For the EO support project, the main requirements were related to land use and spatial planning for future city expansion as well as climate change resilient urban infrastructure design. Hence, elements from all the above mentioned service components were covered, with a focus on urban extent and development (urban physiognomy) as well as urban land cover (urban structure and function) and various sector-specific products in relation to the exposure of these coastal cities to flooding, sea level rise, erosion and saline intrusion.

 

Urban baseline assessment and change mapping

 

This service provided very high-resolution baseline urban information, including the delineation of different urban areas, housing types and urban land cover. This is required to support assessment of the distribution of different demand areas for access to water, waste water treatment and solid waste management as well as to estimate risk levels linked to climate change related coastal flooding.

 

An important component of the service was the urban change mapping, which supports analysis of current trends in the development of the identified secondary cities in order to analyse intensification of agriculture, expansion of industrial areas and informal settlement areas as well as assessment of contamination in surrounding estuary regions.

 

For each of Dong Hoi and Hoi An, the product suite in this service included:

• Urban land cover / land use for 2014, based on Pléiades imagery,

• Soil cover for 2014,

• Coastal risk assessment: inland flooding potential, sea level rise (SLR), coastal erosion potential,

• Risk of saline intrusion to groundwater, and

• Urban land cover change for the years 2002–2006–2014.

 

Statistical analysis of the derived data underpins the slight continuous urbanisation between 2002 to 2014 in both Dong Hoi and Hoi An. A total of 182 ha and 246 ha were newly developed with urban land use in the two cities, respectively. In both cities, depending on the hazard under evaluation, significant parts of the urban environment are exposed. Especially the very high-resolution land cover and change mapping would benefit from in-situ data to additionally improve the differentiation of urban land use classes . For the modelling of the risk of saline intrusion to groundwater local measurements of salinity and water levels were used, since it is not possible to directly map groundwater salinity from satellite data.

 

Coastal bathymetry mapping

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Changes in bathymetry will impact the dynamics of coastal current systems and the propagation of ocean swell into shallow waters which in turn will impact on the risk of coastal flooding. By combining recent satellite-derived shallow water bathymetry with previously acquired conventional bathymetric information, changes in bathymetry can be analysed and areas of highest risk identified for remediation work.

 

The service provided information on water depth for shallow water areas, derived from WorldView-2 imagery. Depending on conditions, high-resolution maps can be derived with water depths down to approximately 10 m for coastal areas in Viet Nam. High resolution bathymetry could not be produced at any of the two study areas due to a combination of high sediment concentrations and sun glints. To exemplify the method and resulting data, a similar area south at Dung Quat harbour was considered instead. In addition and where applicable, benthic habitat maps were also provided.

 

The product suite included:

• Benthic habitat maps for 1998–2006–2013,

• Shallow area maps for 1998–2006–2013,

• Medium-resolution coastal bathymetry map, and

• High-resolution coastal bathymetry map.

 

The differentiation of the defined habitat classes is in general difficult due to their spectral characteristics. For example, mangrove classification is based also on the knowledge of the most likely occurrence.

 

Coastal habitat change mapping

 

This service collected change information on coastal habitats such as mangroves, which are often a more effective protection for surrounding coastline areas than artificial barriers and man-made dykes. For the years 1998–2006–2013, the service included the following product suite for the extended areas of Dong Hoi and Hoi An:

• Coastal habitat change maps (coastal habitat conversion to agriculture or urban land use, as well as expansion of coastal habitats)

• Loss in vegetation cover,

• Changes in river boundaries, and

• Coastal erosion/deposition mapping.

 

The products are based on SPOT 2/5/6 imagery. The use of more homogenous input data (e.g. the recent Sentinel satellite series) with a better quality and consistency over time opens the possibility of constant and sustained habitat monitoring. The major period of change was after 2006 in both cities, leading to a significant loss of marshes, coastal vegetation and sand dunes. Around Dong Hoi, 198 ha of coastal habitats were converted to agriculture or urban land between 1998 and 2013. In Hoi An, the equivalent area is 789 ha. Inversely, a total of approximately 800 ha of gains in (semi-)natural coastal habitats was observed, including in the detriment of water-covered areas (coastal aggradation).

 

Impact and benefits

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In general, EO products are a key tool and a unique information source to support urban environment climate change activities. Land cover and land use information (including detailed urban classes, coastal bathymetry and habitats) derived from satellite data provide a standardised, reliable and costefficient view on the current situation and the changes that occur over time. This information is useful for the planning, monitoring and evaluation of urban and rural development activities as well as for disaster risk modelling. The delivered maps allow for a remote assessment of e.g. urban growth, areas affected by high potential of natural risks. They can be used by local staff in the field to locate and examine hotspots of change or risk. Controlling and verification are supported by providing an independent source of information. Such a repeatable, scalable and expandable EO-based product portfolio is therefore suited to support ADB projects at different scales and stages.