Xuyen Quadrangle Research Articles

<span>Assessing the impact of land-use/land-cover change on provisioning ecosystem services in the Long Xuyen Quadrangle from 2000 to 2021</span>

Changes in land use/land cover (LULC) have a significant impact on the changes in ecosystem service values. This study aims to assess the impacts of LULC changes on provisioning ecosystem services (pES) in the Long Xuyen Quadrangle region (LXQ) from 2000 to 2021. Using Landsat 5 TM and Landsat 8 OLI imagery, this study analyzes the normalized difference vegetation index (NDVI) time series using MODIS imagery to monitor and evaluate the impacts of LULC changes in the LXQ region. Additionally, interviews with farmers were conducted to estimate the ecosystem service values of different rice cultivation models. The research results in the creation of LULC maps for the LXQ in 2000 and 2021, with relatively high reliability, including overall accuracy (OA) of 83.18% (K = 0.772) and 94.26% (K = 0.9284), respectively. The main LULC change observed in the LXQ region from 2000 to 2021 is the conversion from wetlands to double-cropped rice and triple-cropped rice systems. The study identified an area of 54,667.722 ha (26.24%) where wetlands were converted to double-cropped rice, and an area of 36,779.633 ha (17.65%) where wetlands were converted to triple-cropped rice. Furthermore, the estimated ecosystem service values after the conversion from wetlands to triple-cropped rice were approximately 122,504,931 VND/ha/year, and for double-cropped rice, it was approximately 87,772,604.88 VND/ha/year. The research findings indicate that wetland agriculturalization, including double-cropped rice and triple-cropped rice, has affected the ecosystem service provision in the LXQ region. These research results provide significant considerations for future comprehensive valuation of ecosystem service values in the LXQ, Vietnamese MD.

An initial assessment of mobile dam efficiency in raising low-flow water levels in the Vietnamese Mekong Delta

In recent years, the Tien and Hau rivers have experienced a downtrend in water levels during the low flow season. This decrease has led to detrimental effects on agricultural production and ecological health in the VMD’s upper regions, such as the Long Xuyen Quadrangle (LXQ) and the Plain of Reeds (PoR). This research employs a numerical hydraulic model for a preliminary assessment of the potential effectiveness of mobile dams in increasing water levels in the VMD’s upper part. A calibrated 1D hydraulic model was utilized to evaluate the performance of the proposed mobile dams: one situated near the My Thuan bridge on the Tien river, and the other near the Can Tho bridge on the Hau river. Initial results indicate that setting the crest of mobile dams at -1.0 m could raise minimum and maximum water levels in the Tien river near Tan Chau by 1.0 m and 0.15 m, respectively, and in the Hau river near Chau Doc by 1.1 m and 0.07 m, respectively. Furthermore, these mobile dams could significantly enhance the minimum and maximum water levels in An Binh channel within the PoR and Ba The channel in the LXQ, by up to 0.55 m and 0.26 m, and 0.42 m and 0.29 m, respectively. These findings provide an essential foundation for initially understanding how mobile dams can improve water resource management in the VMD. However, additional investigation is required to assess the effects of mobile dams on salinity intrusion, ecological balance, hydrological dynamics, sediment deposition, and erosion.

Evaluation of the change in crop structure under the impact of flood prevention dikes in the Long Xuyen Quadrangle in the period 2005-2020

The study was conducted to monitor spatial fluctuations of dikes affecting the rice crop structure and evaluate changes in rice crop structure inside and outside the dikes in the Long Xuyen Quadrangle in the period 2005-2020. That serves as a basis for assessing the current status of flood control and the changing trend of rice production in the region in the future. The study uses LANDSAT images and applies the normalized difference water index (NDWI) and shoreline extraction to determine the current condition of dikes in the Long Xuyen Quadrangle region, while combining a series of normalized difference vegetation index (NDVI) on moderate resolution imaging spectroradiometer (MODIS) image data to determine the structure of rice crops in 2005 and 2020. The results show that the embankment length increased by 1,910.15 km compared to 2005 and the natural embankment area increased to 123,020.31 ha (accounting for 24.63% of the area’s natural area) in the period 2005-2020. The farming system in the study area impacted by flood prevention dike changes from other crops to triple-rice crop cultivation. Specifically, the total area of the other cultivation types converted into triple-rice crop cultivation is 90,904.77 ha, accounting for 51.92% of the total area of structural transformation of farming types, concentrated in districts with large dike areas such as Thoai Son, Chau Phu, and Chau Thanh districts (An Giang province). The research results contribute to supporting environmental management and orienting rice production trends in the region in the future.

