Channel networks on the plateau adjacent to the Juventae outflow channel source region and chaos have the highest drainage densities reported on Mars .
We model frozen precipitation on the Juventae plateau , finding that the trigger for forming these channel networks could have been ephemeral lakeshore precipitation , and that they do not require past temperatures higher than today .
If short-lived and localized events explain some dendritic channel networks on Mars , this would weaken the link between dendritic valley networks and surface climate conditions that could sustain life .
Our analysis uses Mars Regional Atmospheric Modeling System ( MRAMS ) simulations and HiRISE Digital Terrain Models .
Following a suggestion from \citet man08 , we model localized weather systems driven by water vapor release from ephemeral lakes during outflow channel formation .
At Juventae Chasma , the interaction between lake-driven convergence , topography , and the regional wind field steers lake-induced precipitation to the southwest .
Mean snowfall reaches a maximum of 0.9 mm/hr water equivalent ( peak snowfall 1.7 mm/hr water equivalent ) on the SW rim of the chasm .
Radiative effects of the thick cloud cover raise mean plateau surface temperature by up to 18K locally .
The key result is that the area of maximum modeled precipitation shows a striking correspondence to the mapped Juventae plateau channel networks .
Three independent methods show this fit is unlikely to be due to chance .
We use a snowpack energy balance model to show that if the snow has the albedo of dust ( 0.28 ) , and for a solar luminosity of 0.8 ( \equiv 3.0 Gya ) , then if the atmospheric greenhouse effect is unchanged from today only 0.4 % of lake-induced precipitation events produce snowpack that undergoes melting ( for a 6K increase in the atmospheric greenhouse effect , this rises to 21 % ) .
However , warming from associated dense cloud cover would allow melting over a wider range of conditions .
Complete melting of the snow from a single event is sufficient to move sand and gravel through the observed channel networks .
At Echus Chasma , modeled precipitation maxima also correspond to mapped plateau channel networks .
In these localized precipitation scenarios , global temperatures need not be higher than today , and the rest of the planet remains dry .