Changes in Peak Streamflow and Its Associated Rainfall across the Hawaiian Islands from 1970 to 2005

Flooding is a significant threat to life and property. As climate warming continues to alter precipitation patterns and hydrological processes in tropics, improving our understanding of future flood risks will benefit land use planning and community development. Understanding how peakflow events have shifted in magnitude, seasonality, and location will improve our understanding of the consequences of changing climate patterns as well as the predictability of future flooding events. We examined trends in annual maximum rainfall and annual peakflow across five major Hawaiian Islands using the Mann-Kendall test and Senʻs slope. We compared the relationship between the trends in annual maximum rainfall and annual peakflow, then analyzed the seasonality by circular analysis. We found that annual maximum rainfall mostly decreased from 1970 to 2005 Hawaiʻi, in contrast to global trends. Across five major Hawaiian Islands, downward trends in annual peakflow occurred, but were not as strong as the decline rainfall trends and daily streamflow trends. In addition, annual peakflow did not correspond with the timing of annual maximum rainfall. A shift in the occurring timing of annual maximum rainfall and annual peakflow was detected, towards earlier in the year. The findings in this study will aid watershed management and flood risk mitigationto increase resilience of downstream communities and near-shore environments to climate change.