Assessing impacts on rice production and quantifying economic cost losses with PM2.5–based damage – A case of the Long Xuyen Quadrangle, Vietnam Mekong Delta

Control measures of PM2.5 pollution mitigation are identified as an important strategy for food security. This is remarkably crucial with Long Xuyen Quadrangle (LXQ), which exports more than 50% of Vietnams rice. PM2.5 pollution impacts on rice production need to be assessed to determine the extent of effects on economic losses. The given objectives of this study are to build a research framework that combines models and data to quantify the economic damage to rice seasons affected by PM2.5 pollution, taking LXQ as a research case study. The models used include quantitative models of output loss due to loss of productivity, productivity function, and quantification of economic loss model to assess economic loss due to loss of productivity caused by PM2.5, based on damage to rice plants. The data used included: (i) 24-hour average PM2.5 concentration data in the environment to represent the process of estimating negative impacts on rice yield, (ii) formal characteristics of rice crops, (iii) rice area/total agricultural land area, (iv) rice production level achieved by each crop, and (v) minimum support prices for rice. The total loss of rice yield in the LXQ in 2018 was estimated at 15,729 tons/ha. The results associated with calculated damage levels into economic values showed that the total losses due to the reduction of rice production in 2018 in LXQ were at about 2,728 billion VND, which was equivalent to approximately 121 million USD, or 1.47% of the total GRDP of LXQ in 2018. The obtained results will be the basis for further development, contributing to the building of a dataset for the management of the air environment as well as effective agricultural farming solutions for the LXQ area.

Post Rationality of a Hydraulic Civilization: An Ecological Transition for the Vietnamese Mekong Delta

A radical project is proposed for the Vietnamese Mekong Delta, calling for the urgency to realize its Ecological Transition, as a response to the need to reverse the detrimental environmental impacts accumulated over the course of its history of agrarian colonization. The article reveals the evolution of the delta’s territory, through an atlas of palimpsests regarding the delta’s past transformations primarily driven by the hydraulic management of its territory. The resulting environmental degradation and obliteration of much of the Mekong Delta’s ability to self-regenerate are found in large part as the consequence of the devotion of the delta’s ecosystem resources to mass rice production; driven by vast irrigation infrastructural expansion. However, as an unintentional consequence of the investments made in infrastructural networks during the Green Revolution, a new value was propelled by farmers and the local community through the diversification of infrastructural uses, resulting in hybrid rururban land transformations, indicating the potential for Ecological Transition in the delta.
 Through the theoretical perspective of alternative ways for metropolization defined in the ‘Horizontal Metropolis’ and the conceptual approach developed under the ‘Project of Isotropy’, post-rationality of the agrarian territory is proposed through the reorganization and design of the primary canals established for irrigation after the 1986 ‘Doi Moi’ reform period. Social-Techno-Ecological corridors are proposed to transform the currently overlooked and engineered canal settlements living in Long Xuyen Quadrangle and Can Tho province, through a resilient community-based living and cultivation paradigm based on the advancement of the traditional Vietnamese VAC (Garden-Pond-Animal) model. In addition, the Water Ecological Framework is proposed as a wider Delta Intervention whereby a series of circular water processes can take place ecologically across the territory, to promote the partial reinstatement of the Mekong’s deltaic regenerative processes. 
 As a radical integration between the wider Water Ecological Framework and the Social-Techno-Ecological corridors, the evolution of the deltaic territory is envisioned to create new social ecologies across the Mekong Delta, offering valuable climate-resilient ecosystems through biodiversity and a synergetic coexistence. Bringing into reality an Ecological Transition for the delta’s resilient future, whereby the regeneration of its deltaic processes shall be reinstated with a more conducive coexistence between humans and nature, as a new paradigm to address the wicked problems of our time.

