In this study, the spatiotemporal variability of drought over the entire Southeast Asia (SEA) reg... more In this study, the spatiotemporal variability of drought over the entire Southeast Asia (SEA) region and its associations with the large-scale climate drivers during the period 1960–2019 are investigated for the first time. The 12-month Standardized Precipitation Evapotranspiration Index (SPEI) was computed based on the monthly Global Precipitation Climatology Centre (GPCC) precipitation and the monthly Climate Research Unit (CRU) 2-m temperature. The relationships between drought and large-scale climate drivers were examined using the principal component analysis (PCA) and maximum covariance analysis (MCA) techniques. Results showed that the spatiotemporal variability of drought characteristics over SEA is significantly different between mainland Indochina and the Maritime Continent and the difference has been increased substantially in recent decades. Moreover, the entire SEA is divided into four homogeneous drought subregions. Drought over SEA is strongly associated with oceanic ...
This study first evaluates the performance of three model experiments in representing rainfall ov... more This study first evaluates the performance of three model experiments in representing rainfall over part of Vietnam and the Lower Mekong Basin for the historical period 1986-2005. The three experiments include the Coupled Model Intercomparison Project Phase 5 (CMIP5) EC-EARTH Global Climate Model (GCM) and two downscaling runs based on a regional climate model at 25km resolution with the GCM forcing (RCM-25km) and at 5km resolution with the RCM-25km forcing (RCM-5km). Verifications against observations show that the experiments generally capture the spatial distribution of climatological rainfall. While the GCM well represents the observed average rainfall cycles, its coarse resolution limits its capability in reproducing extreme rainfall values. The downscaling experiments do not clearly show their advantage in simulating average rainfall but exhibit significant added values when representing extreme rainfall in the study region. The RCM-5km does not outperform its driving 25km exp...
The onset of the rainy season is an important date for the mostly rain-fed agricultural practices... more The onset of the rainy season is an important date for the mostly rain-fed agricultural practices in Vietnam. Subseasonal to seasonal (S2S) ensemble hindcasts from the European Centre for Medium-Range Weather Forecasts (ECMWF) are used to evaluate the predictability of the rainy season onset dates (RSODs) over five climatic subregions of Vietnam. The results show that the ECMWF model reproduces well the observed interannual variability of RSODs, with a high correlation ranging from 0.60 to 0.99 over all subregions at all lead times (up to 40 days) using five different RSOD definitions. For increasing lead times, forecasted RSODs tend to be earlier than the observed ones. Positive skill score values for almost all cases examined in all subregions indicate that the model outperforms the observed climatology in predicting the RSOD at subseasonal lead times (∼28–35 days). However, the model is overall more skillful at shorter lead times. The choice of the RSOD criterion should be consid...
In this study, the projected drought characteristics over Vietnam for the future periods of the m... more In this study, the projected drought characteristics over Vietnam for the future periods of the middle (2046–2065) and end of the 21st century (2080–2099) were investigated under the Representative Concentration Pathway (RCP) scenarios RCP4.5 and RCP8.5. The drought characteristics (duration, severity, intensity, inter‐arrival time, and geographic extent) were estimated based on the Palmer Drought Severity Index (PDSI). The PDSI was calculated using temperature and precipitation data from six regional climate downscaling experiments and their ensemble conducted by the Coordinated Regional Climate Downscaling Experiment‐Southeast Asia (CORDEX‐SEA) project. Projected changes of drought characteristics in the future periods were determined with respect to those in the baseline period 1986–2005. Results show biases in the regional climate model (RCM) outputs, namely an underestimation of temperature and an overestimation of precipitation, which also affect the representation of drought characteristics by overestimating the PDSI. In terms of projections, substantial increases of drought duration, severity and intensity, and decreases in the inter‐arrival time are found over the Red River Delta, northern parts of the North Central sub‐region, parts of the Central Highlands and over southern Vietnam. The droughts are projected to be more widespread under scenario RCP8.5 than RCP4.5, especially in southern Vietnam. With the increasing likelihood of droughts in Vietnam as a result of climate change, sustainable water resources management should be taken into account for agriculture, natural ecosystems and social development.
