Regional climate trends in Hawai'i

Despite the buffering effects of the tropical Pacific Ocean, secular trends in air temperature, precipitation, and stream discharge, especially during the past three decades, suggest that Hawai'i is already experiencing rapid climate change. Temperature increased statewide at 0.164 degrees C per decade during the 30 years ending in 2006, with more rapid warming (0.268 degrees C per decade) for high elevation stations. Statewide area-averaged precipitation has declined at an average rate of about 0.8% per decade since 1920. During the most recent 30 years, precipitation declined at 6% per decade, an exceptionally high rate partly explained by inter-decadal variability associated with Pacific Decadal Oscillation. The frequency of occurrence of heavy precipitation days, which account for a high proportion of annual rainfall in drier areas of Hawai'i, declined around the time of the mid-1970s Pacific-wide climate shift. During 1913-2002, base flows declined in all streams with observations, indicating a systematic decrease in groundwater recharge over the period. At high elevations, the numbers of zero rainfall days and cloud-free days, and the amount of solar radiation have all increased during the past 20 years. These trends are point toward a warmer and drier future for Hawai'i. If maintained over this century, these trends and other regional outcomes of global climate change will have severe impacts on Hawai'i's terrestrial ecosystems, agriculture, water supply, and economic well being.