In battle
When a Pokémon with Desolate Land enters the battle or a Pokémon gains the Ability Desolate Land, the Ability creates extremely harsh sunlight, a unique variation of intense sunlight. The extremely harsh sunlight lasts as long as the Pokémon with Desolate Land is in battle. In a Rotation Battle, Desolate Land will not activate if the Pokémon is sent out in a rotated-out position and will not activate if the Pokémon is rotated in; extremely harsh sunlight will dissipate if the Pokémon is rotated out.
Along with the usual effects of intense sunlight, extremely harsh sunlight causes damage-dealing Water-type moves to fail. Additionally, extremely harsh sunlight causes the weather modifying moves Sunny Day, Rain Dance, Hail and Sandstorm to fail if used; and it causes the Abilities Drought, Drizzle, Sand Stream and Snow Warning to fail to activate.
If Desolate Land is suppressed or replaced, the extremely harsh sunlight it causes will disappear. If another Pokémon in battle has the Ability Primordial Sea or Delta Stream, the dominant weather conditions will be determined by whichever Ability activated last.
Outside of battle