Pub Date : 2024-01-12DOI: 10.15625/2615-9783/19912
Khuong Pham Le, Anh Nguyen Xuan, Hiep Van Nguyen, Son Hoang Hai, Vinh Nguyen Nhu, Minh Bui Ngoc
This paper evaluates the estimated total precipitable water (TPW) and studies its characteristics in the Nghia Do area (Hanoi) using Global Positioning System (GPS) data and the Canadian Spatial Reference System-Precise Point Positioning (CSRS-PPP) processing technique and calculation tool. The TPW was estimated from GPS data from September 22, 2022 to March 31, 2023 using CSRS-PPP provided by Natural Resources Canada. The calculated TPW was validated with TPW products from Aeronet data and radiosonde data. Taking advantage of its high time resolution, the TPW estimated from GPS data was used to analyze the temporal variation of TPW during cold surges affecting the Nghia Do area. The results indicate a strong agreement between the estimated TPW from GPS data and TPW products derived from Aeronet and radiosonde data. The mean error (ME), root mean square error (RMSE), and correlation coefficient between the estimated TPW from GPS data and the Aeronet-derived product are 0.68 mm, 2.05 mm, and 0.988, respectively. The corresponding values between the estimated TPW and the radiosonde-derived product are -3.01 mm, 3.24 mm, and 0.996, respectively. The study of TPW variation over the Nghia Do area during the research period revealed that, generally, TPW values in December and January were lower than those in the other months. Before the arrival of a specific cold surge at a station, TPW tends to increase by about 6 mm within 12 hours as convection activities ahead of the cold front intensify. After the cold air passes over the station, the TPW value decreases by about 8 mm within 12 hours due to the influx of cold and dry winter air brought by the prevailing winds. This distinct TPW variation pattern suggests that GPS data can be effectively employed to define the arrival of cold surges in the station area.
{"title":"Precipitable water characterization using global navigation satellite system data: A case study in Nghia Do area, Vietnam","authors":"Khuong Pham Le, Anh Nguyen Xuan, Hiep Van Nguyen, Son Hoang Hai, Vinh Nguyen Nhu, Minh Bui Ngoc","doi":"10.15625/2615-9783/19912","DOIUrl":"https://doi.org/10.15625/2615-9783/19912","url":null,"abstract":"This paper evaluates the estimated total precipitable water (TPW) and studies its characteristics in the Nghia Do area (Hanoi) using Global Positioning System (GPS) data and the Canadian Spatial Reference System-Precise Point Positioning (CSRS-PPP) processing technique and calculation tool. The TPW was estimated from GPS data from September 22, 2022 to March 31, 2023 using CSRS-PPP provided by Natural Resources Canada. The calculated TPW was validated with TPW products from Aeronet data and radiosonde data. Taking advantage of its high time resolution, the TPW estimated from GPS data was used to analyze the temporal variation of TPW during cold surges affecting the Nghia Do area. The results indicate a strong agreement between the estimated TPW from GPS data and TPW products derived from Aeronet and radiosonde data. The mean error (ME), root mean square error (RMSE), and correlation coefficient between the estimated TPW from GPS data and the Aeronet-derived product are 0.68 mm, 2.05 mm, and 0.988, respectively. The corresponding values between the estimated TPW and the radiosonde-derived product are -3.01 mm, 3.24 mm, and 0.996, respectively. The study of TPW variation over the Nghia Do area during the research period revealed that, generally, TPW values in December and January were lower than those in the other months. Before the arrival of a specific cold surge at a station, TPW tends to increase by about 6 mm within 12 hours as convection activities ahead of the cold front intensify. After the cold air passes over the station, the TPW value decreases by about 8 mm within 12 hours due to the influx of cold and dry winter air brought by the prevailing winds. This distinct TPW variation pattern suggests that GPS data can be effectively employed to define the arrival of cold surges in the station area.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139531652","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-21DOI: 10.15625/2615-9783/19460
Luu Anh The, Mai Van Dinh, Do Trung Quang, Ali Feizi, Hoang Duyen Thi Thu
