Impacts of Future Climate on Groundwater Resources and Management in Maui, Hawai’i
The Pacific RISA team conducted interdisciplinary research to inform decisions about the sustainability of groundwater resources on the island of Maui under future climate conditions. The Hawaiʻi Commission on Water Resources Management (CWRM) assesses the state’s groundwater resources using simplified models. However, recent water budget model outputs indicate that changes to their estimates may be warranted for several aquifer systems on Maui. While existing work about water resources on Maui assumes a future climate that is the same as historical conditions, both global and regional data and models show that future climate may be significantly different from the past, making those assumptions invalid. To aid in planning and adaptation for the future, a new hydrological model was used to assess the impact of changing climate and land cover on groundwater recharge over the entire island, encompassing a vast diversity of urban and natural ecosystems and topography. This study aimed to: 1) Integrate future climate and land and water management decisions on Maui with a groundwater budget model that evaluates freshwater availability, for county-level adaptation and planning; 2) Assess decision makers’ understanding of climate vulnerability and adaptation, and identify the trusted sources of climate information as well as the barriers to using that information in planning for change; and 3) Evaluate how uncertainty about future climate change and groundwater resources can influence decision makers’ (a) understanding of climate change impacts on water resource sustainability and (b) preferences among possible management solutions.
Future Climate and Hydrology Modeling
Researchers at the University of Hawaiʻi (UH) International Pacific Research Center (IPRC) generated a dynamically downscaled global climate model that forecasts rainfall and other meteorological parameters for the island of Maui at 1 km resolution. A separate research team led by the UH Geography Department and the University of Albany has produced statistical downscaled climate projections for the State. The US Geological Survey (USGS) Pacific Islands Water Science Center used these two sets of projections as inputs to a soil-water balance model to calculate the Maui water budget, particularly groundwater recharge, under a set of future land and water management scenarios that were developed with Pacific RISA researchers through a participatory, stakeholder-driven process.
The Scenario Development Process
All RISA projects aim to translate climate science into real-world scenarios and help create practical tools that inform decision making with the most current scientific knowledge. To ensure that the groundwater modeling analyses directly addressed the needs of Maui’s decision makers, Pacific RISA solicited input from over stakeholders to generate a set of feasible future land use scenarios that may impact the sustainability of groundwater resources. Scenario development was conducted with policy makers, land managers, and community members, representing diverse sectors at the local, county, and state level, including the State of Hawaiʻi CWRM and Department of Agriculture, the Maui County Department of Water Supply and Department of Long-Range Planning, and an array of watershed management partners, rangeland managers, and conservation practitioners. See the section below (Building the Land Cover Scenarios) for more details of this process.
Resources
For more information on how the scenario dataset was produced, including where to download the data, please see below.
The Pacific RISA generated four future scenarios and accompanying maps for this project, using many different datasets to represent future land cover classes for the island of Maui. Below are descriptions of each scenario narrative and a summary of the steps that were taken to build the maps.
The current version of the data provided on this page (Version 1.1) was finalized in October 2018. A previous version (Version 1) was finalized in May 2015 and has been has been updated to reflect the cessation of sugarcane farming activities in central Maui, based on a new land cover map representing circa 2017 conditions. These data were used as the input land cover classes for the future climate/hydrological modeling component of this project. The data is available for download and modification to suit the needs of different users and projects. The Pacific RISA assumes no responsibility for any modifications to or products derived from the original datasets. To download the ArcGIS shapefile that contains the most recent Version 1.1 of the future scenario land cover classes and associated source information, please click here. For a more detailed description of how the scenario maps were created, please read the metadata, which is attached to the downloadable shapefile in xml format. The previous Version 1 and associated metadata can be found here.
Building the Scenarios
The Pacific RISA generated four stakeholder-defined future scenarios for this project to engage decision makers in the research and increase the relevance of the scenarios to policy and public audiences. During numerous meetings, several main land use components emerged: forest conservation, urban development, agriculture, ranching, withdrawals, streamflow restoration, and new recharge sources. These components formed the backbone of four narratives that described different “futures,” or menus of realistic management options for the island of Maui.
