Impacts and adaptive measures for groundwater use in the Mekong delta. case study : Tra Vinh province

Because of the rapid growth of population and fast economic development in the Vietnamese Mekong Delta (VMD), the surface water resources are unable to meet these demands and groundwater is also over-abstracted.  Groundwater depletion and saline water intrusion become the main problems that threaten drinking water supplies, farming systems, and livelihoods in the delta, especially coastal areas. It is necessary to provide a fully comprehensive picture of groundwater use (GWU) and its impact issues In Tra Vinh Province, a coastal province of VMD, dependency on GW increases from north to south which has a strong relation with availability of freshwater in major rivers during the dry season. In the dry season 2018,  GWU was estimated to be 346,279 m3day-1 based on the field survey data;  approximately 52 % of this use is for agricultural activities. Land surface temperature sensing technology is proved to be a good tool for interpolating distribution of GWU. In Tra Vinh Province for better GW management. The GW system in the study area has moved from a pristine system to a developed system then become a depleted system at present. Thus, the existing status of groundwater resources is unsustainable due to increasing of 25 years of GWU. The concept for sustainable yields in both quantity and quality, in the long run, has been introduced and proved to be beneficial by determining equilibrium state and controlling saline GW movement. The results of the sustainable models indicate that the current GWU (2018) needs to be reduced by 49 % to match with the sustainable yield of the aquifer system in Tra Vinh Province. In order to propose adaptive measures for sustainable GWU, a new land use structure of the Mekong Delta Plan is considered as a suitable measure to reduce a high proportion of GW demand in Tra Vinh Province. Adaptive behavior models (ABM) are developed based on Fogg Theories to understand behavior of local farmers in term of changing agricultural activities to cope with the effect of climate change.  ABM can help to clarify additional recommendations to enhance the successful implementation of the Mekong Delta Plan by adding more incentive and resources suited to each specific farmers and zones.