In this study, a subset of the downscaled simulations of the Southeast Asia Regional Climate Down... more In this study, a subset of the downscaled simulations of the Southeast Asia Regional Climate Downscaling/Coordinated Regional Climate Downscaling Experiment—Southeast Asia (SEACLID/CORDEX‐SEA) was analysed to examine the representation of tropical cyclone (TC) climatology over Southeast Asia, in terms of pattern, intensity, frequency, and lifetime. A modified vortex tracking algorithm is used to detect TCs over the SEACLID/CORDEX‐SEA domain in the historical simulations from 1986 to 2005. Sensitivity tests for the detection method criteria, including vorticity, outer core wind strength, sea level pressure anomaly, and temperature anomaly at 300, 500, 700, and 850 hPa, were conducted to determine the optimum threshold configuration for each SEACLID/CORDEX‐SEA simulation used in the study. Comparison with the best track data of the Joint Typhoon Warning Center showed that model simulations underestimated the total number of TCs east of the Philippines for the 1986–2005 period but captured the annual cycle of the total number of TCs. This underestimation of TCs is possibly due to the domain used, which does not extend further east to cover most of the TC genesis area in the Western North Pacific. The structure of a typical TC from the regional climate model simulation is comparable to observed TC structure. However, results indicate that the resolution of the simulations is still not sufficient to capture the fine details of the observed TC structure, which could explain in part the lower intensification rate of TCs in the model output.
This study investigated rainfall trends and their associations with tropical cyclones (TCs) durin... more This study investigated rainfall trends and their associations with tropical cyclones (TCs) during the period of 1979−2019, using TC best-track data from the Regional Specialized Meteorological Center Tokyo-Typhoon Center and daily rainfall data from 138 meteorological stations in Vietnam. The radius of influence of TCs on local rainfall was limited to 500 km from TC centers. The average annual number of TCs affecting Vietnam has decreased slightly in the last two decades compared to previous decades. The ratio of TC-induced rainfall to total rainfall attained the highest value of 37.3% in the central region, in July. The temporal distribution of TC-induced rainfall coincided with the frequency of TCs, with an active period from June to November. During 1979−2019, the non-TC rainfall was the main contributor to the change in total rainfall, especially in relation to the decline in the north and the increase in the coastal South Central region. The rainfall trend during the entire period was principally explained by the interdecadal shift in the late 1990s. Rainfall intensity and the number of heavy rainfall days were intensified for total rainfall and non-TC rainfall, indicating that TCs contributed minimally to the changes of extreme rainfall events during 1979−2019.
This study investigated the temporal occurrence of dry conditions in the seven climatic sub-regio... more This study investigated the temporal occurrence of dry conditions in the seven climatic sub-regions of Vietnam during the 1980–2017 period. This assessment was performed using the Standardized Precipitation Evapotranspiration Index (SPEI) and the Standardized Precipitation Index (SPI) at 1 to 24 months timescales. Results show that the main periods of extreme drought occurred simultaneously throughout the country in 1992–1993 and 2003–2004, except for 2015–2016, when it was not identified in the southern region. In addition, a slight temporal lag was identified latitudinally (north–south) at the beginning of dry conditions, revealing the largest difference between the northern and southern regions. A positive trend in the time series of both indices (SPEI and SPI) prevailed in all sub-regions, with the SPEI minus SPI difference always being negative, suggesting the importance of temperature and evapotranspiration for this trend. Further detailed analyses were then performed using SP...
This study investigates the ability to apply National Centers for Environmental Prediction (NCEP)... more This study investigates the ability to apply National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFS) products and their downscaling by using the Regional Climate Model version 4.2 (RegCM4.2) on seasonal rainfall forecasts over Vietnam. First, the CFS hindcasts (CFS_Rfc) from 1982 to 2009 are used to assess the ability of the CFS to predict the overall circulation and precipitation patterns at forecast lead times of up to 6 months. Second, the operational CFS forecasts (CFS_Ope) and its RegCM4.2 downscaling (RegCM_CFS) for the period 2012–14 are used to derive seasonal rainfall forecasts over Vietnam. The CFS_Rfc and CFS_Ope are validated against the ECMWF interim reanalysis, the Global Precipitation Climatology Centre (GPCC) analyzed rainfall, and observations from 150 meteorological stations across Vietnam. The results show that the CFS_Rfc can capture the seasonal variability of the Asian monsoon circulation and rainfall distribution. The higher-resoluti...
VNU Journal of Science: Earth and Environmental Sciences, 2019
This study has selected a vortex tracking algorithm scheme for simulating the activity of tropica... more This study has selected a vortex tracking algorithm scheme for simulating the activity of tropical cyclone in the Vietnam East Sea by CCAM model. The results show that the CCAM model is able to simulate well the large scale in each month through a reasonable description of the movement rules of the tropical cyclone in the study area. Then, this vortex tracking algorithm scheme was applied to test the seasonal forecast with the outputs of the CCAM model with a resolution of 20km for September 2018 and October 2018. The obtaining results are forecasted quite closely in terms of both quantity and high potential occurrence areas of the tropical cyclone when compared with reality. In particular, for October 2018, although the activity area of the tropical cyclone-YUTU is significantly different from the multi-year average activity position, the seasonal forecast results are obtained from the 120 members of the CCAM model captured this difference. This suggests that it is possible to apply the CCAM model in combination with the selected vortex tracking algorithm scheme for the seasonal forecast of the tropical cyclone over the Vietnam East Sea region in the future.
