Article

Evaluating the Fate of Freshwater Lenses on Atoll Islands After Eustatic Sea-Level Rise and Cyclone-Driven Inundation: A Modelling Approach

May 2012
Global and Planetary Change 88-89:76-84

DOI:10.1016/j.gloplacha.2012.03.008

Authors:

James P. Terry

Zayed University

Ting Fong May Chui

The University of Hong Kong

Dispersed human populations inhabiting remote atolls across the tropical Pacific Ocean are reliant on the viability of thin freshwater lenses (FWLs) contained within the island coralline sediments for their survival. Yet FWLs are uniquely fragile and easily damaged by saline intrusion. Eustatic sea-level rise (SLR) and sea flooding generated by intense tropical cyclones therefore pose special perils for continued existence on atolls. In this work, mathematical modelling is used to examine the effects on an atoll freshwater lens of various projected long-term SLR scenarios (10, 20, and 40 cm). A cyclone-driven wave washover event is then simulated in order to observe the responses and recovery of the FWL, subsequent to the SLR scenarios imposed. A key attribute of our model design is the inclusion of a topographic depression containing a low-lying fresh swamp in the atoll islet interior (which is often ignored), where seawater accumulates during inundation. Results indicate that a 40 cm SLR produces a major impact: the FWL decreases in thickness by approximately 50%, develops a brackish centre and contracts to a shrunken ‘doughnut’ morphology. Following cyclone inundation, observed salinity profiles are illuminating. Steep salinity gradients show how a strong saline plume forms at shallow depths, but also reveal the existence of an undisturbed fresh horizon beneath the salt plume under both present conditions and the modest 10 cm SLR scenario. Within the preserved fresh horizon, salt concentrations are maintained below 1.5 g/L (i.e. within usable limits) for at least a year. In contrast, the diminished freshwater lenses that exist after 20 and 40 cm SLR then exhibit far less resilience to saline damage over comparable post-cyclone timeframes. The findings point towards Pacific atolls becoming increasingly uninhabitable long before their complete submergence by sea-level rise, owing to irrecoverable groundwater salinisation seriously reducing the availability of freshwater.

Infrastructure Vulnerability to Disruption: A Particularly Pacific Problem

Chapter

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Apr 2024

Infrastructure and climate have important roles in driving the water-energy-food nexus in the Pacific region. The significance of infrastructure is woven throughout the United Nation’s 2030 Agenda for Sustainable Development, with Sustainable Development Goals relevant to infrastructure and its links to the water-energy-food nexus. Pacific Island Countries and Territories (PICTs) differ from larger developed neighbouring countries in Oceania such as Australia and New Zealand, bringing about a unique set of challenges for infrastructure. Physical characteristics include small, remote populations and small land masses, and susceptibility to natural hazards. Institutional challenges such as governance, small economies, and limited infrastructure expertise are prevalent. Yet, despite all these challenges, climate change is perhaps the largest. This chapter considers the interconnectivity of infrastructure and the water-energy-food nexus, and the importance of building climate resilience within the infrastructure sector reflected through the lens of three key infrastructure areas namely maritime transport, coastal protection, and Water, Sanitation and Hygiene (WaSH) infrastructure.

Coastal hazards and groundwater salinization on low coral islands.

Conference Paper

Apr 2016

Remote oceanic communities living on low-lying coral islands (atolls) without surface water rely for their survival on the continuing availability of fragile groundwater resources. These exist in the form of fresh groundwater lenses (FGLs) that develop naturally within the porous coral sand and gravel substrate. Coastal hazards such as inundation by high-energy waves driven by storms and continuing sea-level rise (SLR) are among the many possible threats to viable FGL size and quality on atolls. Yet, not much is known about the combined effects of wave washover during powerful storms and SLR on different sizes of coral island, nor conversely how island size influences lens resilience against damage. This study investigates FGL damage by salinization (and resilience) caused by such coastal hazards using a modelling approach. Numerical modelling is carried out to generate steady-state FGL configurations at three chosen island sizes (400, 600 and 800 m widths). Steady-state solutions reveal how FGL dimensions are related in a non-linear manner to coral island size, such that smaller islands develop much more restricted lenses than larger islands. A 40 cm SLR scenario is then imposed. This is followed by transient simulations to examine storm-induced wave washover and subsequent FGL responses to saline damage over a 1 year period. Smaller FGLs display greater potential for disturbance by SLR, while larger and more robust FGLs tend to show more resilience. Further results produce a somewhat counterintuitive finding: in the post-SLR condition, FGL vulnerability to washover salinization may actually be reduced, owing to the thinner layer of unsaturated substrate lying above the water table into which saline water can infiltrate during a storm event. Nonetheless, combined washover and SLR impacts imply overall that advancing groundwater salinization may lead to some coral islands becoming uninhabitable long before they are completely submerged by sea-level rise, thereby calling into question the sustainability of atoll communities that face recurrent coastal hazards.

Halophytes can salinize soil when competing with glycophytes, intensifying effects of sea level rise in coastal communities

Article

Full-text available

Jul 2017
OECOLOGIA

Sea level rise (SLR) and land-use change are working together to change coastal communities around the world. Along Florida's coast, SLR and large-scale drying are increasing groundwater salinity, resulting in halophytic (salt-tolerant) species colonizing glycophytic (salt-intolerant) communities. We hypothesized that halophytes can contribute to increased soil salinity as they move into glycophyte communities, making soils more saline than SLR or drying alone. We tested our hypothesis with a replacement-series greenhouse experiment with halophyte/glycophyte ratios of 0:4, 1:3, 2:2, 3:1, 4:0, mimicking halophyte movement into glycophyte communities. We subjected replicates to 0, 26, and 38‰ salinity for one, one, and three months, respectively, taking soil salinity and stomatal conductance measurements at the end of each treatment period. Our results showed that soil salinity increased as halophyte/glycophyte ratio increased. Either osmotic or ionic stress caused decreases in glycophyte biomass, resulting in less per-plant transpiration as compared to halophytes. At 38‰ groundwater, soil salinity increased as halophyte density increased, making conditions more conducive to further halophyte establishment. This study suggests that coastal plant community turnover may occur faster than would be predicted from SLR and anthropogenic disturbance alone.

Pitfalls of monetizing relational values in the context of climate change adaptation

Article

Full-text available

Nov 2024

Relational values emphasize the desirable characteristics of nature–society relationships. Unlike instrumental values, relational values have not yet been subjected to monetary quantification, although they may be relevant to environmental policymaking or climate change adaptation decisions which often rely on cost–benefit approximations. This paper explores the quantification of relational values within a contingent valuation scenario both in monetary (one-time donation) and non-monetary terms (Likert-scale, ranking) as well as using a measure that elicits the desired allocation of government budget for adaptation. We conduct two surveys within the context of adaptation projects, aiming to protect the traditional lifestyles of atoll islanders on the Solomon Islands and coastal communities in Bangladesh. In these surveys, we employ two valuation scenarios – one with explicit mention of relational value losses, and one without. Information on relational losses led to no increases in monetary or non-monetary valuation but to a slightly higher allocation of government budget in Bangladesh. We further assess and discuss the validity of our measures, also accounting for respondents’ financial situation. Our findings suggest that emphasizing relational losses could significantly increase disaster management funding in Bangladesh, with a potential 55% budget increase based on our treatment effect. We further discuss the difficulties in quantifying relational values in a context with limited ability to pay and the importance of considering deliberative approaches for ensuring that all dimensions of human-nature relationships are adequately considered in adaptation policy decision-making.

Emerging Issues for Small Island Developing States

Technical Report

Full-text available

May 2014

This report is the outcome of the UNEP-UN DESA foresight process on emerging issues for small island developing states (SIDS). It identifies 20 environmental and 15 socioeconomic emerging issues that should be addressed to ensure the sustainable development of the SIDS. The report recognized that many of the social and economic issues identified have strong environmental components and vice versa. Therefore, the report recommends that all issues should be viewed and addressed in a holistic and integrative manner.

Density-driven vertical transport of saltwater through the freshwater lens on the island of Baltrum (Germany) following the 1962 storm flood

Article

Feb 2017
J HYDROL

Due to the growing vulnerability of low-lying coastal zones to flooding by seawater, there is a current need for studies of the impact of such inundations on fresh groundwater resources. The knowledge from the literature is biased towards tropical atoll environments, and only few studies specifically investigated the effect of density-driven downward flow, even though its importance is widely acknowledged. The present study is based on previously unpublished hydrochemical data collected on the island of Baltrum following a devastating storm in 1962, which uniquely show the impact of seawater inundation on a freshwater lens in a siliciclastic aquifer. The field data show that about 3kg of Cl per m² of inundated land area, or 18cm of seawater, infiltrated, and that elevated salinities persisted at the measurement depths of 4 and 6m for at least 4years, and at least for 6years at greater depths. Numerical models support the assertion that the shape of the measured salinographs, i.e. an initial sharp rise in the salt concentration with time, followed by a continually-slowing decrease, must be attributed to density-driven salt fingering. Models that did not consider density effects fail to simulate the observed patterns. Transient recharge, model dimension and lateral flow modify the details of the simulation results, but in all models density-driven vertical flow dominates the overall system behaviour. The diminishing importance of density-driven flow at greater depths, however, in combination with slow recharge-driven flow rates prolongs flushing times, and enhances the risk of brackish-water up-coning when pumping is resumed too soon.

Emerging Issues for Small Island Developing States Results of the UNEP Foresight Process

Technical Report

Full-text available

Jun 2014

Emerging Issues for Small Island Developing States ISBN: 978-92-807-3391-4 Job Number: DEW/1804/NA Results of the UNEP Foresight Process

Storm surge, seawater flooding, and sea-level rise paradoxically drive fresh surface water expansion

Article

Full-text available

Nov 2024
ENVIRON RES LETT

Coastal storms and sea-level rise (SLR) are expected to increase seawater flooding in low-elevation coastal zones. High sea levels and seawater flooding can drive groundwater table rise via ocean-aquifer connections. These dynamics are often overlooked but can cause groundwater flooding and salinization hazards, increasing freshwater security challenges for coastal communities and driving ecosystem transgressions. Field data and numerical modeling were used to evaluate how heavy rainfall, storm surge, and seawater flooding and infiltration during Hurricane Fiona (September 2022) and projected SLR impact groundwater levels, inland surface waters, and saltwater intrusion on Sable Island National Park Reserve, Canada. During the passage of Hurricane Fiona, precipitation increased groundwater and pond levels before seawater flooded the beach. Seawater flooding and infiltration caused a sharp rise in beach groundwater levels, which in turn caused inland pond levels to rise without coincident direct inputs from precipitation or seawater. Model simulations reveal that seawater infiltration on beaches flooded the subsurface and drove the observed inland groundwater rise and freshwater pond expansion. Simulations of projected SLR show that seawater flooding will only inundate a small area of land along the coast; however, inland groundwater rise and flooding, which is less well-studied, may inundate up to 30 times more land area. Further, groundwater flooding driven by rising sea levels decreases hydraulic gradients and increases saltwater intrusion via freshwater lens (FWL) contraction. Findings demonstrate that seawater flooding from coastal storms and SLR paradoxically cause concurrent fresh surface water expansion but FWL contraction. This study provides new insights into the spatiotemporal dynamics of island freshwater resources and highlights that unseen and often overlooked groundwater-surface water exchanges are critical to consider when evaluating coastal flooding and groundwater salinization hazards and management strategies for low-elevation coastlines.

Noise‐tolerant matched filter scheme supplemented with neural dynamics algorithm for sea island extraction

Article

Full-text available

Mar 2024

Achieving high‐precision extraction of sea islands from high‐resolution satellite remote sensing images is crucial for effective resource development and sustainable management. Unfortunately, achieving such accuracy for sea island extraction presents significant challenges due to the presence of extensive background interference. A more widely applicable noise‐tolerant matched filter (NTMF) scheme is proposed for sea island extraction based on the MF scheme. The NTMF scheme effectively suppresses the background interference, leading to more accurate and robust sea island extraction. To further enhance the accuracy and robustness of the NTMF scheme, a neural dynamics algorithm is supplemented that adds an error integration feedback term to counter noise interference during internal computer operations in practical applications. Several comparative experiments were conducted on various remote sensing images of sea islands under different noisy working conditions to demonstrate the superiority of the proposed neural dynamics algorithm‐assisted NTMF scheme. These experiments confirm the advantages of using the NTMF scheme for sea island extraction with the assistance of neural dynamics algorithm.

