Egypt was not always a desert. And the earth did not used to be so hot. There was an impact to the Earth around 30,000-40,000 years ago that was so powerful that it tilted the Earth's axis to what it is now. Which causes both extreme heat and extreme cold from the way it is tilted. The whole Earth used to all be a more moderate temperature before this.
This is why you can see Pyramids in Antarctica and the Arctic circle in the north and south pole, and these pyramids are buried under the ice. Because when these were built, these locations were warmer and the ice was not there. In the same way, Egypt was not so hot at that time.
There was a nuclear war on Earth, and the impacts of these nuclear weapons have destroyed the environments and turned everything into dust and sand. This is how the Gobi and Sahara deserts were formed, as nuclear impacts which crumbled the rocks to sand and erased all of the natural environment.
There have been cities discovered under these deserts that are far older, larger, and more advanced than any other ancient cities we know about. These were extremely important places, and that is why they were targeted in the war. And people who investigate these places, they find that the level of Radiation is extremely high in these places, which is still left over from the nuclear weapon that was used.
Before all of this, most of the Earth was all a similar temperature. And the Golden Age Civilization of the Gods was spread across every area of the world, and including all human races.