Evidences show that Mars was once wetter with liquid water flowing long enough on the surface to form valley networks. Previous studies indicate climate responsible for valley formation was short lived, although older craters are much more degraded than can be explained by short‐term climate change.
A landform evolution model was used to recreate the landforms we see at two locations on Mars, Noachis Terra and Terra Cimmeria, to estimate the possible climatic conditions responsible for shaping the topography of early Mars before the formation of valley networks (~4.0‐3.7 Ga). We controlled parameters such as aridity, weathering rate of the surface material, and how much of precipitation contributes to surface runoff.
Our model runs indicate conditions similar to those of arid to semi‐arid environment on Earth with a very low erosion rate and inefficient runoff during the Middle and Late Noachian Epochs. Our results also showed that crater impacts and aqueous weathering produced abundant loose material that are transportable by surface flow.
A major portion of early Mars was more arid than around the time of intense valley formation, but supported occasional precipitation (snow or rain) that weathered and transported surface sediments. [More at link]