia. The results show that DBUX is: 1) flexible in integrating optical data (MODIS or Landsat) with microwave (AMSR series) and Seasonal (day of year) information; 2) able to generate long-term, frequent Landsat-like datasets; and 3) more reliable than an existing approach (spatial and temporal adaptive reflectance fusion model; STARFM) for tracking dynamic temporal variations in Seasonal Wetlands. Water maps retrieved from the resulting STF dataset for the Wetlands had a 30-m spatial resolution and a temporal frequency of 1 or 2 days, and the dataset covered from 2002 to 2015. The time series water maps accurately described both Seasonal and interannual changes in the Wetlands, and could act as a basis for understanding the hydrological features of the region. Further studies are required to enable application of DBUX in other regions, and for other landscapes with different satellite sensor combinations.
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analysing the origin of rain and subsurface water in Seasonal Wetlands of north central namibia
Environmental Research Letters, 2017Co-Authors: Tetsuya Hiyama, Hironari Kanamori, Jack R Kambatuku, Ayumi Kotani, Kazuyoshi Asai, Hiroki Mizuochi, Yuichiro Fujioka, Morio IijimaAbstract:We investigated the origins of rain- and subsurface waters of north-central Namibia's Seasonal Wetlands, which are critical to the region's water and food security. The region includes the southern part of the Cuvelai system Seasonal Wetlands (CSSWs) of the Cuvelai Basin, a transboundary river basin covering southern Angola and northern Namibia. We analysed stable water isotopes (SWIs) of hydrogen (HDO) and oxygen (H2 18O) in rainwater, surface water and shallow groundwater. Rainwater samples were collected during every rainfall event of the rainy season from October 2013 to April 2014. The isotopic ratios of HDO (δD) and oxygen H2 18O (δ 18O) were analysed in each rainwater sample and then used to derive the annual mean value of (δD, δ 18O) in precipitation weighted by each rainfall volume. Using delta diagrams (plotting δD vs. δ 18O), we showed that the annual mean value was a good indicator for determining the origins of subsurface waters in the CSSWs. To confirm the origins of rainwater and to explain the variations in isotopic ratios, we conducted atmospheric water budget analysis using Tropical Rainfall Measuring Mission (TRMM) multi-satellite precipitation analysis (TMPA) data and ERA-Interim atmospheric reanalysis data. The results showed that around three-fourths of rainwater was derived from recycled water at local–regional scales. Satellite-observed outgoing longwave radiation (OLR) and complementary satellite data from MODerate-resolution Imaging Spectroradiometer (MODIS) and Advanced Microwave Scanning Radiometer (AMSR) series implied that the isotopic ratios in rainwater were affected by evaporation of raindrops falling from convective clouds. Consequently, integrated SWI analysis of rain-, surface and subsurface waters, together with the atmospheric water budget analysis, revealed that shallow groundwater of small Wetlands in this region was very likely to be recharged from surface waters originating from local rainfall, which was temporarily pooled in small Wetlands. This was also supported by tritium (3H) counting of the current rain- and subsurface waters in the region. We highly recommend that shallow groundwater not be pumped intensively to conserve surface and subsurface waters, both of which are important water resources in the region.
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evaluation of surface water dynamics for water food security in Seasonal Wetlands north central namibia
Proceedings of ICWRS2014 - 6th IAHS-EGU International Symposium on Integrated Water Resources Management Bologna Italy 4–6 June 2014, 2014Co-Authors: Tetsuya Hiyama, Jack R Kambatuku, Hiroki Mizuochi, Yuichiro Fujioka, Tetsuji Suzuki, Takeshi Ohta, Miho Hanamura, Johanna Ngula Niipele, Morio IijimaAbstract:Abstract. Agricultural use of Wetlands is important for food security in various regions. However, land-use changes in wetland areas could alter the water cycle and the ecosystem. To conserve the water environments of Wetlands, care is needed when introducing new cropping systems. This study is the first attempt to evaluate the water dynamics in the case of the introduction of rice-millet mixed-cropping systems to the Cuvelai system Seasonal Wetlands (CSSWs) in north-central Namibia. We first investigated Seasonal changes in surface water coverage by using satellite remote sensing data. We also assessed the effect of the introduction of rice-millet mixed-cropping systems on evapotranspiration in the CSSWs region. For the former investigation, we used MODIS and AMSR-E satellite remote sensing data. These data showed that at the beginning of the wet season, surface water appears from the southern (lower) part and then expands to the northern (higher) part of the CSSWs. For the latter investigation, we used data obtained by the classical Bowen ratio-energy balance (BREB) method at an experimental field site established in September 2012 on the Ogongo campus, University of Namibia. This analysis showed the importance of water and vegetation conditions when introducing mixed-cropping to the region.
