The rapidly developing urbanization since the last decade of the 20th century has led to extensive groundwater extraction, resulting in subsidence in Ho Chi Minh City, Vietnam. Recent advances in multi-temporal spaceborne SAR interferometry, especially with a persistent scatters interferometry (PSI) approach, has made this a robust remote sensing technique for measuring large-scale ground subsidence with millimetric accuracy. This work has presented an advanced PSI analysis, to provide an unprecedented spatial extent and continuous temporal coverage of the subsidence in Ho Chi Minh City from 2006 to 2010. The study shows that subsidence is most severe in the Holocene silt loam areas along the Sai Gon River and in the southwest of the city. The groundwater extraction resulting from urbanization and urban growth is mainly responsible for the subsidence. Subsidence in turn leads to more flooding and water nuisance. The correlation between the reference leveling velocity and the estimated PSI result is R² = 0.88, and the root mean square error is 4.3 (mm/year), confirming their good agreement. From 2006 to 2010, the estimation of the average subsidence rate is -8.0 mm/year, with the maximum value up to -70 mm/year. After four years, in regions along Sai Gon River and in the southwest of the city, the land has sunk up to -12 cm. If not addressed, subsidence leads to the increase of inundation, both in frequency and spatial extent. Finally, regarding climate change, the effects of subsidence should be considered as appreciably greater than those resulting from rising sea level. It is essential to consider these two factors, because the city is inhabited by more than 7.5 million people, where subsidence directly impacts urban structures and infrastructure.

Food security has become a key global issue due to rapid population growth, extensive conversion of arable lands, and declining overall productivity in some areas because of the effects of floods, water shortage, salinity intrusion, and plant diseases. In this study, we analyzed the relationship between the pattern of salinity intrusion and the spatiotemporal distribution of rice cultivation in the winter–spring crops of 2015, 2016, 2019 and 2020 in coastal provinces of the Vietnamese Mekong Delta. Sentinel-1 (S-1) data were used to extract the spatial distribution information of six rice growth stages based on a rice age algorithm. The classification accuracy of rice crop growth stages was found to have an overall accuracy of 85% and a Kappa coefficient of 0.80 (n = 373). For evaluating salinity intrusion effects, salinity isolines (4 g/L) were used to determine the percentage of rice areas affected. Results show that in the years observed to have severe salinity intrusion such as 2016 and 2020, a strong shift in planting calendar was identified to avoid salinity intrusion, with some areas being sown or transplanted 10–30 days earlier than normal planting. In addition, the lack of irrigation water and salinity intrusion limits rice cultivation in the dry season of coastal areas. Further analysis from the S-1 data confirms that the spatiotemporal distribution of rice cultivation is related to the change in government policy/recommendation affected by salinity intrusion. These findings demonstrate the potential and feasibility of using S-1 data to develop an operational rice crop adaptation framework on the delta scale.

GIS and Remote Sensing technology had been widely applied in Viet Nam. However, research orientation and development of Web GIS and Remote Sensing solutions for regional management approach also indicates many difficulties and challenges. This paper aims to introduce Web GIS and Remote sensing solutions that can be used in monitoring salinity intrusion and land cover mapping to support the implementation of sustainable development strategy of the Mekong Delta region. The experimental results show the online mapping applications based on Landsat images open a new way that can be effectively applied in monitoring salinity intrusion in river network, updating the status of land cover changes and analysing the trend of forest-cover changes in this region. Results of this study also illustrate the suitable technology available to support regional organizations to create thematic maps in monitoring and managing the natural resources and environment of provinces/cities that can achieve high accuracy and save time.

Mapping hydrological drought under the CMIP6 climate change scenarios in sub-basin scale: A case study in the upper part of Dong Nai river basin

This paper describes a new approach for urban land use management by using Unmanned Aerial Vehicles (UAV). Experimental result covers 121 ha (1.21 km²) at Binh Tho ward, Thu Duc district of the Ho Chi Minh city and shows that UAV technology is most suitable and cost effective for cadastral mapping and updating the database with high accuracy. In this research, 36 GCPs (Ground Control Points) and 2433 parcel boundaries (GIS data) were used to compare the achieved accuracy of UAV method in which 10381 orthophoto imageries produced had a resolution of 1.8 cm (with flying altitude 70 m) to be used to inform urban database. This technology opens a new way that is most suitable and cost effective for small areas, where digital maps and 3D models need to be produced in a short period of time with high data quality and accuracy. There are no significant barriers to imbed the technology at the local level and it can speed up the process of updating database in developing the Spatial Data Infrastructure (SDI) of the smart city.