The frequency and severity of drought are projected to increase due to climate change, and Southeast Asia is no exception. Water scarcity hampers all biochemical processes in soil and induces stunted plant growth. While the rhizosphere harbors the most dynamic biochemical processes in the biosphere, the interaction mechanisms between residing microbes and plant roots under drought are poorly understood. In this research, soybean was planted in soil collected from the Red River Delta of Vietnam to test two hypotheses: (i) drought reduces rhizosphere enzyme activities and hampers the extent of the high enzyme activity along single root (from the root tips), and (ii) the turnover time of substrate by enzymes increases with decreasing soil moisture. The research aimed to characterize distributions of β-glucosidase and acid phosphatase enzymes in a distance from root tips. In addition, enzyme activities and plant root and shoot characteristics (length and weight) were investigated. The results demonstrated that shoot length was more impacted by drought than root length with the reduction of 25% for the former and 5% for the later. Meanwhile, the reduction in shoot weight was 61%, and root weight was 90% as the plant experienced drought conditions. The extent of a hotspot for enzymes along a single plant root, measured from the root tips, also decreased in response to drought. Furthermore, drought reduced both rhizosphere enzyme activities, resulting in a slower turnover time of β-D-glucopyranoside (MUF-G) and 4-methylumbelliferyl-phosphate(MUF-P) substrates. The research has shed light on the adverse impacts of drought on root-microbe interactions, which ultimately lead to poor crop growth.
{"title":"Effects of drought on enzyme activities and hotspot distribution along plant roots","authors":"Luu Anh The, Mai Van Dinh, Do Trung Quang, Ali Feizi, Hoang Duyen Thi Thu","doi":"10.15625/2615-9783/19460","DOIUrl":"https://doi.org/10.15625/2615-9783/19460","url":null,"abstract":"The frequency and severity of drought are projected to increase due to climate change, and Southeast Asia is no exception. Water scarcity hampers all biochemical processes in soil and induces stunted plant growth. While the rhizosphere harbors the most dynamic biochemical processes in the biosphere, the interaction mechanisms between residing microbes and plant roots under drought are poorly understood. In this research, soybean was planted in soil collected from the Red River Delta of Vietnam to test two hypotheses: (i) drought reduces rhizosphere enzyme activities and hampers the extent of the high enzyme activity along single root (from the root tips), and (ii) the turnover time of substrate by enzymes increases with decreasing soil moisture. The research aimed to characterize distributions of β-glucosidase and acid phosphatase enzymes in a distance from root tips. In addition, enzyme activities and plant root and shoot characteristics (length and weight) were investigated. The results demonstrated that shoot length was more impacted by drought than root length with the reduction of 25% for the former and 5% for the later. Meanwhile, the reduction in shoot weight was 61%, and root weight was 90% as the plant experienced drought conditions. The extent of a hotspot for enzymes along a single plant root, measured from the root tips, also decreased in response to drought. Furthermore, drought reduced both rhizosphere enzyme activities, resulting in a slower turnover time of β-D-glucopyranoside (MUF-G) and 4-methylumbelliferyl-phosphate(MUF-P) substrates. The research has shed light on the adverse impacts of drought on root-microbe interactions, which ultimately lead to poor crop growth.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2023-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139251608","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-21DOI: 10.15625/2615-9783/19459
Nhan Nguyen Thi Thanh, Hiroshi Matsuda, Quoc Duong Trung, Thach Tran Xuan, An Tran Thi Phuong, Quynh Tran Thi Ngoc, Nhan Tran Thanh, Tien Pham Van, Huyen Nguyen Thi Le
Granulated blast furnace slag (GBFS) has more advantageous properties over natural sand, such as lightweight, higher shear strength, and higher permeability. Therefore, it is regarded as a potentially promising substitute for natural sand in the ground improvement using the sand compaction pile (SCP) method. Due to the relatively rapid solidification, however, which is induced by the latent hydraulic property of GBFS, the permeability of the installed GBFS compaction pile (GBFSCP) decreases quickly, and such an application becomes difficult for the case of SCP with low sand replacement area ratio (LSRAR). So, to decelerate the permeability reduction of GBFSCP, different GBFSs, and natural sands were collected in Japan and Vietnam, and the specimens were prepared by changing the mixing ratio of sand to GBFS from 20% to 80%. Then, firstly, fundamental geotechnical properties of sand-mixed GBFS without hydration were observed. Secondly, the specimens of sand-GBFS mixture were cured in seawater at the temperature of 80°C for 3 days to 380 days. The unconfined compressive strength, permeability, and hydration reaction rate of the hydrated sand-mixed GBFS specimen were measured. In conclusion, the geotechnical properties of the unhydrated sand-mixed GBFS become more advantageous than those of natural sand. In addition, by mixing with natural sand, the hydration reaction rate and the solidification of GBFS are controlled. This means that it is possible to keep the compressive strength and the permeability at the predetermined conditions and, in turn, to satisfy requirements for the SCP method with LSRAR. In addition, a simple estimation method of the unconfined compressive strength was proposed for the hydrated sand-mixed GBFS specimen.