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effects of the introduction of rice on evapotranspiration in Seasonal Wetlands
Hydrological Processes, 2014Co-Authors: Tetsuji Suzuki, Tetsuya Hiyama, Takeshi Ohta, Yasuhiro Izumi, Osmund Mwandemele, Morio IijimaAbstract:Land use changes in wetland areas can alter evapotranspiration, a major component of the water balance, which eventually affects the water cycle and ecosystem. This study assessed the effect of introduced rice-cropping on evapotranspiration in Seasonal Wetlands of northern Namibia. By using the Bowen ratio–energy balance method, measurements of evapotranspiration were performed over a period of 2.5 years at two wetland sites—a rice field (RF) and a natural vegetation field (NVF)—and at one upland field (UF) devoid of surface water. The mean evapotranspiration rates of RF (1.9 mm daytime−1) and NVF (1.8 mm daytime−1) were greater than that in UF (1.0 mm daytime−1). RF and NVF showed a slight difference in Seasonal variations in evapotranspiration rates. During the dry season, RF evapotranspiration was less than the NVF evapotranspiration. The net radiation in RF was less in this period because of the higher albedo of the non-vegetated surface after rice harvesting. In the early growth period of rice during the wet season, evapotranspiration in RF was higher than that in NVF, which was attributed to a difference in the evaporation efficiency and the transfer coefficient for latent heat that were both affected by leaf area index (LAI). Evapotranspiration sharply negatively responded to an increase in LAI when surface water is present according to sensitivity analysis, probably because a higher LAI over a surface suppresses evaporation. The control of LAI is therefore a key for reducing evaporation and conserving water. Copyright © 2013 John Wiley & Sons, Ltd.
Tetsuya Hiyama - One of the best experts on this subject based on the ideXlab platform.
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development and evaluation of a lookup table based approach to data fusion for Seasonal Wetlands monitoring an integrated use of amsr series modis and landsat
Remote Sensing of Environment, 2017Co-Authors: Hiroki Mizuochi, Tetsuya Hiyama, Jack R Kambatuku, Yuichiro Fujioka, Morio Iijima, Takeshi Ohta, Kenlo Nishida NasaharaAbstract:Abstract Broad scale monitoring of inland waters is essential to research on carbon and water cycles, and for application in the monitoring of disasters including floods and droughts on various spatial and temporal scales. Satellite remote sensing using spatiotemporal data fusion (STF) has recently attracted attention as a way of simultaneously describing spatial heterogeneity and tracking the temporal variability of inland waters. However, existing STF approaches have limitations in describing abrupt temporal changes, integrating “dissimilar” datasets (i.e., fusions between microwave and optical data), and compiling long-term, frequent STF datasets. To overcome these limitations, in this study we developed and evaluated a lookup table (LUT)-based STF, termed database unmixing (DBUX), using multiple types of satellite data (AMSR series, MODIS, and Landsat), and applied it to semi-arid Seasonal Wetlands in Namibia. The results show that DBUX is: 1) flexible in integrating optical data (MODIS or Landsat) with microwave (AMSR series) and Seasonal (day of year) information; 2) able to generate long-term, frequent Landsat-like datasets; and 3) more reliable than an existing approach (spatial and temporal adaptive reflectance fusion model; STARFM) for tracking dynamic temporal variations in Seasonal Wetlands. Water maps retrieved from the resulting STF dataset for the Wetlands had a 30-m spatial resolution and a temporal frequency of 1 or 2 days, and the dataset covered from 2002 to 2015. The time series water maps accurately described both Seasonal and interannual changes in the Wetlands, and could act as a basis for understanding the hydrological features of the region. Further studies are required to enable application of DBUX in other regions, and for other landscapes with different satellite sensor combinations.