VNU Journal of Science: Earth and Environmental Sciences, 2019
In this paper, the relationship between Tropical Cyclone (TC) Genesis Potential Index (GPI) and t... more In this paper, the relationship between Tropical Cyclone (TC) Genesis Potential Index (GPI) and the number of TC (NTC) associated with ENSO over the Vietnam East Sea (VES) was investigated. Observed TC data of the Regional Specialized Meteorological Center (RSMC) Tokyo Typhoon Center and ERA Interim reanalysis data for the period 1985-2015 were used. The results show a good agreement between GPI and NTC over the VES with the correlation coefficient is 0.84. There were more TCs formed over the VES during La Nina years and less TCs during El Nino years. There were positive anomalies of GPI, environmental factors (relative humidity, sea surface temperature, absolute vorticity, potential intensity)over the region where the highest densityof TCs genesis locatedduring La Nina years while there were negative anomalies found during El Nino years. Relative humidity has the largest contribution to the positive difference GPI between La Nina years and El Nino years, the less contribution comes from the potential intensity, absolute vorticity, and wind shear.
Drought may have severe societal, economic, and environmental consequences. However, the space-ti... more Drought may have severe societal, economic, and environmental consequences. However, the space-time characteristics of drought over Vietnam remain poorly understood. In this study, we investigate the spatio-temporal variability of drought using the Palmer Drought Severity Index (PDSI) over mainland Vietnam for the 1980-2014 period. Through data analysis at 131 stations, we identified the main characteristics, historical trends, and dominant variability of drought across seven climatic sub-regions in Vietnam. The results show regional patterns of drought duration, inter-arrival time, frequency, and severity, but no consistent trend of drought variation during the study period. Based on the supply and demand concepts of water balance, PDSI captures well the large frequency and severity of drought in some sub-regions that are related to soil moisture deficit associated with high temperature and low rainfall during summer. Moreover, drought over Vietnam was predominantly controlled by climate seasonality. The linkages between drought in Vietnam and large-scale drivers are quite different among areas, suggesting a possibility of early prediction for drought at some sub-regions using ENSO.
This paper highlights detailed projected changes in rainfall over Thailand for the early (2011-20... more This paper highlights detailed projected changes in rainfall over Thailand for the early (2011-2040), middle (2041-2070) and late (2071-2099) periods of the 21st century under the Representative Concentration Pathways (RCP) 4.5 and RCP 8.5 using the high-resolution multi-model simulations of the Coordinated Regional Climate Downscaling Experiment (CORDEX) Southeast Asia. The ensemble mean is calculated based on seven members consisting of six General Circulation Models (GCMs) and three Regional Climate Models (RCMs). Generally, the ensemble mean precipitation agrees reasonably well with observations, best represented by the Global Precipitation Climatology Center (GPCC) data, over Thailand during the historical period (1976-2005). However, inter-model variations can be large among ensemble members especially during dry months (December to March) for northern-centraleastern parts, and throughout the year for the southern parts of Thailand. Similarly for future projection periods, inter-model variations in the sign and magnitude of changes exist. The ensemble means of projected changes in rainfall for both RCPs during dry months show distinct contrast between the northern-central-eastern parts and the southern parts of Thailand with generally wetter and drier conditions, respectively. The magnitude of change can be as high as 15% of the historical period, which varies depending on the sub-region, season, projection period and RCP scenario. In contrast, This article is protected by copyright. All rights reserved. generally drier conditions are projected during the wet season (June to September) throughout the country for both RCPs where the rainfall reduction can be as high as 10% in some areas. However, the magnitude of projected rainfall changes of some individual models can be much larger than the ensemble means, exceeding 40% in some cases. These projected changes are related to the changes in regional circulations associated with the winter and summer monsoons, which are projected to weaken. The drier (wetter) condition is associated with the enhanced subsidence (rising motion).