{"title":"Geotechnical properties of natural sand-mixed granulated blast furnace slag applied to the sand compaction pile method","authors":"Nhan Nguyen Thi Thanh, Hiroshi Matsuda, Quoc Duong Trung, Thach Tran Xuan, An Tran Thi Phuong, Quynh Tran Thi Ngoc, Nhan Tran Thanh, Tien Pham Van, Huyen Nguyen Thi Le","doi":"10.15625/2615-9783/19459","DOIUrl":"https://doi.org/10.15625/2615-9783/19459","url":null,"abstract":"Granulated blast furnace slag (GBFS) has more advantageous properties over natural sand, such as lightweight, higher shear strength, and higher permeability. Therefore, it is regarded as a potentially promising substitute for natural sand in the ground improvement using the sand compaction pile (SCP) method. Due to the relatively rapid solidification, however, which is induced by the latent hydraulic property of GBFS, the permeability of the installed GBFS compaction pile (GBFSCP) decreases quickly, and such an application becomes difficult for the case of SCP with low sand replacement area ratio (LSRAR). So, to decelerate the permeability reduction of GBFSCP, different GBFSs, and natural sands were collected in Japan and Vietnam, and the specimens were prepared by changing the mixing ratio of sand to GBFS from 20% to 80%. Then, firstly, fundamental geotechnical properties of sand-mixed GBFS without hydration were observed. Secondly, the specimens of sand-GBFS mixture were cured in seawater at the temperature of 80°C for 3 days to 380 days. The unconfined compressive strength, permeability, and hydration reaction rate of the hydrated sand-mixed GBFS specimen were measured. In conclusion, the geotechnical properties of the unhydrated sand-mixed GBFS become more advantageous than those of natural sand. In addition, by mixing with natural sand, the hydration reaction rate and the solidification of GBFS are controlled. This means that it is possible to keep the compressive strength and the permeability at the predetermined conditions and, in turn, to satisfy requirements for the SCP method with LSRAR. In addition, a simple estimation method of the unconfined compressive strength was proposed for the hydrated sand-mixed GBFS specimen.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2023-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139252555","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-01DOI: 10.15625/2615-9783/19327
Da Le Nhu, Huong Nguyen Thi Mai, Ha Hoang Thi Thu, Thuy Duong Thi, Binh Phung Thi Xuan, Huong Pham Thi Mai, Hanh Pham Thi Minh, Quynh Le Thi Phuong
Coliform bacteria are essential variables for assessing riverine water quality. In this study, the faecal indicator bacteria (FIB) in relationship with some physico-chemical variables were investigated during the period 2020-2022 for four urban rivers (To Lich, Lu, Set, and Kim Nguu) in the inner Hanoi city to provide the updated water quality of these rivers. The results demonstrated severe faecal coliforms contamination in riverine waters compared to the permissible values of the Vietnam technical regulation for surface water quality, QCVN08-MT:2015/BTNMT column B1. Nutrients (ammonium and phosphate) concentrations and dissolved oxygen (DO) values exceeded the permissible values, whereas pH was within the standard. The Pearson analysis demonstrated the significant positive correlation between total coliforms (TC) and Escherichia coli (EC) densities and ammonium concentration in the riverine water. Besides, these variables were higher in the dry season than the rainy one for all sites observed. All these reflect the critical role of the point sources, notably domestic wastewater inputs in the four river basins. Considering these rivers' deteriorating condition, developing an effective wastewater treatment system is necessary for the rivers in Hanoi.
