There is only one known scenario according to which all the oceans on Earth can evaporate - this will happen in billions of years, when, under the influence of natural processes, the Sun will become brighter and the atmosphere of our planet will heat up to several hundred degrees. Although, and so every year on Earth, an area the size of a small American state turns into a barren desert. And yet: let's assume that one day all the oceans, for one reason or another, took over and evaporated.
The primary function of the oceans is to absorb and distribute solar radiation and maintain the water cycle. With their disappearance, the equator will turn into an underworld, and the poles will no longer receive either light or heat.
Evaporation of the oceans will not lead to the complete disappearance of water on the planet. There will remain lakes, rivers, groundwater, as well as glaciers, ice caps and permafrost, concentrated mainly in Antarctica. This is about 3.5 percent of the water volume that we have now.
The remaining amount will in no way be enough for a full-fledged water cycle in nature, even if we manage to melt the ice caps at the poles. It will rarely rain …
For some time, however, humanity will still be able to exist in such conditions. With access to groundwater, we can build hydroponic farms. But on the surface, trees and plants will dry up, and animals will die. Due to constant droughts, continents will be engulfed in fires, and global warming will accelerate.
The equator will become red-hot, it will be impossible to live there. Greenhouse gases will keep solar energy close to the ground. It will certainly be colder at night than during the day, but the average earth temperature will reach 67 degrees Celsius. Most living organisms, even those resistant to high temperatures, will not be able to exist in such conditions.
People, most likely, will begin to migrate en masse to the southern hemisphere of the planet, because there it will be possible to extract water from the Antarctic underground ice. However, Antarctica will not be easy to reach. The mainland will be a flooded wasteland devoid of any resources needed to live - for example, roads, mines, or visible food sources. Many people simply cannot wait to create the infrastructure necessary for their existence in Antarctica. Those who nevertheless wait for this day will be able to live only underground.
But staying in underground bunkers does not guarantee a long and high-quality life on a planet devoid of oceans. The atmosphere of the Earth will gradually lose oxygen, and in fact it is needed underground too. The temperature will also gradually rise. Sooner or later, all life on the planet will die out, with the exception of small colonies of chemosynthetic bacteria, which will be hidden under the ground near hot springs.