Deltas are among the most productive and diverse global ecosystems. However, these regions are highly vulnerable to natural disasters and climate change. Nature-based solutions (Nbs) have been increasingly adopted in many deltas to improve their resilience. Among decision support tools, assessment of ecosystem services (ES) through spatially explicit modelling plays an important role in advocating for Nbs. This study explores the use of the Land Utilisation and Capability Indicator (LUCI) model, a high-resolution model originally developed in temperate hill country regions, to map changes in multiple ecosystem services (ES), along with their synergies and trade-offs, between 2010 and 2018 in the Vietnamese Mekong Delta (VMD). In so doing, this study contributes to the current knowledge in at least two aspects: high-resolution ES modelling in the VMD, and the combination of ES biophysical and economic values within the VMD to support Nbs implementation. To date, this is the highest resolution (5 by 5 m) ES modelling study ever conducted in the VMD, with ~1500 million elements generated per ES. In the process of trialling implementations of LUCI within the VMD’s unique environmental conditions and data contexts, we identify and suggest potential model enhancements to make the LUCI model more applicable to the VMD as well as other tropical deltaic regions. LUCI generated informative results in much of the VMD for the selected ES (flood mitigation, agriculture/aquaculture productivity, and climate regulation), but challenges arose around its application to a new agro-hydrological regime. To address these challenges, parameterising LUCI and reconceptualising some of the model’s mechanisms to specifically account for the productivity and flood mitigation capability of water-tolerant crops as well as flooding processes of deltaic regions will improve future ES modelling in tropical deltaic areas. The ES maps showed the spatial heterogeneity of ES across the VMD. Next, to at least somewhat account for the economic drivers which need to be considered alongside biophysical valuations for practical implementations of ES maps for nature-based solutions (Nbs) in the upstream VMD, economic values were assigned to different parcels using a benefit transfer approach. The spatially explicit ES economic value maps can inform the design of financing incentives for Nbs. The results and related work can be used to support the establishment of Nbs that ultimately contribute to the security of local farmers’ livelihoods and the sustainability of the VMD.

Information on soil hydraulic properties (e.g. soil moisture pressure relationships and hydraulic conductivity) is valuable for a wide range of disciplines including hydrology, ecology, environmental management and agriculture. However, this information is often not readily available as direct measurements are costly and time-consuming. Furthermore, as more complex representations of soils are being built into environmental models, users and developers often require sound hydraulic property information, while having limited access to specialist knowledge. Although indirect methods have been developed to obtain soil hydraulic properties from easily measurable or readily available soil properties via pedo-transfer functions (PTFs), few articles provide guidance for obtaining soil hydraulic properties over a wide range of geoclimatic and regional data availability contexts. The aim of this study is, therefore, to develop guidelines and an associated spatially referenced toolbox, NB_PTFs, to speed the process of acquiring sensible soil hydraulic properties for different geoclimatic and data-rich/sparse regions. The guide compiles available information about soil hydraulic properties, as well as a large number (151) of PTFs, not collated in any other guidance to date. NB_PTFs is an open-source ArcGIS toolbox which allows users to quickly get values, graphs and spatial distributions of soil hydraulic properties. The soil hydraulic properties, obtained using the guide and the toolbox, can be used as inputs for various models amongst other purposes. To demonstrate the use of the guidelines and the toolbox in different geoclimatic and data-availability contexts, the paper presents two case studies: the Vietnamese Mekong Delta and New Zealand Hurunui catchment. The Vietnamese Mekong Delta shows the use of these guidelines in a tropical, flat location with limited information on soil physical, chemical and hydraulic properties. The Hurunui catchment represents a case study for a semi-arid and hilly area in an area with detailed soil information.

In the mitigation strategies of climate change, improving soil carbon storage is considered as one of the main tasks to enhance agricultural sustainability and sequester atmospheric carbon dioxide. Agricultural patterns have been changing significantly and causing many impacts on soil organic carbon (SOC) storage in the upper Vietnamese Mekong Delta (VMD). Therefore, this study aims to evaluate how typical agricultural pattern changes are affecting SOC by estimating the SOC stock and identifying the correlation with soil physic-chemical properties. Soil samples were collected in both depths of 0-20 cm and 20-50 cm and analyzed physic-chemical properties such as soil texture, bulk density, pHKCl, EC and SOC. In topsoil layers, the SOC stock of the wetland forest was the highest in the opened depression of floodplain (24.42±1.38 kg C m-2; p<0.05) while that of paddy rice was the richest at depth of 20-50 cm (27.69±2.97 kg C m-2; p<0.05). In other agro-ecological areas, SOC stock in croplands was lower than forest and grassland in topsoil layer, especially in mountainous areas. SOC stock correlated positively with SOC content, clay, bulk density, and EC (p<0.05) but had a negative correlation with sand and pHKCl (p<0.05). The decrease in SOC stock in dry cultivating patterns indicated the impact of agricultural management practices and soil fertility on SOC storage. Thus, improving SOC stock is needed to maintain sustainable soil management. That can be done by increasing C input and decreasing C loss in the atmosphere.