Sandstorm is a cool effect which I absolutely love. But I do feel they need to be stronger, for its so easy to triviliase them. Maybe have a random megastrom hit the settlements at random intervals that do more damage and cannot be survived with simple mask on. It could even deal slight damage on T1 buildings.
example ideas:
Snowstorm: similiar to sandstorm but at the north, decreases all tempatures and causes severe blindness. Risk of freezing to death
Lightning Storm, severe rain and lighting, risk of getting hit by bolts and severe blindness.
Heatwave: Severely increases all tempatures and reduces stamina regeneration.
-Brim