Changes in the vertical profiles of mean temperature and humidity in the Hawaiian Islands

Recent drought and warmer than normal temperatures affecting the Hawaiian Islands have raised concern among natural resource managers that impacts associated with global warming are becoming manifest in the region. A number of studies published over the past few decades have documented changes in the climate of Hawaiʹi that are generally consistent with expectations from climate change projections, such as those found in the latest Intergovernmental Panel on Climate Change assessment report (IPCC, 2007). In this study we examine a suite of climate variables that are important from the point of view of ecosystem impacts, but that also relate to societal concerns such Island water resources. Our results are consistent with previous studies in showing a significant warming trend, especially evident at higher elevations. In particular, we document a decrease in the frequency of occurrence of freezing temperatures in the upper slopes of the higher terrain on Maui and the Big Island and a concomitant rise in the freezing level surface in the region that is in good agreement with analogous studies done for other mountainous areas of the world. Temperatures at standard reference surfaces in the free atmosphere have warmed throughout the troposphere, with a maximum near the 850 mb level. The warming peak at this level could be associated with an increased frequency of occurrence and/or lowering of the trade wind inversion layer.