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I once visited a friend in Las Vegas for two weeks during July, the hottest part of the summer. The average daily temperature outside was 120. So one might think you'd want to run around in shorts and a slight top, but no. The sun was intense and the few rain showers that happened consisted of sprinkles that lasted a few minutes and barely wet the top soil.
One afternoon, I decided to take a walk in the nearby desert (she lived on the northern edge of the city near the airport and there weren't really any other houses out there at the time). I wore long corduroy pants, a long sleeve shirt and a hat and boots. I wasn't hot at all.
The clothes were for protection since the dry heat would dehydrate me quickly. I was advised to turn back the minute I felt tired or thirsty. The vegetation was mostly scrub brush and the lizards zipped around in the heat, but I don't think wearing less would have been a good idea. It soon became clear to me why men and women in the middle East would wear clothing that covered them to such an extent.