In coral islands, groundwater is a crucial
freshwater resource for terrestrial life, including human
water supply. Response of the freshwater lens to
expected climate changes and subsequent vegetation
alterations is quantified for Grande Glorieuse, a lowlying
coral island in the Western Indian Ocean.
Distributed models of recharge, evapotranspiration and
saltwater phytotoxicity are integrated into a variabledensity
groundwater model to simulate the evolution of
groundwater salinity. Model results are assessed against
field observations including groundwater and geophysical
measurements. Simulations show the major control
currently exerted by the vegetation with regards to the
lens morphology and the high sensitivity of the lens to
climate alterations, impacting both quantity and salinity.
Long-term changes in mean sea level and climatic
conditions (rainfall and evapotranspiration) are predicted
to be responsible for an average increase in
salinity approaching 140 % (+8 kg m−3) when
combined. In low-lying areas with high vegetation
density, these changes top +300 % (+10 kg m−3).
However, due to salinity increase and its phytotoxicity,
it is shown that a corollary drop in vegetation activity
can buffer the alteration of fresh groundwater. This
illustrates the importance of accounting for vegetation
dynamics to study groundwater in coral islands