Arboriculture & Urban Forestry 46(3): May 2020 For globe temperatures, a 5-min average temperature was recorded using a thermometer set on a stand at a height of 1.2 m positioned at three sites within each surface type. For air temperatures, the 41382LF2 temperature/humidity sensor coupled with a data log- ger was used to determine temperature readings above each surface type and also at 6 urban locations outside the park. These 6 measurement points were selected to ensure that the data collected represented the entire external park setting. The readings were made at a height of 1.2 m, and a 5-min average tem- perature was recorded. RESULTS Small Patches of Vegetation Mean surface temperature data over a 3-month period in 2017—namely, February, June, and December—is presented in Figure 2. These months were selected as they represented warm temperatures, very hot tem- peratures, and a period of highest precipitation, respectively. Given the highly uniform climate in the tropics, the fluctuations in the diurnal temperature were not pronounced except for a slight elevation in surface temperatures between 12:00 and 14:00 hrs (Figure 2). Therefore, in general, the data for surface temperatures was observed to be constant across all 3 months. The data was subjected to analysis using one-way ANOVA. The concrete surface exposed to the sun was always warmer and reaching a peak of 53 °C in June, which is typically the warmest month in the year. Conversely, the same hard surface set in the shade displayed a maximum temperature of 48 °C, which was some 5 °C lower than the results for the same surface type exposed to solar radiation (Figure 2). The surface temperature when turf was present was found to be greatly reduced. This was especially pro- nounced when shade and turf were present (Figure 2). Surface temperatures for shaded turf surfaces in the warmer months of February and June were found to be close to the prevailing air temperatures (Figure 2a and 2b). The maximum surface temperature for the warmest month of June for surfaces covered in turf and exposed to solar radiation was some 43 °C. When this was compared to a hard surface also exposed to the sun, there was a 10 °C reduction in temperature when vegetation was present. Comparatively, a turf surface in the shade had peak temperatures of around 36 °C. The difference between a shaded hard and a 233 shaded vegetated surface was far greater with a 12 °C reduction (Figure 2) in temperature. To confirm that the data observed in Figure 2 is not a result of abnormal temperature conditions in that particular year, the study also took into account the long-term relationship between surface and air tem- peratures across hard and vegetated surfaces that were exposed to sunny and shaded conditions (Figure 3). In general, the data exhibited similar results to what was observed in Figure 2, where the warmest surface was concrete exposed to solar radiation, with mean temperatures peaking at 44.6 °C in 2017 (Fig- ure 3). Conversely, vegetated surfaces exposed to sun had mean temperatures peaking at 36 °C in the same year (8.6 °C difference)(Figure 3). Data for shaded conditions also indicated peaked readings in 2017. Mean temperatures were 36 and 30.2 °C for hard and vegetated surfaces, respectively. Though smaller, one- way ANOVA still showed a significant 5.8 °C differ- ence (P ≤ 0.02), indicating the benefit of temperature reduction when vegetation is present (Figure 3). The temperature trends for globe thermometers were similar to those for surface temperatures. This was to be expected given the fairly uniform ambient temperatures experienced in the tropics. It is, how- ever, important to look at globe temperatures because of the high humidity present in the tropics. This data will serve as a means of assessing the combined effects of radiation, air temperatures, and air velocity on human comfort. Temperature results of the globe thermometers in the months of February, June, and December in 2017 are presented in Figure 4. Similar to surface temperatures, globe tempera- tures rose from a minimum around dawn to reach a maximum at noon and gradually decline. Unlike sur- face temperatures, globe temperatures tended to reach higher temperatures more swiftly and, by 14:00 hrs, had started to decline. This was potentially a result of cloud cover or strong gusts of wind. Conversely, with surface temperatures, there were still increases observed at 14:00 hrs. Similar to surface temperature, the concrete sur- face exposed to the sun was always warmer, reaching a peak of 59 °C in June, which was 6 °C warmer than surface temperature (Figure 4). Data for hard surfaces set in the shade displayed a maximum temperature of 54 °C, which was some 6 °C higher than the results for surface temperature (Figure 4). With turf present, the maximum globe temperature for sun-exposed and shade conditions were 49 and 42 °C, respectively. ©2020 International Society of Arboriculture
May 2020
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