Learn how the USGS studies sea-level rise and climate change impacts to coral reefs.
This study is part of the USGS Coral Reef Project.
The Problem
There is a growing body of evidence indicating that the rate of sea-level rise has increased relative to the past century and will continue to increase in the 21st century; that evidence has recently been summarized by the Intergovernmental Panel on Climate Change (IPCC). If all aspects of reef morphology—colony size and shape, cross-reef relief, surface rugosity, and so on—keep pace with the rising sea levels, then it is likely that changes in depth-controlled physical processes will be minimal to non-detectible. However, based on rates of vertical reef accretion in Hawaiʻi and throughout the Pacific (which are an order of magnitude smaller than predicted rates of sea-level rise), it is unlikely that reefs there and other locations will keep pace, and their inability to do so will lead to subtle but important changes in selected physical processes on some coral reefs.
In addition, recent studies indicate the flux of submarine groundwater discharge from land to coral reefs in Hawaiʻi and other high islands is substantial, and often significantly colder and enriched in terrestrial-derived nutrients than surrounding seawater. Ecosystem functions of submarine groundwater discharge to coral reef ecosystems are not quantified but can be hypothesized to (1) buffer thermal stress (bleaching) in corals experiencing warming, and (2) supply nutrients to otherwise oligotrophic coastal waters. While an excess of the latter has been observed to cause complete phase shifts in the form of wholesale loss of coral and replacement by macroalgae, the role of the former has not been tested. Both may be significantly altered by impending climate change and proposed land use that alter groundwater quantity, quality, flux, composition, and fate, especially in rapidly developing areas. This effort is focused on submarine groundwater discharge, its role in shaping coral reef ecosystem structure, and the ecosystem services it provides.
The Approach
The overall objective of this research effort is to better understand how climate change may impact coral reefs. Achievement of this objective requires an understanding of the physical parameters driving change in coral reefs and the resulting ecosystem processes. The goals of this effort are to:
- How will reefs respond to rapid sea-level rise at a decadal time-scale?
- How will increased wave energy and altered circulation across reefs affect circulation and sediment, nutrient, contaminant, and larval dynamics?
- Do thresholds exist in the rate of sea-level rise that would push a reef ecosystem from a state of stability to one of net loss?
- How may changes in precipitation, recharge, and human-induced withdraws impact submarine groundwater discharge to the coastal zone?
- How will coral reefs respond to variations in submarine groundwater discharge predicted to occur due to climate change?

The approach to these interdisciplinary studies will rely on a combination of field measurements and physics-based numerical monitoring. We use a wide range of tools to try to answer these questions, including: oceanographic instruments (for example, acoustic Doppler current profilers, wave/tide gauges, temperature sensors, salinity sensors, chemical sensors) mounted on the seabed or on moorings, water-column profilers with similar suites of sensors, coral cores, geophysical water-column and sub-bottom surveys, and physics-based numerical models.
Below are data releases associated with this project.
Modeled effects of depth and semidiurnal temperature fluctuations on predictions of year that coral reef locations reach annual severe bleaching for various global climate model projections
Coral reef profiles for wave-runup prediction
Model parameter input files to compare wave-averaged versus wave-resolving XBeach coastal flooding models for coral reef-lined coasts
Dynamically downscaled future wave projections from SWAN model results for the main Hawaiian Islands
Physics-based numerical model simulations of wave propagation over and around theoretical atoll and island morphologies for sea-level rise scenarios
Projected flooding extents and depths based on 10-, 50-, 100-, and 500-year wave-energy return periods, with and without coral reefs, for the States of Hawaii and Florida, the Territories of Guam, American Samoa, Puerto Rico, and the U.S. Virgin Islands,
HyCReWW database: A hybrid coral reef wave and water level metamodel
Below are publications associated with this study.
Internal tides can provide thermal refugia that will buffer some coral reefs from future global warming
The importance of explicitly modelling sea-swell waves for runup on reef-lined coasts
Hydro-morphological characterization of coral reefs for wave runup prediction
Pulse sediment event does not impact the metabolism of a mixed coral reef community
Assessing morphologic controls on atoll island alongshore sediment transport gradients due to future sea-level rise
HyCReWW: A hybrid coral reef wave and water level metamodel
Physical mechanisms influencing localized patterns of temperature variability and coral bleaching within a system of reef atolls
A 50-year Sr/Ca time series from an enclosed, shallow-water Guam coral: In situ monitoring and extraction of a temperature trend, annual cycle, and ENSO and PDO signals
Most atolls will be uninhabitable by the mid-21st century because of sea-level rise exacerbating wave-driven flooding
Carbonate system parameters of an algal-dominated reef along west Maui
Challenges of forecasting flooding on coral reef–lined coasts
A Bayesian-based system to assess wave-driven flooding hazards on coral reef-lined coasts
- Overview
Learn how the USGS studies sea-level rise and climate change impacts to coral reefs.