Native forest cover on Maui. (Source: Victoria Keener)
Forests: The type of forest cover influences groundwater recharge at a species-specific level, and the scenarios reflect varying degrees of native Hawaiian forest cover, versus the presence or dominance of alien trees.
Urban development: The impact of future urban impervious surfaces and development density on water availability are important considerations for city planners and water managers when weighing anticipated demands for housing and infrastructure against uneven water availability across the island.
Agriculture and ranching: Irrigation for agriculture, pasture, and livestock maintenance requires high volumes of water. Changes in crop cover and diversity, as well as rangeland practices, can significantly influence both surface and groundwater supplies.
Withdrawals: The amount of groundwater withdrawn from wells has a direct impact on the thickness of the freshwater lens. If a wellfield is pumped above its calculated sustainable yield, the water quality or quantity can be impaired through saltwater intrusion or lack of freshwater. Water managers use a range of projected withdrawal demands to determine how to best meet future supply.
In Iao Valley on Maui, some plantation-era diversions still capture all base flow from streams. Some groups advocate restoring historic flows to these streams. (Source: Jonathan L. Scheuer)
Streamflow restoration: The Commission for Water Resources Management is responsible for the protection and conservation of freshwater resources for the state of Hawaiʻi. This includes arbitrating disputes over streamflow diversions in designated water resource management areas. Changes in the location and amount of streamflow will impact the future Maui water budget.
New recharge sources: As Maui continues to develop, new policies and technologies have the potential to add potable or non-potable freshwater supply back into the water budget. Possible sources of additional recharge include wastewater treatment plants or stormwater capture systems.
A set of 25 land cover classes was chosen to correspond to known parameter values for the hydrological model. Each future scenario narrative and key assumptions/components were translated into the 25 land cover classes. If participants did not agree with the spatial representation of a scenario assumption or component, the group identified potential alternative inputs and the maps were adjusted accordingly. Additionally, concepts evolved as each narrative component was depicted in a map. Four final scenario maps were produced.
Future Scenario I: Low development, high forest conservation, local agriculture
This scenario reflected an interest to see how climate change could impact groundwater recharge in a future where more emphasis is placed on maintaining existing and actively restoring native forest, preventing spread of invasive species, and adding diversified agriculture and biofuels for food and energy self-sufficiency. Almost all of the current native forest cover is retained, and high investments in watershed protection facilitate the construction of additional ungulate fencing and active forest restoration within fence boundaries in the high elevations or east and west Maui. Alien forest expands in unprotected or unmanaged areas, particularly on southeast Maui, but not within ranch boundaries. Biofuel production replaces some sugarcane in central Maui as a renewable energy source, while land owned by the Department of Hawaiian Homelands (DHHL) in west Maui is also designated for future biofuel production. Remaining area that was formerly sugarcane is fallow or grassland.
Diversified agriculture as a sustainable local food source expands on new IALs, and assumes streamflow diversions or reservoir catchment for irrigation. Grasslands expand in ranching areas to promote mob grazing techniques, and some ranchland with suitable regions is converted to diversified agriculture. The Hawaiian cultural practice of taro cultivation is promoted, and assumes additional surface water use. Urban development proceeds at a slow pace, with around 60% of the projects in the 2013 Maui Island Plan database achieving completion.
Variables in the dataset that correspond to this scenario: LC_F1, iluF1, Source_F1
Future Scenario II: Business-as-usual
This scenario is a status quo continuation of existing practices, reflecting what many stakeholders perceive to be Maui’s current trajectory. Most of the existing native forest is maintained, and some funding is allocated to create a limited number of new ungulate fences at the highest elevations, but no active forest restoration is done within them. Alien forest expands outside of fenced areas, including ranchlands and higher elevation areas that were not forested in 2010. Sugarcane production has ceased in the central Maui plain and is now fallow, with limited flow restored to currently diverted streams and the addition of supplementary groundwater pumping for irrigation. The current production of boutique crops like coffee and pineapple continue, along with existing diversified agricultural practices. Minor biofuel production is added to DHHL lands in west Maui, with undeveloped areas that are currently fallow shifting to ranching grasslands. Managed tree plantations are added to ranchlands, but some are invaded by alien forest expansion. All of the fully entitled development projects in the 2013 Maui Island Plan are built out, replacing almost all taro cultivation with impervious surfaces.