Temporal dynamics of groundwater flooding on atolls caused by storm surge

Presentation

Aug 2023

Groundwater Flooding on Atolls Caused by Storm Surges: Effects of the Dual‐Aquifer Configuration

Article

Full-text available

Oct 2023
WATER RESOUR RES

Storm surges associated with tropical cyclones endanger atolls through groundwater flooding, wherein groundwater is discharged from the land surface at elevated sea levels. Atolls are characterised by a ‘dual‐aquifer’ configuration, where recent Holocene sediments unconformably overlie highly permeable Pleistocene limestone creating an interface called a ‘Thurber discontinuity.’ This study aimed to quantitatively analyse how the dual‐aquifer configuration of atolls controls the temporal dynamics of groundwater flooding caused by storm surges. To this end, we ran surface‐subsurface coupled synthetic numerical simulations using the HydroGeoSphere code and compared 12 scenarios with different Thurber discontinuity elevations and hydraulic conductivities of the Pleistocene aquifer ( K P ). The results showed that the shallower the Thurber discontinuity and the higher the K P , the higher the maximum water depth in the freshwater swamp on the atoll during the storm surge and the longer the flooding duration. Despite the effects of the different dual‐aquifer configurations, the initial water table elevation and salinity distribution were almost identical in all simulation cases. These findings suggest that accurate information on the dual‐aquifer configuration is necessary to evaluate the potential risk of groundwater flooding in atolls accompanying storm surges. Furthermore, the results indicate that groundwater flooding caused by storm surges substantially contributes to cyclone‐driven flooding on atolls, and hence, it should not be neglected in flood predictions to avoid underestimation. This article is protected by copyright. All rights reserved.

Coral reef island shoreline change and the dynamic response of the freshwater lens, Huvadhoo Atoll, Maldives

Article

Full-text available

Jun 2023

Low-lying coral reef islands have been projected to become uninhabitable by the end of the century due to sea level rise, but such projections of vulnerability assume that reef islands are static landforms that flood incrementally with sea level rise. In fact, GIS-based reef island shoreline analyses have demonstrated that reef islands are highly dynamic landforms that may adjust their shorelines in response to changing environmental conditions. However, the vast majority of reef island shoreline analyses have been undertaken in the Pacific Ocean, leaving our understanding of changes in the Indian Ocean more limited. Further, our knowledge of how island dynamics can impact groundwater resources is restricted due to the assumption that islands will exhibit purely erosional responses to sea level rise. Here, we analyse shoreline evolution on 49 reef islands over a 50-year timeframe in Huvadhoo Atoll, Maldives. Additionally, rates of shoreline change were used to undertake numerical modelling of shifts in freshwater lens volume in 2030, 2050 and 2100 in response to changes in recharge. Despite sea level rising at 4.24 mm/year (1969-2019), accretion was prevalent on 53% of islands, with the remaining islands eroding (25%) or remaining stable (22%). Average net shoreline movement was 4.13 m, ranging from -17.51 to 65.73 m; and the average rate of shoreline change (weighted linear regression) was 0.13 m/year, ranging from -0.07 to 2.65 m/year. The magnitudes and rates of reef island evolution were found to be highly site-specific, with island type found to be the only significant predictor of either net shoreline movement or weighted linear regression. Results suggest that freshwater lens volume was substantially impacted by shoreline change compared to changes in recharge whereby accretion and erosion led to large increases (up to 65.05%) decreases (up to -50.4%) in les volume, respectively. We suggest that the capacity of reef islands to both (1) adjust their shorelines, and even accrete, under conditions of sea level rise; and (2) increase their storage of groundwater over the coming decades represents highly valuable geomorphic ecosystem services.

Impact of flooding on microbiological contamination of domestic water sources: a longitudinal study in northern Ghana

Article

Full-text available

Sep 2022

Flooding is the most frequent natural hazard globally, but evidence of its impact on domestic water point contamination remains limited. This study aimed to assess dam-related flooding’s impact on microbiological contamination of rural water points and to evaluate agreement of satellite-derived flood maps with ground-based observations of water point flooding. Fieldwork took place in two Ghanaian districts frequently flooded following dam overspill. Fifty-seven water points were tested for bacterial parameters during and immediately after flooding. Forty water points were resampled in the dry season, with the remainder having run dry. Ground-based observations of flooding were compared with three satellite-derived flood maps. Boreholes were less contaminated than wells or surface waters (geometric mean E. coli = 20.2, 175.6, and 590.7 cfu/100 ml, respectively). Among groundwater points, a Wilcoxon signed-rank test indicated significantly greater median E. coli and thermotolerant coliform contamination during flooding ( p = 0.025 and p < 0.001, respectively), but Shigella, salmonella, and intestinal enterococci counts were not significantly different between seasons. In contrast, among surface water points, E. coli , Shigella, and Salmonella counts were significantly greater in dry season samples ( p < 0.005 for all parameters), possibly reflecting a “concentration” effect. Satellite-derived flood maps had no or low agreement with ground-based observations of water point flooding. Although groundwater quality deteriorated during and after flooding, surface waters were the most microbiologically contaminated in both seasons. The greatest public health risk thus occurred where households switched to surface water collection during or following flood season. Flood risk should be assessed before borehole installation and existing flood-prone boreholes remediated to mitigate population exposure to contaminated water.

Large Dataset Analysis to Identify Anthropogenic Shifts in Ecosystem Function for the Nearshore Environs of Small Carbonate Islands

Thesis

Full-text available

Aug 2022

Jacob Patus

The waters of the Florida Keys are naturally oligotrophic, however, discharge from the Everglades, anthropogenic changes to the coastline, and groundwater runoff from the carbonate islands contribute excess nutrients to the ecosystem. Eutrophication is acknowledged as a major threat to coastal ecosystems and successful efforts have been made to reduce direct anthropogenic nutrient pollution. The main driver of eutrophication is nutrient input; this study focuses on the nitrogen and phosphorous content of the water column. Eutrophication is also driven by hydrologic exchange, as the main method of transport of anthropogenic nutrients into the system is groundwater runoff. Chemical responses in the water column are indicated by reductions in dissolved oxygen saturation and pH. Benthic response to eutrophication is measured in this study by quantification of submerged aquatic vegetation (SAV) using Braun-Blanquet cover abundance (BBCA) surveys. The Florida Keys Residential Canal Project (2019-2021) was a rigorous water quality sampling project that included SAV surveys within thirteen study areas located across the Keys. The sampling strategy of the project was designed to capture ecological information across a range of shorelines with varying anthropogenic disturbances with quarterly water quality sampling and semiannual SAV surveys. The water quality feature space is reduced by principal component analysis and ordinated by uniform manifold approximation and projection. Gaussian mixed modeling identifies two clusters of points based on water quality characteristics. The clusters reflect opposing eutrophic states, with one cluster representing relatively good water quality and the other representing relatively poor conditions. Linear discriminant analysis is presented as a method by which the multi-dimensional eutrophic state of the water column can be expressed with a single metric. SAV data is summarized by calculating the mean BBCA score as well as transforming that data into relative taxon composition for each transect. The presence of the taxa is used as input for functional clustering of redundant components of systems to model the abundance of the functional groups found in the surveys. The redundant taxa generated by each model is aggregated into an adjacency matrix for the generation of a taxon network. The network structure is determined by maximizing the modularity of the minimum spanning tree of the network overall possible partitions to generate eight functionally redundant SAV taxon motifs. SAV communities are delineated by projecting bootstrap aggregated pairwise Goodman-Kruskal γ coefficient matrix between transects and identifying clusters with the density-based spatial clustering of applications with noise algorithm. A Thalassia testudinum dominated community, a mixed SAV community, and two macroalgae-dominated communities are recognized. Water quality parameters as a function of distance from the shore to show verify that the 500 m “halo zone” used to define the border between local and regional influences on the water column is sufficient. Residential canals can have two significantly different patterns of influence on the adjacent waters relative to the waters outside state parks: nutrient pollution and impacted water quality can proliferate from the canal mouth to the extent of the study area at moderate levels, or the zone immediately influenced by the canal mouth is highly impacted but recovers to state park equivalent levels of impact at the 500m boundary. Finally, the ecological relationship between measured water quality parameters and SAV abundance is examined using redundancy analysis (RDA). pH is identified as a strong indicator of the eutrophic state of the water column. The seagrass-dominated community stands out as occupying a separate space within the RDA results, with dynamics among the macroalgae taxa being primarily driven by nitrogen availability. Seagrasses drive a high variability in dissolved oxygen saturation resultant of variation in light availability. A macroalgal gradient exists that aligns with the degree of eutrophic stress imposed on the water column in the form of dissolved oxygen reduction and acidification with increased stratification of the water column. This gradient is representative of a qualitative succession that is observed across the study areas as a response to, or recovery from, eutrophication.

Chapter 15: Small Islands

Book

Full-text available

Feb 2022

The Economic Impact of Climate Change on the Agricultural System in Fiji

Article

Full-text available

Jan 2022

Mohammed Rasheed Igbal

Climate change is one of the most crucial challenges identified in this century for the Pacific Region, such as Fiji, Samoa, Solomon Islands and many more. Citizens of Fiji have gone through peculiarly climatic and weather conditions over the past years like globalization, which had led to many consequences, especially in the agricultural sector which is the main income of many livelihoods not only in Fiji but in other Pacific countries as well. Climatic conditions have been changing adversely from past decades, such as temperature, rise in the sea level, precipitation changes, atmospheric composition changes, flooding, and tropical cyclones. These changes have led to alterations in the environment, thus, affecting crop and livestock production in the agricultural system. For instance, crops that require specific soil and temperature situations are vastly influenced when the temperature level changes suddenly, making the crops vulnerable to adapt to the alterations and therefore, the crops eventually die. Likewise, animal species also get affected by temperature changes, such as heat stress which specifically affects the fertility of male and female livestock. Due to these events, Fiji’s economies have also been affected since agriculture plays a vital role in boosting our economy through local market sales and exporting. Thereby, this review illustrates the impacts of climate change and ways to move forward/ solutions, for example, FAO (Food and Agriculture Organization) and Pacific Islands Climate Change Assistance Program (PICCAP) have supported Fiji in bringing adaptation programs for preparing farmers and all other individuals on the upcoming climatic conditions such as adapting tolerant crops that can handle droughts and other adverse weather conditions.

Water Availability and Access in the Pacific

Chapter

Jan 2021

Patila Amosa

Introduction: The Archaeology of Island Colonization

Chapter

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May 2021

Inundation Exposure Assessment for Majuro Atoll, Republic of the Marshall Islands Using A High-Accuracy Digital Elevation Model

Article

Full-text available

Jan 2020

Majuro Atoll in the central Pacific has high coastal vulnerability due to low-lying islands, rising sea level, high wave events, eroding shorelines, a dense population center, and limited freshwater resources. Land elevation is the primary geophysical variable that determines exposure to inundation in coastal settings. Accordingly, coastal elevation data (with accuracy information) are critical for assessments of inundation exposure. Previous research has demonstrated the importance of using high-accuracy elevation data and rigorously accounting for uncertainty in inundation assessments. A quantitative analysis of inundation exposure was conducted for Majuro Atoll, including accounting for the cumulative vertical uncertainty from the input digital elevation model (DEM) and datum transformation. The project employed a recently produced and validated DEM derived from structure-from-motion processing of very-high-resolution aerial imagery. Areas subject to marine inundation (direct hydrologic connection to the ocean) and low-lying lands (disconnected hydrologically from the ocean) were mapped and characterized for three inundation levels using deterministic and probabilistic methods. At the highest water level modeled (3.75 ft, or 1.143 m), more than 34% of the atoll study area is likely to be exposed to inundation (68% chance or greater), while more than 20% of the atoll is extremely likely to be exposed (95% chance or greater). The study demonstrates the substantial value of a high-accuracy DEM for assessing inundation exposure of low-relief islands and the enhanced information from accounting for vertical uncertainty.

Green Leadership as an Emerging Style for Addressing Climate Change Issues in Schools

Article

Full-text available

Jan 2019

Wahab Ali

Modeling the Evolution of a Freshwater Lens under Highly Dynamic Conditions on a Currently Developing Barrier Island

Article

Full-text available

Aug 2019
GEOFLUIDS

The drinking water supply on barrier islands largely depends on freshwater lenses, which are also highly relevant for island ecosystems. The freshwater lens presented in this study is currently developing (since the 1970s) below the very young eastern part of the North Sea barrier island Spiekeroog, the so-called “Ostplate.” Due to the absence of coastal protection measures, formation, shape, and extent of the freshwater lens below the Ostplate are unaffected by human activities but exposed to dynamic changes, e.g., geomorphological variations and storm tides. The main aim of this paper was to reconstruct the evolution of the freshwater lens over several decades in order to explain the present-day groundwater salinity distribution. In addition, the study assessed the impact of geomorphological variations and storm tides on the freshwater lens formation. Detailed field observations were combined with a transient 2-D density-dependent modeling approach. Both field observations and simulations show an asymmetric freshwater lens after ~42 years of formation, whereby the horizontal extent is limited by the elevated dune area. The simulations indicate that the young freshwater lens has nearly reached quasi-steady-state conditions mainly due to the continuous mixing with seawater infiltrating during storm tides, which inhibits further growth of the freshwater lens on the narrow island. The findings further show that (i) a neglection of storm tides results in a significant overestimation of the freshwater lens extent, and (ii) the modeled present groundwater salinity distribution and shape of the freshwater lens are predominantly determined by the position and extent of the elevated dune area at the past ~20 years. Hence, annual storm tides have to be directly implemented into numerical models to explain the groundwater salinity distribution and the extent of young freshwater lenses located in highly dynamic tidal environments.

