yemen drainage

This shows some dendritic desert drainage.

I do not agree with the authors, however, that this drainage could not have formed under the current desert conditions. It is well known that the Sahara and fertile crescent region were much wetter even just a few thousand years ago - so this picture is not my proof. My proof is that every desert region contains dendritic drainage.

I do not agree with the authors that desert conditions lead to less dense drainage networks. The opposite is usually true due to a lack of stabilizing plants. Try going to the desert and see how many small channels there are - usually more than forested or grassland areas. I am not arguing that there are no differences, such as fewer large channels in the desert. These are easier to see from space, and could give a false account of drainage density. I am arguing that these author's conclusions about Mars drainage are not taking into account the planation from wind erosion that has occurred after the formation of all of these Martian drainage basins.

I disagree with the authors of the above referenced web page. Photo B does show dense drainage - modified by 1 - 3 billion years or so of wind erosion.

Photo C shows more severe erasure of the smaller drainages by erosion and infilling.

Photo D shows either a complete planation of smaller trributaries, or possibly a mode of formation independant of precipitation. I have seen many examples like this on Mars, and think that these may be produced from subsurface flows, caving, sapping, etc. The simplest explanation, however, remains planation after normal dendritic formation.

This obviously very deep canyon in photo D is supposed to have formed in desert conditions with hardly any tributaries? What did it do , keep raining in one spot only? I think not.

My principal point is that I believe it is incorrect to try and assign a frequency of rain to a resultant drainage pattern. The same end results could be obtained from different rainfall and wind regimes. Applying near equilibrium Earth concepts such as drainage density to Mars, where the drainage processes principally stopped billions of years ago, is not what I'd call good science, references or not.