Monsoon rain storms have become more intense in the southwestern United States in recent decades, according to a recent study. Monsoon rains — highly localized bursts of rain — have become stronger since the 1970s, meaning the same amount of rain falls in a shorter amount of time — by 6 to 11 percent. In addition, the number of rainfall events per year increased on average 15 percent during the 1961-2017 period.