Laboratory study of wave transformation around reef coasts with various rough surfaces

Article

Mar 2019

With global climate change and sea level rise, low-lying atoll islands fringed by coral reefs are especially vulnerable to wave-driven inundation during extreme wave events. In recent years, China has implemented large-scale engineering constructions on some low-lying reef atolls in the South China Sea. Hence, accurate prediction of the nearshore waves on the reefs is important to assess the wave runup on such constructed coastal structures. Wave runup near the reef coast is primarily contributed from sea and swell waves (0.04-0.4 Hz), infragravity waves (0.001-0.04 Hz) and wave setup. A typical coral reef profile is characterized by a seaward sloping fore-reef and an inshore shallow reef flat extending towards the coastline, and the reefs have been reported as efficient buffers to the wind-driven wave energy over decades. Reefs often have fully developed coral communities on the fore reef and reef flat, resulting in complex topography and reef surface roughness. The wave energy loss caused by bottom friction maybe even be greater than that caused by wave breaking. This laboratory study modeled a variety of rough surfaces around the reef surfzone by using an array of cylinders with different arrangements. The results show that the swell waves height near the coastline is significantly lower than the incident waves height due to the breaking of the short waves at the reef edge and the continuous attenuation of the friction along the reef flat during the irregular waves propagation to the shore. The infragravity waves height increases significantly at the reef edge due to wave breaking, and then the infragravity waves height are amplified by the resonance effect on the reef flat, and the infragravity waves height increases gradually along the reef until it reaches the maximum value near the coastline. Near the coastline, both the swell waves height and the infragravity waves height increase with the incident waves height and period increasing. The swell waves height increases with reef-flat still water level increasing, while the low frequency long wave height decreases with the increase of reef-flat still water level. Both wave heights with the rough reef surface are found to be smaller than those with the smooth surface. When the roughness of reef surface varies, both wave heights near the shoreline decrease with the increasing surface roughness density. We also analyze the coherence and transfer functions to show that the infragravity waves on the reef flat are generated by the breaker-point shift when the grouped short waves break around the reef edge. Resonant modes exist assciated with the infragravity wave motions on the reef flat. For the smooth reef surface, the infragravity wave energy is amplified due to the first-order resonance when it propagates from the reef edge to the shoreline. For the rough reef surface, the infragravity wave energy is dissipated by bottom friction on the reef flat, and the effect of resonance is insignificant.

The hydrological response of surface water to recent climate variability: A remote sensing case study from the central tropical Pacific

Article

Full-text available

Apr 2019

For small tropical islands with limited freshwater resources, understanding how island hydrology is influenced by regional climate is important, considering projected hydroclimate and sea level changes as well as growing populations dependent on limited groundwater resources. However, the relationship between climate variability and hydrologic variability for many tropical islands remains uncertain due to local hydroclimatic data scarcity. Here we present a case study from Kiritimati, Republic of Kiribati (2°N, 157°W), utilizing the normalized difference vegetation index (NDVI) to investigate variability in island surface water area, an important link between climate variability and groundwater storage. Kiritimati surface water area varies seasonally, following wet and dry seasons, and interannually, due to hydroclimate variability associated with the El Niño/Southern Oscillation (ENSO). The NIÑO3.4 sea surface temperature (SST) index, satellite‐derived precipitation, precipitation minus evaporation, and local sea level all had significant positive correlations with surface water area. Lagged correlations show sea level changes and precipitation influence surface water area up to 6 months later. Differences in the timing of surface water area changes and variable climate‐surface water area correlations in island sub‐regions indicate that surface hydrology on Kiritimati is not uniform in response to climate variations. Rather the magnitude of the ocean‐atmosphere anomalies and island‐ocean connectivity determine the extent to which sea level and precipitation control surface water area. The very strong 2015‐2016 El Niño event led to the largest surface water area measured in the 18‐year dataset. Surface water area decreased to pre‐event values in a similarly rapid manner (<6 months) after both the very strong 2015‐2016 event and the 2009‐2010 moderate El Niño event. Future changes in the frequency and amplitude of interannual hydroclimate variability as well as seasonal duration will thus alter surface water coverage on Kiritimati, with implications for freshwater resources, flooding, and drought.

1.5°C Hotspots: Climate Hazards, Vulnerabilities, and Impacts

Article

Oct 2018

Differentiating the impacts of climate change between 1.5°C and 2°C requires a regional and sector-specific perspective. Whereas for some regions and sectors the difference in climate variables might be indistinguishable from natural variability, other areas especially in the tropics and subtropics will experience significant shifts. In addition to region-specific changes in climatic conditions, vulnerability and exposure also differ substantially across the world. Even small differences in climate hazards can translate into sizeable impact differences for particularly vulnerable regions or sectors. Here, we review scientific evidence of regional differences in climate hazards at 1.5°C and 2°C and provide an assessment of selected hotspots of climate change, including small islands as well as rural, urban, and coastal areas in sub-Saharan Africa and South Asia, that are particularly affected by the additional 0.5°C global mean temperature increase. We interlink these with a review of the vulnerability and exposure literature related to these hotspots to provide an integrated perspective on the differences in climate impacts between 1.5°C and 2°C.

Using Bi-Seasonal WorldView-2 Multi-Spectral Data and Supervised Random Forest Classification to Map Coastal Plant Communities in Everglades National Park

Article

Full-text available

Mar 2018
SENSORS-BASEL

Coastal plant communities are being transformed or lost because of sea level rise (SLR) and land-use change. In conjunction with SLR, the Florida Everglades ecosystem has undergone large-scale drainage and restoration, altering coastal vegetation throughout south Florida. To understand how coastal plant communities are changing over time, accurate mapping techniques are needed that can define plant communities at a fine-enough resolution to detect fine-scale changes. We explored using bi-seasonal versus single-season WorldView-2 satellite data to map three mangrove and four adjacent plant communities, including the buttonwood/glycophyte community that harbors the federally-endangered plant Chromolaena frustrata. Bi-seasonal data were more effective than single-season to differentiate all communities of interest. Bi-seasonal data combined with Light Detection and Ranging (LiDAR) elevation data were used to map coastal plant communities of a coastal stretch within Everglades National Park (ENP). Overall map accuracy was 86%. Black and red mangroves were the dominant communities and covered 50% of the study site. All the remaining communities had ≤10% cover, including the buttonwood/glycophyte community. ENP harbors 21 rare coastal species threatened by SLR. The spatially explicit, quantitative data provided by our map provides a fine-scale baseline for monitoring future change in these species’ habitats. Our results also offer a method to monitor vegetation change in other threatened habitats.

Inundation of a low-lying urban atoll island: Majuro, Marshall Islands

Article

Full-text available

Apr 2018
NAT HAZARDS

Majuro is a low-lying island perched on a coral atoll in the central Pacific Ocean and is home to nearly 28,000 people. Considered highly vulnerable to the impacts of marine inundation, Majuro is expected to experience increasingly severe inundation as a result of continued sea-level rise. Popular media, academic papers, government reports, disaster declarations and other online resources are used to document 18 inundation events at Majuro over the past 36 years, which caused considerable impact to local physical and anthropogenic systems. The physical drivers and impacts of the documented inundation events are examined using tide gauge and weather observations and wave model hindcasts. The ocean-facing shorelines of Majuro experience frequent inundation caused by swell waves generated by distant storms from both the north and the south Pacific Ocean. In some instances, complete overwashing of the island by swell waves has been reported. Less frequent, although potentially far more damaging, are inundation events associated with typhoons and tropical storms, with the most recent in 1997. Inundation along the sheltered lagoon-facing shoreline of Majuro has occurred in the absence of waves due to the coincidence of high sea levels during La Niña conditions and seasonally high tides, as in 2011. Lagoon inundation also appears to have been caused by offshore swell penetrating into the lagoon, most effectively at high tide, and by locally generated wind waves within the lagoon. The classes of inundation identified in this study have unique drivers and the impacts have varying spatial and temporal characteristics in terms of impact and predictability. The inundation events are discussed with respect to the drivers of inundation and the future outlook under rising sea-level conditions.

Assessing Groundwater Availability of the Maldives under Future Climate Conditions: Future Groundwater Availability of Maldives

Article

Full-text available

Jun 2017
HYDROL PROCESS

Groundwater resources of the Republic of the Maldives are threatened by a variety of factors including variable future rainfall patterns, continued population growth and associated pumping demands, rising sea level, and contamination from the land surface. This study assesses changes in groundwater availability due to variable rainfall patterns and sea level rise (SLR) in the coming decades, a key component of water resources management for the country. Using a suite of two-dimensional density-dependent groundwater flow models, time-dependent thickness of the freshwater lens is simulated for a range of island sizes (200 m to 1100 m) during the time period of 2011 to 2050, with recharge to the freshwater lens calculated using rainfall patterns provided by General Circulation Models (GCM) for the three distinct geographic regions of the Maldives. The effect of SLR on the freshwater lens is quantified using estimates of shoreline recession and associated decreases in island width. If rainfall is solely considered, groundwater availability is projected to increase, as lens thickness during the 2031-2050 time periods is slightly greater (1-5%) than during the 2011-2030 time period. However, including the impact of SLR indicates an overall decrease in lens thickness, with drastic decreases (60% to 100%) projected for small islands (200 m) and moderate decreases (12% to 14%) expected for 400 m islands, which accommodate one-third of the national population. Similar methodologies can be used for other atoll island nations, such as the Republic of Marshall Islands, Federated States of Micronesia and the Republic of Kiribati. For the Maldives, results from this study can be used in conjunction with population growth estimates to determine the feasibility of including groundwater in water resources planning and management for the country.

Geohydrologic Factors Governing Atoll Island Groundwater Resources

Article

Full-text available

Feb 2017

The groundwater systems of small coral islands are highly dynamic, fluctuating in response to variable rainfall patterns, sea-level rise, and human management of water resources. Using a three-dimensional modeling approach, this study investigates the behavior of the freshwater lens in relation to major geohydrologic factors, including annual recharge rate, hydraulic conductivity (K) of the Holocene aquifer, depth to the contact between the Holocene and Pleistocene-age aquifers, and annual rate of coconut palm transpiration. Multiple islands within the Federated States of Micronesia are assessed, and therefore, the relations to island width, island surface area, and island orientation on the atoll (leeward versus windward) also are investigated. Results indicate that Holocene K and the rate of annual recharge are most influential on lens behavior. In general, a hydraulic conductivity of 25 m/day (0.03 cm/s) and between 100 and 200 m/day (0.12-0.23 cm/s) is found for leeward and windward islands, respectively. Results can be used to guide freshwater resource management by estimating extractable volume of a given atoll island aquifer if island surface area, atoll orientation, and rainfall are known.

What we can learn from a COVID-19-related lockdown period

Chapter

Jan 2025

Discussion on “An assessment of small island hydrological research activity conducted in the Oceania Region”

Article

Jun 2024

Global Impact of Sea Level Rise on Coastal Fresh Groundwater Resources

Article

Full-text available

Jan 2024

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.

Groundwater flow and water pumping method during drought in atoll islands: Laura Island in the Republic of the Marshall Islands

Article

Full-text available

Mar 2023

Securing water pumping is a considerable challenge in small, flat atoll islands where rivers and lakes do not develop. Excess pumping due to water shortages during severe droughts has caused up-coning in the fresh groundwater lens (FGL). Since FGL may not recover from up-coning, very few researchers have attempted to clarify the three-dimensional pumping effect on the saltwater–freshwater interface of FGL. The purpose of this research is twofold: (1) to clarify the three-dimensional distributed pumping effect on the FGL flow in Laura Island, and (2) to suggest the up-coning mitigation method for the FGL on Laura Island (Laura Lens). The Republic of the Marshall Islands (RMI), a region of increasing population growth that could burden Laura Lens, was selected as the research site. First, we collected various on-site information and analyzed the hydrological data. We observed a correlation between the rainfall data recorded on Laura Island and Majuro Atoll. Subsequently, numerical simulation using the SEAWAT model clarified the movement of Laura Lens during water pumping in a drought situation. As a result, we could also report the optimum period and the volume of water pumping for the Laura Lens. In conclusion, findings for RMI can facilitate sustainable management and conservation of FGL on atoll islands to reduce up-coning by realizing distributed pumping.