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analysing the origin of rain and subsurface water in Seasonal Wetlands of north central namibia
Environmental Research Letters, 2017Co-Authors: Tetsuya Hiyama, Hironari Kanamori, Jack R Kambatuku, Ayumi Kotani, Kazuyoshi Asai, Hiroki Mizuochi, Yuichiro Fujioka, Morio IijimaAbstract:We investigated the origins of rain- and subsurface waters of north-central Namibia's Seasonal Wetlands, which are critical to the region's water and food security. The region includes the southern part of the Cuvelai system Seasonal Wetlands (CSSWs) of the Cuvelai Basin, a transboundary river basin covering southern Angola and northern Namibia. We analysed stable water isotopes (SWIs) of hydrogen (HDO) and oxygen (H2 18O) in rainwater, surface water and shallow groundwater. Rainwater samples were collected during every rainfall event of the rainy season from October 2013 to April 2014. The isotopic ratios of HDO (δD) and oxygen H2 18O (δ 18O) were analysed in each rainwater sample and then used to derive the annual mean value of (δD, δ 18O) in precipitation weighted by each rainfall volume. Using delta diagrams (plotting δD vs. δ 18O), we showed that the annual mean value was a good indicator for determining the origins of subsurface waters in the CSSWs. To confirm the origins of rainwater and to explain the variations in isotopic ratios, we conducted atmospheric water budget analysis using Tropical Rainfall Measuring Mission (TRMM) multi-satellite precipitation analysis (TMPA) data and ERA-Interim atmospheric reanalysis data. The results showed that around three-fourths of rainwater was derived from recycled water at local–regional scales. Satellite-observed outgoing longwave radiation (OLR) and complementary satellite data from MODerate-resolution Imaging Spectroradiometer (MODIS) and Advanced Microwave Scanning Radiometer (AMSR) series implied that the isotopic ratios in rainwater were affected by evaporation of raindrops falling from convective clouds. Consequently, integrated SWI analysis of rain-, surface and subsurface waters, together with the atmospheric water budget analysis, revealed that shallow groundwater of small Wetlands in this region was very likely to be recharged from surface waters originating from local rainfall, which was temporarily pooled in small Wetlands. This was also supported by tritium (3H) counting of the current rain- and subsurface waters in the region. We highly recommend that shallow groundwater not be pumped intensively to conserve surface and subsurface waters, both of which are important water resources in the region.
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evaluation of surface water dynamics for water food security in Seasonal Wetlands north central namibia
Proceedings of ICWRS2014 - 6th IAHS-EGU International Symposium on Integrated Water Resources Management Bologna Italy 4–6 June 2014, 2014Co-Authors: Tetsuya Hiyama, Jack R Kambatuku, Hiroki Mizuochi, Yuichiro Fujioka, Tetsuji Suzuki, Takeshi Ohta, Miho Hanamura, Johanna Ngula Niipele, Morio IijimaAbstract:Abstract. Agricultural use of Wetlands is important for food security in various regions. However, land-use changes in wetland areas could alter the water cycle and the ecosystem. To conserve the water environments of Wetlands, care is needed when introducing new cropping systems. This study is the first attempt to evaluate the water dynamics in the case of the introduction of rice-millet mixed-cropping systems to the Cuvelai system Seasonal Wetlands (CSSWs) in north-central Namibia. We first investigated Seasonal changes in surface water coverage by using satellite remote sensing data. We also assessed the effect of the introduction of rice-millet mixed-cropping systems on evapotranspiration in the CSSWs region. For the former investigation, we used MODIS and AMSR-E satellite remote sensing data. These data showed that at the beginning of the wet season, surface water appears from the southern (lower) part and then expands to the northern (higher) part of the CSSWs. For the latter investigation, we used data obtained by the classical Bowen ratio-energy balance (BREB) method at an experimental field site established in September 2012 on the Ogongo campus, University of Namibia. This analysis showed the importance of water and vegetation conditions when introducing mixed-cropping to the region.
