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Some of the American Southwest’s most famous outdoor destinations including Moab, Carlsbad Caverns, and Zion National Park have faced an onslaught of flash floods over the last few weeks.  Flash flooding can be particularly dangerous in the area’s many famous slot canyons.  On August 22, Moab received over one inch of rain within 20 minutes, causing significant flooding within the surrounding parks and town and leading to closure of many areas.  This was considered a 100-year flood (meaning 1% chance of occurring every year).  This was the third flash flood in Arches National Park in the past month.  Not far away in New Mexico, over 200 people were stranded in Carlsbad Caverns after a storm brought severe flooding making exits impassable.  When initial evacuation efforts by the park were unsuccessful, visitors ended up having to shelter in place for several hours until the zone was deemed safe.  Flash floods in Zion’s famous slot canyon known as the Narrows left many hikers scrambling for higher ground, while others were swept downstream.  One missing hiker from Arizona was found dead several days later downstream along the Virgin River, suspected to have drowned in the surging waters.  Multiple trails in the park remained closed for safety.

Link to Climate Change

The Southwest US is in a 22-year drought, beginning in 2000.  These recent heavy rains have only made a small dent in the prolonged drought – several high-precipitation winters will be needed to help reverse the long-term trend.  There has been an increase in the intensity between the wet and dry seasons, and the worsening dry seasons prevent the heavier rains of the monsoon season from being absorbed into the ground leading to more severe flooding over time.  For every one degree Fahrenheit increase in temperature, the air can hold 4% more water. Moab has seen more flooding over recent months, especially after a 2021 wildfire in the surrounding La Sal mountains has affected the local terrain’s ability to retain water; rainwater will rush unhindered over the large burn scar area and into low-lying areas.

Flash Flood and Canyon Country

Canyons, ubiquitous in the US Southwest, present unique dangers to the wilderness explorer.  A quick internet search will yield many fatal events due to flash floods over the past several years.  One of the most notable events, known as the Keyhole Seven, occurred in 2015 when seven canyoneers died in Zion National Park during a flash flood after local storms dropped 0.63 inches of rain increasing local river peak flows from 55 cfs to 2630 cfs.  Flash floods are the largest cause of disaster-related deaths in the United States.  In flash floods, 90% of deaths are attributed to drowning, although trauma and hypothermia may be important factors as well.  Flooding in the Southwest US is most common during the monsoon season which occurs from April to October.  During these months, visitors to canyon country must pay close attention to the weather before hiking, climbing, or canyoneering.  It does not need to rain in the spot where you are for a canyon to flood.  In slot canyons, flash flooding, originating from much farther upstream, can overwhelm an area within minutes or even seconds.  There are some hints that a canyon is about to flood:  there may be smaller initial waves and water levels may rise before a large wave comes fully flooding into a canyon.  Flash floods can still occur in an area where there is as little as a 30% chance of rain.  Indications for a flash flood include any deterioration in weather, sudden changes of water color from clear to muddy, rising water levels, stronger currents, or an increasing roar of water.  To protect yourself when in a slot canyon, seek higher ground immediately.  If this is not possible, find something to hold onto such as trees or rocks.  It is of the utmost importance to be prepared prior to adventuring within a slot canyon; always look ahead at the forecast, always take maps and ample food and water, have a backup plan, and always tell someone where you are going and when you expect to be back!

Carlsbad Caverns after recent rains image from NYT

Video of flooding in a slot canyon: