Thanks for your questions Jerome. The key system drivers diagram was developed to determine which of the drivers were changing, identify direct and indirect relationships and find feedback loops. This diagram was used to select which drivers to vary in our model – we chose to vary the external variables so that stakeholders could see the plausible future conditions in which their policies would operate. We modeled the impact of higher temperatures, decreased precipitation and rising sea levels on the aquifer’s ability to meet projected demands. The hypothesis behind this work is that demands projected for the Pearl Harbor Aquifer could not be sustainably met under a range of projected conditions and that understanding that transition point would allow stakeholders to develop policies that could perform well in a wider range of future conditions.

We first modeled the impact of temperature and precipitation changes on recharge. We developed a mathematical model that runs on a daily time step. Within the model, the soil conservation service runoff method was used to determine how much runoff is generated for each rainfall event based on land cover and soil data. Potential evaporation for each day was calculated using the Hamon formulae based on day of the year, latitude and temperature. A modified version of the Thornthwaite water balance was then used to determine actual evaporation and recharge.

We then ran a sensitivity analysis of the RAM2 developed by Liu (2006). The RAM2 Model is a one dimensional basal aquifer model which incorporates salinity transport. At steady state sustainable yield is a function of equilibrium hydraulic head and recharge: % Sustainable Yield = D/[(1 – (he/ho)^2)*I] where D is demand, he equilibrium head, ho is pre-development equilibrium head and I is recharge. The he is specified by determining the equilibrium height needed to maintain acceptable salinity levels at current well depths and a given sea level. This simple model was selected so that we could run a wide range of scenarios to see what demand, recharge and sea level combinations marked the threshold between a sustainable and an unsustainable aquifer. The outputs of the model are intended to help stakeholders identify scenarios for discussion in a way that makes them less vulnerable to future surprises by allowing them to see the cumulative effects of demand, recharge and sea level changes. In practice the model would be rerun to test potential policies.

Thank you for your question Govindarajan. There would be some infrastructure investments needed to reallocate the rich resource of the Waiahole Ditch water. We have not done a detailed study of infrastructure required but can describe general cost factors. Returning a portion of the flow to the windward side would require only minor infrastructure investment – perhaps changes to a diversion structure. Redirecting some of the flow to the urban areas such as Pearl City and Honolulu would require investments in both transmission and storage infrastructure. At the field level, as crops and agricultural practices change farmers may need to invest in irrigation system modifications and upgrades.

Thank you for your questions Markus. Our next step is sending a field team to Oahu over the summer to study the movements and habitat use of endangered hawaiian wetland birds and begin building a network of water experts in the area. In cooperation with the U.S. Fish and Wildlife Service and Hawai`i’s department of Fisheries and Wildlife, our team will gain insights into the ways that threatened wetland wildlife use the landscape and what aspects of wetland habitats are most important to them. Using this information to project the needs of wildlife “stakeholders” on Oahu, we will integrate this study with economic analysis to compare a set of proposed plans for using the Waiahole waters and the former sugarcane land in Central Oahu, with special attention to increasing the recharge of the Pearl Harbor Aquifer, preserving or increasing the connectivity of the wetland habitat network on Oahu, bringing income to central Oahu, and satisfying water needs between the original users of the Waiahole waters and resort developers in the leeward plains. Among possible suggestions are the use of treated sewage effluent for golf course irrigation and using a reduced leeward allotment of Waiahole waters to support an artificial wetland for agro-eco-tourism and groundwater recharge. We also plan to improve our recharge model by incorporating surface water routing and gathering additional data for better calibration.

Our Oahu team has received a research grant from the U.S. Fish and Wildlife service to carry out bird tracking and banding studies this summer, and is applying for additional funding to collaborate with the Hawai`i Audubon Society to help educate the public on the habitat needs of endangered waterbirds, the ecological services they provide, and their value and prominence in native Hawaiian culture (for example, the Hawaiian Gallinule or alae`ula, pictured on the poster, was said to have brought fire to the islands). Using our relationship with Hawai`i Audubon, various federal and state organizations, and hopefully members of the faculty from University of Hawai`i at Manoa, we hope to create the capacity for implementing the Water Diplomacy Framework on an even greater scale on Oahu and throughout the Hawaiian Archipelago.

The wave on the timeline metaphorically represents the ups and downs in the history of water on Oahu – but really its just decoration : )

Thank you for your questions Kristin. The ‘Annual Pearl Harbor Aquifer Recharge’ figure shows the spatial distribution of recharge for current land use and climate. Recharge is a function of land cover, soil permeability and rainfall. The figure below, ‘Pearl Harbor Recharge (MGD): Climate Induced Changes’, shows the spatially averaged recharge volume (in million gallons per day) for each precipitation and temperature combination (still with current land use). The colors coorespond with the magnitude of recharge with, for example, bright red indicated around 55 million gallons per day. Increased evapotranspiration was included in the development of the Climate Induced Changes figure and is computed within the model based on increased temperature. Increased precipitation intensity was not included but we plan to incorporate it in the future as it is an important factor.

Thank you for your question Zhaomin. The availability of the Waiahole Ditch waters and former sugarcane land presents a unique situation. Each potential use for the disputed land has both water demand and recharge implications. We modeled these effects on sustainability of the Pearl Harbor Aquifer (bottom left figures in our poster). As you can see in the ‘Annual Pearl Harbor Recharge’ figure land cover impacts recharge – the urban areas have low recharge (shown in yellow) due to their low permeability. As the population continues to grow, policy makers could use our model results to guide urbanization to minimize impacts to recharge by, for example, discouraging suburban sprawl in areas with high recharge potential. Land available after the collapse of the sugarcane industry can be used in a way that facilitates aquifer recharge, like agriculture and wildlife conservation. With current and future agricultural land use, aquifer sustainability also requires mitigating migration of chemicals, like pesticides and fertilizers, into the aquifer.

Managing demands can also lead to substantial water savings. Policy makers can institute efficient irrigation requirements, adopt stricter water conservation requirements in new building codes, offer incentives for retrofits and provide conservation education. A number of conservation incentive and eduction programs have already been started by the local Board of Water Supply.

The disputed Waiahole ditch waters offer an opportunity to supplement the supply to one or more sectors at a time when resources such as the Pearl Harbor Aquifer are at their sustainable limit. In reallocating the water, policy makers can look for uses of water that meet more than one goal. For example, smart golf course design can provide wildlife habitat while boosting the tourism industry and diversified agriculture can provide food while promoting biodiversity. We believe that viewing water as a flexible resource can open up new ways of looking at water and of creating additional value with a limited supply – we hope that our science can inform this conversation and enable innovative, practical solutions.