{"title":"Faecal contamination and its relationship with some environmental variables of four urban rivers in inner Hanoi city, Vietnam","authors":"Da Le Nhu, Huong Nguyen Thi Mai, Ha Hoang Thi Thu, Thuy Duong Thi, Binh Phung Thi Xuan, Huong Pham Thi Mai, Hanh Pham Thi Minh, Quynh Le Thi Phuong","doi":"10.15625/2615-9783/19327","DOIUrl":"https://doi.org/10.15625/2615-9783/19327","url":null,"abstract":"Coliform bacteria are essential variables for assessing riverine water quality. In this study, the faecal indicator bacteria (FIB) in relationship with some physico-chemical variables were investigated during the period 2020-2022 for four urban rivers (To Lich, Lu, Set, and Kim Nguu) in the inner Hanoi city to provide the updated water quality of these rivers. The results demonstrated severe faecal coliforms contamination in riverine waters compared to the permissible values of the Vietnam technical regulation for surface water quality, QCVN08-MT:2015/BTNMT column B1. Nutrients (ammonium and phosphate) concentrations and dissolved oxygen (DO) values exceeded the permissible values, whereas pH was within the standard. The Pearson analysis demonstrated the significant positive correlation between total coliforms (TC) and Escherichia coli (EC) densities and ammonium concentration in the riverine water. Besides, these variables were higher in the dry season than the rainy one for all sites observed. All these reflect the critical role of the point sources, notably domestic wastewater inputs in the four river basins. Considering these rivers' deteriorating condition, developing an effective wastewater treatment system is necessary for the rivers in Hanoi.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135320931","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-30DOI: 10.15625/2615-9783/19302
Mohamad K. Najib, Sri Nurdiati, Ardhasena Sopaheluwakan
Hotspots in Kalimantan are significantly correlated with local and global climatic conditions. These hotspots have been represented in previous explorations using copula-based mean regression technique. However, this study focused on advancing hotspots model through the use of copula-based quantile regression. Probabilistic method was also introduced to depict the characteristics of hotspots in Kalimantan. To achieve this objective, the technique of the inference of functions for margins was applied. Several copula functions, including Gumbel, Clayton, Frank, Joe, Galambos, BB1, BB6, BB7, and BB8, were meticulously chosen. The selection of the most suitable copula was based on the results of the Anderson-Darling and Cramer-von Mises hypothesis tests. The results showed that the combination of quantile and mean regression yielded satisfactory results. Moreover, an uncertainty range was established by assessing the outermost quantile, which aided the assessment of the reliability of estimated hotspots. Probabilistic model introduced a fresh viewpoint to modeling process. Instead of forecasting an exact value, model estimated the probability of hotspots occurrences based on specific climatic conditions. Among the three scenarios examined, precipitation-based model showed an average accuracy of 89.7%, while dry spells-based outperformed the value with a score of 90.3%. After evaluating the results from both regression and probabilistic model, dry spells-based method outperformed precipitation-based. On the other hand, precipitation-based performed better in capturing certain minor details compared to dry spells-based model.
