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Global climate change

Southwest U.S. monsoon has been getting more intense in recent decades

By Brett Anderson, AccuWeather senior meteorologist
7/24/2019, 11:04:06 AM

For the first time, a study has measured the long term changes of individual, localized monsoon storms in the southwestern United States.

The study, which was led by the Agricultural Research Service scientists, found that there has been an increasing trend with intense monsoon rainfall since the 1970s. The southwest U.S. monsoon typically peaks during the months of July and August.

The number of monsoon rainfall events per year has increased an average of 15 percent during the 1961-2017 period. Bursts of rainfall have also increased by 6 to 11 percent (same amount of rainfall, falling in a shorter time period).

The research team attributes these changes to a warming atmosphere. Southwestern U.S. temperatures have risen by 0.22 of a degree Celsius (0.4 of a degree Fahrenheit) per decade, which is likely a result of global climate change, according to the report.

The study did note that it found no evidence that the storms were larger or covered more area.

Key excerpts from the USDA report........

Some studies reported increases in rainfall intensities over time and others found decreases. These discrepancies hail from an inadequate number of rain gauges being used in the analysis that were too far apart to capture the variability of monsoon storms, or climate models with grid cells that were too large to represent intense, but isolated thunderstorms.

While as many as 90 percent of the individual rain gauges, which are now as close as 2,100 feet (640 m) apart, showed an increase in rainfall intensity, there were still some rain gauges that showed either a decrease or no change in intensity, which reflects the wide variability in where and how monsoon rains fall.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or


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Global climate change