Variables in the dataset that correspond to this scenario: LC_F2, iluF2, Source_F2
Future Scenario III: Aggressive development, high energy production, low forest conservation
In this scenario, development proceeds aggressively, and environmental concerns are not actively addressed. Existing native forest shrinks in response to stalled funding for watershed conservation and no new ungulate fences are constructed, while alien forest expands to the limits of predicted suitable habitat, even at the highest elevations of west Maui. Biofuel production to meet rising energy demands and petroleum costs replaces sugarcane in the existing IALs in central Maui, now classified as “diversified agriculture,” while the surrounding sugarcane land becomes fallow. Ranchlands are extensively invaded by alien forest, particularly in south and east Maui, and grasslands are lost reflecting reduced livestock production. In response to population growth and commercial and housing demands for tourism, all development projects in the Maui Island Plan are completed, and build-out to the full limits of the designated future growth boundaries occurs.
Variables in the dataset that correspond to this scenario: LC_F3, iluF3, Source_F3
Future Scenario IV: Balanced development and forest conservation
The final future scenario stemmed from stakeholders’ interest in exploring groundwater resources under a future with balanced development, economic, and conservation interests. To facilitate comparisons across scenarios, this scenario was built using components of the other three future scenarios. Native and alien forest cover was selected from the first, conservation-oriented scenario, with added tree plantations, grasslands, and west Maui biofuel from the second, business-as-usual scenario. The extensive urban land cover, in conjunction with biofuel production on IALs in central Maui, was chosen from the third, development-oriented scenario. The addition of this scenario resolved a recurring tension throughout the scenario planning process – namely, that there was an assumed conflict between conservation and development.
Variables in the dataset that correspond to this scenario: LC_F4, iluF4, Source_F4
Frequently Asked Questions
Who created these maps?
The Pacific RISA generated the maps using input from interviews and workshops with people on Maui and Oahu who are concerned about future water resources and were responsible for management or regulation of natural resources on Maui. Study participants developed different feasible narratives about future land cover on Maui, and spatial information was collected or created to represent those different futures.
What are the source files that were used to build these maps?
There is a long list of data files that went into these maps to make them as plausible as possible. Some of that data is available online and listed in the metadata. Other datasets are not publicly available due to the sensitive nature of the information. Study participants reviewed the maps as they were being generated to ensure that they accurately reflected their ideas of future land cover and management options.
How should I use the dataset?
First, download and unzip the files and check that you have a GIS software package installed that’s compatible with ArcGIS shapefile formats. For those who do not have ArcGIS installed, QGISis an excellent open source alternative with a user-friendly interface. Once you open the dataset, you’ll notice that there are over 500,000 polygons, and depending on your computer it may be slow to load. You can switch between land cover classes easily by changing the symbology from variable to variable.
What do the different variable names mean?
This is only a brief summary; please read the metadata for a complete description of each of the variables and their individual values.
POLYGON_ID: Unique identification number of each water-budget subarea
AREA_SQ_M: Area of each polygon, in square meters
LC_2017: Name of land cover or vegetation, 2017
LC_FX (example LC_F3): Name of land cover or vegetation, future scenario X
iluFX: Identification number of future scenario X land cover classes
Source_FX: Source(s) of derived future land cover for scenario X
Why are there so many polygons?
The number of polygons corresponds to the USGS water-budget model, described here, which predicts groundwater recharge based on the land cover and climate information inputs. We chose to join our land cover classes to the USGS polygons, because without it the geometry of our file was an arbitrary mashup of the many different input datasets. If you’re interested in the individual water budget components, the USGS report and associated data files can be downloaded here, and the POLYGON_ID fields in both shapefiles can be joined to assign water budget components to each of the scenario land cover classes.
