Global Impact of Sea Level Rise on Coastal Fresh Groundwater Resources

Groundwater is the main freshwater source in many densely populated and industrialized coastal areas around the world. Growing future freshwater demand is likely to increase the water stress in these coastal areas, possibly leading to groundwater overexploitation and salinization. This situation will likely be aggravated by climate change and the associated projected sea level rise. Here, we assess the impact of sea level rise exclusively on coastal fresh groundwater resources worldwide (limited to areas with unconsolidated sedimentary systems) by estimating future decline in inland fresh groundwater volumes under three sea level rise scenarios following Representative Concentration Pathway (RCP) 2.6, 4.5, and 8.5. For that, 2D groundwater models in 1,200 coastal regions estimate the past, present and future groundwater salinity. Our results show that roughly 60 (range 16-96) million people living within 10 km from current coastline could lose more than 5% of their fresh groundwater resources by 2100 according to RCP 8.5 scenario compared to only 8 (range 0-50) million people based on RCP 2.6 scenario. We conclude that sea level rise will have severe consequences for many coastal populations heavily dependent on fresh groundwater. Sea level rise predictions for the upcoming centuries show that large strips of current coastal regions can be directly flooded. However, an often overlooked and hidden threat linked to sea level rise is the salinization of groundwater in those affected coastal regions. This can be caused by either direct lateral infiltration of saline water into the subsurface as well as by changes in groundwater pressure balance. Our modeling results show that different sea level rise magnitudes, based on future climate change scenarios, can lead to severe declines in fresh groundwater volumes in various coastal regions worldwide. Sea level rise under Representative Concentration Pathway (RCP) 8.5 scenario will severely impact fresh groundwater availability in low lying coastal regionsCoastal areas with more than 5% loss of fresh groundwater by 2100 harbor around 60 million people and represent a collective gross domestic product of hundreds of billion USDOur results are globally indicative but comparison with local studies show that uncertainties are high