Effects of Future Increases in Tidal Flooding on Salinity and Groundwater Dynamics in Coastal Aquifers

Article

Full-text available

Dec 2022
WATER RESOUR RES

Future increases in the frequency of tidal flooding due to sea level rise (SLR) are likely to affect pore water salinities in coastal aquifers. In this study, we investigate the impact of increased tidal flooding frequency on salinity and flow dynamics in coastal aquifers using numerical variable‐density variably‐saturated groundwater flow and salt transport models. Short (sub‐daily) and long (decadal) period tides are combined with SLR projections to drive continuous 80‐year models of flow and salt transport. Results show that encroaching intertidal zones lead to both periodic and long‐term vertical salinization of the upper aquifer. Salinization of the upper aquifer due to tidal flooding forces the lower interface seaward, even under SLR. System dynamics are controlled by the interplay between SLR and long period tidal forcing associated with perigean spring tides and the 18.6‐year lunar nodal cycle. Periodic tidal flooding substantially enhances intertidal saltwater‐freshwater mixing, resulting in a 6‐ to 10‐fold expansion of the intertidal saltwater‐freshwater mixing area across SLR scenarios. The onset of the expansion coincides with extreme high water levels resulting from lunar nodal cycling of tidal constituent amplitudes. The findings are the first to demonstrate the combined effects of gradual SLR and short and long period tides on aquifer salinity distributions, and reveal competing influences of SLR on saltwater intrusion. The results are likely to have important implications for coastal ocean chemical fluxes and groundwater resources as tidal flooding intensifies worldwide.

Vertical Saltwater Intrusion in Coastal Aquifers Driven by Episodic Flooding: A Review

Article

Full-text available

Nov 2022
WATER RESOUR RES

Low‐elevation coastal areas are increasingly vulnerable to seawater flooding as sea levels rise and the frequency and intensity of large storms increase with climate change. Seawater flooding can lead to the salinization of fresh coastal aquifers by vertical saltwater intrusion (SWI). Vertical SWI is often overlooked in coastal zone threat assessments despite the risk it poses to critical freshwater resources and salt‐intolerant ecosystems that sustain coastal populations. This review synthesizes field and modeling approaches for investigating vertical SWI and the practical and theoretical understanding of salinization and flushing processes obtained from prior studies. The synthesis explores complex vertical SWI dynamics that are influenced by density‐dependent flow and oceanic, hydrologic, geologic, climatic, and anthropogenic forcings acting on coastal aquifers across spatial and temporal scales. Key knowledge gaps, management challenges, and research opportunities are identified to help advance our understanding of the vulnerability of fresh coastal groundwater. Past modeling studies often focus on idealized aquifer systems, and thus future work could consider more diverse geologic, climatic, and topographic environments. Concurrent field and modeling programs should be sustained over time to capture interactions between physical processes, repeated salinization and flushing events, and delayed aquifer responses. Finally, this review highlights the need for improved coordination and knowledge translation across disciplines (e.g., coastal engineering, hydrogeology, oceanography, social science) to gain a more holistic understanding of vertical SWI. There also needs to be more education of communities, policy makers, and managers to motivate societal action to address coastal groundwater vulnerability in a changing climate.

Water Availability and Access in the Pacific

Chapter

Jan 2022

Patila Amosa

Permeability of porous media in coral reefs

Article

Apr 2021

The formation and storage of fresh groundwater in coral reefs is affected by many factors. The permeability of porous media in island and reef formation is one of the main controlling factors. Coral sand is the only medium for the formation of coral reefs. Its permeability characteristics are very different from the permeability characteristics of quartz sand from land sources. In this study, a series of indoor model tests and microphysical property tests were designed in order to reveal the reasons for the special permeability of coral sand from the microcosmic point of view. The conversion equation of the hydraulic conductivity between quartz sand and coral sand was established. Finally, through numerical simulation, the variation rule and the parameter sensitivity of a freshwater lens were studied when the hydraulic conductivity changed within the reasonable range of natural existence. It was found that the special permeability of coral sand was caused by four factors, including roundness (Φ), roughness (Ψ), surface charge, and the surface hydrophilicity of the particles. Among the four factors, the main factors and the secondary factors were classified according to the influencing degree that changed with the sizes of the particles. The influencing sensitivity of the hydraulic conductivity on the properties of the freshwater lens had the following order: freshwater appearance time > steady-state freshwater reserves > thickness of the steady-state freshwater lens> lens stabilization time.

Climate Change and Small Islands

Chapter

Jan 2021

Robert Maliva

Small, low-lying islands are particularly vulnerable to global climate change and sea level rise with the principal impacts falling into three main categories: shoreline erosion, inundation and flooding, and saline water intrusion into surficial freshwater aquifers. Fresh groundwater on small islands occurs primarily as freshwater lenses, floating atop saline groundwater, whose natural size depends on island area, shape, and topography, aquifer properties (transmissivity), and rainfall. Freshwater lenses are limited resources that are vulnerable to salinization from over exploitation and from storm overwash. The sustainability of freshwater lenses depends on maintaining a balance between recharge, captured discharge, and pumping. Decreases in recharge during drought periods can result is a profound shrinkage of freshwater lenses. Anthropogenic activities can impact freshwater lenses through induced changes in recharge rates caused by increased impervious covers. Management of freshwater lenses can be improved through improved well and wellfield design, monitoring of aquifer water levels and salinity, controls on groundwater pumping, implementation of land use practices to reduce the risk of anthropogenic contamination, and managed aquifer recharge.

NUMERICAL SIMULATION ON FORMATION OF FRESH WATER LENS IN ATOLL ISLANDS環礁州島の淡水レンズ形成に関する数値計算

Article

Jan 2020

Daisaku Sato

Atoll islands has resources of fresh water under the ground which called freshwater lens. Freshwater lens has been used traditionally by residents of island, however, the rapid urbanization and salinitation changed the freshwater lens as unusable resources. this study conducted that the numerical simulation on formation of freshwater lens forcused on the width of island, recharge rate and influence of tidal change of water surface. the results revealed that the volume of freshwater lens increase with direct proportion by recharge rate. Additionally the volume of freshwater lens increased exponentionally by width of island. It was estimated that the potential volume of freshwater lens formed Fongafale island of Funafuti atoll provides residents resource of freshwater for 40 to 90 years. Tidal change influenced to salinity concentrtion and shape of the edge of freshwater lens but the influence is locally.

How lime-sand islands in the South China Sea have responded to global warming over the last 30 years: Evidence from satellite remote sensing images

Article

Dec 2020
GEOMORPHOLOGY

As global warming threatens their existence, there are widespread concerns regarding the persistence of lime-sand islands and the future of mid-ocean atoll nations. To investigate how climate change has affected lime-sand islands, changes in vegetation and other characteristics of such islands in the South China Sea (SCS) were investigated from 1989 to 2019 using 67 satellite images. First, boundaries of the lime-sand islands and their vegetation were extracted using an active contour extraction procedure called the gradient vector flow snake model. Afterwards, the spatial extents were estimated by enclosing the extracted boundaries, and the digital shoreline analysis system was used to calculate beach widths. Finally, area growth rates and speeds were used to evaluate areal changes in the lime-sand islands and their respective vegetation. Based on the estimated area growth rates, area growth speeds, and beach widths, the lime-sand islands in SCS eroded over the past three decades whereas their vegetation expanded. Further analysis suggested that direct inundation caused by sea-level rise might not be clearly identified from the satellite images. However, other climate change-related factors were most likely responsible for the observed island erosions. These factors included higher wave energy, stronger typhoon intensity and destructiveness, and accelerated coral reef degradation. In addition, the observed expansion of vegetation on the lime-sand islands was likely due to the increase in precipitation in a warming world. The results show that 1) the lime-sand islands will continue to erode whereas vegetation will continue to expand; 2) As vegetation growth is significantly inhibited by salt water when it is adjacent to the ocean, vegetation areas on lime-sand islands may start to continuously decline. Overall, this study is the first to quantitatively examine changes in SCS lime-sand islands due to global warming.

Modeling of biogeochemical processes in a barrier island freshwater lens (Spiekeroog, Germany)

Article

Jun 2019
J HYDROL

Freshwater lenses present valuable water resources on barrier islands. Yet, the biogeochemical processes that control the groundwater quality of these freshwater lenses and how they are affected by the prevailing groundwater dynamics is largely unexplored. In this study we investigated the biogeochemistry of a barrier island freshwater lens with a focus on understanding and quantifying organic matter mineralization, sulfur cycling, and chemical fluxes to the land-ocean interface. We analyzed a comprehensive set of hydrogeochemical field data from Spiekeroog Island (Germany), including stable sulfur isotope signatures of dissolved sulfur species, with a reactive transport modeling approach. Tritium-Helium groundwater ages were used to constrain the hydrogeochemistry as a function of residence time. Our results revealed that freshwater lenses can act as archives for anthropogenic pollution, conserving the high sulfur loads associated with historic atmospheric deposition. We observed two distinct (hydro)biogeochemical patterns, which we attribute to a heterogeneous distribution of reactive organic matter. Those patterns were well replicated by two separate reactive transport models that considered the variations in organic matter reactivity. Simulation and field results demonstrated that net sulfur cycling is dominated by microbial sulfate reduction and subsequent iron sulfide precipitation. In the absence of dissolved oxidants, we attribute the observed high stable sulfur isotope fractionation between dissolved sulfate and sulfide of up to 67‰ to low (<20 pmol mL⁻¹ d⁻¹) microbial sulfate reduction rates. We show that older groundwater becomes progressively enriched in ammonium and phosphate due to the mineralization of organic matter, and we speculate that lens-derived nutrient fluxes may be important for the benthic zone at local groundwater discharge sites, at least seasonally in spring and summer.

Climate Migration and Cultural Preservation: The Case of the Marshallese Diaspora: Concepts, Methods and Policy Options

Chapter

Full-text available

Jan 2019

Alison Heslin

Potential land loss in Pacific island countries from rising sea levels raises many concerns regarding how nation states will continue to function politically and economically in the event of climate-induced relocation of their populations. This piece expands that conversation, addressing the impacts of relocation on cultural heritage , drawing on data from interviews with migrants from the Marshall Islands to the United States. The study seeks to understand the challenges and opportunities of cultural preservation among the Marshallese diaspora . Marshallese accounts of life in the United States indicate many opportunities for cultural preservation, particularly for those living in communities with large Marshallese populations, while also presenting challenges based on social, economic, and geographic differences between the U.S. and the Marshall Islands . Understanding the means through which Marshallese migrants maintain cultural traditions and the challenges current migrants face, can help us address potentially irreversible, but avoidable losses of cultural traditions in the event of mass displacement.KeywordsCultural heritageMigrationNon-economic lossesMarshall islandsDiaspora

Remote sensing of unhelpful resilience to sea level rise caused by mangrove expansion: A case study of islands in Florida Bay, USA

Article

Feb 2019
ECOL INDIC

Growth stress response to sea level rise in species with contrasting functional traits: A case study in tidal freshwater forested wetlands

Article

Jul 2018
ENVIRON EXP BOT

Quantifying Threats to Groundwater Resources in the Republic of Maldives Part I: Future Rainfall Patterns and Sea Level Rise

Article

Mar 2018

Reserves of fresh groundwater on atoll islands are extremely fragile due to climatic and anthropogenic stresses. Of major concern is the quantity of water to be available in the coming decades under the influence of variable rainfall patterns, rising sea level, environmental conditions, and expected population growth that depends on groundwater resources. In this study, a three‐dimensional numerical modeling approach using the SEAWAT modeling code is used to estimate freshwater lens volume fluctuation for four representative islands in the Republic of Maldives in response to long‐term changes in rainfall, sea level rise, and anthropogenic stresses such as groundwater pumping, and short‐term impacts from tsunami‐induced marine over‐wash events. This work is divided into two papers. This first paper presents numerical model set‐up and calibration, and the effect of future rainfall patterns and sea level rise (SLR) on fresh groundwater reserves. The second paper focuses on marine overwash events. The results of simulated future freshwater lens volume presented in the first study contribute to efficient groundwater resources planning and management for the Maldives in the upcoming decades. Freshwater lenses in small atoll islands (area < 0.6 km²) are shown to have a strong variability trends in the upcoming decades with expected reduction in lens volume between 11‐36% due to SLR. In contrast, freshwater lenses in larger atoll islands (area > 1.0 km²) are shown to have less variability to changing patterns with expected reduction in lens volume between 8‐26% due to SLR. Study results can provide water resource managers with valuable findings for consideration in water security measures.