You mention biofuel in the summaries of the scenarios, but there is no “biofuel” land cover class in the dataset. Why is this?
There are many different crop varieties that could be used as “biofuel,” ranging from sugarcane to hemp. Because of the diversity of options and uncertainty about the different hydrological components for each one, the land cover class “diversified agriculture” is used to represent all types of biofuel.
What do the “fog” and “no fog” distinctions mean in the land cover class names?
This designation was given by the USGS in their baseline 2017 land cover file that was used to make these maps, and refers only to forest and tree species. “Fog” simply means that the land cover is above the 2,000-ft elevation contour, the base of the fog-interception zone. “No fog” means that the land cover is below the 2,000-ft elevation contour.
When I zoom in on my study area or region of interest, some of the future land cover classes don’t make sense or look strange. Why is this?
As described in the metadata, future land cover classes were created by layering existing datasets on current and future types of land cover, resulting in the intersection of many different data sources. It would have been impossible to examine each of the 300,000+ polygons for “rationality” – instead, we chose not to modify the resulting maps and leave it to the user to make changes where they think they should be made.
Can I change the land cover classes or add and delete some information?
We encourage you to modify the shapefiles in any way you wish! Please remember, however, that our objective was to provide a set of agreed-upon, plausible future land cover maps for Maui, so any changes to the land cover classes should be carefully considered with your particular study participants and objectives in mind. The original files will remain available on our project website.
How should I cite these maps?
Please cite the most current version of the maps as follows: Brewington, L. 2018. Maui Future Land Cover Scenarios Version 1.1. East-West Center: Honolulu, Hawaii.
Our Vision
Pacific Island communities that are resilient to climate impacts and using climate information to manage risks.
Freshwater Resources on Maui
Impacts of Future Climate on Groundwater Resources and Management in Maui, Hawai’i
The Pacific RISA team conducted interdisciplinary research to inform decisions about the sustainability of groundwater resources on the island of Maui under future climate conditions. The Hawaiʻi Commission on Water Resources Management (CWRM) assesses the state’s groundwater resources using simplified models. However, recent water budget model outputs indicate that changes to their estimates may be warranted for several aquifer systems on Maui. While existing work about water resources on Maui assumes a future climate that is the same as historical conditions, both global and regional data and models show that future climate may be significantly different from the past, making those assumptions invalid. To aid in planning and adaptation for the future, a new hydrological model was used to assess the impact of changing climate and land cover on groundwater recharge over the entire island, encompassing a vast diversity of urban and natural ecosystems and topography. This study aimed to: 1) Integrate future climate and land and water management decisions on Maui with a groundwater budget model that evaluates freshwater availability, for county-level adaptation and planning; 2) Assess decision makers’ understanding of climate vulnerability and adaptation, and identify the trusted sources of climate information as well as the barriers to using that information in planning for change; and 3) Evaluate how uncertainty about future climate change and groundwater resources can influence decision makers’ (a) understanding of climate change impacts on water resource sustainability and (b) preferences among possible management solutions.
Future Climate and Hydrology Modeling
Researchers at the University of Hawaiʻi (UH) International Pacific Research Center (IPRC) generated a dynamically downscaled global climate model that forecasts rainfall and other meteorological parameters for the island of Maui at 1 km resolution. A separate research team led by the UH Geography Department and the University of Albany has produced statistical downscaled climate projections for the State. The US Geological Survey (USGS) Pacific Islands Water Science Center used these two sets of projections as inputs to a soil-water balance model to calculate the Maui water budget, particularly groundwater recharge, under a set of future land and water management scenarios that were developed with Pacific RISA researchers through a participatory, stakeholder-driven process.
