Unequal Rainfall Science Project Idea

Reasons for Unequal Distribution of Rainfall

A study of the average annual rainfall map of the United States shows that the distribution of rainfall is very unequal, varying from 80 to 100 inches per year in a narrow strip along the ocean in Washington and Oregon, to less than 5 inches per year in portions of Nevada, southern California, and Arizona.

With maps of topography of the country and the prevailing winds, explain the following:

(1) The great rainfall of the northwest coast of the United States. What is the prevailing wind? (Air cools as it rises along the side of a mountain.) Why is this rainfall belt so narrow?

(2) The small rainfall of the great region just east of this coast area.

(3) The sources of rainfall of the Mississippi Valley and region east of it to the Atlantic Coast.

(4) In middle and southern California, the prevailing wind from December to May is from the ocean, while during the remainder of the year it is from the land toward the ocean. Explain the dry and rainy seasons of this region.