effects of desert on armoured units

Cavalry Armour Level 2&3 (depletion 50%/recovery 50%)
Cavalry Armour Level 4&5 (depletion 75%/recovery 25%)
Cavalry Armour Level 6&+ (depletion 100%/recovery 0%)

Infantry Armour Level 1&2 (depletion 50%/recovery 50%)
Infantry Armour Level 3&4 (depletion 75%/recovery 25%)
Infantry Armour Level 5&+ (depletion 100%/recovery 0%)

more from my compilation of info :)

remember if you invade the desert dont make the army from a place with an armourer it tends to make them worse rather than better

also the camel penaltys

Fear of camels

+4 def for camels against horses
+2 atk for camels against horses

and fatigue levels just so you know how bad it is
Exhaustion

-2 atk when quite tired
-3 atk, -1 def very tired
-4 atk, -2 def exhausted
-6 atk, -3 def totally exhausted