APN Science Bulletin 8 (1) www.apn-gcr.org/bulletin Future changes in annual precipitation extrem... more APN Science Bulletin 8 (1) www.apn-gcr.org/bulletin Future changes in annual precipitation extremes over Southeast Asia under global warming of 2°C This article provides detailed information on projected changes in annual precipitation extremes over Southeast Asia under global warming of 2°C based on the multi-model simulations of the Southeast Asia Regional Climate Downscaling/Coordinated Regional Climate Downscaling Experiment Southeast Asia (SEACLID/CORDEX-SEA). Four indices of extreme precipitation are considered: annual total precipitation (PRCPTOT), consecutive dry days (CDD), frequency of rainfall exceeding 50 mm day-1 (R50mm), and intensity of extreme precipitation (RX1day). The ensemble mean of 10 simulations showed reasonable performance in simulating observed characteristics of extreme precipitation during the historical period of 1986-2005. The year 2041 was taken as the year when global mean temperature reaches 2°C above pre-industrial levels under unmitigated climate change scenario based on Karmalkar and Bradley (2017). Results indicate that the most prominent changes during the period of 2031-2051 were largely significant. Robust increases in CDD imply impending drier conditions over Indonesia, while increases in RX1day suggest more intense rainfall events over most of Indochina under 2°C global warming scenario. Furthermore, northern Myanmar is projected to experience increases in CDD, R50mm and RX1day, suggesting that the area may face more serious repercussions than other areas in Southeast Asia.
Rainfall extremes have a large socioeconomic relevance for southern Vietnam. More than 30 million... more Rainfall extremes have a large socioeconomic relevance for southern Vietnam. More than 30 million people live in this low-lying, flood-prone region in Southeast Asia. In this study the influence of the Madden–Julian oscillation (MJO) and convectively coupled equatorial waves on the modulation of daily rainfall during the rainy season (May–October) is evaluated and quantified using an extensive station database and the gridded Asian Precipitation–Highly Resolved Observational Data Integration Toward Evaluation of Water Resources (APHRODITE) product for different phases of the equatorial waves. The MJO, Kelvin, and equatorial Rossby (ER) waves significantly modulate daily rainfall in Vietnam south of 16°N. The MJO shows the most coherent signals across the region, followed by ER waves, whose influence is strongest in central Vietnam; Kelvin waves only affect the southern parts of Vietnam. For all waves, the frequency of occurrence of intense daily rainfall larger than 25 mm is signifi...
VNU Journal of Science: Earth and Environmental Sciences, 2017
Trong nghiên cứu này, sử dụng số liệu quan trắc lượng mưa ngày trên các trạm khí tượng khu vực Tâ... more Trong nghiên cứu này, sử dụng số liệu quan trắc lượng mưa ngày trên các trạm khí tượng khu vực Tây Nguyên giai đoạn 1981-2010, một vài đặc điểm chế độ mưa bao gồm ngày bắt đầu mùa mưa và sự biến đổi cũng như khả năng dự báo ngày bắt đầu mùa mưa đã được khảo sát. Kết quả nhận được cho thấy: 1) Ngày bắt đầu mùa mưa ở Tây Nguyên biến thiên mạnh qua các năm. Mùa mưa bắt đầu sớm hơn ở phía nam Tây Nguyên sau đó là phía bắc và muộn nhất ở miền trung. Nhìn chung, mùa mưa ở Tây Nguyên bắt đầu vào khoảng giữa tháng 4 đến giữa tháng 5, trung bình vào khoảng 30 tháng 4 hàng năm; 2) Mùa mưa ở Tây Nguyên có xu thế đến sớm hơn 5-7 ngày/thập kỷ; 3) Ngày bắt đầu mùa mưa ở Tây Nguyên có tương quan dương cao với nhiệt độ bề mặt biển (SST) ở khu vực trung tâm Thái Bình dương xích đạo và nam Ấn Độ dương xích đạo, gió vĩ hướng mực 850hPa khu vực tây bắc và trung tâm Thái Bình dương xích đạo và với khí áp mực biển trung bình trên các khu vực tây Thái Bình dương và Ấn Độ dương, có tương quan âm với SST tr...
The daily rainfall data at 13 stations over the Central Highlands (CH) Vietnam were collected for... more The daily rainfall data at 13 stations over the Central Highlands (CH) Vietnam were collected for the period 1981-2014. Two different sets of criteria using daily observed rainfall and 850 hPa daily reanalysis wind data were applied to determine the onset (retreat) dates of the summer rainy season (RS) and summer monsoon (SM) season, respectively. Over the study period, the mean RS and SM onset dates were April 20 and May 13 with standard deviations of 17.4 and 17.8 days, respectively. The mean RS and SM retreat dates were November 1 and September 30 with standard deviations of 17.9 and 10.2 days, respectively. The year-to-year variations of the onset dates and the rainfall amount within the RS and SM season were closely linked with the preceding winter and spring sea surface temperature in the central-eastern and western Pacific. It was also found that the onset dates were significantly correlated with the RS and SM rainfall amount.