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effects of the introduction of rice on evapotranspiration in Seasonal Wetlands
Hydrological Processes, 2014Co-Authors: Tetsuji Suzuki, Tetsuya Hiyama, Takeshi Ohta, Yasuhiro Izumi, Osmund Mwandemele, Morio IijimaAbstract:Land use changes in wetland areas can alter evapotranspiration, a major component of the water balance, which eventually affects the water cycle and ecosystem. This study assessed the effect of introduced rice-cropping on evapotranspiration in Seasonal Wetlands of northern Namibia. By using the Bowen ratio–energy balance method, measurements of evapotranspiration were performed over a period of 2.5 years at two wetland sites—a rice field (RF) and a natural vegetation field (NVF)—and at one upland field (UF) devoid of surface water. The mean evapotranspiration rates of RF (1.9 mm daytime−1) and NVF (1.8 mm daytime−1) were greater than that in UF (1.0 mm daytime−1). RF and NVF showed a slight difference in Seasonal variations in evapotranspiration rates. During the dry season, RF evapotranspiration was less than the NVF evapotranspiration. The net radiation in RF was less in this period because of the higher albedo of the non-vegetated surface after rice harvesting. In the early growth period of rice during the wet season, evapotranspiration in RF was higher than that in NVF, which was attributed to a difference in the evaporation efficiency and the transfer coefficient for latent heat that were both affected by leaf area index (LAI). Evapotranspiration sharply negatively responded to an increase in LAI when surface water is present according to sensitivity analysis, probably because a higher LAI over a surface suppresses evaporation. The control of LAI is therefore a key for reducing evaporation and conserving water. Copyright © 2013 John Wiley & Sons, Ltd.
Dominic Mazvimavi - One of the best experts on this subject based on the ideXlab platform.
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leveraging google earth engine platform to characterize and map small Seasonal Wetlands in the semi arid environments of south africa
Science of The Total Environment, 2022Co-Authors: Siyamthanda Gxokwe, Timothy Dube, Dominic MazvimaviAbstract:Abstract Although significant scientific research strides have been made in mapping the spatial extents and ecohydrological dynamics of Wetlands in semi-arid environments, the focus on small Wetlands remains a challenge. This is due to the sensing characteristics of remote sensing platforms and lack of robust data processing techniques. Advancements in data analytic tools, such as the introduction of Google Earth Engine (GEE) platform provides unique opportunities for improved assessment of small and scattered Wetlands. This study thus assessed the capabilities of GEE cloud-computing platform in characterising small Seasonal flooded Wetlands, using the new generation Sentinel 2 data from 2016 to 2020. Specifically, the study assessed the spectral separability of different land cover classes for two different Wetlands detected, using Sentinel-2 multi-year composite water and vegetation indices and to identify the most suitable GEE machine learning algorithm for accurately detecting and mapping semi-arid Seasonal Wetlands. This was achieved using the object based Random Forest (RF), Support Vector Machine (SVM), Classification and Regression Tree (CART) and Naive Bayes (NB) advanced algorithms in GEE. The results demonstrated the capabilities of using the GEE platform to characterize Wetlands with acceptable accuracy. All algorithms showed superiority, in mapping the two Wetlands except for the NB method, which had lowest overall classification accuracy. These findings underscore the relevance of the GEE platform, Sentinel-2 data and advanced algorithms in characterizing small and Seasonal semi-arid Wetlands.
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leveraging google earth engine platform to characterize and map small Seasonal Wetlands in the semi arid environments of south africa
arXiv: Image and Video Processing, 2021Co-Authors: Siyamthanda Gxokwe, Timothy Dube, Dominic MazvimaviAbstract:Small Seasonal Wetlands are a distinctive feature of the semi-arid environments. Although these systems are small and ephemeral in nature, they provide habitats to aquatic flora and fauna, and play a critical role in sustaining livelihoods through the provision of ecological services. There is a great concern that these Wetlands are not routinely monitored, which has contributed to their poor management. So far, scientific research strides have been noted in mapping and understanding the spatial coverage and ecohydrological dynamics of Wetlands in semi-arid areas using broadband multispectral data. However, because of the sensing characteristics of these platforms, mapping and monitoring of small Wetlands remains a challenge.
Hiroki Mizuochi - One of the best experts on this subject based on the ideXlab platform.
