Ecosystem-based adaptations for sustainable groundwater resources management in the Transboundary Cambodia-Vietnam Mekong Delta Aquifer, Lower Mekong region

Water is essential for many human activities, including agriculture, industry, and many more. In the transboundary Cambodia-Vietnam Mekong Delta Aquifer (TCVA), groundwater is a major supply of water. As a result, the groundwater table is steadily dropping. Therefore, it is important to conserve groundwater, and Ecosystem-based Adaptation (EbA) appears to be a promising method for doing so on a local level. The provinces of Siem Reap Province in Cambodia and Tra Vinh Province in Vietnam were chosen as study areas. The objective of this study is to assess EbA to lessen the effect of stressors on groundwater. In this study, firstly, non-parametric statistical tests were conducted on (12 observation well data from 2015-2021 in Siem Reap Province and 13 observations well data from 1994-2018 with 13 observations well in Tra Vinh Province with monthly time steps) to identify the current status of groundwater and community for a survey to be conducted. Secondly, surveys were conducted in 2 district of Siem Reap Province and 5 districts of Tra Vinh Province and around 200 households each were interviewed in both study areas to identify the potential stressors on groundwater and people’s willingness to accept EbA. Thirdly, land use maps from 2017 to 2021 on both study area and various literatures paper were reviewed to correlate with the survey data. Lastly, GMS MODFLOW software was used to develop the groundwater model of both study areas.70% of the observation groundwater level data were used to calibrate, and 30% of the data were used to validate the model in a transient state. These models were applied to evaluate the impact of the stressor and the various EbA measures to mitigate the impact in the study area. For the years of 2015-2021 of Siem Reap Province and from 1994 to 2018 of Tra Vinh Province, we discover that the province's groundwater has been declining at a rate of 32.8cm/year and 27.8 cm/year respectively. According to an analysis of the survey results and the land use map, In Siem Reap Province the urban area has grown by 62%, the agricultural sector by 94% and the drought in 2019 further increased groundwater resource exploitation whereas in case of Tra Vinh Province urban areas grew by 36%, while agricultural areas shrank by 13%.In both the study area, urbanization and agriculture are the two main anthropogenic stressors on groundwater, along with variations in rainfall as a natural stressor. According to the groundwater model of Siem Reap Province, the groundwater level decline rate in agricultural and nearby forest zones is about 38 cm/year and 52.56 cm/year respectively whereas of Tra Vinh Province the upper middle Pleistocene and middle Pleistocene had substantial groundwater level loss, with rates of groundwater decline of roughly 31 cm/year and 45 cm/year, respectively. Finally, it might be advised to safeguard riparian areas, ecosystems that depend on groundwater, and crucial recharge zones to efficiently manage groundwater resources based on analyzing the various EbA scenarios.

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