Abstract
This study assesses the future groundwater supply of a large coral island, Gan Island, Republic of Maldives, under influences of rainfall patterns, sea level rise, and population growth. The method described in this paper can be used to estimate the future groundwater supply of other coral islands. Gan is the largest inhabited island (598 ha) of the Republic of Maldives with a population of approximately 4500. An accurate estimate of groundwater supply in the coming decades is important for island water security measures. To quantify future groundwater volumes in Gan, a three-dimensional, density-dependent groundwater and solute transport model was created using the SUTRA (Saturated Unsaturated Transport) modeling code. The Gan model was tested against observed groundwater salinity concentrations and then run for the 2012–2050 period to compare scenarios of future rainfall (from General Circulation Models), varying rates of population growth (i.e., groundwater pumping), and sea level rise. Results indicate that the total fresh groundwater volume increases approximately 20% if only future rainfall patterns are considered. If moderate pumping is included (2% annual population growth rate), the volume increases only by 13%; with aggressive pumping (9% annual population growth rate), the volume decreases by 24%. Sea level rise and associated shoreline recession leads to an additional 15–20% decrease in lens thickness and lens volume. Results can be used to make decisions about water resource management on Gan and other large coral islands in the Indian and Pacific Oceans. Methods used herein can be applied to any coral island to explore future groundwater security.
Highlights
Groundwater in oceanic coral islands often is a principal water source for residents, used for sanitary cleansing, toilet flushing, bathing, and clothes washing
The objective of this study is to present a modeling method for estimating the future groundwater supply of coral islands under the effect of climate change and population growth
Groundwater flow and salt transport model was used to simulate the development and response of the island’s freshwater lens to future rainfall patterns, future groundwater pumping rates corresponding to population growth, and sea level rise, which results in shoreline recession and a smaller island surface area
Summary
Groundwater in oceanic coral islands often is a principal water source for residents, used for sanitary cleansing, toilet flushing, bathing, and clothes washing. Total water usages for coral island communities range from 50 to 175 L/person/day [1,2], of which only 5–10 L is from rain catchment systems [3]. Communities on oceanic coral islands are some of the most vulnerable worldwide in terms of freshwater scarcity and the depletion of water resources due to small island surface areas, low elevations, geographic remoteness, and expected changes in climate, population, and land use [5,6,7,8]. Less vulnerable to drought than rainwater catchment systems, which can become depleted in a matter of weeks during extreme drought, groundwater is still under continual threat from natural and anthropogenic stresses.
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