Search Results (4)

Optimal restoration and management of coastal wetland are contingent on reliable assessment of hydrological processes. In this study, we used the Soil and Water Assessment Tool (SWAT) model to assess the impacts of a proposed coastal wetland restoration plan on the water balance components of the Heeia watershed (Hawaii). There is a need to optimize between water needs for taro cultivation and accompanying cultural practices, wetland ecosystem services, and streamflow that feeds downstream coastal fishponds and reefs of the Heeia watershed. For this, we completed two land use change scenarios (conversion of an existing California grassland to a proposed taro field and mangroves to a pond in the wetland area) with several irrigation water diversion scenarios at different percent of minimum streamflow values in the reach. The irrigation water diversion scenarios aimed at achieving sustainable growth of the taro crop without compromising streamflow value, which plays a vital role in the health of a downstream fishpond and coastal environment of the watershed. Findings generally suggest that the conversion of a California grassland to a patched taro field is expected to decrease the baseflow value, which was a major source of streamflow for the study area, due to soil layer compaction, and thus decrease in groundwater recharge from the taro field. However, various taro irrigation water application and management scenarios suggested that diverting 50% of the minimum streamflow value for taro field would provide sustainable growth of taro crop without compromising streamflow value and environmental health of the coastal wetland and downstream fishponds. Full article

Hydrological modeling is an important tool that can be used to assess water resources’ availability and sustainability that are necessary for food security and ecological health of coastal regions. In this study, we assessed the impacts of land use and climate changes on water balance components (WBCs) of the Heeia coastal wetland. We developed a Soil and Water Assessment Tool (SWAT) model to capture the unique characteristics of the Hawaiian Islands, including its volcanic soil’s nature and high initial infiltration rates. We used the sequential uncertainty fitting algorithm to assess the sensitivity and uncertainty of WBCs under different climate change scenarios. Results of the statistical analysis of daily streamflow simulations showed that the model performance was within the generally acceptable criteria. Under future climate scenarios, rainfall change was the determinant factor most negatively impacting WBCs. Recharge and baseflow components had the highest sensitivity to the combined effects of land use and climate changes, especially during dry season. The uncertainty analysis indicated that the streamflow is projected to slightly increase by the middle of 21st century, but expected to decline by 40% during the late 21st century of Representative Concentration Pathways (RCP) 8.5. Full article

There are growing efforts around the world to restore biocultural systems that produce food while also providing additional cultural and ecological benefits. Yet, there are few examples of integrated assessments of these efforts, impeding understanding of how they can contribute to multi-level sustainability goals. In this study, we collaborated with a community-based non-profit in He‘eia, O‘ahu to evaluate future scenarios of traditional wetland and flooded field system agriculture (lo‘i kalo; taro fields) restoration in terms of locally-relevant cultural, ecological, and economic outcomes as well as broader State of Hawai‘i sustainability goals around food, energy, and water. Families participating in the biocultural restoration program described a suite of community and cultural benefits stemming from the process of restoration, including enhanced social connections, cultural (re)connections to place, and physical and mental well-being, which inspired their sustained participation. We also found benefits in terms of local food production that have the potential to provide economic returns and energy savings over time, particularly when carried out through a hybrid non-profit and family management model. These benefits were coupled with potential changes in sediment and nutrient retention with implications for water quality and the health of an important downstream fish pond (loko i‘a) and coral reef social-ecological system. Compared with the current land cover (primarily invasive grasses), results suggest that full restoration of lo‘i kalo would decrease sediment export by ~38%, but triple nitrogen export due to organic fertilizer additions. However, compared with an urban scenario, there were clear benefits of agricultural restoration in terms of reduced nitrogen and sediment runoff. In combination, our results demonstrate that a biocultural approach can support the social and financial sustainability of agricultural systems that provide multiple benefits valued by the local community and non-profit while also contributing to statewide sustainability goals. Full article

Evaluating the performance of watershed models is essential for a reliable assessment of water resources, particularly in Pacific island watersheds, where modeling efforts are challenging due to their unique features. Such watersheds are characterized by low water residence time, highly permeable volcanic rock outcrops, high topographic and rainfall spatial variability, and lack of hydrological data. The Soil and Water Assessment Tool (SWAT) model was used for hydrological modeling of the Nuuanu area watershed (NAW) and Heeia watershed on the Island of Oahu (Hawaii). The NAW, which had well-distributed rainfall gauging stations within the watershed, was used for comparison with the Heeia watershed that lacked recoded rainfall data within the watershed. For the latter watershed, daily rain gauge data from the neighboring watersheds and spatially interpolated 250 m resolution rainfall data were used. The objectives were to critically evaluate the performance of SWAT under rain gauge data scarce conditions for small-scale watersheds that experience high rainfall spatial variability over short distances and to determine if spatially interpolated gridded rainfall data can be used as a remedy in such conditions. The model performance was evaluated by using the Nash–Sutcliffe efficiency (NSE), the percent bias (PBIAS), and the coefficient of determination (R²), including model prediction uncertainty at 95% confidence interval (95PCI). Overall, the daily observed streamflow hydrographs were well-represented by SWAT when well-distributed rain gauge data were used for NAW, yielding NSE and R² values of > 0.5 and bracketing > 70% of observed streamflows at 95PCI. However, the model showed an overall low performance (NSE and R² ≤ 0.5) for the Heeia watershed compared to the NAW’s results. Although the model showed low performance for Heeia, the gridded rainfall data generally outperformed the rain gauge data that were used from outside of the watershed. Thus, it was concluded that finer resolution gridded rainfall data can be used as a surrogate for watersheds that lack recorded rainfall data in small-scale Pacific island watersheds. Full article