Quantifying Threats to Groundwater Resources in the Republic of Maldives Part II: Recovery from Tsunami Marine Overwash Events

Article

Feb 2018
HYDROL PROCESS

Marine overwash events are among the most serious short-term threats to groundwater supply of small coral islands. During such events, seawater can inundate small islands partially or completely, causing salinization of the aquifer. A comprehensive knowledge of freshwater lens recovery is essential for water planners on these islands. In this study, a numerical modeling approach is used to quantify recovery of the freshwater lens on four islands of the Maldives after a tsunami-induced overwash event similar to that experienced from the Indian Ocean earthquake in December 2004. The islands vary in size (0.2 km2 to 10.1 km2) and span the climatic regions of the Maldives. A tested three-dimensional SEAWAT groundwater model for each island is used to simulate the recovery process. Recharge rates from historical rainfall data and from global climate models are imposed on each island during the post-overwash recovery period. The effect of groundwater pumping on lens recovery also is examined. Results show abrupt decrease in fresh groundwater volumes for each island, followed by recovery that is significantly influenced by island size and recharge patterns. Overall, salinization is more widespread on small islands (< 1 km2), but recovery is more rapid than for large islands. Between 50% and 90% of lens recovery occurs after two years for small islands (< 1 km2), whereas only 35% and 55% for large islands. Imposing pumping rates required to sustain the local population lengthened the recovery time between 5% and 15%, with smaller islands having the higher percentage. However, the governing factor on recovery time is the spatial extent of land surface inundation by the overwash event, with wave height and duration of the event having a negligible impact. A strong relationship exists between required recovery time and island surface area, thereby providing a method to determine recovery time for other atoll islands not investigated in this study with similar geologic structure. Our results can be used to aid in managing water resources during the post-overwash period.

Mitten im Nirgendwo – Kiritimati

Chapter

Nov 2018

Gabriele Kerber

Gut 6500 Menschen und 13 Millionen Seevögel kämpfen schon heute auf Kiritimati, dem größten Atoll der Erde, mit den Folgen des Klimawandels, in erster Linie mit den intensiveren El Niño Ereignissen der vergangenen Jahrzehnte. Besonders der 2015/16 El Niño hat die Insel getroffen, mit monatelangem Starkregen, dauerhaften Überschwemmungen und erhöhtem Meeresspiegel. Viele Menschen von anderen Inseln des Landes ziehen nach Kiritimati, da die Insel bessere Voraussetzungen hat, dem Klimawandel zu widerstehen, als die meisten anderen. Aber ob die Bevölkerung und Regierung es schaffen die Insel nachhaltig sozial und wirtschaftlich zu entwickeln, unter den verschärften Bedingungen des Klimawandels, bleibt fraglich.

Marakei – Das traditionelle Kiribati

Chapter

Nov 2018

Gabriele Kerber

Die Menschen auf Marakei leben noch relativ traditionell: Sie leben in selbstgebauten Holzhäusern aus Kokosholz und Pandanenblättern, sie betreiben Agroforstwirtschaft und Landwirtschaft, sie gehen fischen. Aber das traditionelle Leben wir schwerer – einerseits durch die Verlockungen der bequemen Welt des globalen Nordens, andererseits durch die Auswirkungen der Kolonialzeit, die grundlegende Veränderungen bewirkt hat, die heute die Widerstandsfähigkeit der I-Kiribati gegen die Folgen des Klimawandels dramatisch senken. Diese Folgen sind in Marakei derzeit in erster Linie die Erosion der Küste und die Versalzung des Grundwassers.

Seawater-flooding events and impact on freshwater lenses of low-lying islands: Controlling factors, basic management and mitigation

Article

Mar 2017
J HYDROL

An unprecedented set of hydrologic observations was collected after the Dec 2008 seawater-flooding event on Roi-Namur, Kwajalein Atoll, Republic of the Marshall Islands. By two days after the seawater flooding that occurred at the beginning of dry season, the observed salinity of water withdrawn by the island’s main skimming well increased to 100% seawater concentration, but by ten days later already decreased to only 10%–20% of seawater fraction. However, the damaging impact on the potability of the groundwater supply (when pumped water had concentrations above 1% seawater fraction) lasted 22 months longer. The data collected make possible analyses of the hydrologic factors that control recovery and management of the groundwater-supply quality on Roi-Namur and on similar low-lying islands.

Hydrogeology and management of freshwater lenses on atoll islands: Review of current knowledge and research needs

Article

Feb 2017
J HYDROL

On atoll islands, fresh groundwater occurs as a buoyant lens-shaped body surrounded by saltwater derived from the sea, forming the main freshwater source for many island communities. A review of the state of knowledge of atoll island groundwater is overdue given their susceptibility to adverse impacts, and the task to address water access and sanitation issues within the United Nations’ Sustainable Development Goals framework before the year 2030. In this article, we review available literature to summarise the key processes, investigation techniques and management approaches of atoll island groundwater systems. Over fifty years of investigation has led to important advancements in the understanding of atoll hydrogeology, but a paucity of hydrogeological data persists on all but a small number of atoll islands. We find that the combined effects of buoyancy forces, complex geology, tides, episodic ocean events, strong climatic variability and human impacts create highly dynamic fresh groundwater lenses. Methods used to quantify freshwater availability range from simple empirical relationships to three-dimensional density-dependent models. Generic atoll island numerical models have proven popular in trying to unravel the individual factors controlling fresh groundwater lens behaviour. Major challenges face the inhabitants and custodians of atoll island aquifers, with rising anthropogenic stresses compounded by the threats of climate variability and change, sea-level rise, and some atolls already extracting freshwater at or above sustainability limits. We find that the study of atoll groundwater systems remains a critical area for further research effort to address persistent knowledge gaps, which lead to high uncertainties in water security issues for both island residents and surrounding environs.

Piecing Together the Adaptation Puzzle for Small Island States

Chapter

Feb 2017

Island states are especially at risk of climate impacts and are already feeling the effects of rising sea levels, acidification, climate extremes and other impacts. Small islands face several unique challenges: They usually have limited resources to react, but are exceptionally exposed due to their physical setting and limited livelihood options. In addition, they are remote and not easily reached in time of crisis, making adaptation an imperative. This contribution presents the concept for an integrated database on climate impacts and adaptation, focussing specifically on the requirements of small island states. The database contains information on climate impact projections, linked to examples of existing adaptation projects. The database provides a structured overview of success-factors and limitations, piecing together fragmented knowledge and fostering knowledge exchange across regions in order to support science-based adaptation. While adaptation experience is increasing, including an evolving understanding of prerequisites and limitations to specific forms of adaptation, knowledge is still fragmented, due to the mostly local nature of adaptation. Island states across the world can benefit from a structured exchange, focussing on the transferability of success-criteria for adaptation. An improved knowledge base is also important for other regions, which will face similar challenges in the coming years.

ASSESSMENT OF SALINITY OF GROUNDWATER IN SWAMP TARO (CYRTOSPERMA CHAMISSONIS) "PULAKA" PITS IN TUVALU

Technical Report

Full-text available

Mar 2007

Arthur Webb

Pits on all islands of Tuvalu (except Niulakita) were surveyed between January and April 2006. At the time of study, only three islands (Nukulaelae, Niutao and Funafuti) had pits which showed salinity concentrations thought to be too high for successful swamp taro growth, (≥ 3 000, 4 000 and 5 000 μS cm–1, respectively). In the case of both Nukulaelae and Niutao these high readings were restricted to one pit area. Otherwise, conductivity readings in the remaining pits on these islands were generally low (≤1 000 μS cm–1) and adequate for swamp taro growth. There is anecdotal evidence to suggest that causeway engineering activities in Niutao’s central lagoon may have contributed to higher salinity in localised areas. Alternatively, sampling in Funafuti (Fongafale) showed that all pits were either too saline or very marginal and swamp taro production is unlikely to succeed anywhere on Fongafale islet.

Freshwater Lens, Settlement Patterns, Resource Use and Connectivity in the Marshall Islands

Article

Full-text available

Jun 2006

Dirk H. R. Spennemann

Life on coral atolls can be very precarious. The sand cay islets are low-lying (in the main less than 2m above high water) and small. Only the larger islands (over 500m by 1000m) are suitable for permanent human habitation, as they possess a fragile lens of freshwater floating on top of a saltwater base. It is this lens of groundwater that allows for a variety of plant life, and it is this source of fresh water that allows humans to exist on the island. Environmental disasters, such as typhoons with waves of over 10m washing across an entire islet, can swamp the groundwater lens with saltwater, causing salinisation and thus imperilling human survival. To reduce the consequences of the environmental disasters, Marshallese chiefs had land holdings scattered over several islands of the same atoll, as well as land rights and, importantly, rights to resources, on other atolls. In times of disaster there were thus other resources to call upon. That level of connectivity allowed the Marshallese society to thrive on the marginal land they inhabited.

Physical geography of Majuro and the Marshall Islands

Chapter

Full-text available

Jan 2008

Tropical Cyclones. Climatology and Impacts in the South Pacific

Book

Full-text available

Dec 2007

James P. Terry

This book describes the behaviour of tropical cyclones in the South Pacific and investigates the broad range of disturbance effects these violent storms have on the physical environments of the islands that lie in their path and the people who live on them. It is the first book to link these two themes – the characteristics of cyclones and their landscape impacts. Students of physical geography will find this book an authoritative source. It should also appeal to those concerned with climate change, extreme events, natural hazards, tropical islands, tropical geomorphology and hydrology, and to all those who have a general curiosity about the vast Oceania region and its remote, vulnerable islands. The volume is divided into two complementary parts. The first part explains the nature of tropical cyclones, their genesis, structure, behaviour, and extreme meteorological conditions. Future cyclone activity related to climate change is also considered. Part two deals with geomorphological and hydrological responses to tropical cyclones on South Pacific islands. Attention is focused on the effects of cyclones on coral reefs, coasts, slopes and rivers, which often lead to profound landform changes and have lasting influences on both island evolution and on the lives of the Islanders. Examples and illustrations are drawn widely from across the South Pacific. Numerous maps, informative drawings, and many spectacular photographs are used with great effect throughout, resulting in a highly readable volume.

Environmental Water Quality. A Guide to Sampling and Measurement.

Book

Full-text available

Jul 1996

Increased demand for high quality water has caused mounting pressure on limited water resources in the south west of Western Australia. Traditionally important for agriculture and commercial forestry, the south west is also a major region for tourism and industrial development. Consequently, water derived from forested and cleared catchments, and groundwater in some areas, is in demand for a diverse range of uses. Competing uses include: • conservation of the environment • agricultural and industrial supply • stock and domestic supply • propagation of fish and other aquatic life • swimming and fishing • boating and other recreational activities • water power and navigation • transport, dispersion and assimilation of wastes. Water users are understandably keen to maintain or improve their water supply and its quality. Monitoring allows managers and users to assess the amount and conditions of water in our environment. For effective monitoring of water quality and pollution, certain practices or 'standard procedures' must be followed when collecting water samples for analysis. These procedures vary according to the specific contaminant under investigation and may cover many aspects, from the selection of appropriate sampling methods to the use of suitable containers and storage techniques. A lack of familiarity with water sampling techniques or failure to store samples correctly may result in significant and unacceptable errors. These errors can be expensive. It is important to know: • Why you are sampling, • What you are sampling for, • How to collect useful samples from the field, and • How to analyse and interpret the results properly. Information on how to sample for and measure water quality is often difficult to find, being either buried in technical manuals or in research literature. This manual introduces guidelines for correctly sampling and measuring major water pollution parameters that are of concern in the south west Western Australia.

Climatological aspects of South Pacific tropical cyclones, based on analysis of the RSMC-Nadi (Fiji) regional archive

Article

Full-text available

Sep 2010
CLIM RES

This study analyses the regional cyclone archive for the tropical South Pacific (160 degrees E-120 degrees W, 0 degrees-25 degrees S) maintained by the designated Regional Specialized Meteorological Centre located at Nadi in the Fiji Islands. The historical cyclone record was examined over 4 decades from the 1969-1970 cyclone season to the 2007-2008 season. Cyclogenesis origins, minimum pressures, durations and track parameters (azimuth and length) of 291 individual storms were investigated. Temporal variability in separate cyclone parameters was highly variable but not necessarily matching on an interannual basis. Anomalous periods of cyclone behaviour can be detected in 1976, 1981, 1983, 1991, 1998, 2001-2002 and 2003. Strong and significant inter-relationships are indicated between storm longevity, track length and minimum sea-level pressure (MSLP) attained, and also between seasonally averaged measures of latitude of cyclone origin and the strength of the Southern Oscillation Index and Multivariate ENSO Index. Yet no overall long-term linear trends were detected in the data, with the exception of MSLP which showed a spurious decreasing trend-a problem already highlighted in other cyclone archives. These findings suggest that the South Pacific cyclone basin and the islands therein will continue to experience strong but irregular interannual fluctuations in cyclone and track characteristics. Such anomalies will remain a much more dominant feature of temporal patterns than possibly evolving changes in long-term average cyclone activity resulting from climate change.

ENSO and tropical cyclone activity

Article

Full-text available

Pao-Shin Chu

The present state of knowledge regarding tropical cyclone activity in various ocean basins and the El Niño-Southern Oscillation phenomenon is reviewed in this chapter. The ocean basins include the western North Pacific, the eastern and central North Pacific, the southwestern Pacific, the southeastern Pacific, and the North Atlantic. Following a description of the ENSO phenomenon, tropical cyclone activity in each basin is discussed in the context of frequency, genesis location, track, life span, and intensity. For the western North Pacific, the pronounced change in tropical cyclone activity due to warm ENSO is the eastward and equatorial shift in genesis loca- tion, longer life span, and more recurvature of tropical cyclone tracks (Chan, chapter 10 in this volume). There is also a notable decrease in tropical cyclone counts in the year following a warm ENSO event. For the eastern North Pacific, the formation point shifts farther west, more intense hurricanes are observed, and tropical cyclones track farther westward and maintain a longer lifetime in associ- ation with warm ENSO events. The central North Pacific sees more tropical cyclone counts in the El Niño year due to more tropical cyclone formation in this region and a tendency for tropical cyclones that originate in the eastern North Pacific to enter the central North Pacific. As in the North Pacific, tropical cyclones in the South Pacific originate farther east during El Niño years, result- ing in more storms in the southeastern Pacific and fewer storms in the south- western Pacific. The North Atlantic features fewer tropical cyclone counts, slightly weaker intense storms, and hurricane genesis farther north during El Niño years. Changes are approximately opposite in cold ENSO years.

Climatic and Human Influences on Groundwater in Low Atolls

Article

Full-text available

Aug 2007
VADOSE ZONE J

Population centers in low, small islands have water supply problems that are among the most critical in the world. Limited land areas and extremely large soil hydraulic conductivities severely reduce surface runoff and surface storage, so that thin lenses of fresh groundwater floating over seawater comprise the major source of fresh water for people in many atolls. Atoll groundwater is extremely vulnerable to frequent El Nino Southern Oscillation (ENSO)-related droughts, salinization due to storm surges and sea-level rise, and to human activities with vadose zone transit times from surface to shallow groundwater being less than 1 h. We examine the relationship between groundwater, rainfall, and ENSO events in a low atoll, Tarawa, in the central and western Pacifi c Republic of Kiribati. Droughts can last as long as 43 months and occur with a current frequency of 6 to 7 years. The impact of droughts on the quality and quantity of a fresh groundwater lens is explored. The local drawdown of the water table due to pumping from long horizontal infiltration galleries is found to be less than diumal tidal variations. The saturated hydraulic conductivity, K-0, of the Holocene unconsolidated coral sands was estimated from infiltration gallery drawdown in two islands. The geometric mean K-0 was 14.6 m d(-1) with a range from 0.9 to 111 m d-(1). These large K-0 values cause the rapid transmission of rainfall and surface pollutants through the unsaturated zone to groundwater. An example is given of Escherichia coli pollution due to traditional activities. Strategies for improving the adaptation of island communities and increasing resilience to climate change are discussed.

A Closed-form Equation for Predicting the Hydraulic Conductivity of Unsaturated Soils1

Article

Full-text available

Sep 1980

Martinus Th. Van Genuchten

A new and relatively simple equation for the soil-water content-pressure head curve is described. The particular form of the equation enables one to derive closed-form analytical expressions for the relative hydraulic conductivity, when substituted in the predictive conductivity models of N. T. Burdine or Y. Mualem. The resulting expressions contain three independent parameters which may be obtained by fitting the proposed soil-water retention model to experimental data. Results obtained with the closed-form analytical expressions based on the Mualem theory are compared with observed hydraulic conductivity data for five soils with a wide range of hydraulic properties.

Droughts in Small Coral Islands: Case Study, South Tarawa, Kiribati

Article

Full-text available

Jan 1999

Climate change impacts on tropical cyclones and extreme sea levels in the South Pacific — A regional assessment

Article

Full-text available

Jan 2012
GLOBAL PLANET CHANGE

This paper reviews the current understanding of the effect of climate change on extreme sea levels in the South Pacific region. This region contains many locations that are vulnerable to extreme sea levels in the current climate, and projections indicate that this vulnerability will increase in the future. The recent publication of authoritative statements on the relationship between global warming and global sea level rise, tropical cyclones and the El Niño-Southern Oscillation phenomenon has motivated this review. Confident predictions of global mean sea level rise are modified by regional differences in the steric (density-related) component of sea level rise and changing gravitational interactions between the ocean and the ice sheets which affect the regional distribution of the eustatic (mass-related) contribution to sea level rise. The most extreme sea levels in this region are generated by tropical cyclones. The intensity of the strongest tropical cyclones is likely to increase, but many climate models project a substantial decrease in tropical cyclone numbers in this region, which may lead to an overall decrease in the total number of intense tropical cyclones. This projection, however, needs to be better quantified using improved high-resolution climate model simulations of tropical cyclones. Future changes in ENSO may lead to large regional variations in tropical cyclone incidence and sea level rise, but these impacts are also not well constrained. While storm surges from tropical cyclones give the largest sea level extremes in the parts of this region where they occur, other more frequent high sea level events can arise from swell generated by distant storms. Changes in wave climate are projected for the tropical Pacific due to anthropogenically-forced changes in atmospheric circulation. Future changes in sea level extremes will be caused by a combination of changes in mean sea level, regional sea level trends, tropical cyclone incidence and wave climate. Recommendations are given for research to increase understanding of the response of these factors to climate change. Implications of the results for adaptation research are also discussed.

Groundwater pollution by sanitation on tropical islands

Article

Full-text available

Jan 1999

Peter Dillon

Sea level variations at tropical Pacific islands since 1950

Article

Full-text available

Jan 2012
GLOBAL PLANET CHANGE

Mechanical and Thermal Characteristics of Insulation Materials for the KSTAR Magnet System at Cryogenic Temperature

Article

Full-text available

Jun 2004

The KSTAR(Korea Superconducting Tokamak Advanced Research) superconducting magnet is electrically insulated by the composite material of epoxy resin and glass fiber (2.5 kV/mm) and Kapton (8 kV/mm). The insulation composite material of epoxy resin and glass fiber is prepared using a VPI (Vacuum Pressure Impregnation) process. The superconducting magnet is under mechanical stress caused by the large temperature difference between the operation temperature of the magnet and room temperature. The large electro‐magnetic force during the operation of the magnet is also exerted on the magnet. Therefore, the characteristics of the insulation material at cryogenic temperatures are very important and the tensile stress and thermal expansion coefficient for the insulation materials of the KSTAR superconducting magnet are measured. This paper presents results on mechanical properties of the insulation material for KSTAR magnets, such as density, ultimate tensile stress and thermal contraction between room temperature and cryogenic temperatures. © 2004 American Institute of Physics

Nature and stability of atoll island shorelines: Gilbert Island chain, Kiribati, equatorial Pacific

Article

Full-text available

May 2011
SEDIMENTOLOGY

Eugene C. Rankey

Islands rimming Pacific atolls typically form narrow, low-lying lands that are commonly perceived to be particularly vulnerable to global changes such as sea-level rise. As these, low islands form the only habitable land for many island nations, understanding the character of shorelines, and the rates and controls that operate to bring about changes, is an issue of central importance. The purpose of this study is to unravel the characteristics of coastal change on atoll islands of the Gilbert Island chain of the equatorial Pacific nation of Kiribati, especially as they relate to autogenic shoreline processes and El Niño/Southern Oscillation variability. Integration of field observations, differential global positioning system data, historical aerial photographs and ultra-high resolution remote sensing images demonstrates the nature, spatial patterns and rates of change from 17 islands on Maiana and Aranuka atolls. The results illustrate that, between 2005 and 2009, ca 50% of the shorelines on these islands displayed a discernable shift in position; some shorelines were accretionary (at net rates up to ca 8 m year−1) and others were erosional (up to ca 18 m year−1). Long-term net rates of change on Maiana between 1969 and 2009 were lower than short-term net rates measured between 2005 and 2009. Both short-term and long-term observations illustrate some of the greatest change occur near terminations of the largest, north–south oriented islands, associated with longshore movement of coarse sand and gravel. Direct hits by tropical depressions and marked seasonality, factors interpreted as being essential in island growth and shoreline dynamics elsewhere, do not directly impact these equatorial atolls and can be eliminated as fundamental controls on shoreline dynamics. Similarly, observations over four years suggested that shoreline variability probably is not influenced directly by marked sea-level change, although a recent increase in the rates of shoreline change could reflect instability related to the cumulative effect of a long-term increase in the rate of sea-level rise. Within this framework of global change, local anthropogenic effects, autogenic shoreline processes and El Niño/Southern Oscillation-influenced wind and wave variability control many aspects of these dynamic shorelines. These results provide quantitative insights into the character and variability of rates of shoreline change, information essential for evaluating and mitigating the vulnerability of island nations such as Kiribati.

Responses of Atoll Freshwater Lenses to Storm-Surge Washover in the Northern Cook Islands

Article

Full-text available

May 2010

A category 5 tropical cyclone swept a storm surge across remote Pukapuka Atoll in the Northern Cook Islands (South Pacific Ocean) in late February 2005. Groundwater salinity (specific conductance) observations are reported for the 2-year post-storm period, with the aim of investigating the effects of saltwater intrusion on thin freshwater lenses within the atoll islets. This is the first article to present field observations of such an event. Specific conductance at shallow depths increased dramatically from potable conditions (approximately 1,000 mu S/cm) to brackish levels unsuitable for drinking (up to 10,000 mu S/cm) shortly after the cyclone. Subsequently, the freshwater lenses required 11 months to recover. Within the thickest aquifer, a well-defined saline plume formed at 6 m depth, sandwiching a freshwater layer beneath it and the base of the lens. Plume dispersal proceeded only gradually, owing to its formation at the start of the SW Pacific regional dry season and the low tidal range on Pukapuka. Consequently, the remnant of the plume was still present 26 months after the saltwater incursion. An important finding was that the freshwater horizon preserved at depth maintained salinity levels below 1,800 mu S/cm (i.e. within usable limits) for at least 5 months after surface overwash.

El Niño-Southern Oscillation determines the salinity of the freshwater lens under a coral atoll in the Pacific Ocean

Article

Full-text available

Nov 2006

The freshwater resources of coral atolls occur mainly as lenses floating on salt water underneath the islands. The size and shape of these lenses are determined by hydrogeologic characteristics, the rainfall recharge rate and its temporal variation, plus extractions (Underwood et al., 1992; Jones and Banner, 2003; Jocson et al., 2002). In the South Pacific, rainfall exhibits seasonal as well as interannual variability related to the El Nino-Southern Oscillation (ENSO) (Ropelewski and Halpert, 1987). We used electric conductivity measurements from pumped wells on Tongatapu to show a moderate ENSO control on the temporal fluctuation of the pumped freshwater salinity. The salinity dynamics depended on low or increased rainfall recharge during respectively dry El Nino periods or wet La Nina events. ENSO events cause a large variation around the mean salinity and determine the relative salinity over the time-scale of several years, while a smaller variation is introduced by seaso

Challenges in Freshwater Management in Low Coral Atolls

Article

Full-text available

Nov 2007
J CLEAN PROD

Population centres in low atoll islands have water supply problems that are amongst the most critical in the world. Fresh groundwater, the major source of water in many atolls, is extremely vulnerable to natural processes and human activities. Storm surges and over-extractions cause seawater intrusion, while human settlements and agriculture can pollute shallow groundwaters. Limited land areas restrict freshwater quantities, particularly in frequent ENSO-related droughts. Demand for freshwater is increasing and availability is extremely limited. At the core of many groundwater management problems are the traditional water ownership rights inherent in land tenure and the conflict between the requirements of urbanised societies and the traditional values and rights of subsistence communities living on groundwater reserves. Resource limitations and geographic isolation restrict the potential for increasing wealth through crop exports. Water governance reforms and the provision of knowledge to communities are critical. Regional water organisations, fostering self-support, are a key to developing island-adopted and owned solutions.

The dynamic response of reef islands to sea-level rise: Evidence from multi-decadal analysis of island change in the Central Pacific

Article

Full-text available

Jun 2010
GLOBAL PLANET CHANGE

Low-lying atoll islands are widely perceived to erode in response to measured and future sea-level rise. Using historical aerial photography and satellite images this study presents the first quantitative analysis of physical changes in 27 atoll islands in the central Pacific over a 19 to 61 yr period. This period of analysis corresponds with instrumental records that show a rate of sea-level rise of 2.0 mm yr− 1 in the Pacific. Results show that 86% of islands remained stable (43%) or increased in area (43%) over the timeframe of analysis. Largest decadal rates of increase in island area range between 0.1 to 5.6 ha. Only 14% of study islands exhibited a net reduction in island area. Despite small net changes in area, islands exhibited larger gross changes. This was expressed as changes in the planform configuration and position of islands on reef platforms. Modes of island change included: ocean shoreline displacement toward the lagoon; lagoon shoreline progradation; and, extension of the ends of elongate islands. Collectively these adjustments represent net lagoonward migration of islands in 65% of cases. Results contradict existing paradigms of island response and have significant implications for the consideration of island stability under ongoing sea-level rise in the central Pacific. First, islands are geomorphologically persistent features on atoll reef platforms and can increase in island area despite sea-level change. Second, islands are dynamic landforms that undergo a range of physical adjustments in responses to changing boundary conditions, of which sea level is just one factor. Third, erosion of island shorelines must be reconsidered in the context of physical adjustments of the entire island shoreline as erosion may be balanced by progradation on other sectors of shorelines. Results indicate that the style and magnitude of geomorphic change will vary between islands. Therefore, island nations must place a high priority on resolving the precise styles and rates of change that will occur over the next century and reconsider the implications for adaption.

