(NAFB) – Dry periods between rainstorms have become longer, and annual rainfall has become more erratic across most of the western United States during the past 50 years.

A study published by The Department of Agriculture’s Agricultural Research Service finds rain has been falling in fewer and sometimes larger storms, with longer dry intervals between. Total yearly rainfall has decreased by an average of four inches over the last half century, while the longest dry period in each year increased from 20 to 32 days across the West.

Extreme droughts are also occurring more often in the majority of the West, according to historical weather data, as there has been an increase in the year-to-year variation of both total rainfall amounts and the duration of dry periods.

Notable exceptions to these drought patterns were seen in Washington, Oregon and Idaho and the Northern Plains region of Montana, Wyoming, and the most western parts of North and South Dakota.