An Analysis of Biometeorological Thermal Comfort in an Oasis City within The Sub-tropical Climate Zone: The Case of Al Ain City, UAE

Outdoor thermal comfort is an important issue of public health concern, especially for an arid region like the UAE where summer air temperatures can soar to 50^oC inducing heat discomfort conditions. Excessive outdoor heat exposure pose well-known health risks such as heat stroke and limits the outdoor workers' capacity to sustain physical activity. Several thermal indices have been developed for evaluating human thermal comfort. In order to evaluate human thermal comfort in the Oasis City of Al Ain, in the United Arab Emirate (UAE), variation in the biometeorological thermal conditions as indicated by a number of heat indices were analyzed using pertinent meteorological data (air temperature, relative humidity and wind speed) for the year 2012. The thermal indices analysed include effective temperature (ET), Temperature Humidity Index (THI), Discomfort Index (DI), and Humidex (H). Results show that severe thermal conditions occur in Al Ain for most part of the summer months which prevail from April through to September. During the study period, mean air temperature was 29.0^oC (range: 12.0 to 40.8 ^oC), mean maximum temperature 36.1 ^oC (18.3 to 48.6 ^oC) and mean minimum temperature 22.8 ^oC (6.6 to 36.0^oC). The mean relative humidity was 41.8 % (14.9 to 85.2%). Mean maximum effective temperature (ETmax), Mean effective temperature (ETmean) and mean minimum effective temperature (ETmin) values ranged from 53.1^oC to 20.2^oC, 43.1 ^oC to 12.2 ^oC, and 37.9 ^oC to 5.4 oC, respectively. The mean THI was 34.3 (17.9 to 51.6), DI was 23.8 (12.4 to 31.6) and mean H was 32.2 (11.8 to 51.1). The Humidex analysis results show that comfortable conditions prevail for 114 days, representing 31% of the total days in the year; some discomfort is experienced for 42 days (11%); great discomfort for 117 days (32%); and dangerous conditions prevail for 93 of the days (25%). Great discomfort and dangerous conditions occur during summer, beginning from May through to September. Based on the Discomfort index results, comfortable thermal conditions occur in 101 of the days (28%) with days when 10% of population experience discomfort prevailing in 103 of the days (28%); days when approximately 50% of population experience discomfort being 21 (6%); when 100% of population experience discomfort occurring in 19 of the days (5%) and days when discomfort is considerably high and hazardous were 122, accounting for 33% of the total days in the year of study. Comfortable thermal conditions prevail during the winter period which begins from December and ends in late February, but as is clearly demonstrated by both the THI and H indices, severe thermal conditions prevail in Al Ain most of the days in the year, mainly as a result of extremely high summer temperatures. Diurnal variation of Humidex on selected days in summer show that dangerous thermal conditions prevail for 70.83% of the time while great discomfort occur for the remaining 29.17%. Exposure to these extreme thermal conditions increases the heat stress of outdoor workers during summer considerably.