In this study, the spatiotemporal variability of drought over the entire Southeast Asia (SEA) reg... more In this study, the spatiotemporal variability of drought over the entire Southeast Asia (SEA) region and its associations with the large-scale climate drivers during the period 1960–2019 are investigated for the first time. The 12-month Standardized Precipitation Evapotranspiration Index (SPEI) was computed based on the monthly Global Precipitation Climatology Centre (GPCC) precipitation and the monthly Climate Research Unit (CRU) 2-m temperature. The relationships between drought and large-scale climate drivers were examined using the principal component analysis (PCA) and maximum covariance analysis (MCA) techniques. Results showed that the spatiotemporal variability of drought characteristics over SEA is significantly different between mainland Indochina and the Maritime Continent and the difference has been increased substantially in recent decades. Moreover, the entire SEA is divided into four homogeneous drought subregions. Drought over SEA is strongly associated with oceanic ...
This study first evaluates the performance of three model experiments in representing rainfall ov... more This study first evaluates the performance of three model experiments in representing rainfall over part of Vietnam and the Lower Mekong Basin for the historical period 1986-2005. The three experiments include the Coupled Model Intercomparison Project Phase 5 (CMIP5) EC-EARTH Global Climate Model (GCM) and two downscaling runs based on a regional climate model at 25km resolution with the GCM forcing (RCM-25km) and at 5km resolution with the RCM-25km forcing (RCM-5km). Verifications against observations show that the experiments generally capture the spatial distribution of climatological rainfall. While the GCM well represents the observed average rainfall cycles, its coarse resolution limits its capability in reproducing extreme rainfall values. The downscaling experiments do not clearly show their advantage in simulating average rainfall but exhibit significant added values when representing extreme rainfall in the study region. The RCM-5km does not outperform its driving 25km exp...
The onset of the rainy season is an important date for the mostly rain-fed agricultural practices... more The onset of the rainy season is an important date for the mostly rain-fed agricultural practices in Vietnam. Subseasonal to seasonal (S2S) ensemble hindcasts from the European Centre for Medium-Range Weather Forecasts (ECMWF) are used to evaluate the predictability of the rainy season onset dates (RSODs) over five climatic subregions of Vietnam. The results show that the ECMWF model reproduces well the observed interannual variability of RSODs, with a high correlation ranging from 0.60 to 0.99 over all subregions at all lead times (up to 40 days) using five different RSOD definitions. For increasing lead times, forecasted RSODs tend to be earlier than the observed ones. Positive skill score values for almost all cases examined in all subregions indicate that the model outperforms the observed climatology in predicting the RSOD at subseasonal lead times (∼28–35 days). However, the model is overall more skillful at shorter lead times. The choice of the RSOD criterion should be consid...
In this study, the projected drought characteristics over Vietnam for the future periods of the m... more In this study, the projected drought characteristics over Vietnam for the future periods of the middle (2046–2065) and end of the 21st century (2080–2099) were investigated under the Representative Concentration Pathway (RCP) scenarios RCP4.5 and RCP8.5. The drought characteristics (duration, severity, intensity, inter‐arrival time, and geographic extent) were estimated based on the Palmer Drought Severity Index (PDSI). The PDSI was calculated using temperature and precipitation data from six regional climate downscaling experiments and their ensemble conducted by the Coordinated Regional Climate Downscaling Experiment‐Southeast Asia (CORDEX‐SEA) project. Projected changes of drought characteristics in the future periods were determined with respect to those in the baseline period 1986–2005. Results show biases in the regional climate model (RCM) outputs, namely an underestimation of temperature and an overestimation of precipitation, which also affect the representation of drought characteristics by overestimating the PDSI. In terms of projections, substantial increases of drought duration, severity and intensity, and decreases in the inter‐arrival time are found over the Red River Delta, northern parts of the North Central sub‐region, parts of the Central Highlands and over southern Vietnam. The droughts are projected to be more widespread under scenario RCP8.5 than RCP4.5, especially in southern Vietnam. With the increasing likelihood of droughts in Vietnam as a result of climate change, sustainable water resources management should be taken into account for agriculture, natural ecosystems and social development.
