Participatory Scenario Planning to Simulate Impacts of Land Cover Change and Climate Change on Groundwater Recharge in Maui, Hawai‘i

Abstract:

The objective of this study was to develop an integrated land cover/hydrological modeling framework using GIS data, stakeholder input, climate information and projections, and empirical data to estimate future groundwater recharge on the island of Maui, Hawai‘i. Four future land-cover scenarios and two downscaled climate projections representing wet and dry climate futures were used to estimate the end of the century mean annual groundwater recharge. The future land-cover scenarios were co-developed with over 100 diverse stakeholders: Future 1 – conservation-focused, Future 2 - status quo, Future 3 – development-focused, and Future 4 - balanced conservation and development. To understand how the changing land management and climate could influence groundwater recharge, the results were compared to the estimated recharge using a 2017 baseline land cover. The estimated mean island-wide recharge rate increased under all future land -cover and climate combinations and was dominated by specific land -cover transitions. Conversion from fallow/grassland to diversified agriculture increased irrigation, and therefore recharge. Above the cloud zone (610 m), conversion from grassland to native or alien forest led to increased fog interception, which increased recharge. Results showed that urban expansion is currently slated for coastal areas that are already water-stressed and had low recharge projections. Through co-development of and participation in this project, municipal water utilities, policy makers, and planners increased their familiarity with uncertainty and climate projections and are using results to choose watersheds to develop for new freshwater sources. These findings demonstrate how the scenario planning process and modeling framework can help communicate the consequences and tradeoffs of alternative land management strategies under a changing climate, and serve as a tool for decision making.