hy·drol·o·gy 
(hī-drŏlə-jē)
(hī-drŏlə-jē)n.
The scientific study of the properties, distribution, and effects of water on the earth's surface, in the soil and underlying rocks, and in the atmosphere.
hy′dro·logic (-drə-lŏjĭk), hy′dro·logi·cal adj.
hy′dro·logi·cal·ly adv.
hy·drolo·gist n.