Hanoi City of Vietnam changes quickly, especially after its state implemented its Master Plan 2030 for the city’s sustainable development in 2011. Then, a number of environmental issues are brought up in response to the master plan’s implementation. Among the issues, the Urban Heat Island (UHI) effect that tends to cause negative impacts on people’s heath becomes one major problem for exploitation to seek for mitigation solutions. In this paper, we investigate the land surface thermal signatures among different land-use types in Hanoi. The surface UHI (SUHI) that characterizes the consequences of the UHI effect is also studied and quantified. Note that our SUHI is defined as the magnitude of temperature differentials between any two land-use types (a more general way than that typically proposed in the literature), including urban and suburban. Relationships between main land-use types in terms of composition, percentage coverage, surface temperature, and SUHI in inner Hanoi in the recent two years 2016 and 2017, were proposed and examined. High correlations were found between the percentage coverage of the land-use types and the land surface temperature (LST). Then, a regression model for estimating the intensity of SUHI from the Landsat 8 imagery was derived, through analyzing the correlation between land-use composition and LST for the year 2017. The model was validated successfully for the prediction of the SUHI for another hot day in 2016. For example, the transformation of a chosen area of 161 ha (1.61 km²) from vegetation to built-up between two years, 2016 and 2017, can result in enhanced thermal contrast by 3.3 °C. The function of the vegetation to lower the LST in a hot environment is evident. The results of this study suggest that the newly developed model provides an opportunity for urban planners and designers to develop measures for adjusting the LST, and for mitigating the consequent effects of UHIs by managing the land use composition and percentage coverage of the individual land-use type.

This article summarizes the results of research on the possible reactivation of the fault system in the Earth’s crust of the South China Sea with likely dangerous consequences for the coastal area of Vietnam. The research was carried out over several years with the publication of interim results. The solution to this problem required the determination of the regional stress field in the Earth’s crust. Analysis of the focal mechanisms of local earthquakes, as well as the structural characteristics of faults obtained by gravity and seismic data was used. The possibility of renewal of fault activity was determined by the inversed-stress method in the calculated regional stress field. The parameters of the present-day stress field were used to estimate the required slip force along the pre-existing faults. The possibility of horizontal and vertical structural (block) displacements in the Earth’s crust of the study area was calculated to assess the probability of reactivation of the entire system of faults. Based on a comprehensive analysis of the data, a forecast of the probability of reactivation of the fault system in the South China Sea has been made. This could be the cause of earthquakes, underwater landslides, and other dangerous natural processes in the coastal area of Vietnam.

Marine debris is a prevalent problem that affects oceans and coastal regions worldwide, particularly beaches. The problem of marine litter pollution is also severe on beaches in Nha Trang. In this study, marine debris with a size ≥ 5 mm was collected at seven locations along the coastline of Nha Trang during both dry and rainy seasons, accruing a total of 4436 items. During the rainy season, most beaches had more debris than that in the dry season, and marine debris density ranged between 0.009 items/m2 to 0.418 items/m2. Results from the beach cleanliness index (CCI) assessment showed that CCI values ranged from 0.2 to 4.4 during the dry season, with beaches classified as either very clean or clean. Meanwhile, during the rainy season, CCI values ranged from 0.36 to 8.35, resulting in beaches being categorized as very clean, clean, or average. The Plastic Abundance Index (PAI) showed that the PAI ranged from 0.004 to 0.061 during the dry season, while during the rainy season, it ranged from 0.006 to 0.118. PAI values for both seasons indicated low levels of plastic debris distribution on the beaches. However, local authorities and managers need to pay attention to potential sources of pollution, such as waste from food service activities in restaurants, ports and unsustainable waste from aquaculture activities.

Accretion and erosion processes recorded in the estuary of Cua Dai, Quang Nam province from 2014 to present have directly affected the issues of flooding drainage system, waterway traffic, aquaculture and seafood exploitation services. These have been drawing special attentions of national and international scientists. So far, several solutions are implemented to overcome these problems such as concreted embankments or dredging operations of the channel to open the sea. The solutions, however, are just temporary to solve immediate situations but not long-term. As a result of passive solutions, the shoreline is still seriously eroded and then the estuary of Cua Dai is re-accreted. Annually, Vietnam government and local offices still spend a large budget and time for recovering and minimizing the effects of such catastrophes without long-term effectiveness. One of the main causes of erosion and accretion of the Cua Dai estuary is hydrodynamic factors and the complex of sediment transportation. The results show that the northeast waves with high frequency and intensity in combination with floods during the Northeast monsoon are considered to be main causes. The accretion of estuary and formation of “Dinosaur island” in front of Cua Dai estuary is partly due to the combined sediment sources caused by the nearshore currents of northeast waves from the north direction and from the river by floods, especially the historical flood event in November, 2017.

Along with storms, tides,... human activities have also affected the erosion - accretion process of the coast and estuaries. When global climate change increases the risk of shoreline change in a negative manner, monitoring and quick assessment of this change is of great importance. Google has developed a cloud computing platform, called Google Earth Engine, to effectively address the challenges of big data analysis. This study aims at exploiting and processing multi-temporal satellite images of the Google Earth Engine platform (GEE), combined with topographic data since 1965 to monitor changes in estuary and shoreline of the coastal area of Cua Dai, Tra Khuc river, Quang Nam province during a period of 1965–2021. The analysis results show shoreline changes and hot spots of erosion and landslides along the coast, on both sides of Cua Dai river. After 56 years, the process of erosion - accretion in the river occurs strongly. The eroded riverbanks are located mainly along alluvial plains away from residential areas. Meanwhile, the coast along Cua Dai estuary changes in favor of accretion. However, in recent years, local erosion still occurs in some coastal areas with a length of 0.7–1.2 km in the territory of Pho An - Tan My villages (Nghia An commune). The study shows the potential for directly exploiting and processing large amounts of free satellite image on the GEE for resource monitoring and management applications.