1601 East-West Road, Honolulu, HI 96848 info@pacificrisa.org 808.944.7111

Climate Scenarios

Impacts of Future Climate on Groundwater Resources and Management in Maui, Hawai’i

The Pacific RISA team is conducting interdisciplinary research to inform decisions about the sustainability of groundwater resources on the island of Maui under future climate conditions. The Hawaiʻi Commission for Water Resources Management (CWRM) currently assesses the state’s groundwater resources using simplified models. However, a recent water budget indicates 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 is being 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. Specifically, the study aims 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) have generated a dynamically downscaled global climate model that forecasts rainfall and other meteorological parameters for the island of Maui at 1 km resolution. The US Geological Survey (USGS) and the UH Water Resources Research Center (WRRC) uses this 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 address the needs of Maui’s decision makers, Pacific RISA solicited input from over 50 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.   During scenario development meetings, participants were encouraged to consider “best case”, “middle-of-the-road”, and “worst case” aspects of future water demand and and supply for Maui, and incorporate those into the following components (click here to find out how the final spatial data was produced):

Native forest cover on Maui. (Source: Victoria Keener)

Land use/land cover – 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.

Land use/land cover – 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.

Land Use / Land Cover – 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.

Resources for Project Participants

  • Click here to view the Maui Project Information Sheet
  • For more information on how the scenario dataset was produced, including where to download the data, please click here. Before using the data, please read the associated metadata found here (and also included in the download file).
  • For full reports on hydrologic conditions and groundwater availability in specific Maui regions, please see the following USGS publications:
Ground-Water Availability in the Wailuku Area, Maui, Hawai‘i, USGS
Groundwater Availability in the Lahaina District, West Maui, Hawaiʻi, USGS

 

 

 

 

 

 

 

The Pacific RISA program is funded by a grant from the US National Oceanic and Atmospheric Administration (NOAA). If you have questions or concerns about this project, please contact a member of the core research team, below:

East-West Center

Melissa Finucane, East-West Center; RAND | 412.683.2300 ext 4279
Victoria Keener, East-West Center | 808.944.7220
Laura Brewington, East-West Center | 808.944.7233

University of Hawaii

Aly El-Kadi, Water Resources Research Center, University of Hawai’i (WRRC) | 808.956.6331

USGS

Stephen Anthony, Pacific Islands Water Science Center | 808.587.2406
Alan Mair, Pacific Islands Water Science Center | 808.587.2402

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