In this study, a subset of the downscaled simulations of the Southeast Asia Regional Climate Down... more In this study, a subset of the downscaled simulations of the Southeast Asia Regional Climate Downscaling/Coordinated Regional Climate Downscaling Experiment—Southeast Asia (SEACLID/CORDEX‐SEA) was analysed to examine the representation of tropical cyclone (TC) climatology over Southeast Asia, in terms of pattern, intensity, frequency, and lifetime. A modified vortex tracking algorithm is used to detect TCs over the SEACLID/CORDEX‐SEA domain in the historical simulations from 1986 to 2005. Sensitivity tests for the detection method criteria, including vorticity, outer core wind strength, sea level pressure anomaly, and temperature anomaly at 300, 500, 700, and 850 hPa, were conducted to determine the optimum threshold configuration for each SEACLID/CORDEX‐SEA simulation used in the study. Comparison with the best track data of the Joint Typhoon Warning Center showed that model simulations underestimated the total number of TCs east of the Philippines for the 1986–2005 period but captured the annual cycle of the total number of TCs. This underestimation of TCs is possibly due to the domain used, which does not extend further east to cover most of the TC genesis area in the Western North Pacific. The structure of a typical TC from the regional climate model simulation is comparable to observed TC structure. However, results indicate that the resolution of the simulations is still not sufficient to capture the fine details of the observed TC structure, which could explain in part the lower intensification rate of TCs in the model output.
This study investigated rainfall trends and their associations with tropical cyclones (TCs) durin... more This study investigated rainfall trends and their associations with tropical cyclones (TCs) during the period of 1979−2019, using TC best-track data from the Regional Specialized Meteorological Center Tokyo-Typhoon Center and daily rainfall data from 138 meteorological stations in Vietnam. The radius of influence of TCs on local rainfall was limited to 500 km from TC centers. The average annual number of TCs affecting Vietnam has decreased slightly in the last two decades compared to previous decades. The ratio of TC-induced rainfall to total rainfall attained the highest value of 37.3% in the central region, in July. The temporal distribution of TC-induced rainfall coincided with the frequency of TCs, with an active period from June to November. During 1979−2019, the non-TC rainfall was the main contributor to the change in total rainfall, especially in relation to the decline in the north and the increase in the coastal South Central region. The rainfall trend during the entire period was principally explained by the interdecadal shift in the late 1990s. Rainfall intensity and the number of heavy rainfall days were intensified for total rainfall and non-TC rainfall, indicating that TCs contributed minimally to the changes of extreme rainfall events during 1979−2019.
This study investigated the temporal occurrence of dry conditions in the seven climatic sub-regio... more This study investigated the temporal occurrence of dry conditions in the seven climatic sub-regions of Vietnam during the 1980–2017 period. This assessment was performed using the Standardized Precipitation Evapotranspiration Index (SPEI) and the Standardized Precipitation Index (SPI) at 1 to 24 months timescales. Results show that the main periods of extreme drought occurred simultaneously throughout the country in 1992–1993 and 2003–2004, except for 2015–2016, when it was not identified in the southern region. In addition, a slight temporal lag was identified latitudinally (north–south) at the beginning of dry conditions, revealing the largest difference between the northern and southern regions. A positive trend in the time series of both indices (SPEI and SPI) prevailed in all sub-regions, with the SPEI minus SPI difference always being negative, suggesting the importance of temperature and evapotranspiration for this trend. Further detailed analyses were then performed using SP...
This study investigates the ability to apply National Centers for Environmental Prediction (NCEP)... more This study investigates the ability to apply National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFS) products and their downscaling by using the Regional Climate Model version 4.2 (RegCM4.2) on seasonal rainfall forecasts over Vietnam. First, the CFS hindcasts (CFS_Rfc) from 1982 to 2009 are used to assess the ability of the CFS to predict the overall circulation and precipitation patterns at forecast lead times of up to 6 months. Second, the operational CFS forecasts (CFS_Ope) and its RegCM4.2 downscaling (RegCM_CFS) for the period 2012–14 are used to derive seasonal rainfall forecasts over Vietnam. The CFS_Rfc and CFS_Ope are validated against the ECMWF interim reanalysis, the Global Precipitation Climatology Centre (GPCC) analyzed rainfall, and observations from 150 meteorological stations across Vietnam. The results show that the CFS_Rfc can capture the seasonal variability of the Asian monsoon circulation and rainfall distribution. The higher-resoluti...
VNU Journal of Science: Earth and Environmental Sciences, 2019
This study has selected a vortex tracking algorithm scheme for simulating the activity of tropica... more This study has selected a vortex tracking algorithm scheme for simulating the activity of tropical cyclone in the Vietnam East Sea by CCAM model. The results show that the CCAM model is able to simulate well the large scale in each month through a reasonable description of the movement rules of the tropical cyclone in the study area. Then, this vortex tracking algorithm scheme was applied to test the seasonal forecast with the outputs of the CCAM model with a resolution of 20km for September 2018 and October 2018. The obtaining results are forecasted quite closely in terms of both quantity and high potential occurrence areas of the tropical cyclone when compared with reality. In particular, for October 2018, although the activity area of the tropical cyclone-YUTU is significantly different from the multi-year average activity position, the seasonal forecast results are obtained from the 120 members of the CCAM model captured this difference. This suggests that it is possible to apply the CCAM model in combination with the selected vortex tracking algorithm scheme for the seasonal forecast of the tropical cyclone over the Vietnam East Sea region in the future.
