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Impact of Global Warming‐Induced Sea‐Surface Salt Concentration Changes on Island Groundwater System

Year: 2026
Type: article
Abstract: Global warming is altering sea‐surface salt concentration (SSC) through intensified evaporation, shifted precipitation patterns, and accelerated melting of polar ice. Subsurface freshwater in oceanic islands is typically shaped like a thin lens due to limited land area and recharge, often the primary freshwater source for local communities and highly vulnerable to seawater intrusion (SWI). However, the effects of SSC changes on freshwater lens (FWL) and SWI extent in island aquifers remain unknown, and there is little knowledge on how hydraulic conductivity (HK), local aquifer recharge (RCH) and island width ( L ) affect these effects. To end this, this study employs a simplified two‐dimensional, variable‐density island groundwater simulation model to investigate how SSC affects FWL and SWI extent across seven distinct hydrogeological scenarios, using six quantitative indicators: relative changes in (a) average water table elevation (WTE), (b) maximum WTE, (c) FWL depth, (d) FWL thickness, (e) fresh groundwater volume, (f) aquifer salt mass. Simulation results demonstrate that rising SSC increases aquifer salt mass and elevates WTE while shrinking FWL (reducing its depth, thickness, and freshwater volume), as enhanced freshwater‐saltwater density contrasts drive more vertical flow pushing FWL upward. Island aquifers with higher HK, lower RCH, or smaller L show minimal changes in WTE and aquifer salt mass but are more sensitive to SSC changes in terms of FWL depth, thickness and fresh groundwater volume. Moreover, WTE and FWL characteristics show greater sensitivity to SSC declines than to SSC increases.
DOI: 10.1029/2025wr042036
Language: English
Open Access status: gold
Estimated APC paid: $3,000
OpenAlex ID: W7222705023
FWCI:
Cites: 34
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Related to: 10