AN APPLICATION OF 1-D MODEL FOR ASSESSING SALINE INTRUSION IN THE COASTAL AREAS OF THE VIETNAMESE MEKONG DELTA

Many studies in present years have been conducted to predict the effects of changes in the upstream discharge, hydrodynamics, and saline intrusion in the coastal of the Vietnamese Mekong Delta (VMD) (Smajgl et al., 2015; T. Van et al., 2013); however, the models for the entire delta did not show detail for small areas such as the Ca Mau Peninsula, and other studies were only considered in upstream flooding condition such as the Long Xuyen Quadrangle (Nguyen et al., 2012; T. Van et al., 2013). Besides, several study were using hydraulic models for the whole VMD region; Nevertheless, these studies were only interested in major river systems that applied the Mike 11 salt simulation model for the VMD region. Some hydraulic studies were simulated in specific region such as Long Xuyen Quadrangle. However, a few studies have focused on a complex river system such as Quan Lo Phung Hiep (QLPH) area of the Ca Mau peninsula, which is characterized by a complex river system, inter-regional irrigation works, and a variety of water demands, including marine, brackish, and freshwater-based agriculture. However, coastal studies, particularly those of an inter-regional character with complicated river networks like the QLPH, have received little attention. As a result, this research was carried out to assess the hydrodynamics and saline intrusions of the interwoven river network's coastal area, a complex operating system in a large area affected by both tidal regimes in the West and East Sea, which is characteristic of the Mekong Delta.

A Model-Based Approach for Improving Surface Water Quality Management in Aquaculture Using MIKE 11: A Case of the Long Xuyen Quadangle, Mekong Delta, Vietnam

This study utilized MIKE 11 to quantify the spatio-temporal dynamics of water quality parameters (Biochemical Oxygen Demand (BOD5), Dissolved Oxygen (DO) and temperature) in the Long Xuyen Quadrangle area of the Vietnamese Mekong Delta. Calibrated for the year of 2019 and validated for the year of 2020, the developed model showed a significant agreement between the observed and simulated values of water quality parameters. Locations near to cage culture areas exhibited higher BOD5 values than sites close to pond/lagoon culture areas due to the effects of numerous point sources of pollution, including upstream wastewater and out-fluxes from residential and tourism activities in the surrounding areas, all of which had a direct impact on the quality of the surface water used for aquaculture. Moreover, as aquacultural effluents have intensified and dispersed over time, water quality in the surrounding water bodies has degraded. The findings suggest that the effective planning, assessment and management of rapidly expanding aquaculture sites should be improved, including more rigorous water quality monitoring, to ensure the long-term sustainable expansion and development of the aquacultural sector in the Long Xuyen Quadrangle in particular, and the Vietnamese Mekong Delta as a whole.

Long-term hydrological alterations and the agricultural landscapes in the Mekong Delta: Insights from remote sensing and national statistics

The Vietnamese Mekong Delta (VMD) is one of the most important food baskets in Southeast Asia, contributing to more than half of the country's food production capacity and the majority of its rice exports. Constantly threatened by a multitude of environmental pressures, including climate change-induced sea-level rise, delta-wide land subsidence, sedimentation reduction and, more recently, riverbed mining, steps towards the sustainable development of the VMD is becoming increasingly vulnerable. In this paper, we examine the effect of hydrological alterations of agricultural landscape in the VMD, more specifically, the temporal trends of triple rice crop in the Long Xuyen Quadrangle (LXQ). Landsat satellite data was used to map active rice paddy sites across the three major rice cropping seasons and identify the temporal distribution of triple rice crop areas over the last 24 years (1995–2019). Results were interpreted alongside official statistical data on agriculture from Vietnam and corroborated with ground truth data points from the study site. Our results reveal a notable fall in Landsat-detected triple rice crop area between 2016 and 2019, corroborating with both literature and agricultural data indicating an increase in aquaculture areas. Here, we take note for the first time the underlying links between riverbed mining and agricultural shifts in the VMD, which could highlight important policy and management implications for the local government in order to ensure environmental sustainability and food security. We argue that a tighter and more effective regulation of riverbed mining practices in the region is both integral and necessary for the agricultural sustainability of the VMD.