The Scenario Development Process
All RISA projects aim to translate climate science into real-world scenarios and help create practical tools that inform decision making with the most current scientific knowledge. To ensure that the groundwater modeling analyses directly addressed the needs of Maui’s decision makers, Pacific RISA solicited input from over stakeholders to generate a set of feasible future land use scenarios that may impact the sustainability of groundwater resources. Scenario development was conducted with policy makers, land managers, and community members, representing diverse sectors at the local, county, and state level, including the State of Hawaiʻi CWRM and Department of Agriculture, the Maui County Department of Water Supply and Department of Long-Range Planning, and an array of watershed management partners, rangeland managers, and conservation practitioners. See the section below (Building the Land Cover Scenarios) for more details of this process.
Resources
Building the Maui Land Cover Scenarios and Maps
The Pacific RISA generated four future scenarios and accompanying maps for this project, using many different datasets to represent future land cover classes for the island of Maui. Below are descriptions of each scenario narrative and a summary of the steps that were taken to build the maps.
The current version of the data provided on this page (Version 1.1) was finalized in October 2018. A previous version (Version 1) was finalized in May 2015 and has been has been updated to reflect the cessation of sugarcane farming activities in central Maui, based on a new land cover map representing circa 2017 conditions. These data were used as the input land cover classes for the future climate/hydrological modeling component of this project. The data is available for download and modification to suit the needs of different users and projects. The Pacific RISA assumes no responsibility for any modifications to or products derived from the original datasets. To download the ArcGIS shapefile that contains the most recent Version 1.1 of the future scenario land cover classes and associated source information, please click here. For a more detailed description of how the scenario maps were created, please read the metadata, which is attached to the downloadable shapefile in xml format. The previous Version 1 and associated metadata can be found here.
Building the Scenarios
The Pacific RISA generated four stakeholder-defined future scenarios for this project to engage decision makers in the research and increase the relevance of the scenarios to policy and public audiences. During numerous meetings, several main land use components emerged: forest conservation, urban development, agriculture, ranching, withdrawals, streamflow restoration, and new recharge sources. These components formed the backbone of four narratives that described different “futures,” or menus of realistic management options for the island of Maui.
Forests: The type of forest cover influences groundwater recharge at a species-specific level, and the scenarios reflect varying degrees of native Hawaiian forest cover, versus the presence or dominance of alien trees.
Urban development: The impact of future urban impervious surfaces and development density on water availability are important considerations for city planners and water managers when weighing anticipated demands for housing and infrastructure against uneven water availability across the island.
Agriculture and ranching: Irrigation for agriculture, pasture, and livestock maintenance requires high volumes of water. Changes in crop cover and diversity, as well as rangeland practices, can significantly influence both surface and groundwater supplies.
Withdrawals: The amount of groundwater withdrawn from wells has a direct impact on the thickness of the freshwater lens. If a wellfield is pumped above its calculated sustainable yield, the water quality or quantity can be impaired through saltwater intrusion or lack of freshwater. Water managers use a range of projected withdrawal demands to determine how to best meet future supply.
Streamflow restoration: The Commission for Water Resources Management is responsible for the protection and conservation of freshwater resources for the state of Hawaiʻi. This includes arbitrating disputes over streamflow diversions in designated water resource management areas. Changes in the location and amount of streamflow will impact the future Maui water budget.
New recharge sources: As Maui continues to develop, new policies and technologies have the potential to add potable or non-potable freshwater supply back into the water budget. Possible sources of additional recharge include wastewater treatment plants or stormwater capture systems.
A set of 25 land cover classes was chosen to correspond to known parameter values for the hydrological model. Each future scenario narrative and key assumptions/components were translated into the 25 land cover classes. If participants did not agree with the spatial representation of a scenario assumption or component, the group identified potential alternative inputs and the maps were adjusted accordingly. Additionally, concepts evolved as each narrative component was depicted in a map. Four final scenario maps were produced.