Plots of numerical model results showing how predicted future sea-level rise will likely reduce sediment residence time (how long it stays in place, top) and increase sediment flux (how much sediment moves how quickly, bottom) on the fringing coral reef flat off south-central Molokaʻi. This study is part of the USGS Coral Reef Project.
The Problem
There is a growing body of evidence indicating that the rate of sea-level rise has increased relative to the past century and will continue to increase in the 21st century; that evidence has recently been summarized by the Intergovernmental Panel on Climate Change (IPCC). If all aspects of reef morphology—colony size and shape, cross-reef relief, surface rugosity, and so on—keep pace with the rising sea levels, then it is likely that changes in depth-controlled physical processes will be minimal to non-detectible. However, based on rates of vertical reef accretion in Hawaiʻi and throughout the Pacific (which are an order of magnitude smaller than predicted rates of sea-level rise), it is unlikely that reefs there and other locations will keep pace, and their inability to do so will lead to subtle but important changes in selected physical processes on some coral reefs.
Photograph of the shallow fringing coral reef flat and adjacent land at Kaulana, Kahoʻolawe. In addition, recent studies indicate the flux of submarine groundwater discharge from land to coral reefs in Hawaiʻi and other high islands is substantial, and often significantly colder and enriched in terrestrial-derived nutrients than surrounding seawater. Ecosystem functions of submarine groundwater discharge to coral reef ecosystems are not quantified but can be hypothesized to (1) buffer thermal stress (bleaching) in corals experiencing warming, and (2) supply nutrients to otherwise oligotrophic coastal waters. While an excess of the latter has been observed to cause complete phase shifts in the form of wholesale loss of coral and replacement by macroalgae, the role of the former has not been tested. Both may be significantly altered by impending climate change and proposed land use that alter groundwater quantity, quality, flux, composition, and fate, especially in rapidly developing areas. This effort is focused on submarine groundwater discharge, its role in shaping coral reef ecosystem structure, and the ecosystem services it provides.
The Approach
The overall objective of this research effort is to better understand how climate change may impact coral reefs. Achievement of this objective requires an understanding of the physical parameters driving change in coral reefs and the resulting ecosystem processes. The goals of this effort are to:
- How will reefs respond to rapid sea-level rise at a decadal time-scale?
- How will increased wave energy and altered circulation across reefs affect circulation and sediment, nutrient, contaminant, and larval dynamics?
- Do thresholds exist in the rate of sea-level rise that would push a reef ecosystem from a state of stability to one of net loss?
- How may changes in precipitation, recharge, and human-induced withdraws impact submarine groundwater discharge to the coastal zone?
- How will coral reefs respond to variations in submarine groundwater discharge predicted to occur due to climate change?
Sources/Usage: Public Domain. Visit Media to see details.Maps of suspended-sediment concentrations under low tide conditions and high tide conditions off south-central Molokaʻi. Such comparisons over a range of water levels are useful to provide insight on how processes on reefs may respond to predicted future sea-level rise. The approach to these interdisciplinary studies will rely on a combination of field measurements and physics-based numerical monitoring. We use a wide range of tools to try to answer these questions, including: oceanographic instruments (for example, acoustic Doppler current profilers, wave/tide gauges, temperature sensors, salinity sensors, chemical sensors) mounted on the seabed or on moorings, water-column profilers with similar suites of sensors, coral cores, geophysical water-column and sub-bottom surveys, and physics-based numerical models.
- Data
Below are data releases associated with this project.
