"下稀疏小雨" can be translated as "It's drizzling lightly" or "There's a light, sporadic drizzle".
Here, “drizzling” specifically refers to light, fine rain, while “lightly” and “sporadic” (in the second phrase) convey the idea of the rain being sparse and not continuous. Both expressions capture the essence of "稀疏小雨" (light and sparse rain).