Coastal groundwater is a vital freshwater source threatened by overabstraction and sea-level rise, yet global patterns of declining groundwater levels and susceptibility to seawater intrusion (SWI) remain poorly constrained. Here we present a global assessment based on in situ observations from ~480,000 coastal monitoring locations. From 1990 to 2024, 21% of gridded coastal areas show statistically detectable rising or falling groundwater-level trends with magnitudes ≥0.1 m yr−1 and with declines becoming more frequent in the last 9 years. More pronounced changes are observed for deeper water tables (ρs = 0.63), in arid settings (ρs = 0.56) and in some rural areas. Seawater intrusion susceptibility is higher where seaward freshwater discharge is weak or where hydraulic gradients reverse landward, leaving limited hydraulic resistance to seawater intrusion. Extrapolating observed trends suggests that these conditions mostly persist (93.4%), while 3.5% newly emerge and 3.1% stabilize (gradients strengthen seaward). The results provide global evidence for prioritizing monitoring and management of coastal groundwater at risk of salinization.
Nolte A., Bender S., Hartmann J., Baltruschat S., Moosdorf N. and Reinecke R. (2026) Coastal groundwater-level trends reveal global susceptibility to seawater intrusion. Nature Water. 10.1038/s44221-026-00619-8
@article{Nolte2026,
Title = {Coastal groundwater-level trends reveal global susceptibility to seawater intrusion},
Author = {Nolte, Annika and Bender, Steffen and Hartmann, Jens and Baltruschat, Stefan and Moosdorf, Nils and Reinecke, Robert},
Editor = {},
Journal = {Nature Water},
Year = {2026},
Doi = {10.1038/s44221-026-00619-8},
Abstract = {Coastal groundwater is a vital freshwater source threatened by overabstraction and sea-level rise, yet global patterns of declining groundwater levels and susceptibility to seawater intrusion (SWI) remain poorly constrained. Here we present a global assessment based on in situ observations from ~480,000 coastal monitoring locations. From 1990 to 2024, 21% of gridded coastal areas show statistically detectable rising or falling groundwater-level trends with magnitudes ≥0.1 m yr−1 and with declines becoming more frequent in the last 9 years. More pronounced changes are observed for deeper water tables (ρs = 0.63), in arid settings (ρs = 0.56) and in some rural areas. Seawater intrusion susceptibility is higher where seaward freshwater discharge is weak or where hydraulic gradients reverse landward, leaving limited hydraulic resistance to seawater intrusion. Extrapolating observed trends suggests that these conditions mostly persist (93.4%), while 3.5% newly emerge and 3.1% stabilize (gradients strengthen seaward). The results provide global evidence for prioritizing monitoring and management of coastal groundwater at risk of salinization.},
}
TY - JOUR
AU - Nolte, Annika
AU - Bender, Steffen
AU - Hartmann, Jens
AU - Baltruschat, Stefan
AU - Moosdorf, Nils
AU - Reinecke, Robert
TI - Coastal groundwater-level trends reveal global susceptibility to seawater intrusion
T2 - Nature Water
PY - 2026
DO - 10.1038/s44221-026-00619-8
AB - Coastal groundwater is a vital freshwater source threatened by overabstraction and sea-level rise, yet global patterns of declining groundwater levels and susceptibility to seawater intrusion (SWI) remain poorly constrained. Here we present a global assessment based on in situ observations from ~480,000 coastal monitoring locations. From 1990 to 2024, 21% of gridded coastal areas show statistically detectable rising or falling groundwater-level trends with magnitudes ≥0.1 m yr−1 and with declines becoming more frequent in the last 9 years. More pronounced changes are observed for deeper water tables (ρs = 0.63), in arid settings (ρs = 0.56) and in some rural areas. Seawater intrusion susceptibility is higher where seaward freshwater discharge is weak or where hydraulic gradients reverse landward, leaving limited hydraulic resistance to seawater intrusion. Extrapolating observed trends suggests that these conditions mostly persist (93.4%), while 3.5% newly emerge and 3.1% stabilize (gradients strengthen seaward). The results provide global evidence for prioritizing monitoring and management of coastal groundwater at risk of salinization.
ER -