Future Scenario I: Low development, high forest conservation, local agriculture
This scenario reflected an interest to see how climate change could impact groundwater recharge in a future where more emphasis is placed on maintaining existing and actively restoring native forest, preventing spread of invasive species, and adding diversified agriculture and biofuels for food and energy self-sufficiency. Almost all of the current native forest cover is retained, and high investments in watershed protection facilitate the construction of additional ungulate fencing and active forest restoration within fence boundaries in the high elevations or east and west Maui. Alien forest expands in unprotected or unmanaged areas, particularly on southeast Maui, but not within ranch boundaries. Biofuel production replaces some sugarcane in central Maui as a renewable energy source, while land owned by the Department of Hawaiian Homelands (DHHL) in west Maui is also designated for future biofuel production. Remaining area that was formerly sugarcane is fallow or grassland.
Diversified agriculture as a sustainable local food source expands on new IALs, and assumes streamflow diversions or reservoir catchment for irrigation. Grasslands expand in ranching areas to promote mob grazing techniques, and some ranchland with suitable regions is converted to diversified agriculture. The Hawaiian cultural practice of taro cultivation is promoted, and assumes additional surface water use. Urban development proceeds at a slow pace, with around 60% of the projects in the 2013 Maui Island Plan database achieving completion.
Future Scenario II: Business-as-usual
This scenario is a status quo continuation of existing practices, reflecting what many stakeholders perceive to be Maui’s current trajectory. Most of the existing native forest is maintained, and some funding is allocated to create a limited number of new ungulate fences at the highest elevations, but no active forest restoration is done within them. Alien forest expands outside of fenced areas, including ranchlands and higher elevation areas that were not forested in 2010. Sugarcane production has ceased in the central Maui plain and is now fallow, with limited flow restored to currently diverted streams and the addition of supplementary groundwater pumping for irrigation. The current production of boutique crops like coffee and pineapple continue, along with existing diversified agricultural practices. Minor biofuel production is added to DHHL lands in west Maui, with undeveloped areas that are currently fallow shifting to ranching grasslands. Managed tree plantations are added to ranchlands, but some are invaded by alien forest expansion. All of the fully entitled development projects in the 2013 Maui Island Plan are built out, replacing almost all taro cultivation with impervious surfaces.
Future Scenario III: Aggressive development, high energy production, low forest conservation
In this scenario, development proceeds aggressively, and environmental concerns are not actively addressed. Existing native forest shrinks in response to stalled funding for watershed conservation and no new ungulate fences are constructed, while alien forest expands to the limits of predicted suitable habitat, even at the highest elevations of west Maui. Biofuel production to meet rising energy demands and petroleum costs replaces sugarcane in the existing IALs in central Maui, now classified as “diversified agriculture,” while the surrounding sugarcane land becomes fallow. Ranchlands are extensively invaded by alien forest, particularly in south and east Maui, and grasslands are lost reflecting reduced livestock production. In response to population growth and commercial and housing demands for tourism, all development projects in the Maui Island Plan are completed, and build-out to the full limits of the designated future growth boundaries occurs.
Future Scenario IV: Balanced development and forest conservation
The final future scenario stemmed from stakeholders’ interest in exploring groundwater resources under a future with balanced development, economic, and conservation interests. To facilitate comparisons across scenarios, this scenario was built using components of the other three future scenarios. Native and alien forest cover was selected from the first, conservation-oriented scenario, with added tree plantations, grasslands, and west Maui biofuel from the second, business-as-usual scenario. The extensive urban land cover, in conjunction with biofuel production on IALs in central Maui, was chosen from the third, development-oriented scenario. The addition of this scenario resolved a recurring tension throughout the scenario planning process – namely, that there was an assumed conflict between conservation and development.
Frequently Asked Questions
Who created these maps?
What are the source files that were used to build these maps?
How should I use the dataset?
What do the different variable names mean?
Why are there so many polygons?
You mention biofuel in the summaries of the scenarios, but there is no “biofuel” land cover class in the dataset. Why is this?
What do the “fog” and “no fog” distinctions mean in the land cover class names?
When I zoom in on my study area or region of interest, some of the future land cover classes don’t make sense or look strange. Why is this?
Can I change the land cover classes or add and delete some information?
How should I cite these maps?
Our Vision
Pacific Island communities that are resilient to climate impacts and using climate information to manage risks.
Follow Pacific RISA
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