September 8th, 2014 flash flooding

Remnants from Hurricane Norbert interacted with a low-pressure system to produce very intense rainfall during the early morning through midday of September 8, 2014 in the Phoenix and Tucson metro areas. The amount of rain produced in Phoenix during a 12-hour span was rare (<1% chance of occurring), but for areas such as Tempe, Mesa or Chandler it was an extremely rare event (<0.1% chance of occurring). This storm closed major highways and schools, flooded many homes, and caused multiple swift-water rescues. Unfortunately, fast-flowing washes in Tucson drowned two commuters.

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The rainfall totals from September 8, 00:00 to 12:00 in the Phoenix metro from the  Maricopa County ALERT network  is shown in the image below. It is incredible to see that most of the Phoenix metro received more than 2 inches of rain in 12 hours.

According to the data, stations around the Sky Harbor International Airport (black rectangle) received 3.30 inches in 7 hours while a site in Chandler (purple rectangle) received >5.5 inches in 12 hours.

The Maricopa County Flood Control District  estimated that the volume of water produced by this storm (261,233 acre-feet) could almost fill Horseshoe Reservoir AND Bartlett Reservoir (287,400 acre-feet) . That's a lot of water!

The bulk of the rain occurred from 02:00 to 10:00, and peaked during the early hours (02:00-04:00) as illustrated below.

The rainfall totals from September 8th, 00:00 to 12:00 in the Tucson metro from the  Pima County ALERT network  is shown in the image below. We can see that most of the rain was concentrated around midtown, Catalina foothills, Oro Valley, Saddlebrooke and Mt. Lemmon.

Compared to Phoenix, most of the rain occurred from 08:00 to 12:00, and peaked from 09:00-11:00 (depending on location).

What was the hydrologic response in the metro and surrounding areas? We'll show you the evolution from September 7th at 00:00 to September 9th at 23:59 for four streamflow stations:

1. Verde River near Scottsdale, a large tributary of the Salt River, located northeast of the Phoenix metro,
2. Indian Bend Wash at Curry Road, a small tributary of the Salt River, located inside the Phoenix metro,
3. Salt River at Priest Drive, a large tributary of the Gila River, located just east of Sky Harbor International airport, and
4. Gila River near Estrella Parkway, downstream station located southwest of Phoenix metro.

In the US, we measure the volume of water flowing in a river in cubic feet per second (cfs). The easiest way to imagine this is 1 cubic foot being the size of a basketball.

One cubic foot of water is about 7.5 gallons, and 1 gallon weighs approximately 8 pounds. So, 1 cubic foot per second is the equivalent of a basketball weighing 60 pounds passing by every second!

The large amount of rain in such a short period of time caused major flash flooding in the Phoenix and Tucson metro areas. This situation was worsened by the timing of the storm; it rained on a Monday during the early morning hours through lunch time.

In Phoenix,  five major highways were closed stranding commuting residents, 23 schools closed and 16,500 customers lost power .  More than 3,400 emergency calls were answered in a 10 hour span . Moreover,  residences near Emerald Park in Mesa were inundated due to a pump system failure .  Insurance companies rejected residents' claims since they didn't have flood insurance  and, ultimately, had to sue the city.  Mesa settled for $1.6 million in early 2020 .  Repair and cleanup of highways and streets cost $18 million and insurance companies paid $15 million in claims.   According to a Maricopa County Flood Control District report , this event was rare (<1% chance of occurring), especially in areas such as Tempe, Mesa or Chandler (<0.1% chance of occurring).

In Tucson, no major damage was reported, but there were plenty of swift-water rescues.  Unfortunately, a 53 year-old female drowned when her car submerged under 12 feet of water as she tried to drive through Alamo Wash. Outside of Tucson, a 76 year-old female drowned as her husband drove through Cadillac Wash. 

• Phoenix NWS  preliminary report 
• Maricopa Flood Control District  storm report 
• The Arizona Republic newspaper  extensive coverage 
• Videos of flooded washes and rivers in Tucson from  Arizona Daily Star 
• National/Local coverage clips:
1.  NBC : national coverage on September 8, 2014
2.  CBS : national coverage on September 8, 2014
3.  CBS : national coverage on September 9, 2014
4.  ABC-NY : coverage from New York affiliate
5.  CBS-Phoenix : Mesa aftermath video with residents (2019)
6.  NBC-Phoenix : Mesa flooding
7.  NBC-Phoenix : interview with ADOT spokesman Doug Nintzel