Abstracts Category : Other

Regional Temperature Trends in Hawai`i: A Century of Change, 1916-2015

by Marie McKenzie

M.A. University of Hawaii at Manoa 2016. This thesis is focused on surface air temperature (SAT) changes (19192006) in the topo-climatically complex Hawaiian Islands. A prior study showed a long-term increase in temperature for Hawaii and enhanced warming in the more recent decades (19752006), particularly at high elevations. In this study, 12 additional years of data have been added to the time series, now totalling 100 years (19162015), and the Hawaii Temperature Index (HTI) has been revised and modified for the entire period. The results indicate that mean air temperature has a statistically significant (p=0.01) upward trend of 0.042C/decade over the past 100 years, with 2015 as the warmest year on record, 0.794C above the 100-year average. During each of the last three decades, the mean statewide air temperature anomalies were higher than those of any of the previous decades. Significant warming trends for the last 100 years are evident at low- (0.048C/decade, p=0.02) and high-elevation stations (0.033C/decade, p=0.02). As shown previously, warming in Hawaii is largely attributed to increases in nighttime; mean minimum temperature (Tmin) increased significantly (0.072C/decade, p=0.00001) while mean maximum temperature (Tmax) did not, resulting in a significant downward trend in the diurnal temperature range (DTR) (-0.055C/decade, p=0.00002) over the period.The 100-year study period was divided into subsets based on apparent periods of warming and cooling for Tmean, Tmin, Tmax and for all, low- and high-elevations stations. Statewide, the 19401957 period had negative trends in Tmean, Tmin, and Tmax of -0.555 (p<0.0001), -0.250 (p<0.0001), -0.568 (p<0.0001) and -0.314 (p=0.004) C/decade, respectively. During the same period, both high- and low-elevations also had significant negative trends for Tmean, Tmin, Tmax of -0.452 (p=0.007), -0.321 (p=0.048), -0.620 (p=0.00003) C/decade, respectively, at high elevations, and -0.654 (p=0.00001), -0.249 (p=0.00003), and -0.528 (p=0.0018) C/decade, respectively, at low elevations. The 19581999 period experienced a significant increase in Tmean of 0.133C/decade (p=0.00009). During the 20002013 period, DTR had a significant upward trend of 0.486C/decade (p=0.0013). Positive correlations were found between HTI and the Pacific Decadal Oscillation (PDO) and the Multivariate ENSO Index (MEI) suggesting that natural climate variability has a significant impact on temperature variability in Hawaii.High elevation temperature trends in Hawaii were similar to those on another tropical island in the Atlantic. Hawaiis highest elevation station, Mauna Loa Observatory (3397 m elevation) had significant warming of 0.21C/decade (p=0.006) between 1955 and 2015, very similar to the trend at the Mt Izaa, Tenerife, Canary Islands (2390 m elevation), with a significant (p=0.001) warming trend of 0.29C/decade for the same period.HTI results are consistent with SAT data from NCEP/NCAR Reanalysis data for the region of Hawaii over the last 68 years