VNU Journal of Science: Earth and Environmental Sciences, 2019
In this paper, the relationship between Tropical Cyclone (TC) Genesis Potential Index (GPI) and t... more In this paper, the relationship between Tropical Cyclone (TC) Genesis Potential Index (GPI) and the number of TC (NTC) associated with ENSO over the Vietnam East Sea (VES) was investigated. Observed TC data of the Regional Specialized Meteorological Center (RSMC) Tokyo Typhoon Center and ERA Interim reanalysis data for the period 1985-2015 were used. The results show a good agreement between GPI and NTC over the VES with the correlation coefficient is 0.84. There were more TCs formed over the VES during La Nina years and less TCs during El Nino years. There were positive anomalies of GPI, environmental factors (relative humidity, sea surface temperature, absolute vorticity, potential intensity)over the region where the highest densityof TCs genesis locatedduring La Nina years while there were negative anomalies found during El Nino years. Relative humidity has the largest contribution to the positive difference GPI between La Nina years and El Nino years, the less contribution comes from the potential intensity, absolute vorticity, and wind shear.
Drought may have severe societal, economic, and environmental consequences. However, the space-ti... more Drought may have severe societal, economic, and environmental consequences. However, the space-time characteristics of drought over Vietnam remain poorly understood. In this study, we investigate the spatio-temporal variability of drought using the Palmer Drought Severity Index (PDSI) over mainland Vietnam for the 1980-2014 period. Through data analysis at 131 stations, we identified the main characteristics, historical trends, and dominant variability of drought across seven climatic sub-regions in Vietnam. The results show regional patterns of drought duration, inter-arrival time, frequency, and severity, but no consistent trend of drought variation during the study period. Based on the supply and demand concepts of water balance, PDSI captures well the large frequency and severity of drought in some sub-regions that are related to soil moisture deficit associated with high temperature and low rainfall during summer. Moreover, drought over Vietnam was predominantly controlled by climate seasonality. The linkages between drought in Vietnam and large-scale drivers are quite different among areas, suggesting a possibility of early prediction for drought at some sub-regions using ENSO.
This paper highlights detailed projected changes in rainfall over Thailand for the early (2011-20... more This paper highlights detailed projected changes in rainfall over Thailand for the early (2011-2040), middle (2041-2070) and late (2071-2099) periods of the 21st century under the Representative Concentration Pathways (RCP) 4.5 and RCP 8.5 using the high-resolution multi-model simulations of the Coordinated Regional Climate Downscaling Experiment (CORDEX) Southeast Asia. The ensemble mean is calculated based on seven members consisting of six General Circulation Models (GCMs) and three Regional Climate Models (RCMs). Generally, the ensemble mean precipitation agrees reasonably well with observations, best represented by the Global Precipitation Climatology Center (GPCC) data, over Thailand during the historical period (1976-2005). However, inter-model variations can be large among ensemble members especially during dry months (December to March) for northern-centraleastern parts, and throughout the year for the southern parts of Thailand. Similarly for future projection periods, inter-model variations in the sign and magnitude of changes exist. The ensemble means of projected changes in rainfall for both RCPs during dry months show distinct contrast between the northern-central-eastern parts and the southern parts of Thailand with generally wetter and drier conditions, respectively. The magnitude of change can be as high as 15% of the historical period, which varies depending on the sub-region, season, projection period and RCP scenario. In contrast, This article is protected by copyright. All rights reserved. generally drier conditions are projected during the wet season (June to September) throughout the country for both RCPs where the rainfall reduction can be as high as 10% in some areas. However, the magnitude of projected rainfall changes of some individual models can be much larger than the ensemble means, exceeding 40% in some cases. These projected changes are related to the changes in regional circulations associated with the winter and summer monsoons, which are projected to weaken. The drier (wetter) condition is associated with the enhanced subsidence (rising motion).
