Regionalization of Low Flows in Hawaii Streams for Past and Future Rainfall Conditions

Abstract:

The Hawaiian Islands experience large inter-annual rainfall variations and statistically significant long-term downward trends in streamflow, especially low flows, have been detected. Low flows in Hawaii streams provide a variety of beneficial uses that include maintaining fish habitat, supplying freshwater for irrigation and domestic uses, and protecting traditional and customary Hawaiian rights. However, the variability of low flows in ungaged streams in Hawaii has not been quantified and potential effects of climate change on low flows need to be better understood to properly manage surface-water resources. Regionalization of streamflow for ungaged areas in Hawaii provides a useful case study because streamflow, climate, and basin characteristics are extremely spatially and temporally variable. Here we present the development of statistical models to estimate low flows of ungaged streams in Hawaii for past and future rainfall conditions. We discuss the benefits and limitations of applying simple statistical approaches to improve understanding of changes in low flows in heterogeneous and data poor regions and to explicitly evaluate uncertainty and data needs in the context of climate change predictions for regional water-resources management.