Irrigation water requirement of rice in Long Xuyen Quadrangle area, Vietnam in the context of climate change

Climate variability is deeply affecting all aspects of human life including agricultural sector. In the present study the CROPWAT model was used to estimate reference evapotranspiration (ETo), crop evapotranspiration (ETc), effective rainfall (ER) and crop water requirement (CWR) of summer-autumn rice crop and its yield during baseline period (2002-2017) and also under representative concentration pathways (RCPs) 4.5 scenario for 2020s, 2055s and 2090s-time scales for Long Xuyen Quadrangle (LXQ) area of Vietnam. It was found that the ER significantly increased by 6.2, 16.9 and 15.4 per cent, respectively in 2020, 2055 and 2090; ETo and ETc increased by 2.1 and 2.3 per cent, respectively in 2020s; 4.4 and 5.8 in 2055; and 5.8 and 7.7 per cent in 2090 compared to baseline. The CWR also increased approximately 4.6, 4.4 and 3.5 per cent, respectively in 2020, 2055 and 2090 and consequent decrease in rice yield by 6.5, 7.9 and 10.4 per cent, respectively. Results showed that if the crop planting date is delayed by 20 days, the rice yield would increase approximately 4.9, 7.9 and 9.9 per cent, respectively in three-time scales of RCP 4.5 scenario, compared to base line period.

Change trends of rainfall features for the Long Xuyen Quadrangle, Vietnam

Change trends of rainfall features for the Long Xuyen Quadrangle, Vietnam

Study on assessing the impact of climate change (temperature and rainfall) on rice yield in the Long Xuyen Quadrangle region (LXQR) – Vietnam

Study on assessing the impact of climate change (temperature and rainfall) on rice yield in the Long Xuyen Quadrangle region (LXQR) – Vietnam

Dramatic decrease of flood frequency in the Mekong Delta due to river-bed mining and dyke construction

Here we present a proof of concept evaluation of the impacts of riverbed-mining on river-wetland connectivity by analyzing the temporal trends of the flood frequencies in the Vietnamese Mekong Delta (VMD), while accounting for the effect of dyke constructions. We focus on the Long Xuyen Quadrangle (LXQ), which is significant in terms of biodiversity and economic contribution to the VMD as it is one of the most important food baskets of Southeast Asia that depends on seasonal flooding. Our results indicate that the flood frequency in LXQ has decreased significantly over the past 20 years (1995–2015). Time-series analyses of water level data at Chau Doc, Tan Chau, and Can Tho stations confirmed that the overall descending trend is statistically significant (p-value < 0.001 and tau ~ 0.1). However, the river discharge at Kratie showed no significant trend (p-value = 0.98) over the same period. This indicates that the flood frequency is associated with the lowering of the riverbed (incision) other than climatic factors. The connectivity analysis also revealed a remarkable drop in the inundation duration after early 2000, which corresponds to the previous observations of the shifting shoreline of the VMD from construction to shrinking. Finally, regression and principal component analyses underpinned the strong causality between the riverbed-mining and the decreased seasonal flooding patterns in LXQ, while accounting for the effect of the dyke system over the last decades (R2 = 0.75). This study offers compelling evidences on the relationship between sand-mining in the river and the disrupted flood regimes in VMD. The reduction in water and sediments that is necessary for sustaining current rates of agricultural production in the long term would endanger the livelihoods of millions of VMD inhabitants.

