Exploring Freshwater Regimes and Impact Factors in the Coastal Estuaries of the Vietnamese Mekong Delta

Statistical and Hydrological Evaluations of Water Dynamics in the Lower Sai Gon-Dong Nai River, Vietnam

The water levels downstream of the Sai Gon and Dong Nai river in Southern Vietnam have been significantly changed over the last three decades, leading to severe impacts on urban flooding and salinity intrusion and threating the socio-economic development of the region and lives of many local people. In this study, the Mann-Kendall (MK) and trend-free prewhitening (TFPW) tests were applied to detect the water level trends and changepoints based on a water level time series at six gauging stations that were located along the main rivers to the sea over 1980–2019. The results indicated that the water level has rapidly increased by about 0.17 to 1.8 cm/year at most gauge stations surrounding Ho Chi Minh City, strongly relating to urbanization and the dike polder system’s impacts that eliminates the water storage space. In addition, the operation of upstream reservoirs has contributed to water level changes with significant consequences since the high-water level at Tri An station on the Dong Nai river occurs 1000–1500 times compared to 300–500 times before the operation. Although the effects of the flows from the sea are less than the two other factors, the local government should seriously consider water level changes, especially in the coastal regions. Our study contributes empirical evidence to evaluate the water level trends in the planning and development of infrastructure, which is necessary to adapt to future changes in Southern Vietnam’s hydrologic system.

Moving towards sustainable coastal adaptation: Analysis of hydrological drivers of saltwater intrusion in the Vietnamese Mekong Delta

Coastal lowlands are of particular importance in providing food, shelter, and livelihoods for large populations; yet aggravating effects caused by human activities and climate change have exposed these areas to multiple challenges. Located in the southernmost part of the Lower Mekong Basin, the Vietnamese Mekong Delta (VMD) is adversely affected by upstream hydropower development, localised water-engineering systems (dykes), climatic factors, and sea level rise. This paper examines how these drivers shape the adaptation strategies of rural communities in the coastal areas. Using mixed sources of historical measured data, numerical modelling and qualitative data gathered in three coastal provinces (Ben Tre, Tra Vinh, and Soc Trang), we find that hydrological alterations are manipulated by various drivers with more immediate effects of the tidal systems and sea level rise in the Vietnamese East Sea. The study results suggest that while these impacts are not adequately addressed by delta-scale measures, a mixed policy approach including control and adaptation measures has been adopted to tackle saltwater intrusion on the local scale. The paper provides a holistic insight into the complex temporal-spatial dimensions of hydrological change which have distressed coastal agroecosystems and resource-dependent communities. The paper argues that while voicing concerns over transboundary hydropower impacts is essential, in situ collaborative efforts among salinity-affected jurisdictions are equally important in addressing high uncertainty and complexity of saltwater intrusion in the future.

Livelihood Vulnerability and Adaptation Capacity of Rice Farmers under Climate Change and Environmental Pressure on the Vietnam Mekong Delta Floodplains

Agricultural production is the primary source of income and food security for rural households in many deltas of the world. However, the sustainability of farm livelihoods is under threat, due to the impacts of climate change and environmental pressure, including shifting hydrological regimes, droughts, water pollution, land subsidence and riverbank erosion. This study evaluated the livelihood sustainability and vulnerability of triple rice farmers on the floodplains of the Vietnam Mekong Delta (VMD). We focused on the perceptions of rice farmers, based on a survey of 300 farmers. Increasing temperatures, drought, water pollution and sediment shortages were the four factors considered by farmers to have the most impact on their agricultural livelihoods. We analyzed farmers’ capacity to sustain their livelihoods and adapt to the changing environment. Results show relatively low vulnerability of rice farmers overall, though many of those surveyed reported very low incomes from rice production. Factors of most concern to farmers were rising temperatures and more frequent droughts. Farmers were already taking steps to adapt, for example, increasing production inputs and investing more labor time, as well as switching production methods. Yet, our findings suggest that policymakers and scientists have a role to play in developing more sustainable adaptation paths. The research clarifies the livelihood vulnerability of triple rice farmers on the VMD floodplains, while more generally contributing to the body of literature on farming and climate change and environmental pressure.

New approach of water quantity vulnerability assessment using satellite images and GIS-based model: An application to a case study in Vietnam

Water deficiency due to climate change and the world's population growth increases the demand for the water industry to carry out vulnerability assessments. Although many studies have been done on climate change vulnerability assessment, a specific framework with sufficient indicators for water vulnerability assessment is still lacking. This highlights the urgent need to devise an effective model framework in order to provide water managers and authorities with the level of water exposure, sensitivity, adaptive capacity and water vulnerability to formulate their responses in implementing water management strategies. The present study proposes a new approach for water quantity vulnerability assessment based on remote sensing satellite data and GIS ModelBuilder. The developed approach has three layers: (1) data acquisition mainly from remote sensing datasets and statistical sources; (2) calculation layer based on the integration of GIS-based model and the Intergovernmental Panel on Climate Change's vulnerability assessment framework; and (3) output layer including the indices of exposure, sensitivity, adaptive capacity and water vulnerability and spatial distribution of remote sensing indicators and these indices in provincial and regional scale. In total 27 indicators were incorporated for the case study in Vietnam based on their availability and reliability. Results show that the most water vulnerable is the South Central Coast of the country, followed by the Northwest area. The novel approach is based on reliable and updated spatial-temporal datasets (soil water stress, aridity index, water use efficiency, rain use efficiency and leaf area index), and the incorporation of the GIS-based model. This framework can then be applied effectively for water vulnerability assessment of other regions and countries.

Assessment of Rainfall Distributions and Characteristics in Coastal Provinces of the Vietnamese Mekong Delta under Climate Change and ENSO Processes

Rainwater is considered a promising alternative water source for coastal areas where freshwater resources are increasingly under pressure. This study evaluates rain regime characteristics that influence the ability to exploit rainwater in the coastal provinces of the Vietnamese Mekong Delta (VMD). In particular, it considers the impact of climate change and El Niño–Southern Oscillation (ENSO) processes. We analyzed rainfall data from 102 monitoring stations across the VMD from 1989 to 2017. Using statistical methods, we explored (1) characteristics of the rainy season, including the dates of onset and cessation and season length; (2) average rainfall volumes; and (3) the maximum number of consecutive nonrainy days during the rainy season and over the year. We also analyzed changes in these characteristics over time, in parallel with ENSO processes and climate change. Trend lines were determined using nonparametric methods, utilizing Sen’s slope estimation and the Mann–Kendall test. Results showed a tendency for the rainy season to start earlier and end later in the western coastal zone of the study area, with season length gradually decreasing towards the East Sea and inland. The shortest rainy season was found in the estuary zone (in the northeast of the VMD). Rainfall was abundant on the west coast, again diminishing gradually towards the East Sea and inland. Rain was also quite plentiful during four dry season observation months in the study area, but it lacked the predictability needed for effective exploitation. The number of consecutive days without rain averaged 96 annually, with a difference of 29 days between the largest and smallest observations. The difference between the provinces with the longest and shortest periods without rain averaged 41 days. Although the impact of climate change on the rain regime is complex, we can say that the rainy season now tends to start earlier, end later, and be lengthier, though without exhibiting clear trends. ENSO processes significantly impacted rainfall regime characteristics, especially the dates of onset and cessation, and season length.