Mars Climate, Now and In the Past
Theories About Mars Climate
So, maybe Mars had a thicker atmosphere and periods of intense climate change. There are currently two theories as to the history of Mars' climate.
1.) Since warm weather is needed for the formation of the river channels & floods, episodes of warm climate caused floods, releasing water into the atmosphere and further contributing to the warmer climate via the greenhouse effect. The end result of this process is that *water is returned* to the aquifer by atmospheric condensatation at higher latitudes, and the cycle repeats itself in the next episode of warm climate.
2.) flooding causes a *permanent* transfer of water to low areas.
More research is needed before either of these can be proven or disproven. Future missions to Mars will be very helpful.