North American Monsoon batters US and Mexico

The North American Monsoon has wreaked havoc and caused major disruptions in parts of the United States and Mexico.

Severe thunderstorms have caused flooding in the US state of Arizona and northern Mexico since Friday. The lightning has also triggered wildfires throughout the region.

More than 1,000 people were evacuated from the city of Jimenez in northern Mexico after the heaviest rainfall in 25 years, officials said late on Sunday.

Downpours around the city, located some 400kms south of the border with Texas, have resulted in dangerously swollen rivers, Cesar Duarte, Chihuahua state’s governor told local media.

Duarte ordered the evacuation of areas most affected by the monsoon’s rains that caused flash floods and left some residents stranded.

Heavy rainfall in recent days has affected large swaths of the state and on Friday forced the shutdown of the international airport in Chihuahua, the state capital.

Five airlines were forced to cancel flights, affecting some 1,200 passengers.

In the municipality of Rosales, in Chihuahua state, water rushing out of a burst dam destroyed a bridge and damaged 140 houses.

Arizona floods

A storm also hit Arizona’s capital Pheonix on Sunday morning, flooding homes in and around the city.

An unknown number of houses in Scottsdale, a city adjacent to Pheonix, were also inundated, officials said.

The downpour also prompted the shutdown of main highways in the area.

On Saturday, southeast of Tucson, Arizona’s second largest city, experienced flash flooding from a storm that brought about three-fourths of an inch of rain.

The storm led to several downed electric power lines in Tucson and two water rescue efforts on Saturday.

The annual North American Monsoon is triggered by the heat of summer sun. As the temperatures across the region soar, the air over the mountains of northern Mexico and the southwestern USA rises. To take its place, air rushes in from the Pacific. This air is laden with water.

The rain first falls over Mexico, then spreads northwards along the western slopes of the mountains, the Sierra Madre Occidental. The rain normally starts in Mexico at the beginning of June, reaching Arizona and New Mexico in early July. As the rains push northwards, their intensity eases.

The most dramatic impact is therefore in Mexico, where over 300mm of rain in a single month can transform the scenery to change from desert to tropical rainforest in a matter of weeks.

Even in Arizona, about half of the annual rain falls during the monsoon season, and the storms shouldn’t be under-estimated. They can trigger violent flash floods, thousands of lightning strikes, destructive hail, and walls of damaging winds.