Variations in land surface temperatures in small-scale urban areas in Vietnam during Covid-19 restrictions: Case studies from Da Nang, Hue and Vinh City.

Land surface temperature (LST) is an important variable in urban microclimate research. At the end of 2019, the emergence of Covid-19 pandemic has changed the world in a manner that forced many countries to impose restrictions in human activities. As a measure to prevent the expansion of Covid-19 infections, most of the major cities have entered a prolonged lockdown period and reduction in human activities between the early 2020 and the late 2021. These restrictions were strict in most of the cities in Southeast Asia, particularly in Vietnam. The present study investigated the variations in LST and NDVI observed in three rapidly growing urban areas, namely Da Nang, Hue and Vinh, in Vietnam using Landsat-8 imagery acquired between 2017 and 2022. There has been a slight reduction in LST in the study sites, particularly in Da Nang City, during the lockdown period but not as high as observed in recently conducted studies from big metropolitan cities, including in Vietnam. It is also observed that LST estimated from built-up areas and other impervious surfaces remained relatively stable during the study period which is similar to the results from recent studies.

Anthropogenic influences on coastal environmental changes in the Mekong Delta: a study from Ben Tre Province, Southern Vietnam.

Low-lying coastal environments are highly dynamic and sensitive to natural as well as anthropogenic perturbations. Climate change, sea level rise, storms and tsunamis are the natural phenomena that affect the deltaic coasts in Southeast Asia in general and Vietnam in particular. The effects of these phenomena can be exacerbated by human activities such as mangrove deforestation, aquaculture and infrastructure development. Conversely, the low-lying coastal areas are important in the economic development of Southeast Asian countries. In the Vietnamese Mekong Delta, coastal areas have been affected by a number of factors, such as climate change, sea level rise, aquaculture, pollution and tourism-related activities in recent decades. The present study investigated shoreline changes, expansion of aquaculture ponds, soil salinity changes and salinity intrusion in the river systems along the coastal areas of Ben Tre Province in the Vietnamese Mekong Delta between 1998 and 2020 using satellite imagery and field data. Variations in erosion and accretion were found to be not unique along the coast of Ben Tre. There was a rapid expansion of aquaculture ponds between 1998 and 2015 and a slight decline since then. Soil salinity has been increased between 1998 and 2020; it is seen from recent satellite data that soil is becoming more saline in the inland areas of Ben Tre. Saltwater intrusion into the rivers of Ben Tre is considered associated with El Niño-La Niña conditions. It is suggested that reforestation of abandoned shrimp ponds in Ben Tre by mangrove vegetation can be effective as a bioshield against coastal hazards, such as sea level rise and shoreline erosion.

Did the Covid-19 restrictions influence land surface temperatures in Southeast Asia? A study from Ho Chi Minh City, Vietnam.

There have been a prolonged lockdown period and reduction in human activities in most of the major cities in the world during the Covid-19 pandemic period between the early 2020 and the late 2021. Such a reduction in human activities was believed to have influenced pollution levels and land surface temperatures (LST) in urban areas. This paper describes the variations in LSTs before, during and after the Covid-19 lockdown in Ho Chi Minh City in southern Vietnam, which is the economic hub of the country. For this purpose, Landsat-8 OLI and TIRS images acquired between 2015 and 2022 were used. It is observed that there was a significant reduction of 1 to 1.8 °C in LST in open areas, excepting impervious surfaces and built-up areas, during the strict lockdown period in Ho Chi Minh City, and an increase in LST since then. The observed reduction in LST during the lockdown period in Ho Chi Minh City is in agreement with the reduction in greenhouses gases during the same period in recent studies. Human mobility and industrial activities have been restored in November 2021 in the study area which would explain the regain in LST in the post-lockdown period.