Groundwater Modelling in southeast Cambodia - Facing irrigation and groundwater level changes during a pandemic

Abstract: In the Mekong region, sustainable water resource management is a significant challenge for all countries involved. In Cambodia, where rice production is crucial for household food security and export, groundwater is increasingly used for irrigation during the dry season, leading to higher rice yields. However, this unplanned and unregulated use of groundwater is causing depleting groundwater levels in the region. Economic challenges and pandemic restrictions have likely changed irrigation patterns, affecting groundwater storage. To investigate the impact of changing irrigation patterns on groundwater levels during the pandemic a groundwater model using GMS MODFLOW was established, initially creating a steady-state model and then transitioning to a transient-state model, where evapotranspiration (ET) should be used as an indicator of groundwater irrigation. Furthermore, input data to the model were collected during field visits in Cambodia. The calibrated models performed well, but automated parameter estimation faced computational issues. Analysis showed increased groundwater decline during the pandemic. Data limitations and simplifications were acknowledged, suggesting a need for better data and model enhancements for accurate groundwater modelling and sustainable water management.