{"title":"Prediction of hotspots pattern in Kalimantan using copula-based quantile regression and probabilistic model: a study of precipitation and dry spells across varied ENSO conditions","authors":"Mohamad K. Najib, Sri Nurdiati, Ardhasena Sopaheluwakan","doi":"10.15625/2615-9783/19302","DOIUrl":"https://doi.org/10.15625/2615-9783/19302","url":null,"abstract":"Hotspots in Kalimantan are significantly correlated with local and global climatic conditions. These hotspots have been represented in previous explorations using copula-based mean regression technique. However, this study focused on advancing hotspots model through the use of copula-based quantile regression. Probabilistic method was also introduced to depict the characteristics of hotspots in Kalimantan. To achieve this objective, the technique of the inference of functions for margins was applied. Several copula functions, including Gumbel, Clayton, Frank, Joe, Galambos, BB1, BB6, BB7, and BB8, were meticulously chosen. The selection of the most suitable copula was based on the results of the Anderson-Darling and Cramer-von Mises hypothesis tests. The results showed that the combination of quantile and mean regression yielded satisfactory results. Moreover, an uncertainty range was established by assessing the outermost quantile, which aided the assessment of the reliability of estimated hotspots. Probabilistic model introduced a fresh viewpoint to modeling process. Instead of forecasting an exact value, model estimated the probability of hotspots occurrences based on specific climatic conditions. Among the three scenarios examined, precipitation-based model showed an average accuracy of 89.7%, while dry spells-based outperformed the value with a score of 90.3%. After evaluating the results from both regression and probabilistic model, dry spells-based method outperformed precipitation-based. On the other hand, precipitation-based performed better in capturing certain minor details compared to dry spells-based model.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136105169","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-05DOI: 10.15625/2615-9783/19080
Van- Hao Duong, Tien Chu Trung, Hung Danh Tran, Oanh Nguyen Thi, Duc Do Xuan, Hoang Ha Nguyen Thi, Hung Dinh Viet
210Po, one of the harmful natural isotopes with a long enough half-life, plays a significant role in environmental processes. 48 samples, including groundwater (dug wells, thermal water, and drill wells) and surface water (lakes, rivers, and streams) in the Da Nang - Quang Nam region of Vietnam were analyzed by an alpha spectrometer. Relatively low activities of 210Po have been observed, whose mean values ranged from 0.15 to 4.58 and 1.34 mBq.L-1. There is no significant variation in 210Po activities between groundwater and surface water groups. The average 210Po activity of those groups is 1.28 and 1.40 mBq.L-1, respectively. The geological conditions of the study area, neutral pH values, and predominant oxidizing conditions supported the low 210Po activities in the selected water sources. Average annual effective doses for adults, children, and infants due to the consumption of water containing 210Po were found to be 1.15, 1.21, and 2.94 µSv.y-1, respectively.
{"title":"Radiological risk assessment and characteristics of 210Po in selected water sources in Quang Nam and Da Nang, Vietnam","authors":"Van- Hao Duong, Tien Chu Trung, Hung Danh Tran, Oanh Nguyen Thi, Duc Do Xuan, Hoang Ha Nguyen Thi, Hung Dinh Viet","doi":"10.15625/2615-9783/19080","DOIUrl":"https://doi.org/10.15625/2615-9783/19080","url":null,"abstract":"210Po, one of the harmful natural isotopes with a long enough half-life, plays a significant role in environmental processes. 48 samples, including groundwater (dug wells, thermal water, and drill wells) and surface water (lakes, rivers, and streams) in the Da Nang - Quang Nam region of Vietnam were analyzed by an alpha spectrometer. Relatively low activities of 210Po have been observed, whose mean values ranged from 0.15 to 4.58 and 1.34 mBq.L-1. There is no significant variation in 210Po activities between groundwater and surface water groups. The average 210Po activity of those groups is 1.28 and 1.40 mBq.L-1, respectively. The geological conditions of the study area, neutral pH values, and predominant oxidizing conditions supported the low 210Po activities in the selected water sources. Average annual effective doses for adults, children, and infants due to the consumption of water containing 210Po were found to be 1.15, 1.21, and 2.94 µSv.y-1, respectively.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134976424","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-03DOI: 10.15625/2615-9783/19057
Ly Pham Thi, Ha Pham Thanh, Tan Phan Van, Yen Vu Thuan
There have been several studies on heatwaves (HW) in Vietnam but they all focused on an individual heatwave characteristic. A comprehensive understanding of heat waves is crucial for effective research on their impacts and for making plans for climate change mitigation and adaptation strategies in the country. This study investigates the spatial variability and changing trends in heatwave characteristics across the climatic sub-regions of Vietnam. The analysis is based on the observed daily maximum temperature (Tx) recorded at 144 meteorological stations in the period of 1980-2018. HW is identified using a relative threshold, which is the local 90th percentile of Tx within 183 days during the summer (1st April - 30th September). Results showed that: (1) The threshold values used to determine HW events varied among sub-regions and stations due to their geographical locations; (2) Across the country, HWs were observed to be more frequent, intense, severe, and longer-lasting in the North Delta and North Central sub-regions compared to others; (3) Over recent decades, both the frequency and severity of HWs have significantly increased across Vietnam, particularly in the North-Delta and North Central sub-regions. However, the changing trends in HW duration and intensity remain unclear.