Tempestuous Times in the South Pacific Islands

Article

Full-text available

Apr 2010
SCIENCE

In recent weeks, a number of Central South Pacific nations and territories have suffered a battering from an onslaught of intense cyclones occurring in quick succession. In early February, tropical cyclone (TC) Oli thrashed remote Tubuai in French Polynesia, tearing down buildings and pulverizing

Numerical Modeling of Atoll Island Hydrogeology

Article

Full-text available

Dec 2008
GROUND WATER

We implemented Ayers and Vachers' (1986) inclusive conceptual model for atoll island aquifers in a comprehensive numerical modeling study to evaluate the response of the fresh water lens to selected controlling climatic and geologic variables. Climatic factors include both constant and time-varying recharge rates, with particular attention paid to the effects of El Niño and the associated drought it brings to the western Pacific. Geologic factors include island width; hydraulic conductivity of the uppermost Holocene-age aquifer, which contains the fresh water lens; the depth to the contact with the underlying, and much more conductive, Pleistocene karst aquifer, which transmits tidal signals to the base of the lens; and the presence or absence of a semiconfining reef flat plate on the ocean side. Sensitivity analyses of steady-steady simulations show that lens thickness is most strongly sensitive to the depth to the Holocene-Pleistocene contact and to the hydraulic conductivity of the Holocene aquifer, respectively. Comparisons between modeling results and published observations of atoll island lens thicknesses suggest a hydraulic conductivity of approximately 50 m/d for leeward islands and approximately 400 m/d for windward islands. Results of transient simulations show that lens thickness fluctuations during average seasonal conditions and El Niño events are quite sensitive to island width, recharge rate, and hydraulic conductivity of the Holocene aquifer. In general, the depletion of the lens during drought conditions is most drastic for small, windward islands. Simulation results suggest that recovery from a 6-month drought requires about 1.5 years.

Safe Water for People in Low, Small Island Pacific Nations: The rural–urban dilemma

Article

Full-text available

Jun 2008

The issue of ensuring that growing communities in small island countries have access to safe water and adequate sanitation is examined in Kiribati, whose islands are spread over three million square kilometres in the central Pacific. Its coral island communities have water supply and sanitation problems among the most difficult in the world. Formulaic developed-world approaches, models, techniques and toolboxes that do not consider the social and cultural context have had little success. Changes in approach at the international, national and local levels are called for, and the resourcing of village-level water and sanitation committees would return ownership and control in rural communities to its traditional base. Development (2008) 51, 282–287. doi:10.1057/dev.2008.18

Modelling freshwater lens salinisation and recovery on atoll islands after storm-wave washover.

Conference Paper

Aug 2011

Scattered coral atolls throughout the tropical Pacific Ocean rely heavily on their unconfined groundwater lenses within the islet substrate as freshwater supply. However, these thin groundwater lenses are extremely vulnerable and are subjected to many threats including lens salinisation resulting from islet washover by large waves during severe tropical storms. Using simulations and mathematical modelling, this study examines the immediate response, longer-term behaviour and subsequent (partial) recovery of a Pacific atoll freshwater lens after saline damage caused by cyclone-generated wave washover. Modelling results demonstrate that the saline plume formed by a washover event mostly migrates downwards first through the top coral sand and gravel substrate, but then exits the aquifer to the ocean laterally through the more permeable basement limestone. Findings also suggest that relatively fresher water can possibly be found as a preserved horizon in the deeper part of an aquifer after disturbance, especially if the freshwater lens extends into the limestone under normal conditions. Since shortages of freshwater supply seriously threaten small and isolated atoll communities impacted by tropical cyclones, this study provides insights for authorities tasked with assisting afflicted island communities to cope and recuperate after such climatic disturbances.

The ecosystems and flora of Majuro Atoll

Article

Jan 2008

R.R. Thaman

Pacific atolls: a world apart

Article

Jan 2010

P.D. Nunn

Developing national water resources policy and implementation plans for the Kiribati climate change adaptation program

Article

Jan 2010

Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change

Article

Jan 2007

Geomorphology of reef islands and atoll motu in Tuvalu

Article

Jan 1991
Commonwealth Q

Impacts of eustasy and hydro-eustasy on the evolution and landforms of Pacific atolls

Article

Oct 2004
PALAEOGEOGR PALAEOCL

William R. Dickinson

Consideration of eustatic and hydro-isostatic effects on late Quaternary sea levels in the tropical Pacific Ocean indicates that the configuration of modern atolls with emergent annular reef flats is a transient morphology not developed until post-mid-Holocene time. Annular atoll reefs, perched atop carbonate platforms which cap buried volcanic edifices, are underlain by 8-28 m of Holocene limestone disconformably overlying a substratum of last-interglacial or older limestone. Comparable thicknesses (9-23 m) of Holocene sediment are present beneath atoll lagoons that are uniformly <85 m deep. During glacio-eustatic drawdowns in global sea level by 120-125 m, carbonate platforms of modern atoll provinces rose abruptly from the sea as clusters of subaerial limestone plateaus flanked by steep cliffs. Modern analogues are provided by emergent atolls uplifted on the flexural arches of trench forebulges. Slow subsidence coupled with karstic erosion of emergent atolls during the last glaciation lowered the surfaces of last-interglacial reef edifices by the amounts needed to provide accommodation space for Holocene reef growth during the postglacial eustatic rise in sea level. Modern atoll reef caps began to grow after ∼9 ka when rising Holocene sea level overtopped degraded remnants of interglacial reefs, but remained submerged until carbonate buildups approached sea level in mid-Holocene time (6-4 ka). Classic atoll morphology, with circlets of multiple islets dotting annular reefs, formed in combination with late Holocene hydro-isostatic drawdown in tropical Pacific sea level in response to equatorial ocean siphoning, a facet of global isostatic adjustment (GIA) to deglaciation. Early Holocene eustatic rise in sea level and late Holocene hydro-isostatic decline in sea level combined to produce a regionally variable mid-Holocene highstand in tropical Pacific sea level that stood 1.0-2.6 m above modern sea level. Cemented mid-Holocene paleoreef flats now stranded well above sea level serve as resistant foundations for non-migratory (pinned) islets that were not present along atoll rims until after the local crossover date, when ambient high-tide level first fell below mid-Holocene low-tide level. Existing atoll landforms have a time depth generally <1-2 ka.

Groundwater Lens Dynamics of Atoll Islands

Article

Nov 1992
WATER RESOUR RES

A variable-density groundwater model is used to analyze the effects of various controls on the size of the freshwater lens, the structure of the transition zone, and the propagation of tidal fluctuations in a two-layer atoll island groundwater system. Modeling results indicate that mixing of fresh water and saltwater occurs primarily as a result of oscillating vertical flow due to tidal fluctuations and depends to a lesser extent on transverse dispersion along the dominantly horizontal recharge-discharge path of flow. The controls on the amount of mixing are: (1) the accumulated vertical distance, which increases with tidal range and is restricted by vertical permeabilities, and (2) vertical longitudinal dispersion. Comparison of cross-sectional simulations of atoll islands using nontidal and tidal models shows that the nontidal model must use artificially high values of transverse dispersivity to compensate for the lack of tidally driven, vertical mixing processes. Although the tidal model has high computational requirements, it can be used to calibrate vertical permeabilities and is best suited for problems dealing with groundwater resource evaluations, hydrologic events, and hydrologic processes. The limitations of the nontidal model are that it cannot be used for calibration of vertical permeabilities and will not realistically simulate those cases in which transition zones are thick or recharge low.

Impacts of eustasy and hydro-eustasy on the evolution and landforms of Pacific atolls

Article

Oct 2004
PALAEOGEOGR PALAEOCL

William R. Dickinson

Consideration of eustatic and hydro-isostatic effects on late Quaternary sea levels in the tropical Pacific Ocean indicates that the configuration of modern atolls with emergent annular reef flats is a transient morphology not developed until post-mid-Holocene time. Annular atoll reefs, perched atop carbonate platforms which cap buried volcanic edifices, are underlain by 8–28 m of Holocene limestone disconformably overlying a substratum of last-interglacial or older limestone. Comparable thicknesses (9–23 m) of Holocene sediment are present beneath atoll lagoons that are uniformly <85 m deep. During glacio-eustatic drawdowns in global sea level by 120–125 m, carbonate platforms of modern atoll provinces rose abruptly from the sea as clusters of subaerial limestone plateaus flanked by steep cliffs. Modern analogues are provided by emergent atolls uplifted on the flexural arches of trench forebulges. Slow subsidence coupled with karstic erosion of emergent atolls during the last glaciation lowered the surfaces of last-interglacial reef edifices by the amounts needed to provide accommodation space for Holocene reef growth during the postglacial eustatic rise in sea level. Modern atoll reef caps began to grow after ∼9 ka when rising Holocene sea level overtopped degraded remnants of interglacial reefs, but remained submerged until carbonate buildups approached sea level in mid-Holocene time (6–4 ka). Classic atoll morphology, with circlets of multiple islets dotting annular reefs, formed in combination with late Holocene hydro-isostatic drawdown in tropical Pacific sea level in response to equatorial ocean siphoning, a facet of global isostatic adjustment (GIA) to deglaciation. Early Holocene eustatic rise in sea level and late Holocene hydro-isostatic decline in sea level combined to produce a regionally variable mid-Holocene highstand in tropical Pacific sea level that stood 1.0–2.6 m above modern sea level. Cemented mid-Holocene paleoreef flats now stranded well above sea level serve as resistant foundations for non-migratory (pinned) islets that were not present along atoll rims until after the local crossover date, when ambient high-tide level first fell below mid-Holocene low-tide level. Existing atoll landforms have a time depth generally <1–2 ka.

Tropical cyclones and climate change: Unresolved issues

Article

Aug 2004

Kevin Walsh

This paper reviews our current understanding of the effect of climate change on tropical cyclones. While there are presently no discernible changes in tropical cyclone characteristics that could reasonably be ascribed to global warming, predictions suggest some increases in tropical cyclone maximum intensity in a warmer world. Formation regions are unlikely to change, while little consensus has emerged regarding changes in cyclone numbers or tracks. Some uncertainty in these predictions is created by clear deficiencies in current climate models. If predictions of intensities are correct, however, changes should be detectable in the Atlantic some time after 2050.

Pacific Atolls: A World Apart

Chapter

Jan 2010

Patrick Nunn

Atolls are low islands made from biogenic detritus that are scattered across the low-latitude Pacific Ocean. Atolls mark places where reef-fringed volcanic islands were once emerging but then sank slowly allowing the reef to continue growing at the ocean surface, finally forming an atoll. Owing to their low elevation and mostly soft-sediment composition, atolls are among the most vulnerable island environments on Earth. Some may disappear during this century as a result of sea-level rise.

Three linked risks for development in the Pacific Islands: Climate change, disasters and conflict

Article

Jul 2011
Clim Dev

Pacific Island countries are demonstrably vulnerable to the risks of climate change, disasters and conflict. This article outlines the conceptual links between these risks, briefly describes how each of the risks operates in the Pacific Islands, and goes on to demonstrate the interaction of climate change, disasters and potential for conflict in the Pacific Islands, by applying a new conceptual framework to some illustrative case studies. The case studies include relocation after the Gizo earthquake, ‘environmental refugees’ from sea level rise, and aggravation of the social issues of urbanization and unemployed youth by climate change. Fortunately, none of these cases has yet crossed the threshold into violent conflict, even though relocation of an affected community onto someone else's land is a particularly sensitive issue in the Pacific Islands.

Sea level projections to AD2500 with a new generation of climate change scenarios

Article

Jan 2012
GLOBAL PLANET CHANGE

Sea level rise over the coming centuries is perhaps the most damaging side of rising temperature (Anthoff et al., 2009). The economic costs and social consequences of coastal flooding and forced migration will probably be one of the dominant impacts of global warming (Sugiyama et al., 2008). To date, however, few studies (Nicholls et al., 2008; Anthoff et al., 2009) on infrastructure and socio-economic planning include provision for multi-century and multi-metre rises in mean sea level. Here we use a physically plausible sea level model constrained by observations, and forced with four new Representative Concentration Pathways (RCP) radiative forcing scenarios (Moss et al., 2010) to project median sea level rises of 0.57 for the lowest forcing and 1.10 m for the highest forcing by 2100 which rise to 1.84 and 5.49 m respectively by 2500. Sea level will continue to rise for several centuries even after stabilisation of radiative forcing with most of the rise after 2100 due to the long response time of sea level. The rate of sea level rise would be positive for centuries, requiring 200–400 years to drop to the 1.8 mm/yr 20th century average, except for the RCP3PD which would rely on geoengineering.