APN Science Bulletin 8 (1) www.apn-gcr.org/bulletin Future changes in annual precipitation extrem... more APN Science Bulletin 8 (1) www.apn-gcr.org/bulletin Future changes in annual precipitation extremes over Southeast Asia under global warming of 2°C This article provides detailed information on projected changes in annual precipitation extremes over Southeast Asia under global warming of 2°C based on the multi-model simulations of the Southeast Asia Regional Climate Downscaling/Coordinated Regional Climate Downscaling Experiment Southeast Asia (SEACLID/CORDEX-SEA). Four indices of extreme precipitation are considered: annual total precipitation (PRCPTOT), consecutive dry days (CDD), frequency of rainfall exceeding 50 mm day-1 (R50mm), and intensity of extreme precipitation (RX1day). The ensemble mean of 10 simulations showed reasonable performance in simulating observed characteristics of extreme precipitation during the historical period of 1986-2005. The year 2041 was taken as the year when global mean temperature reaches 2°C above pre-industrial levels under unmitigated climate change scenario based on Karmalkar and Bradley (2017). Results indicate that the most prominent changes during the period of 2031-2051 were largely significant. Robust increases in CDD imply impending drier conditions over Indonesia, while increases in RX1day suggest more intense rainfall events over most of Indochina under 2°C global warming scenario. Furthermore, northern Myanmar is projected to experience increases in CDD, R50mm and RX1day, suggesting that the area may face more serious repercussions than other areas in Southeast Asia.
Rainfall extremes have a large socioeconomic relevance for southern Vietnam. More than 30 million... more Rainfall extremes have a large socioeconomic relevance for southern Vietnam. More than 30 million people live in this low-lying, flood-prone region in Southeast Asia. In this study the influence of the Madden–Julian oscillation (MJO) and convectively coupled equatorial waves on the modulation of daily rainfall during the rainy season (May–October) is evaluated and quantified using an extensive station database and the gridded Asian Precipitation–Highly Resolved Observational Data Integration Toward Evaluation of Water Resources (APHRODITE) product for different phases of the equatorial waves. The MJO, Kelvin, and equatorial Rossby (ER) waves significantly modulate daily rainfall in Vietnam south of 16°N. The MJO shows the most coherent signals across the region, followed by ER waves, whose influence is strongest in central Vietnam; Kelvin waves only affect the southern parts of Vietnam. For all waves, the frequency of occurrence of intense daily rainfall larger than 25 mm is signifi...
VNU Journal of Science: Earth and Environmental Sciences, 2017
Trong nghiên cứu này, sử dụng số liệu quan trắc lượng mưa ngày trên các trạm khí tượng khu vực Tâ... more Trong nghiên cứu này, sử dụng số liệu quan trắc lượng mưa ngày trên các trạm khí tượng khu vực Tây Nguyên giai đoạn 1981-2010, một vài đặc điểm chế độ mưa bao gồm ngày bắt đầu mùa mưa và sự biến đổi cũng như khả năng dự báo ngày bắt đầu mùa mưa đã được khảo sát. Kết quả nhận được cho thấy: 1) Ngày bắt đầu mùa mưa ở Tây Nguyên biến thiên mạnh qua các năm. Mùa mưa bắt đầu sớm hơn ở phía nam Tây Nguyên sau đó là phía bắc và muộn nhất ở miền trung. Nhìn chung, mùa mưa ở Tây Nguyên bắt đầu vào khoảng giữa tháng 4 đến giữa tháng 5, trung bình vào khoảng 30 tháng 4 hàng năm; 2) Mùa mưa ở Tây Nguyên có xu thế đến sớm hơn 5-7 ngày/thập kỷ; 3) Ngày bắt đầu mùa mưa ở Tây Nguyên có tương quan dương cao với nhiệt độ bề mặt biển (SST) ở khu vực trung tâm Thái Bình dương xích đạo và nam Ấn Độ dương xích đạo, gió vĩ hướng mực 850hPa khu vực tây bắc và trung tâm Thái Bình dương xích đạo và với khí áp mực biển trung bình trên các khu vực tây Thái Bình dương và Ấn Độ dương, có tương quan âm với SST tr...
The daily rainfall data at 13 stations over the Central Highlands (CH) Vietnam were collected for... more The daily rainfall data at 13 stations over the Central Highlands (CH) Vietnam were collected for the period 1981-2014. Two different sets of criteria using daily observed rainfall and 850 hPa daily reanalysis wind data were applied to determine the onset (retreat) dates of the summer rainy season (RS) and summer monsoon (SM) season, respectively. Over the study period, the mean RS and SM onset dates were April 20 and May 13 with standard deviations of 17.4 and 17.8 days, respectively. The mean RS and SM retreat dates were November 1 and September 30 with standard deviations of 17.9 and 10.2 days, respectively. The year-to-year variations of the onset dates and the rainfall amount within the RS and SM season were closely linked with the preceding winter and spring sea surface temperature in the central-eastern and western Pacific. It was also found that the onset dates were significantly correlated with the RS and SM rainfall amount.
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