{"title":"Variability of heatwaves across Vietnam in recent decades","authors":"Ly Pham Thi, Ha Pham Thanh, Tan Phan Van, Yen Vu Thuan","doi":"10.15625/2615-9783/19057","DOIUrl":"https://doi.org/10.15625/2615-9783/19057","url":null,"abstract":"There have been several studies on heatwaves (HW) in Vietnam but they all focused on an individual heatwave characteristic. A comprehensive understanding of heat waves is crucial for effective research on their impacts and for making plans for climate change mitigation and adaptation strategies in the country. This study investigates the spatial variability and changing trends in heatwave characteristics across the climatic sub-regions of Vietnam. The analysis is based on the observed daily maximum temperature (Tx) recorded at 144 meteorological stations in the period of 1980-2018. HW is identified using a relative threshold, which is the local 90th percentile of Tx within 183 days during the summer (1st April - 30th September). Results showed that: (1) The threshold values used to determine HW events varied among sub-regions and stations due to their geographical locations; (2) Across the country, HWs were observed to be more frequent, intense, severe, and longer-lasting in the North Delta and North Central sub-regions compared to others; (3) Over recent decades, both the frequency and severity of HWs have significantly increased across Vietnam, particularly in the North-Delta and North Central sub-regions. However, the changing trends in HW duration and intensity remain unclear.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135689617","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-29DOI: 10.15625/2615-9783/19026
Hoi Dang Nguyen, Dung Trung Ngo, Dung Viet Vu
Benthic habitats are critical in shallow sea areas; they regulate the diversity and richness of organisms in each area. Mapping benthic habitats elucidates natural sea characteristics and aids in managing and using natural resources, as well as conserving marine biodiversity. This study established a benthic habitat map for the Da Lon Reef area, Truong Sa Islands, Vietnam, using Pléiades high-resolution remote sensing imaging materials and field survey results from 2020 and 2021. We identified seven classes of benthic habitats with a 91.64% overall accuracy, corresponding to a Kappa coefficient of 0.88. In the Da Lon Reef, seagrass biomes occupy a large area (more than 200 ha) and are distributed mainly inside lagoons at depths of 2–6 m. The field survey results identified five seagrass species and the biodiversity and biomass of seagrass populations in the lagoon of Da Lon Reef. The study results confirm the fundamental value of resources, biodiversity in general and seagrass in particular, in managing and protecting shallow sea ecosystems and biodiversity conservation in the Da Lon Reef area, an important part of the Truong Sa Islands, Vietnam.
