In contrast to other natural disasters, droughts may develop gradually and last for extended periods of time. The World Meteorological Organization advises using the Standardized Precipitation Index (SPI) for the early identification of drought and understanding of its characteristics over various geographical areas. In this study, we use long-term rainfall data from 14 rain gauge stations in the Vietnamese Mekong Delta (1979–2020) to examine correlations with changes in rice yields. Results indicate that in the winter–spring rice cropping season in both 2016 and 2017, yields declined, corresponding with high humidity levels. Excessive rainfall during these years may have contributed to waterlogging, which in turn adversely affected yields. The results highlight that not only drought, but also humidity has the potential to adversely affect rice yield.

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This paper describes a participatory deliberative planning methodology employed in Can Tho, Vietnam to assess sanitation infrastructure options for a new peri-urban area with an expected population of 278,000 people. The study compared four options across a range of scales from centralised to decentralised treatment systems, and also included an innovative resource recovery option with urine collection and reuse in local agriculture. The study was undertaken in close collaboration with the local water utility, a local university, and several city government departments. In the sustainability assessment process key city stakeholders ranked the four options against criteria in five areas: (i) technical and risk, (ii) social and health, (iii) environmental, (iv) economic and financial, (v) city future. Stakeholders were provided with detailed information about each option, including quantitative data such as costs and energy use, and qualitative data against areas such as social acceptability. The assessment made evident the trade-offs between these five areas, and after their prioritisation, stakeholders agreed on the option that combined centralised treatment for the densely populated area to be inhabited earlier, and decentralised treatment for the remaining area. The methodology provided a robust way for stakeholders to engage in informed decision-making on this important planning issue.

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This paper examines the impact of the dike systems on river flows in the Vietnamese Mekong Delta (VMD). The study combined a hydrological change index method and the Mann-Kendall test to assess the temporal dynamics of both discharge and water levels along the main rivers of the VMD. Results highlight that the system of rivers and canals helps facilitate waterway traffic and drainage during the flood season. However, the low elevation of the delta has created conditions suitable for saline water to increasingly penetrate upstream during the dry season. Observed changes in the hydrological indicators at upstream stations of Tan Chau (Mekong river) and Chau Doc (Bassac river) are not only due to the dike system but also upstream alterations to the flow regime. More research is needed to consider the various drivers of flow regime change associated with natural and human activities both inside and outside of the study area.

Agriculture in the Global South is innately susceptible to climatic variability and change. In many arid and semi-mountainous regions of the developing world, drought is regularly cited as a significant threat to agricultural systems. The objective of this study is to assess the impacts of climate change on drought and land use and land cover (LULC) change in a semi-mountainous region of the Vietnamese Mekong Delta. We assessed previous drought trends (1980–2020) and future drought in the context of climate change, in accordance with three selected scenarios from the Coupled Model Intercomparison Project Phase 6 global climate models which have recently been released by the Intergovernmental Panel on Climate Change (IPCC) (2021–2060) using the Standardized Precipitation Index (SPI). The change of land use for the period 2010–2020 was then assessed and the associated climatic variability explored. The results show that for the period 1980–2019, SPI 3 responds quickly to changes in precipitation, whereas SPI 9 showed a clear trend of precipitation over time. The first longest duration occurrence of drought for SPI 3, SPI 6, and SPI 9 patterns were respectively 15–16, 21, and 25 months at Chau Doc station, and respectively 11, 14–15, and 16–17 months at Tri Ton station. Future precipitation and both maximum/minimum temperatures are projected to increase in both the wet and dry seasons. In addition, for all-time series scales and climate change scenarios, the levels of drought were slight, followed by moderate. In the future, the humidity at Chau Doc station is expected to decrease, while the occurrence of drought events is expected to increase at Tri Ton station, particularly in SPI 6 patterns (110 drought events in 1980–2020, and up to 198 drought events in the future). Moreover, between 2010–2020, the agricultural land area was seen to decrease, replaced by non-agricultural land uses that were found to increase by 22.4%. Among the agricultural land area, forestry, rice crops, and upland rice were found to reduce by 7.5, 16.0, and 21.2%, respectively, while cash crops and perennial crops increased by 26.4% and 170.6%, respectively. Amongst other factors, it is concluded that the variability of climate has led to drought and thus impacted on the conversion of LULC in the study area. Due to low economic efficiency, changing climate conditions, and a lack of irrigated water, the area of rice crops, forestry, aquaculture, and upland rice decreased, replaced by land for orchards for fruit production and other cash crops.

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The water balance in six selected crops (mung beans, tomatoes, maize, cassava, yam, and sweet potatoes) was determined at the field block scale in the Vietnamese Mekong Delta for two agricultural growing areas. A novel approach for the calculation of water balance was employed, which combined the reference crop evapotranspiration (ETo), derived from four methods, namely, Penman-Monteith, Blaney-Criddle, Thornthwaite, and Turc. The equation of Penman-Monteith is generally considered to be the most representative to calculate the ETo value. The reference crop evapotranspiration for some crops was calculated. The daily ETo ranges from 1.8 to 7.5 mm, while a monthly ETo ranges from 3.5 to 5.0 mm. The calculations of the water balances show that irrigation is necessary for crops grown on raised beds crops during the dry season. The results show a promising approach for evaluating the water regime to satisfy crop water requirements.