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development and evaluation of a lookup table based approach to data fusion for Seasonal Wetlands monitoring an integrated use of amsr series modis and landsat
Remote Sensing of Environment, 2017Co-Authors: Hiroki Mizuochi, Tetsuya Hiyama, Jack R Kambatuku, Yuichiro Fujioka, Morio Iijima, Takeshi Ohta, Kenlo Nishida NasaharaAbstract:Abstract Broad scale monitoring of inland waters is essential to research on carbon and water cycles, and for application in the monitoring of disasters including floods and droughts on various spatial and temporal scales. Satellite remote sensing using spatiotemporal data fusion (STF) has recently attracted attention as a way of simultaneously describing spatial heterogeneity and tracking the temporal variability of inland waters. However, existing STF approaches have limitations in describing abrupt temporal changes, integrating “dissimilar” datasets (i.e., fusions between microwave and optical data), and compiling long-term, frequent STF datasets. To overcome these limitations, in this study we developed and evaluated a lookup table (LUT)-based STF, termed database unmixing (DBUX), using multiple types of satellite data (AMSR series, MODIS, and Landsat), and applied it to semi-arid Seasonal Wetlands in Namibia. The results show that DBUX is: 1) flexible in integrating optical data (MODIS or Landsat) with microwave (AMSR series) and Seasonal (day of year) information; 2) able to generate long-term, frequent Landsat-like datasets; and 3) more reliable than an existing approach (spatial and temporal adaptive reflectance fusion model; STARFM) for tracking dynamic temporal variations in Seasonal Wetlands. Water maps retrieved from the resulting STF dataset for the Wetlands had a 30-m spatial resolution and a temporal frequency of 1 or 2 days, and the dataset covered from 2002 to 2015. The time series water maps accurately described both Seasonal and interannual changes in the Wetlands, and could act as a basis for understanding the hydrological features of the region. Further studies are required to enable application of DBUX in other regions, and for other landscapes with different satellite sensor combinations.
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analysing the origin of rain and subsurface water in Seasonal Wetlands of north central namibia
Environmental Research Letters, 2017Co-Authors: Tetsuya Hiyama, Hironari Kanamori, Jack R Kambatuku, Ayumi Kotani, Kazuyoshi Asai, Hiroki Mizuochi, Yuichiro Fujioka, Morio IijimaAbstract:We investigated the origins of rain- and subsurface waters of north-central Namibia's Seasonal Wetlands, which are critical to the region's water and food security. The region includes the southern part of the Cuvelai system Seasonal Wetlands (CSSWs) of the Cuvelai Basin, a transboundary river basin covering southern Angola and northern Namibia. We analysed stable water isotopes (SWIs) of hydrogen (HDO) and oxygen (H2 18O) in rainwater, surface water and shallow groundwater. Rainwater samples were collected during every rainfall event of the rainy season from October 2013 to April 2014. The isotopic ratios of HDO (δD) and oxygen H2 18O (δ 18O) were analysed in each rainwater sample and then used to derive the annual mean value of (δD, δ 18O) in precipitation weighted by each rainfall volume. Using delta diagrams (plotting δD vs. δ 18O), we showed that the annual mean value was a good indicator for determining the origins of subsurface waters in the CSSWs. To confirm the origins of rainwater and to explain the variations in isotopic ratios, we conducted atmospheric water budget analysis using Tropical Rainfall Measuring Mission (TRMM) multi-satellite precipitation analysis (TMPA) data and ERA-Interim atmospheric reanalysis data. The results showed that around three-fourths of rainwater was derived from recycled water at local–regional scales. Satellite-observed outgoing longwave radiation (OLR) and complementary satellite data from MODerate-resolution Imaging Spectroradiometer (MODIS) and Advanced Microwave Scanning Radiometer (AMSR) series implied that the isotopic ratios in rainwater were affected by evaporation of raindrops falling from convective clouds. Consequently, integrated SWI analysis of rain-, surface and subsurface waters, together with the atmospheric water budget analysis, revealed that shallow groundwater of small Wetlands in this region was very likely to be recharged from surface waters originating from local rainfall, which was temporarily pooled in small Wetlands. This was also supported by tritium (3H) counting of the current rain- and subsurface waters in the region. We highly recommend that shallow groundwater not be pumped intensively to conserve surface and subsurface waters, both of which are important water resources in the region.
