drought ring

例句：

1. 1. The drought ring isa region where the annual rainfall is lessthan 250 mm.
   干旱环是一个年降雨量少于250毫米的地区。
2. 2. The drought ring is an areathat experiences frequent droughts and floods.
   干旱环是一个经常遭受干旱和洪水的地区。
3. 3. The drought ring is a critical issuefor agriculture in many parts of the world.
   干旱环是世界上许多地区农业面临的一个关键问题。