Closing the irrigation deficit in Cambodia: Implications for transboundary impacts on groundwater and Mekong River flow

•>95% of rice-cultivated land in Cambodia is fallowed during the dry season.•Full dry season irrigation would require up to 31% of Mekong River flow to Vietnam.•Groundwater-irrigated land is increasing by ∼10% per year in Cambodian Mekong Delta.•Groundwater over-extraction threatens domestic suction pump wells for >1.5million.•Projected groundwater overdraft extends into neighboring Vietnam.