Modeled effects of depth and semidiurnal temperature fluctuations on predictions of year that coral reef locations reach annual severe bleaching for various global climate model projections
Using global climate model projections of sea-surface temperature at coral reef sites, we modeled the effects of depth and exposure to semidiurnal temperature fluctuations to examine how these effects may alter the projected year of annual severe bleaching for coral reef sites globally. Here we present the first global maps of the effects these processes have on bleaching projections for three IPCCoral reef profiles for wave-runup prediction
This data release includes representative cluster profiles (RCPs) from a large (>24,000) selection of coral reef topobathymetric cross-shore profiles (Scott and others, 2020). We used statistics, machine learning, and numerical modelling to develop the set of RCPs, which can be used to accurately represent the shoreline hydrodynamics of a large variety of coral reef-lined coasts around the globe.Model parameter input files to compare wave-averaged versus wave-resolving XBeach coastal flooding models for coral reef-lined coasts
This data release includes the XBeach input data files used to evaluate the importance of explicitly modeling sea-swell waves for runup. This was examined using a 2D XBeach short wave-averaged (surfbeat, XB-SB) and a wave-resolving (non-hydrostatic, XB-NH) model of Roi-Namur Island on Kwajalein Atoll in the Republic of Marshall Islands. Results show that explicitly modelling the sea-swell componenDynamically downscaled future wave projections from SWAN model results for the main Hawaiian Islands
Projected wave climate trends from WAVEWATCH3 model output were used as input for nearshore wave models (for example, SWAN) for the main Hawaiian Islands to derive data and statistical measures (mean and top 5 percent values) of wave height, wave period, and wave direction for the recent past (1996-2005) and future projections (2026-2045 and 2085-2100). Three-hourly global climate model (GCM) windPhysics-based numerical model simulations of wave propagation over and around theoretical atoll and island morphologies for sea-level rise scenarios
Schematic atoll models with varying theoretical morphologies were used to evaluate the relative control of individual morphological parameters on alongshore transport gradients. Here we present physics-based numerical SWAN model results of incident wave transformations for a range of atoll and island morphologies and sea-level rise scenarios. Model results are presented in NetCDF format, accompaniProjected flooding extents and depths based on 10-, 50-, 100-, and 500-year wave-energy return periods, with and without coral reefs, for the States of Hawaii and Florida, the Territories of Guam, American Samoa, Puerto Rico, and the U.S. Virgin Islands,
This data release provides flooding extent polygons (flood masks) and depth values (flood points) based on wave-driven total water levels for 22 locations within the States of Hawaii and Florida, the Territories of Guam, American Samoa, Puerto Rico, and the U.S. Virgin Islands, and the Commonwealth of the Northern Mariana Islands. For each of the 22 locations there are eight associated flood maskHyCReWW database: A hybrid coral reef wave and water level metamodel
We developed the HyCReWW metamodel to predict wave run-up under a wide range of coral reef morphometric and offshore forcing characteristics. Due to the complexity and high dimensionality of the problem, we assumed an idealized one-dimensional reef profile, characterized by seven primary parameters. XBeach Non-Hydrostatic was chosen to create the synthetic dataset and Radial Basis Functions implem - Publications
Below are publications associated with this study.
Filter Total Items: 40Internal tides can provide thermal refugia that will buffer some coral reefs from future global warming
Observations show ocean temperatures are rising due to climate change, resulting in a fivefold increase in the incidence of regional-scale coral bleaching events since the 1980s; analyses based on global climate models forecast bleaching will become an annual event for most of the world’s coral reefs within 30–50 yr. Internal waves at tidal frequencies can regularly flush reefs with cooler waters,AuthorsCurt D. Storlazzi, Olivia Cheriton, Ruben Van Hooidonk, Zhongxiang Zhao, Russell E. BrainardThe importance of explicitly modelling sea-swell waves for runup on reef-lined coasts
The importance of explicitly modelling sea-swell waves for runup was examined using a 2D XBeach short wave-averaged (surfbeat, “XB-SB”) and a wave-resolving (non-hydrostatic, “XB-NH”) model of Roi-Namur Island on Kwajalein Atoll in the Republic of Marshall Islands. Field observations on water levels, wave heights, and wave runup were used to drive and evaluate both models, which were subsequentlyAuthorsEllen Quataert, Curt D. Storlazzi, Ap van Dongeren, Robert T. McCallHydro-morphological characterization of coral reefs for wave runup prediction
Many coral reef-lined coasts are low-lying with elevations <4 m above mean sea level. Climate-change-driven sea-level rise, coral reef degradation, and changes in storm wave climate will lead to greater occurrence and impacts of wave-driven flooding. This poses a significant threat to their coastal communities. While greatly at risk, the complex hydrodynamics and bathymetry of reef-lined coasts maAuthorsFred Scott, Jose A. A. Antolinez, Robert T. McCall, Curt D. Storlazzi, Ad Reiners, Stuart PearsonPulse sediment event does not impact the metabolism of a mixed coral reef community