Atoll island vulnerability to flooding and inundation revealed by historical reconstruction: Fongafale Islet, Funafuti Atoll, Tuvalu

Article

Jun 2007
GLOBAL PLANET CHANGE

The reef islands formed on coral atolls are generally small, low, and flat, with elevations of only a few meters. These islands are thus highly vulnerable to elevated sea levels caused by extreme events and global warming. Such vulnerability was recently evidenced at Fongafale Islet, the capital of Tuvalu, when it flooded during accelerated spring high tides possibly related to sea level rise caused by global warming. Many factors, not only environmental but also economic and social, determine the vulnerability of an island to sea level rise. In this study, we used data spanning 108 yrs to reconstruct changes in topography, land use/cover, population, and the distribution of buildings at Fongafale Islet. The results indicate that the vulnerability of Fongafale Islet relates to its original landform characteristics: the central part of the island was formerly dominated by swampland that flooded at high tides. Fongafale Islet experienced greater population in-migration and centralization beginning in the 1970s following the independence of Tuvalu and Kiribati. Migrants were also responding to declines in overseas mining operations and limited options for paid employment. As the population increased, construction took place in vulnerable swampland areas. Our results clearly demonstrate that examinations of global environmental issues should focus on characteristics specific to the region of interest. These characteristics should be specified using historical reconstruction to understand and address the vulnerability of an area to global environmental changes.

Sea Level Rise at Tropical Pacific and Indian Ocean Islands

Article

Sep 2006
GLOBAL PLANET CHANGE

Historical and projected sea-levels for islands in the tropical Pacific and Indian oceans are a subject of considerable interest and some controversy. The large variability (e.g. El Niño) signals and the shortness of many of the individual tide-gauge records contribute to uncertainty of historical rates of sea-level rise. Here, we determine rates of sea-level rise from tide gauges in the region. We also examine sea-level data from the TOPEX/Poseidon satellite altimeter and from a reconstruction of sea level in order to put the sparse (in space and time) tide-gauge data into context. For 1993 to 2001, all the data show large rates of sea-level rise over the western Pacific and eastern Indian Ocean (approaching 30 mm yr− 1) and sea-level falls in the eastern Pacific and western Indian Ocean (approaching − 10 mm yr− 1). Over the region 40°S to 40°N, 30°E to 120°W, the average rise is about 4 mm yr− 1. For 1950 to 2001, the average sea-level rise (relative to land) from the six longest tide-gauge records is 1.4 mm yr− 1. After correcting for glacial isostatic adjustment and atmospheric pressure effects, this rate is 2.0 mm yr− 1, close to estimates of the global average and regional average rate of rise. The long tide-gauge records in the equatorial Pacific indicate that the variance of monthly averaged sea-level after 1970 is about twice that before 1970. We find no evidence for the fall in sea level at the Maldives as postulated by Mörner et al. (2004). Our best estimate of relative sea-level rise at Funafuti, Tuvalu is 2 ± 1 mm yr− 1 over the period 1950 to 2001. The analysis clearly indicates that sea-level in this region is rising. We expect that the continued and increasing rate of sea-level rise and any resulting increase in the frequency or intensity of extreme sea-level events will cause serious problems for the inhabitants of some of these islands during the 21st century.

Holocene Sea-Level Record on Funafuti and Potential Impact of Global Warming on Central Pacific Atolls

Article

Mar 1999

William R. Dickinson

Geomorphic features inherited from the mid-Holocene glacio-hydro-isostatic sea-level highstand that affected the central Pacific region influence the susceptibility of atoll islets to potentially enhanced wave erosion associated with rise in sea level from global warming. Shoreline morphology on multiple islets of Funafuti atoll in central Tuvalu reflects a relative mid-Holocene sea-level highstand 2.2–2.4 m above modern sea level. Typical islets are composed of unconsolidated post-mid-Holocene sediment resting disconformably on cemented coral rubble formed beneath now-emergent mid-Holocene reef flats. Exposed remnants of the lithified islet foundations serve as resistant buttresses protecting the flanks of atoll islets from wave attack. Islets lacking cemented mid-Holocene deposits as part of their internal structure are migratory sand cays with unstable shorelines. Any future sea-level rise ≥0.75 m, bringing high tide above the elevation of mid-Holocene low tide, might trigger enhanced wave erosion of stable atoll islets by overtopping the indurated mid-Holocene reef platforms. As analogous threshold relations are inferred for other central Pacific atolls, the risk of future inundation of island nations cannot be evaluated solely in terms of expected sea-level rise with respect to gross islet elevations.

Reef-Island Topography and the Vulnerability of Atolls to Sea-Level Rise

Article

May 2008
GLOBAL PLANET CHANGE

Colin Woodroffe

Low-lying reef islands on the rim of atolls are perceived as particularly vulnerable to the impacts of sea-level rise. Three effects are inferred: erosion of the shoreline, inundation of low-lying areas, and saline intrusion into the freshwater lens. Regional reconstruction of sea-level trends, supplementing the short observational instrumental record, indicates that monthly mean sea level is rising in the eastern Indian and western Pacific Oceans. This paper reviews the morphology and substrate characteristics of reef islands on Indo-Pacific atolls, and summarises their topography. On most atolls across this region, there is an oceanward ridge built by waves to a height of around 3 m above MSL; in a few cases these are topped by wind-blown dunes. The prominence of these ridges, together with radiocarbon dating and multi-temporal studies of shoreline position, indicate net accretion rather than long-term erosion on most of these oceanward shores. Less prominent lagoonward ridges occur, but their morphology and continuity are atoll-specific, being a function of the processes operating in each lagoon. Low-lying central areas are a feature of many islands, often locally excavated for production of taro. These lower-lying areas are already subject to inundation, which seems certain to increase as the sea rises. Tropical storms play an important role in the geomorphology of reef islands in those regions where they are experienced. Topographical differences, as well as features such as emergence of the reef flat and the stability of the substrate, mean that islands differ in terms of their susceptibility to sea-level rise. Further assessment of variations in shoreline vulnerability based on topography and substrate could form the basis for enhancing the natural resilience of these islands.

Groundwater Dynamics of Fongafale Islet, Funafuti Atoll, Tuvalu

Article

Oct 2011
GROUND WATER

Geoelectric and hydrologic surveys during spring tides revealed the spatiotemporal distribution of groundwater quality produced by tidal forcing in Fongafale Islet, Funafuti Atoll, Tuvalu. The observed low resistivity showed that saline water largely immersed the surficial Holocene aquifer, indicating that there is no thick freshwater lens in Fongafale Islet, unlike in other atoll islands of comparable size. Half of the islet was constructed by reclaiming the original swamp with porous, highly permeable coral blocks; this reclaimed area should not be considered as part of the islet width for calculation of the expected thickness of the freshwater lens. The degree of aquifer salinization depends on the topographic characteristics and the hydrologic controls on the inland propagation of the tidal forcing. Large changes in bulk resistivity and the electrical conductivity of groundwater from wells indicate that periodic salinization in phase with the semidiurnal tides was occurring widely, especially in areas at lower elevation than the high-tide level and in reclaimed areas with high permeability. Thin sheets of nearly fresh and brackish water were observed in the surficial aquifer in areas above the high-tide level and in taro swamps, respectively. The thinness of the brackish and freshwater sheets suggests that the taro swamps and the fresh groundwater resources of the islet are highly vulnerable to salinization from anticipated sea-level rise. An understanding of the inherent geologic and topographic features of an atoll is necessary to evaluate the groundwater resources of the atoll and assess the vulnerability of its water resources to climate change.

Modeling Fresh Water Lens Damage and Recovery on Atolls After Storm-Wave Washover

Article

Aug 2011
GROUND WATER

The principal natural source of fresh water on scattered coral atolls throughout the tropical Pacific Ocean is thin unconfined groundwater lenses within islet substrates. Although there are many threats to the viability of atoll fresh water lenses, salinization caused by large storm waves washing over individual atoll islets is poorly understood. In this study, a mathematical modeling approach is used to examine the immediate responses, longer-term behavior, and subsequent (partial) recovery of a Pacific atoll fresh water lens after saline damage caused by cyclone-generated wave washover under different scenarios. Important findings include: (1) the saline plume formed by a washover event mostly migrates downward first through the top coral sand and gravel substrate, but then exits the aquifer to the ocean laterally through the more permeable basement limestone; (2) a lower water table position before the washover event, rather than a longer duration of storm washover, causes more severe damage to the fresh water lens; (3) relatively fresher water can possibly be found as a preserved horizon in the deeper part of an aquifer after disturbance, especially if the fresh water lens extends into the limestone under normal conditions; (4) post-cyclone accumulation of sea water in the central depression (swamp) of an atoll islet prolongs the later stage of fresh water lens recovery.

The South Pacific sea level & climate monitoring project. Sea Level Data Summary Report

Jun 2010
37

BoM, 2011. The South Pacific sea level & climate monitoring project. Sea Level Data Summary Report, July 2010-June 2011. National Tidal Centre, Australian Bureau of Meteorology. (Accessed November 2011 from: http://www.bom. gov.au/oceanography/projects/spslcmp/reports_6mths.shtml, 37 pp.).

SutraGUI: a graphical user interface for SUTRA, a model for ground-water flow with solute or energy transport

Jan 2004
pp

R B Winston
C I Voss

Winston, R.B., Voss, C.I., 2004. SutraGUI: a graphical user interface for SUTRA, a model for ground-water flow with solute or energy transport. U.S. Geological Survey Open-File Report 03-285. Reston, Virginia, 114 pp.

Properties of unsaturated porous media. Hydrology Paper, 17

Jan 1966

G E Laliberte
A T Corey
R H Brooks

Laliberte, G.E., Corey, A.T., Brooks, R.H., 1966. Properties of unsaturated porous media. Hydrology Paper, 17. Colorado State University, Fort Collins. 40 pp.

Modeling freshwater lens damage and recovery on atoll islands after storm-wave washover. Ground Water. doi:10.1111/j.1745-6584 Sea-level rise at tropical Pacific and Indian Ocean islands

Jan 2006
155-168

T F M Chui
J P Terry

Chui, T.F.M., Terry, J.P., 2011. Modeling freshwater lens damage and recovery on atoll islands after storm-wave washover. Ground Water. doi:10.1111/j.1745-6584.2011.00860.x. Church, J.A., White, N.J., Hunter, J.R., 2006. Sea-level rise at tropical Pacific and Indian Ocean islands. Global and Planetary Change 53, 155–168.

Farm and forestry production and marketing profile for giant swamp taro (Cyrtosperma chamissonis)

Nov 2011

H I Manner

Manner, H.I. 2011 (revised). Farm and forestry production and marketing profile for giant swamp taro (Cyrtosperma chamissonis). In: Elevitch, C.R. (Ed.), Specialty Crops for Pacific Island Agroforestry. Permanent Agriculture Resources (PAR), Holualoa, Hawai'i. 18 pp. Accessed November 2011 from bhttp://agroforestry.net/ scps>.

Republic of the Marshall Islands technical report

Jan 2008
21

S Booth
T Hasan
M Kleppen

Booth, S., Hasan, T., Kleppen, M., 2008. Republic of the Marshall Islands technical report. Water Quality Monitoring & Water Demand Management, Majuro, 21st

SUTRA, a model for saturated-unsaturated variabledensity ground-water flow with solute or energy transport

Jan 2008
270

C I Voss
A M Provost

Voss, C.I., Provost, A.M., 2008. SUTRA, a model for saturated-unsaturated variabledensity ground-water flow with solute or energy transport. U.S. Geological Survey Water-Resources Investigations Report 02-4231. Reston, Virginia, 270 pp.

Hydrology and Water Resources of Small Islands: A Practical Guide

Jan 1991
1-9

A Diaz Arenas
A Falkland

Diaz Arenas, A., Falkland, A., 1991. Characteristics of small islands. In: Falkland, A. (Ed.), Hydrology and Water Resources of Small Islands: A Practical Guide. UNESCO, Paris, pp. 1-9.

Groundwater dynamics of Fongafale Islet

Jan 2011

S Nakada
Y Umezawa
M Taniguchi
H Yamano

Nakada, S., Umezawa, Y., Taniguchi, M., Yamano, H., 2011. Groundwater dynamics of Fongafale Islet, Funafuti Atoll, Tuvalu. Ground Water. doi:10.1111/j.17456584.2011.00874.x.

Evaluating the Fate of Freshwater Lenses on Atoll Islands After Eustatic Sea-Level Rise and Cyclone-Driven Inundation: A Modelling Approach

Abstract

No full-text available

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