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evaluation of surface water dynamics for water food security in Seasonal Wetlands north central namibia
Proceedings of ICWRS2014 - 6th IAHS-EGU International Symposium on Integrated Water Resources Management Bologna Italy 4–6 June 2014, 2014Co-Authors: Tetsuya Hiyama, Jack R Kambatuku, Hiroki Mizuochi, Yuichiro Fujioka, Tetsuji Suzuki, Takeshi Ohta, Miho Hanamura, Johanna Ngula Niipele, Morio IijimaAbstract:Abstract. Agricultural use of Wetlands is important for food security in various regions. However, land-use changes in wetland areas could alter the water cycle and the ecosystem. To conserve the water environments of Wetlands, care is needed when introducing new cropping systems. This study is the first attempt to evaluate the water dynamics in the case of the introduction of rice-millet mixed-cropping systems to the Cuvelai system Seasonal Wetlands (CSSWs) in north-central Namibia. We first investigated Seasonal changes in surface water coverage by using satellite remote sensing data. We also assessed the effect of the introduction of rice-millet mixed-cropping systems on evapotranspiration in the CSSWs region. For the former investigation, we used MODIS and AMSR-E satellite remote sensing data. These data showed that at the beginning of the wet season, surface water appears from the southern (lower) part and then expands to the northern (higher) part of the CSSWs. For the latter investigation, we used data obtained by the classical Bowen ratio-energy balance (BREB) method at an experimental field site established in September 2012 on the Ogongo campus, University of Namibia. This analysis showed the importance of water and vegetation conditions when introducing mixed-cropping to the region.
Siyamthanda Gxokwe - One of the best experts on this subject based on the ideXlab platform.
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leveraging google earth engine platform to characterize and map small Seasonal Wetlands in the semi arid environments of south africa
Science of The Total Environment, 2022Co-Authors: Siyamthanda Gxokwe, Timothy Dube, Dominic MazvimaviAbstract:Abstract Although significant scientific research strides have been made in mapping the spatial extents and ecohydrological dynamics of Wetlands in semi-arid environments, the focus on small Wetlands remains a challenge. This is due to the sensing characteristics of remote sensing platforms and lack of robust data processing techniques. Advancements in data analytic tools, such as the introduction of Google Earth Engine (GEE) platform provides unique opportunities for improved assessment of small and scattered Wetlands. This study thus assessed the capabilities of GEE cloud-computing platform in characterising small Seasonal flooded Wetlands, using the new generation Sentinel 2 data from 2016 to 2020. Specifically, the study assessed the spectral separability of different land cover classes for two different Wetlands detected, using Sentinel-2 multi-year composite water and vegetation indices and to identify the most suitable GEE machine learning algorithm for accurately detecting and mapping semi-arid Seasonal Wetlands. This was achieved using the object based Random Forest (RF), Support Vector Machine (SVM), Classification and Regression Tree (CART) and Naive Bayes (NB) advanced algorithms in GEE. The results demonstrated the capabilities of using the GEE platform to characterize Wetlands with acceptable accuracy. All algorithms showed superiority, in mapping the two Wetlands except for the NB method, which had lowest overall classification accuracy. These findings underscore the relevance of the GEE platform, Sentinel-2 data and advanced algorithms in characterizing small and Seasonal semi-arid Wetlands.
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leveraging google earth engine platform to characterize and map small Seasonal Wetlands in the semi arid environments of south africa
arXiv: Image and Video Processing, 2021Co-Authors: Siyamthanda Gxokwe, Timothy Dube, Dominic MazvimaviAbstract:Small Seasonal Wetlands are a distinctive feature of the semi-arid environments. Although these systems are small and ephemeral in nature, they provide habitats to aquatic flora and fauna, and play a critical role in sustaining livelihoods through the provision of ecological services. There is a great concern that these Wetlands are not routinely monitored, which has contributed to their poor management. So far, scientific research strides have been noted in mapping and understanding the spatial coverage and ecohydrological dynamics of Wetlands in semi-arid areas using broadband multispectral data. However, because of the sensing characteristics of these platforms, mapping and monitoring of small Wetlands remains a challenge.