{"title":"Benthic habitat mapping and assessment of seagrass species diversity in Da Lon Reef, Truong Sa Islands, Vietnam, using very high-resolution satellite imagery and in situ data","authors":"Hoi Dang Nguyen, Dung Trung Ngo, Dung Viet Vu","doi":"10.15625/2615-9783/19026","DOIUrl":"https://doi.org/10.15625/2615-9783/19026","url":null,"abstract":"Benthic habitats are critical in shallow sea areas; they regulate the diversity and richness of organisms in each area. Mapping benthic habitats elucidates natural sea characteristics and aids in managing and using natural resources, as well as conserving marine biodiversity. This study established a benthic habitat map for the Da Lon Reef area, Truong Sa Islands, Vietnam, using Pléiades high-resolution remote sensing imaging materials and field survey results from 2020 and 2021. We identified seven classes of benthic habitats with a 91.64% overall accuracy, corresponding to a Kappa coefficient of 0.88. In the Da Lon Reef, seagrass biomes occupy a large area (more than 200 ha) and are distributed mainly inside lagoons at depths of 2–6 m. The field survey results identified five seagrass species and the biodiversity and biomass of seagrass populations in the lagoon of Da Lon Reef. The study results confirm the fundamental value of resources, biodiversity in general and seagrass in particular, in managing and protecting shallow sea ecosystems and biodiversity conservation in the Da Lon Reef area, an important part of the Truong Sa Islands, Vietnam.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135198988","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-18DOI: 10.15625/2615-9783/18923
Quang Nguyen Minh, Ha Vu Van, Min Nguyen Thi, Dao Ngo Thi, Cuc Nguyen Thi Thu, Tuan Dang Minh, Tung Dang Xuan, Man Tran Thi, Thao Nguyen Thi
Holocene sediment facies in the incised valley of the Ma River Delta were clarified by using analysis of LKTH6 core (30 m depth) such as sedimentary structure analysis, grain-sized, micro-paleontological (foraminifera, spore and pollen, and diatom), clay minerals characteristics, and Radiocarbon dating (14C). Ten sedimentary facies were identified, including (1) flood plain silty clay facies, (2) Salt marsh clayey silt facies, (3) Tidal flat sandy silty clay facies, (4) Tidal creek and tidal branch silty clayey sand facies, (5) Bay silty clay facies, (6) Prodelta silty clay facies, (7) Delta front silty sand facies, (8) Mouth bar sand facies, (9) Point bar silty sand faces, and (10) Alluvial plain silty clay facies.
The sea level change after the last glacial was recorded by sediment facies and radiocarbon dating (14C). It showed that the Thanh Hoa coastal area drowned around 9500 yr. B.P. by transgression. At 9200 yr. B.P. initial marine flooding surface, tidal flats were formed in the coastal estuary area. During the period of 9200 -8300 yr. B.P., due to rapid sea level rise, the study area became an estuarine around 7600 yr. B.P., the sea level rose slowly, leading to the sea level rise rate being smaller than the sedimentary accumulation rate, and the delta was formed.
利用LKTH6岩心(30 m深度)沉积物结构、粒度、微古生物(有孔虫、孢子、花粉、硅藻)、粘粘矿物特征和14C放射性碳测年等分析，厘清了马江三角洲切割谷全新世沉积相。确定了10种沉积相，包括(1)洪泛平原粉质粘土相，(2)盐沼泥质粉质砂相，(3)潮滩砂质粉质粘土相，(4)潮溪和潮支粉质粘土相，(5)海湾粉质粘土相，(6)前三角洲粉质粘土相，(7)三角洲前缘粉质砂相，(8)河口坝砂相，(9)点坝粉质砂相，(10)冲积平原粉质粘土相。
通过沉积物相和放射性碳测年(14C)记录了末次冰期后的海平面变化。结果表明，清化沿海地区在公元前9500年左右被海侵淹没。在B.P. 9200年的初期海水泛滥面，沿海河口地区形成了潮滩。在9200 -8300 yr b.p.期间，由于海平面的快速上升，研究区在7600 yr b.p.左右成为河口，海平面上升缓慢，导致海平面上升速率小于沉积堆积速率，形成了三角洲。
{"title":"Holocene sedimentary facies in the incised valley of Ma River Delta, Vietnam","authors":"Quang Nguyen Minh, Ha Vu Van, Min Nguyen Thi, Dao Ngo Thi, Cuc Nguyen Thi Thu, Tuan Dang Minh, Tung Dang Xuan, Man Tran Thi, Thao Nguyen Thi","doi":"10.15625/2615-9783/18923","DOIUrl":"https://doi.org/10.15625/2615-9783/18923","url":null,"abstract":"Holocene sediment facies in the incised valley of the Ma River Delta were clarified by using analysis of LKTH6 core (30 m depth) such as sedimentary structure analysis, grain-sized, micro-paleontological (foraminifera, spore and pollen, and diatom), clay minerals characteristics, and Radiocarbon dating (14C). Ten sedimentary facies were identified, including (1) flood plain silty clay facies, (2) Salt marsh clayey silt facies, (3) Tidal flat sandy silty clay facies, (4) Tidal creek and tidal branch silty clayey sand facies, (5) Bay silty clay facies, (6) Prodelta silty clay facies, (7) Delta front silty sand facies, (8) Mouth bar sand facies, (9) Point bar silty sand faces, and (10) Alluvial plain silty clay facies.
