Drought-stricken parts of the western United States have been warned to be on alert for flash flooding, with up to 15 centimetres of rain expected in some areas.

The National Weather Service (NWS) said on Friday that "a significant heavy rainfall event" could strike Arizona and New Mexico, leading to sudden inundations –– especially in areas previously ravaged by wildfires.

Very heavy rainfall is "forecast for portions of southeastern Arizona and southwestern New Mexico today and Saturday," the NWS said.

"Average rainfall totals of 2-3 inches, with locally higher amounts approaching 5-6 inches, may lead to numerous instances of flash flooding.

"Complex terrain, slot canyons, arroyos, and burn scars are especially vulnerable," the agency said.

Painful drought and climate crisis

The western United States is more than 20 years into a painful drought that has left rivers and reservoirs badly depleted, and the countryside tinder-dry.

But sudden, intense downpours like that forecast are not necessarily helpful.

"If the water all comes down over a very quick period of time, it'll run off," Chris Rasmussen, an NWS meteorologist in Tucson, Arizona, told AFP news agency.

"It doesn't get a chance to really soak into the ground, as you would like to see.

"It's always nicer to have a good, moderate amount of rain over a long period of time."

Human activity, specifically the runaway use of fossil fuels over the last century, has caused the Earth's average temperature to rise.

This has altered weather patterns, worsening droughts in some parts of the world, and intensifying storms in other areas.

Source: AFP