NGHIÊN CỨU XU THẾ VÀ TÁC ĐỘNG BIẾN ĐỔI KHÍ HẬU Ở VÙNG TỨ GIÁC LONG XUYÊN

NGHIÊN CỨU XU THẾ VÀ TÁC ĐỘNG BIẾN ĐỔI KHÍ HẬU Ở VÙNG TỨ GIÁC LONG XUYÊN

Flooding in the Mekong Delta: the impact of dyke systems on downstream hydrodynamics

Abstract. Building high dykes is a common measure of coping with floods and plays an important role in agricultural management in the Vietnamese Mekong Delta. However, the construction of high dykes causes considerable changes in hydrodynamics of the Mekong River. This paper aims to assess the impact of the high-dyke system on water level fluctuations and tidal propagation in the Mekong River branches. We developed a coupled 1-D to 2-D unstructured grid using Delft3D Flexible Mesh software. The model domain covered the Mekong Delta extending to the East (South China Sea) and West (Gulf of Thailand) seas, while the scenarios included the presence of high dykes in the Long Xuyen Quadrangle (LXQ), the Plain of Reeds (PoR) and the Trans-Bassac regions. The model was calibrated for the year 2000 high-flow season. Results show that the inclusion of high dykes changes the percentages of seaward outflow through the different Mekong branches and slightly redistributes flow over the low-flow and high-flow seasons. The LXQ and PoR high dykes result in an increase in the daily mean water levels and a decrease in the tidal amplitudes in their adjacent river branches. Moreover, the different high-dyke systems not only have an influence on the hydrodynamics in their own branch, but also influence other branches due to the Vam Nao connecting channel. These conclusions also hold for the extreme flood scenarios of 1981 and 1991 that had larger peak flows but smaller flood volumes. Peak flood water levels in the Mekong Delta in 1981 and 1991 are comparable to the 2000 flood as peak floods decrease and elongate due to upstream flooding in Cambodia. Future studies will focus on sediment pathways and distribution as well as climate change impact assessment.

FLOOD HAZARD MAPPING AT LONG XUYEN QUADRANGLE IN 2015 USING GEOGRAPHIC INFORMATION AND REMOTE SENSING

Abstract. In recent year, the flooding has been occurred with higher frequency at Long Xuyen Quadrangle areas of Mekong Delta, Vietnam. It was considered as a major natural disaster which effects on the physical and spiritual in people’s life in this area. This research aims to generate a flood hazard map and assess the flood situation at Long Xuyen quadrangle in 2015. The MNDWI (Modification of Normalized Difference Water Index) extracting from Sentinel 2 image was used to map the flood extent at Long Xuyen quadrangle during rainy season in 2015. The statistics method was estimated correlation coefficient between flooding spatial distribution and hydrological stations on SPSS software. The results showed that the severe flood occurred from August to December in 2015. There were about 47.6% and 28.2% of the total area were inundated in October and August, respectively. The correlation between inundated areas and water level at Ha Tien and Chau Doc hydrological stations was 0.73 and 0.65 (p &lt;0.01), respectively. The derived information was very essential and valuable for local managers in making decision on responding and mitigating to the flood disaster.

The Cattle Grooming Behavior and Some Problems with Technological Grooming Instruments for Cow WelfareFlood Hazard Mapping at Long Xuyen Quadrangle in 2015 Using Geographic Information System and Remote Sensing Technologies

The Cattle Grooming Behavior and Some Problems with Technological Grooming Instruments for Cow WelfareFlood Hazard Mapping at Long Xuyen Quadrangle in 2015 Using Geographic Information System and Remote Sensing Technologies

Predicting the water use-demand as a climate change adaptation strategy for rice planting crops in the Long Xuyen Quadrangle Delta

This work evaluates the impacts of climate change on water use-demand of three rice planting crops including winter–spring (WS), summer–autumn (SA) and autumn–winter crops for Long Xuyen Quadrangle Delta of Vietnam. Climatic variables scenarios were obtained from the updated report on emission scenarios which are issued by Vietnam’s Ministry of Natural Resources and Environment for three future timescales (2016–2035, 2046–2065 and 2080–2099) of representative concentration pathways (RCP) 4.5 and RCP8.5 scenarios. Cropwat model was selected to evaluate the irrigation water demand of three rice planting crops based on simulating actual evapotranspiration (ETc) and effective rainfall for the study area. The results showed that the WS and SA planting crops need more irrigation water demand in the growing and developmental stage for timescales of RCP4.5 and RCP8.5 scenarios. Results also pointed out that compared with current climate condition the tendency to decrease in irrigation water demand in the initial and developmental stages of autumn–winter planting crop with arranging from 2.9–12.9 to 10.0–18.2%, respectively, corresponding to timescales of RCP4.5 and RCP8.5 scenarios is found and a significant downward trend in the late stage approximately 5.8–20.0% and 13.6–20.7%, respectively, for RCP4.5 and RCP8.5 scenarios also recorded.

