Atlanta's urban heat island under extreme heat conditions and potential mitigation strategies
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The urban heat island (hereafter “UHI”), together with summertime heat waves, foster biophysical hazards such as heat stress, air pollution and associated public health problems. Mitigation strategies such as increased vegetative cover and higher albedo surface materials have been proposed. Atlanta, GA is often affected by extreme heat, and has recently been investigated to better understand its heat island and related weather modifications. The objectives of this thesis were to (1) characterize temporal variations in magnitude of the UHI around Metro Atlanta area, (2) identify climatological attributes of the UHI under extreme high temperature conditions during Atlanta’s summer (Jun, July, and Aug) period, and (3) conduct theoretical numerical simulations to quantify the first-order effects of proposed mitigation strategies. Over the period 1984-2007, the climatological mean UHI magnitude for Atlanta-Athens and Athens-Monticello oowas 1.31C and 1.71C, respectively. There were stastically-signifcant minimum temperature ootrends of 0.70C per decade at Athens and -1.79C per decade at Monticello while Atlanta’s minimum temperature remained unchanged. The largest (smallest) UHI magnitudes were in spring (summer) and may be coupled to cloud-radiative cycles. Heat waves in Atlanta occurred during 50% of the years spanning 1984-2007 and were exclusively summertime phenomena. The mean number of heat wave events in Atlanta during a given heat wave year was 1.83. On average, Atlanta heat waves lasted 14.18 days although there was quite a bit of variability (standard deviation of 9.89). The mean maximum temperature during Atlanta’s heat waves was 35.85° C. The Atlanta-Athens UHI was not statistically larger during a heat wave although the Atlanta-Monticello UHI was. Model simulations captured daytime and nocturnal UHIs under heat wave conditions. Sensitivity results suggested that a 100% increase in Atlanta’s surface vegetation or a tripling of its albedo effectively reduced UHI surface temperature. However, from a mitigation and technological standpoint, there is low feasibility of tripling albedo in the foreseeable future. Increased vegetation seems to be a more likely choice for mitigating surface temperature.