Regional Temperature Trends in Hawaiʻi: A Century of Change, 1916–2015
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2016-05
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University of Hawaii at Manoa
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This thesis is focused on surface air temperature (SAT) changes (1919–2006) in the topo-climatically complex Hawaiian Islands. A prior study showed a long-term increase in temperature for Hawaiʻi and enhanced warming in the more recent decades (1975–2006), particularly at high elevations. In this study, 12 additional years of data have been added to the time series, now totalling 100 years (1916–2015), and the Hawaiʻi 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 0.042°C/decade over the past 100 years, with 2015 as the warmest year on record, 0.794°C 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- (0.048°C/decade, p=0.02) and high-elevation stations (0.033°C/decade, p=0.02). As shown previously, warming in Hawai‘i is largely attributed to increases in nighttime; mean minimum temperature (Tmin) increased significantly (0.072°C/decade, p=0.00001) while mean maximum temperature (Tmax) did not, resulting in a significant downward trend in the diurnal temperature range (DTR) (-0.055°C/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 1940–1957 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 1958–1999 period experienced a significant increase in Tmean of 0.133°C/decade (p=0.00009). During the 2000–2013 period, DTR had a significant upward trend of 0.486°C/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 Hawaiʻi. High elevation temperature trends in Hawaiʻi were similar to those on another tropical island in the Atlantic. Hawaiʻi's highest elevation station, Mauna Loa Observatory (3397 m elevation) had significant warming of 0.21°C/decade (p=0.006) between 1955 and 2015, very similar to the trend at the Mt Izaña, Tenerife, Canary Islands (2390 m elevation), with a significant (p=0.001) warming trend of 0.29°C/decade for the same period. HTI results are consistent with SAT data from NCEP/NCAR Reanalysis data for the region of Hawaiʻi over the last 68 years (1948–2015), both yielding a warming rate of 0.10°C/decade (p<0.0001). Confidence in the HTI was also gained by comparing it with an independently derived mean atmospheric layer temperature time series based on pressure data from atmospheric soundings over the last 39 years (1977-2015). HTI for mean temperature and the mean atmospheric layer temperature time series did not have significant trends for that period, and were well correlated with each other (r= 0.8; p<0.0001).
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Atmospheric temperature--Measurement, Time-series analysis
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vii, 52 pages
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Hawaii
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Theses for the degree of Master of Arts (University of Hawaii at Manoa). Geography.
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