Sedimentation can bury corals, cause physical abrasion, and alter both spectral intensity and quality; however, few studies have quantified the effects of sedimentation on coral reef metabolism in the context of episodic sedimentation events. Here, we present the first study to measure coral community metabolism - calcification and photosynthesis - in a manipulative mesocosm experiment simulatingAuthorsKeisha Bahr, Ku'ulei Rodgers, Paul Jokiel, Nancy G. Prouty, Curt D. StorlazziAssessing morphologic controls on atoll island alongshore sediment transport gradients due to future sea-level rise
Atoll islands’ alongshore sediment transport gradients depend on how island and reef morphology affect incident wave energy. It is unclear, though, how potential atoll morphologic configurations influence shoreline erosion and/or accretion patterns, and how these relationships will respond to future sea-level rise (SLR). Schematic atoll models with varying morphologies were used to evaluate the reAuthorsJames B. Shope, Curt D. StorlazziHyCReWW: A hybrid coral reef wave and water level metamodel
Wave-induced flooding is a major coastal hazard on tropical islands fronted by coral reefs. The variability of shape, size, and physical characteristics of the reefs across the globe make it difficult to obtain a parameterization of wave run-up, which is needed for risk assessments. Therefore, we developed the HyCReWW metamodel to predict wave run-up under a wide range of reef morphometric and offAuthorsAna C. Rueda, Laura Cagigal, Stuart Pearson, Jose Antolínez, Curt D. Storlazzi, Ap van Dongeren, Paula Camus, Fernando J. MendezPhysical mechanisms influencing localized patterns of temperature variability and coral bleaching within a system of reef atolls
Interactions between oceanic and atmospheric processes within coral reefs can significantly alter local-scale (< km) water temperatures, and consequently drive variations in heat stress and bleaching severity. The Scott Reef atoll system was one of many reefs affected by the 2015–2016 mass coral bleaching event across tropical Australia, and specifically experienced sea surface temperature anomaliAuthorsRebecca H. Green, Ryan J. Lowe, Mark L. Buckley, Taryn M. Lopez, James GilmourA 50-year Sr/Ca time series from an enclosed, shallow-water Guam coral: In situ monitoring and extraction of a temperature trend, annual cycle, and ENSO and PDO signals
Located on the northern edge of the West Pacific Warm Pool and having a developed economy and modern infrastructure, Guam is well positioned and equipped for obtaining natural records of the west Pacific maritime paleoclimate. This study was a proof of concept to explore whether useful climate proxy records might be obtained from coral at readily accessible, even if geochemically nonoptimal, coastAuthorsTomoko Bell, Mark Lander, John Jenson, Richard Randall, Judson W. Partin, Nancy G. ProutyMost atolls will be uninhabitable by the mid-21st century because of sea-level rise exacerbating wave-driven flooding
Sea levels are rising, with the highest rates in the tropics, where thousands of low-lying coral atoll islands are located. Most studies on the resilience of these islands to sea-level rise have projected that they will experience minimal inundation impacts until at least the end of the 21st century. However, these have not taken into account the additional hazard of wave-driven overwash or its imAuthorsCurt D. Storlazzi, Stephen B. Gingerich, Ap van Dongeren, Olivia Cheriton, Peter W. Swarzenski, Ellen Quataert, Clifford I. Voss, Donald W. Field, Hariharasubramanian Annamalai, Greg A. Piniak, Robert T. McCallCarbonate system parameters of an algal-dominated reef along west Maui
Constraining coral reef metabolism and carbon chemistry dynamics are fundamental for understanding and predicting reef vulnerability to rising coastal CO2 concentrations and decreasing seawater pH. However, few studies exist along reefs occupying densely inhabited shorelines with known input from land-based sources of pollution. The shallow coral reefs off Kahekili, West Maui, are exposed to nutriAuthorsNancy G. Prouty, Kimberly K. Yates, Nathan A. Smiley, Christopher Gallagher, Olivia Cheriton, Curt D. StorlazziChallenges of forecasting flooding on coral reef–lined coasts
Understanding wave-driven coastal flooding is a challenging scientific problem; the need for forecasts is becoming more urgent because of sea level rise, climate change, and ever-growing coastal populations. The tools developed for sandy shorelines are generally not applicable to coral reef–lined coasts with their complex bathymetry, hydrodynamically rough reef platforms, steep and poorly sorted bAuthorsCurt D. StorlazziA Bayesian-based system to assess wave-driven flooding hazards on coral reef-lined coasts
Many low-elevation, coral reef-lined, tropical coasts are vulnerable to the effects of climate change, sea level rise, and wave-induced flooding. The considerable morphological diversity of these coasts and the variability of the hydrodynamic forcing that they are exposed to make predicting wave-induced flooding a challenge. A process-based wave-resolving hydrodynamic model (XBeach Non-HydrostaticAuthorsS. G. Pearson, Curt D. Storlazzi, A. R. van Dongeren, M. F. S. Tissier, A. J. H. M. Reniers