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Modeling the Response of Hawaiʻi’s Streams to Future Rainfall Conditions

Development of Statistical Methods to Estimate Baseline and Future Low Flow Characteristics of Ungaged Streams in Hawai`i


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Surrounded by saltwater, Hawaiian communities depend on freshwater streams for consumption, irrigation, traditional Hawaiian practices, and habitat for native fish and other stream life. It is important to be able to predict how Hawaiʻi’s streams will be affected by changing rainfall patterns to enable sustainable management of critical freshwater resources. However, to date, limited data and the uncertain effects of climate change have hindered predictions of future streamflow. Through this project, scientists developed a model that provides a way to estimate future stream low flow (streamflow during a period of prolonged dryness) by categorizing streams based on their physical characteristics. While the model is based on data from [...]

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Principal Investigator :
Maoya Bassiouni
Funding Agency :
Pacific Islands CSC
CMS Group :
Climate Adaptation Science Centers (CASC) Program

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“Waihee Stream, Maui: Credit- Maoya Bassiouni”
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“Shrimp - Credit: Maoya Bassiouni”
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“Waihee Stream, Maui: Credit - Maoya Bassiouni”
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Climate change will affect the beneficial uses of streamflow, which include supplying freshwater for irrigation and domestic needs, providing for traditional and customary Hawaiian practices, and maintaining habitat for native stream fauna. Statistical models were developed to estimate surface-water availability during low-flow conditions for varying rainfall conditions. Results of this study include a spatial understanding of changes in low flows and usable stream habitat on Maui for a range of projected rainfall conditions for the late 21st century. This analysis indicates that stream responses to rainfall vary spatially in Hawai‘i. For example, a 10-percent decrease in rainfall may result in a 7% decrease in low flows in West Maui streams, compared to a 20-percent decrease in low flows in East Maui streams. The simple models developed for this study are appropriate for regional climate-change impact assessments given the available data and uncertainty in climate projections. The methods developed for this study are transferable to other Pacific islands as well as continental settings. --- Researchers for this study will develop statistical methods to assess the impacts of climate change on natural low-flow duration discharges of streams on the main Hawaiian Islands using available high-resolution projected climate information from the International Pacific Research Center (IPRC). The objectives of this study are to (1) estimate baseline and future low-flow characteristics of ungaged streams in Hawai`i, and (2) quantify changes in physical habitat for native stream fauna associated with projected changes in low flows. To accomplish these objectives, this study will (1) compute baseline low-flow duration discharges for gaged sites, (2) develop regional regression models to estimate low-flow duration discharges at ungaged sites for baseline conditions, and (3) evaluate the applicability of the regional regression models to estimate low-flow duration discharges for future conditions. The results of this study will provide critical information for managing Hawai`i's limited freshwater resources, and for understanding how climate change may impact ecosystems, agriculture, and communities that are entirely dependent on freshwater. The study will produce a tool needed by water-resource managers for estimating baseline and future natural low flows. This tool may be particularly useful in areas where demand for freshwater is high. The study is consistent with the Pacific Islands Climate Science Center’s agenda to provide science to support pressing climate adaptation needs by assessing the potential effects of changing climate on freshwater resources.

Project Extension

typeFY 14 COA

Budget Extension

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