Effects of Scenario-Based Recharge Change on Groundwater Availability, Maui, Hawai‘i
Groundwater recharge in Hawai‘i can be affected by both land cover and climate change. Reduction of groundwater recharge related to loss of irrigation-return flow, changing vegetation characteristics on the landscape, increased areas with pavement, or a drying climate can adversely affect groundwater availability. Given that demand for groundwater on the Island of Maui is likely to increase, understanding how plausible changes in recharge affect groundwater availability is critical for resource management. The objective of this study is to evaluate, using an existing island-wide numerical groundwater-flow model for Maui, changes in groundwater availability in response to changes in groundwater recharge. Groundwater recharge in the model will be varied using existing spatially distributed recharge estimates that consider selected scenarios of climate and land cover changes, which have already been developed by collaborators from the International Pacific Research Center at the University of Hawaiʻi at Mānoa and the Pacific RISA. The Pacific RISA incorporated stakeholder opinions about future management of forest conservation, agriculture and ranching, urban development, and freshwater use to generate four future land-cover scenarios:
Conservation-focused
Business-as-usual
Development-focused
Balanced conservation and development
When combined with two future climate projections (extreme wet and dry futures), eight plausible future scenarios of groundwater recharge were produced. In this study, the groundwater model will be used to determine how much groundwater can be developed from existing wells for each of the eight recharge scenarios.
Potential groundwater availability will be estimated by varying withdrawals in the groundwater model until a comparable freshwater-lens thickness to a baseline condition is attained. Thus, increased recharge can be cast in terms of increased groundwater withdrawals, and reduced recharge can be cast in terms of reduced groundwater withdrawals. Because recharge estimates for the future land-cover scenarios do not consider availability of surface water for taro cultivation, this proposed study may limit taro irrigation to available base flow in nearby streams. The groundwater model will be used to evaluate availability of surface water for irrigation of taro by quantifying stream base flows, and estimated recharge from taro-cultivation areas will be adjusted accordingly. Results of this study will be useful for evaluating how groundwater availability may be affected by plausible changes in groundwater recharge and will build upon information and capabilities developed in previous studies. Results of this proposed study will identify areas that might be most sensitive to changes in groundwater recharge.
Research Team Dr. Laura Brewington, Arizona State University, East-West Center Dr. Victoria Keener, Arizona State University, East-West Center
Kirsten Oleson, Dept. of Natural Resources and Environmental Management, University of Hawai‘i
Kolja Rotzoll, US Geological Survey
Delwyn Oki, US Geological Survey
Eva Blumenstein, Maui County Water Department
Partners U.S. Geological Survey-Pacific Islands Water Science Center, Maui Department of Water Supply, Maui Department of Planning, Maui County Council, and Maui Watershed Partnerships.
Izuka, S. K., Engott, J. A., Rotzoll, K., Bassiouni, M., Johnson, A. G., Miller, L. D., & Mair, A. (2018). Volcanic aquifers of Hawai‘i—Hydrogeology, water budgets, and conceptual models (ver. 2.0, March 2018). Scientific Investigations Report (pp. 158). Reston, VA: US Geological Survey. https://doi.org/10.3133/sir20155164
Resilient and sustainable Pacific Island communities using climate information to manage risks and support practical decision-making about climate variability and change.