 The sea level change after the last glacial was recorded by sediment facies and radiocarbon dating (14C). It showed that the Thanh Hoa coastal area drowned around 9500 yr. B.P. by transgression. At 9200 yr. B.P. initial marine flooding surface, tidal flats were formed in the coastal estuary area. During the period of 9200 -8300 yr. B.P., due to rapid sea level rise, the study area became an estuarine around 7600 yr. B.P., the sea level rose slowly, leading to the sea level rise rate being smaller than the sedimentary accumulation rate, and the delta was formed.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135155592","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-13DOI: 10.15625/2615-9783/18897
Binh Pham-Duc, Quan Tran Anh, Son Tong Si
This work estimates the surface water volume variation of the Cambodian Tonle Sap Lake at a monthly scale from 2015-2022. To achieve this, radar Sentinel-1 imagery was processed using the Google Earth Engine platform to generate backscatter coefficient maps. The Otsu method was utilized to identify the optimal threshold to classify each backscatter coefficient map into water or non-water clusters. Additionally, altimetry data from three satellites (i.e., Sentinel-3, Jason-3, and Jason-CS/Sentinel-6) was processed to estimate Tonle Sap Lake’s water level variation using the AlTiS software. Surface water maps of the lake, derived from MODIS and clear-sky Sentinel-2 imagery, were used to validate the lake’s surface water extent time series, while in situ water level data collected at Prek Kdam station was used to validate the variation of the lake’s water height. Our results estimated that the lake’s open water area varies from 2200 to 6000 km2, while its water level ranges from 3.1 to 10.9 m. Combining the two time series, we estimated that Tonle Sap Lake’s water volume varies between approximately -7.2 and 9.4 km3 month-1, which shows high correlation with the variation of the water volume flowing through Chau Doc and Tan Chau stations (R = 0.9528 after removing the time lag). This study highlights the ability of satellite data for lake monitoring, which is very useful in remote areas where gauge stations are limited or unavailable. Future work aims to test the accuracy of the proposed methodology in other types of environments, particularly in mountainous regions of North Vietnam, where the terrain is very steep.
{"title":"Monitoring monthly variation of Tonle Sap Lake water volume using Sentinel-1 imagery and satellite altimetry data","authors":"Binh Pham-Duc, Quan Tran Anh, Son Tong Si","doi":"10.15625/2615-9783/18897","DOIUrl":"https://doi.org/10.15625/2615-9783/18897","url":null,"abstract":"This work estimates the surface water volume variation of the Cambodian Tonle Sap Lake at a monthly scale from 2015-2022. To achieve this, radar Sentinel-1 imagery was processed using the Google Earth Engine platform to generate backscatter coefficient maps. The Otsu method was utilized to identify the optimal threshold to classify each backscatter coefficient map into water or non-water clusters. Additionally, altimetry data from three satellites (i.e., Sentinel-3, Jason-3, and Jason-CS/Sentinel-6) was processed to estimate Tonle Sap Lake’s water level variation using the AlTiS software. Surface water maps of the lake, derived from MODIS and clear-sky Sentinel-2 imagery, were used to validate the lake’s surface water extent time series, while in situ water level data collected at Prek Kdam station was used to validate the variation of the lake’s water height. Our results estimated that the lake’s open water area varies from 2200 to 6000 km2, while its water level ranges from 3.1 to 10.9 m. Combining the two time series, we estimated that Tonle Sap Lake’s water volume varies between approximately -7.2 and 9.4 km3 month-1, which shows high correlation with the variation of the water volume flowing through Chau Doc and Tan Chau stations (R = 0.9528 after removing the time lag). This study highlights the ability of satellite data for lake monitoring, which is very useful in remote areas where gauge stations are limited or unavailable. Future work aims to test the accuracy of the proposed methodology in other types of environments, particularly in mountainous regions of North Vietnam, where the terrain is very steep.","PeriodicalId":23639,"journal":{"name":"VIETNAM JOURNAL OF EARTH SCIENCES","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135741969","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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