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Model Report

Coral Mortality and Bleaching Output

Last Revision Date: 08/26/2010 View as PDF
General Information Back to Top
Model Abbreviated Name:

COMBO
Model Extended Name:

Coral Mortality and Bleaching Output
Model Overview/Abstract:
COMBO is a spreadsheet-based model for the use of managers, conservationists, and biologists for projecting the effects of climate change on coral reefs at local-to-regional scales. The COMBO (Coral Mortality and Bleaching Output) model calculates the impacts to coral reefs from changes in average SST and CO2 concentrations, and from high temperature mortality (bleaching) events. The model uses a probabilistic assessment of the frequency of high temperature events under a future climate to address scientific uncertainties about potential adverse effects. COMBO offers data libraries and default factors for three selected regions (Hawai’i, Great Barrier Reef, and Caribbean), but it is structured with user-selectable parameter values and data input options, making possible modifications to reflect local conditions or to incorporate local expertise.
Keywords: coral reef, climate change, ocean acidification, vulnerability, bleach
Model Technical Contact Information:
Agency Contact:
Jeremy Martinich
Office of Air and Radiation
Climate Change Division
martinich.jeremy@epa.gov
202-343-9871

Developer Contact:
Bob Buddemeier
Kansas Geologic Survey
buddrw@kgs.ku.edu
785-864-2112

Model Homepage: http://hercules.kgs.ku.edu/coralclimate/ Exiting the EPA Site
Substantive Changes from Prior Version: N/A
Plans for further model development: Model currently exists as an excel-spreadsheet model, however it is being recoded into a new programming structure. The model is also being calibrated for additional locations in the Caribbean and Hawaiian islands.

User Information Back to Top
Technical Requirements
Computer Hardware
Desktop computer
Compatible Operating Systems
Windows
Other Software Required to Run the Model
Microsoft Excel, however the model is being recoded and will have its own programming structure in the future.
Download Information
http://hercules.kgs.ku.edu/coralclimate/Models/models.htmlexit EPA
Using the Model
Basic Model Inputs
Historical monthly mean water temperature and chemistry data, and projected future monthly temperature and chemistry data. There are two modules in COMBO each with its own set of parameters that can be manipulated or the defaults can be selected: 1) long-term change module (variables including baseline growth and mortality and Omega sensitivity and CO2 selection) and 2) episodic event module (variables including long-term sea surface temperature variation, threshold temperature, and mortality factors.
Basic Model Outputs
The final output of the model displays three different time-series of changes in coral cover to compare the effects of different sensitivities to changes in saturation state, combined with the trajectory determined by responses to long-term and episodic changes in ocean temperature. Output can easily be used in a GIS to develop maps of coral cover changes (point data for various reefs).
User Support
User's Guide Available?
http://hercules.kgs.ku.edu/coralclimate/Analysis_docs/Anal_docs.htmlexit EPA
Other User Documents
R.W. Buddemeier, P.L. Jokiel, K.M. Zimmerman, D.R. Lane, J. M. Carey, G.C. Bohling, J.A. Martinich, 2008. A modeling tool to evaluate regional coral reef responses to changes in climate and ocean chemistry. Limnology and Oceanography Methods, 6:395-411.

R.W. Buddemeier, Lane, D.R., Martinich, J.A. (2010) Modeling Regional Coral Reef Responses to Global Warming and Changes in Ocean Chemistry: Caribbean Case Study, Climatic Change, In Press.

Availability of User Support
Not available.
User Qualifications
Moderate level of education and experience related to coral reef response to thermal and chemical changes.

Model Science Back to Top
Problem Identification
The COMBO Model is a tool designed to support biologists, managers, educators, and others in predicting possible impacts of climate change on coral reefs. Its structure is transparent and accessible because it is based on a Microsoft Excel platform – making it available for use and/or development by anyone with spreadsheet familiarity. The model exists in three versions – for the Hawaiian archipelago, the Australian Great Barrier Reef, and the Caribbean. Each version has a library of climate-related data appropriate to that region, but the user is able to select among various options or substitute any more relevant local data that may be available.

The complexities, uncertainties, spatial and temporal variability, and scale mismatches of climate change and organism or ecosystem responses make predictions based on one or a few model results difficult to justify or apply. COMBO, by virtue of its response speed and relative simplicity, provides an option for scenario testing and development or sensitivity analysis that permits exploring and evaluating a range of possibilities appropriate to specific regions or environments.

Summary of Model Structure and Methods
COMBO consists of two modules which are run simultaneously to produce the output. The long-term change module projects the impacts of changes in average SST and ocean chemistry on the growth and mortality of corals. The episodic event module calculates the cumulative probability of abrupt high-temperature stress events (“coral bleaching”), based on future temperature scenarios, intra- and inter-annual distributions of high temperatures derived from historical records, and user-selected values for factors controlling the heat dose and resulting mortality.
Model Evaluation
COMBO has been evaluated and reviewed in several peer-reviewed publications, including the following:
R.W. Buddemeier, P.L. Jokiel, K.M. Zimmerman, D.R. Lane, J. M. Carey, G.C. Bohling, J.A. Martinich, 2008. A modeling tool to evaluate regional coral reef responses to changes in climate and ocean chemistry. Limnology and Oceanography Methods, 6:395-411.

R.W. Buddemeier, D.R. Lane, J.A. Martinich, 2010. Modeling Regional Coral Reef Responses to Global Warming and Changes in Ocean Chemistry: Caribbean Case Study, Climatic Change, In Press.

COMBO was also used by the World Bank in the following study:
Vergara, W., A. Deeb, D. Mira-Salama, N. Toba, (2008) The Consequences of Climate-Induced Coral Loss in the Caribbean by 2050–80, World Bank Environment Matters Annual Review 2008.

Key Limitations to Model Scope
Factors that would contribute to greater rates of coral survival compared to model predictions:
  1. Adaptation
  2. Survival of deep reefs
  3. Lower mortality rates

Factors that would contribute to lower rates of coral survival compared to model predictions:

  1. Additional sources of mortality
  2. Additional impacts from ocean acidification
  3. Increased temperature variability over the next century
  4. Additional high temperature event stress
  5. Pattern and starting temperature biases
  6. Changes in baseline growth and mortality
  7. Direct effects of climate change on reproduction and recruitment

Factors that add uncertainty to model predictions, but the direction of the potential bias is not clear:

  1. Long-term growth and mortality functions
  2. Threshold temperatures for additional bleaching events
  3. Selection of temperature datasets for model use
Case Studies
Covered in the papers cited above.


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