Many have suggested diverting comets and other Kuiper belt objects into a desert planet, to create an ocean of water. That water could also be used to create an atmosphere. But if a star was close to another star that went supernova, the tremendous heat that was generated as a result could simply have vaporized almost all water from the system. We would only be able to use whatever water resources are available.
Scientists would only be able to use available water and gasses from whatever comets might have survived, what was still left in the planet's polar craters or what could be found in the planet's rocks. With all that, they would hardly manage to create an atmosphere and fill 7% of the planet's surface with lakes. The planet would look more like Frank Herbert's Dune, only that it has no sandworms.
Desert Earth (Dune - like planet) Edit
If we place that planet instead of Earth, we will get the following climate patterns: High mountains will be able to attract tiny amounts of moisture from the air. This could generate small rivers and streams that flow into tiny lakes or lose their water in the sand. If that planet has its axis tilted, we will see seasons. In Iran, Afghanistan and the Aral Sea basin, most of the precipitation comes from snow. Rivers have water in spring, but when the snow melts they almost run dry. Reservoirs will be needed to store water for irrigation.
However, streams will provide water for only a limited area, the largest part of the planet will be an endless desert. Even there, some water will fall. In the Sahara, rains are very rare, but sometimes in the morning dew will fall. In deserts, there are devices that used to collect morning dew as a drinkable water. So, life is still possible without much water.
Water basins will suffer, just like endothermic lakes suffer now on earth. They are dependent on water income. Major irrigation projects will destroy many fragile ecosystems (just like happened on Earth with Aral Sea). There will not be a global ocean, but a series of isolated lakes. In time, it would rain less in a water basin. Lakes would dry-up, affecting not only the local ecosystems, but also water cycle in nearby basins, feeding water clouds formed there. Also, it is possible that some water will sink underground or become deposited as ice around the poles.
Water would become a commodity with asking high prices and we can imagine the limited amount of water being brought from any possible resource.
Inner planet Edit
Desert planets are more stable with global warming. Without oceans, it is very hard to create a runaway greenhouse effect. Around the equator, temperatures will rise over 100 C, but still around the poles there will be a good climate within which to stay. Rain and dew will fall more often close to the poles. If the planet is heated enough, there might be no polar ice. It will look similar to Dune, where people live close to the poles, while the equator is uninhabitable.
If the planet rotates slowly, just like Mercury, all the water will accumulate on the night side, as snow. Settlers will have to be nomads and move fast in the morning near an ice deposit and grow crops until the water is lost.
If the planet is tidally locked, water will slowly move to the night side, where it will stay as ice. Settlers will have to build a transportation network, to bring ice to their fields. It will look similar to what we see today, when trains transport coal to the power plants, only instead they will transport ice or liquid water.
Desert Mars Edit
A desert Earth located at Mars orbit will face other challenges. Water and dew falling on the ground closer to the equator will quickly evaporate or be used by plants (then evaporate). If water is falling closer to the poles, it will remain there as ice. So, at some point all water on the planet will accumulate at the poles. However, settlers will likely stay closer to the equator, where it's warm. They will need to build transport routes to take ice from various deposits and bring it close to settled area's, where they will melt it and send it to their cities and farms, using pipelines. A global water engineering network will be needed for this.
Outer planet Edit
If the desert planet is located beyond the orbit of Jupiter, it will need greenhouse gasses to keep its temperatures above freezing. However, as shown on Outer Planet, the planet receives less heat during day and radiates less infrared during night. As a direct result, temperature fluctuations between day and night or even between seasons are very small. On such a planet, if the average temperature is 15 C, the maximum would be 20 and minimum 10 degrees C. The air will get to 100% humidity. Since temperature does not decrease fast, rains will bring very small amounts of water to the ground. Even with no rain, there will be enough water in the atmosphere to sustain life. The ground will be moist from atmospheric moisture. From the 7% of land covered with water, the planet may not have large lakes, but all that water will still be in the air as humidity.
If the amount of water is not enough to have 100% humidity in the atmosphere, let's say 75%, there will be no precipitation. Temperature fluctuations will not be enough to generate rains in these conditions. There will be no liquid water on the ground. Still, people will be able to extract water from the air. The ground will not be completely dried, because it will get some moisture from the air, but it will be highly affected. The planet will not be able to support trees and the majority of superior plants. However, we will see the ground colored in green, because lichens, bacteria and small algae will find some water linked to ground particles, just as we see on Earth, on rocks and walls.
Other models Edit
Around Neutron stars and Black holes, desert planets might exist. Terra-forming them would be a very hard to immpossible task. These planets are supposed to contain mostly metals and rare elements, so they will be a good destination for future miners.