Scenario-based Groundwater Modeling in Hawai‘i
Effects of Scenario-Based Recharge Change on Groundwater Availability, Maui, Hawai‘i
Groundwater recharge in Hawai‘i can be affected by both land cover and climate change. Reduction of groundwater recharge related to loss of irrigation-return flow, changing vegetation characteristics on the landscape, increased areas with pavement, or a drying climate can adversely affect groundwater availability. Given that demand for groundwater on the Island of Maui is likely to increase, understanding how plausible changes in recharge affect groundwater availability is critical for resource management. The objective of this study is to evaluate, using an existing island-wide numerical groundwater-flow model for Maui, changes in groundwater availability in response to changes in groundwater recharge. Groundwater recharge in the model will be varied using existing spatially distributed recharge estimates that consider selected scenarios of climate and land cover changes, which have already been developed by collaborators from the International Pacific Research Center at the University of Hawaiʻi at Mānoa and the Pacific RISA. The Pacific RISA incorporated stakeholder opinions about future management of forest conservation, agriculture and ranching, urban development, and freshwater use to generate four future land-cover scenarios:
When combined with two future climate projections (extreme wet and dry futures), eight plausible future scenarios of groundwater recharge were produced. In this study, the groundwater model will be used to determine how much groundwater can be developed from existing wells for each of the eight recharge scenarios.
Potential groundwater availability will be estimated by varying withdrawals in the groundwater model until a comparable freshwater-lens thickness to a baseline condition is attained. Thus, increased recharge can be cast in terms of increased groundwater withdrawals, and reduced recharge can be cast in terms of reduced groundwater withdrawals. Because recharge estimates for the future land-cover scenarios do not consider availability of surface water for taro cultivation, this proposed study may limit taro irrigation to available base flow in nearby streams. The groundwater model will be used to evaluate availability of surface water for irrigation of taro by quantifying stream base flows, and estimated recharge from taro-cultivation areas will be adjusted accordingly. Results of this study will be useful for evaluating how groundwater availability may be affected by plausible changes in groundwater recharge and will build upon information and capabilities developed in previous studies. Results of this proposed study will identify areas that might be most sensitive to changes in groundwater recharge.
Research Team
Dr. Laura Brewington, Arizona State University, East-West Center
Dr. Victoria Keener, Arizona State University, East-West Center
Kirsten Oleson, Dept. of Natural Resources and Environmental Management, University of Hawai‘i
Kolja Rotzoll, US Geological Survey
Delwyn Oki, US Geological Survey
Eva Blumenstein, Maui County Water Department
Partners
U.S. Geological Survey-Pacific Islands Water Science Center, Maui Department of Water Supply, Maui Department of Planning, Maui County Council, and Maui Watershed Partnerships.
References
Brewington, L., Keener, V., & Mair, A. (2019). Simulating land cover change impacts on groundwater recharge under selected climate projections, Maui, Hawaiʻi. Remote Sensing, 11, 3048. doi: 10.3390/rs11243048.
Engott, J. A., Johnson, A. G., Bassiouni, M., Izuka, S. K., & Rotzoll, K. (2017). Spatially distributed groundwater recharge for 2010 land cover estimated using a water-budget model for the Island of O‘ahu, Hawai‘i (ver 2.0, December 2017). Scientific Investigations Report (pp. 49). Reston, VA: US Geological Survey. https://doi.org/10.3133/sir20155010
Izuka, S. K., Engott, J. A., Rotzoll, K., Bassiouni, M., Johnson, A. G., Miller, L. D., & Mair, A. (2018). Volcanic aquifers of Hawai‘i—Hydrogeology, water budgets, and conceptual models (ver. 2.0, March 2018). Scientific Investigations Report (pp. 158). Reston, VA: US Geological Survey. https://doi.org/10.3133/sir20155164
Johnson, A., Engott, J., Bassiouni, M., & Rotzoll, K. (2018). Spatially distributed groundwater recharge estimated using a water-budget model for the Island of Maui, Hawai‘i, 1978-2007 (ver. 2.0, February 2018). Scientific Investigations Report. Reston, VA: US Geological Survey. https://doi.org/10.3133/sir20145168
Mair, A., Johnson, A. G., Rotzoll, K., & Oki, D. S. (2019). Estimated groundwater recharge from a water-budget model incorporating selected climate projections, Island of Maui, Hawai‘i. Scientific Investigations Report (pp. 46). Reston, VA: US Geological Survey. https://doi.org/10.3133/sir20195064
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