There are some desert areas where dew consists of 100% of all the precipitation–particularly in the Atacama of South America as well as in some areas of the Namib desert (the above picture is from the Namib Desert, sourced here). That dew drop depends entirely on the local foliage–without those plants, the dew would not fall. This leads to some chicken and egg type questions–if the plants need the dew to live, and if the dew only happens because of those plants, how did they get there in the first place? Regardless, even in temperate climates dew can be a significant source of precipitation–up to 30% in some areas (my source on that is Geoff Lawton, in a personal conversation).
In deforested areas, the dew-catching and creating phenomena ceases, and the affect can be enormous. Through reforesting these areas, we can increase total precipitation through dew collection alone–not counting the increase in rainfall and cloud creation caused by the trees.
Here is how that works:
The dew point is the temperature at which water in the air begins condenses on solid surfaces–particularly those that are not connected to the heat of the ground. Leaves, grass blades, metals, or even stones can play this role. If there is no surface for the water vapor to condense on (as in much of Al Baydha) then the water in the air will simply stay as vapor. This is how the Groasis Waterboxx works, how air-wells work, and how many dryland coastal-forests acquire much of their water. Trees especially, that can have acres of surface area along their leaves, can catch a surprising amount of dew, which then drips underneath the tree into their root zone. As the trees grow, their shade further reduces ground temperatures and dessication by way of the wind, which raises the dew point, reduces further evaporation, and makes the whole process more likely to happen.
Dew and other types of condensation should not be underestimated as a source of precipitation, especially in coastal deserts, like those along the coasts of the Arabian Peninsula, and could probably provide enough water for the early stages of their reforestation.