Comparing the distribution and development of Urban Green Spaces in the two Vietnamese delta cities Hanoi and Ho Chi Minh City

Promoting public access to Urban Green Spaces is a central objective in sustainable city planning. Urban Green Spaces can play a vital role in enhancing various aspects of public life, including human recreation, local climate regulation and rainwater infiltration. However, in most metropolitan areas, especially in developing countries and emerging economies, Urban Green Spaces face competition with strong economic interests leading to their deterioration over the last decades. Our study critically examines this assumption for two Vietnamese delta cities, namely Hanoi and Ho Chi Minh City. In particular, we use multi-spectral satellite imagery from the Sentinel-2 mission to create seasonal maps of the Normalized Difference Vegetation Index in order to estimate the local proportion of densely vegetated areas. By blending these maps with population data from the National Census of 2019, we determine the spatial distribution of Urban Green Spaces per capita in both cities and interpret these findings against the background of recent spatial planning efforts. Spanning seven dry seasons in total (Dec 2016 – Jan 2023), the satellite data furthermore allow us to compare the temporal development of Urban Green Spaces and tentatively extrapolate these trends into the near future. Our preliminary results suggest that districts with particularly high percentages of Urban Green Spaces in Hanoi generally encompass the historic city core, while the greenest districts of HCMC are located in the newly established city-within-city Thu Duc east of the Saigon River. Moreover, the Urban Green Space per capita in Hanoi is nearly twice as high as in Ho Chi Minh City amounting to 11.6 and 6.8 square meters, respectively. Judging from the NDVI time series, these figures seem relatively stable with variations in the order of 1 square kilometre per year. Yet, ongoing urbanization trends will put stress on both the proportion of Urban Green Spaces and the number of inhabitants benefitting. Even though the stability of the Normalized Difference Vegetation Index is subjected to atmospheric and climatic boundary conditions, we can report that measurement-inherent variations in our study only accounted for standard deviations below 0.1 at selected locations with constant land cover. Consequently, the applied methodology is considered a valid instrument for documenting spatial distributions and temporal developments in order to support and advocate the advantages of Urban Green Spaces in future spatial planning.