Establishment of irrigation schedule for rice cropping seasons in the Long Xuyen Quadrangle, Vietnam using Cropwat model

This study is conducted to determine the appropriate irrigation water amount for three main cropping seasons (TMCS) of rice in the Long Xuyen Quadrangle, Vietnam (LXQ). In the work, the Cropwat crop model was used to calculate irrigation water amount for winter-spring (WS), summer-autumn (SA) and autumn-winter (AW) crops based on meteorological data collected in period from 1998 to 2017. Simulation results carried out that WS crop was needed more irrigation water than SA and AW crops. The highest irrigation water requirement (IWR) of WS, SA and AW crops occurred on development stage with approximately values 207.1 mm, 205.8 mm and 102.3 mm respectively. The results showed that the proposed model is successfully applied to define crop water requirement (CWR) and irrigation requirement in the context of climate change leading to irrigation water scarcity.

Predicting future water demand for Long Xuyen Quadrangle under the impact of climate variability

Long Xuyen Quadrangle is one of the important agricultural areas of the Mekong Delta of Vietnam accounting for 25% of rice production. In recent years, the area faces drought and salinization problems, as part of climate change impact and sea level rise. These are the main causes that led to the crop water deficits for agricultural production. Therefore, this work was conducted to predict crop water requirement (CWR) based on consideration of other related meteorological factors and further redefine the crop planting calendar (CPC) for three main cropping seasons including winter–spring (WS), summer–autumn (SA) and autumn–spring (AS) using the Cropwat crop model based on the current climate conditions and future climate change scenarios. Meteorological data for the baseline period (2006–2016) and future corresponding to timescales 2020s, 2055s and 2090s of Representative Concentration Pathways (RCP)4.5 and RCP8.5 scenarios are used to predict CWR and CPC for the study area. The results showed that WS and SA crops needed more irrigation water than AS crop and the highest irrigation water requirement of the WS and SA crops occurred on developmental stage, while the AW crop appeared on growth, developmental and late stage for the baseline and timescales of RCP4.5 and RCP8.5 scenarios. Calculation results of the shift of CPC indicated that the CWR of the AW crop decreased lowest approximately 6.6–20.6% for timescales of RCP4.5 scenario and 20.6–25.5% for RCP8.5 scenario compared with the baseline.

Assessing impacts of dike construction on the flood dynamics of the Mekong Delta

Abstract. Recent flood dynamics of the Mekong Delta have raised concerns about an increased flood risk downstream in the Vietnamese Mekong Delta. Accelerated high dike building on the floodplains of the upper delta to allow triple cropping of rice has been linked to higher river water levels in the downstream city of Can Tho. This paper assesses the hydraulic impacts of upstream dike construction on the flood hazard downstream in the Vietnamese Mekong Delta. We combined the existing one-dimensional (1-D) Mekong Delta hydrodynamic model with a quasi-two-dimensional (2-D) approach. First we calibrated and validated the model using flood data from 2011 and 2013. We then applied the model to explore the downstream water dynamics under various scenarios of high dike construction in An Giang Province and the Long Xuyen Quadrangle. Calculations of water balances allowed us to trace the propagation and distribution of flood volumes over the delta under the different scenarios. Model results indicate that extensive construction of high dikes on the upstream floodplains has had limited effect on peak river water levels downstream in Can Tho. Instead, the model shows that the impacts of dike construction, in terms of peak river water levels, are concentrated and amplified in the upstream reaches of the delta. According to our water balance analysis, river water levels in Can Tho have remained relatively stable, as greater volumes of floodwater have been diverted away from the Long Xuyen Quadrangle than the retention volume lost due to dike construction. Our findings expand on previous work on the impacts of water control infrastructure on flood risk and floodwater regimes across the delta.