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STEM

The Futurecast is More Rain

Post-storm clouds in metro-Phoenix, September 2014

Post-storm clouds in metro-Phoenix, September 2014

In addition to a number of other priorities that have kept me extremely busy for the past few weeks, I had the fortunate and unfortunate opportunity to witness an historic weather event. About one week ago, I was awakened by the aggressive pitter-patter of rainfall. I am not exactly sure of the time it started raining, but I’m guessing after midnight. Knowing how much metro-Phoenix and others areas of the desert southwest need rain, I smiled, shifted my position in bed and settled in for what I hoped would be an enjoyable night’s sleep. After all, I am one who likes sleeping when it is raining outside.

Perhaps an hour later, I was aroused by the howl of the wind and pounding rain pellets on the exterior of the house and the windows. T-e-r-r-i-f-i-c! Assuming all was well, and happy that we’d finally get a good soaking outside, I quickly dozed off again. Waking from my sleep for the second time that night, about two hours later around 3 a.m., the chorus for the wind, rain, and thunder had intensified. This time I decided to get up, head for the bathroom, and take a peek outside to see how the Master’s hand was progressing across the sky. However, before going outside, I decided to check the backroom. We’ve had water intrusion problems in this area of the house before. While I was not anticipating any problems, my intuition said better safe than sorry.

A-n-d…..YIKES! Entering the room I quickly discovered water on the floor that has a slight downward slope towards the back wall. Water was coming through the back door faster than a garden hose at full force. My logic kicked into 5th gear and I grabbed a broom, opened the door on the opposite side of the room and started moving water out thru this exit — all while semi-viewing one of the local news stations as their reporters kept the public abreast of the progress of the storm, and the damage that it was causing around metro Phoenix and the State of Arizona. Three hours later, and as the storm was subsiding, I had cleared most of the water off the floor and began the drying process.

According to the National Weather Service, a record 3.29 inches of rain fell at Phoenix Sky Harbor airport – the most precipitation ever received in one day for the city. The previous record was 2.91 inches in 1939. Local cities such as Chandler and Mesa reportedly received even greater amounts – 5.63 and 4.41 inches, respectively – in some locations.

Meteorologist, elected officials, homeowners, and just about everyone else are still assessing the damage done by this 100-year storm, now that the area has dried out. Local media reported that rain from the remnants of Norbert, a Pacific Ocean hurricane, was responsible for the flooding that occurred across Arizona and other southwestern states including California and Nevada.

Storm clouds brewing in metro-Phoenix, September 2014

Storm clouds brewing in metro-Phoenix, September 2014

Local meteorologists reported that Monday was the rainiest single day in the history of Phoenix, AZ based on records that go back to 1895. As seen in numerous photos on regular and social media, freeways were turned into rivers and lakes. A community in California reported a police cruiser floating down the street, and here in Phoenix, rain in low spots on Interstate-10 just to the west of downtown Phoenix left travelers stranded as the water levels rose above the hoods of their cars.

Locally, meteorologist were reporting this historic rainfall and the subsequent flooding that accompanied it as a 100-year storm. Several newscasters referred to this historic event in Phoenix as rainfall that happens once every 100 years. Well, not exactly. The United States Geological Survey (USGS) informs us that referring to the event of last week as a 100-year flood is a misinterpretation of terminology. This leads to a misconception of what a 100-year flood really is.

Instead of the term “100-year flood”, hydrologist and other scientist prefer to describe this extreme hydrologic event as a flood having a 100-year recurrence interval. A short explanation is the probability of flooding is once in 100 years. In other words, a flood of that magnitude has a 1 percent chance of happening in any year. [Ref 1]

So-o-o, we are finally drying out from last week’s historic rainfall, the flooding that followed the rain, and the debris and damage that accompanied the flooding and the futurecast is …. more rain. Channel 12 (KPNX) news meteorologist, Caribe Devine, has provided a futurecast for the rest of this week [Ref 2]: Storms will become more scattered Tuesday through Friday. There will be a strong chance of localized flooding as the moisture from Hurricane Odile arrives on Tuesday through Friday. Highs will be in the 80’s and 90s into the weekend. Two to four inches of rainfall is expected across southern Arizona.

Just so you know, a 100-year recurrence interval of a repeat of last week can happen one week later, or two years in a row. The rain has not yet fallen, and rainfall data has yet to be recorded.

In the meantime, I’m looking for a few sandbags to put at the bottom of the back door. Reference:

    1. USGS Water Science School, Floods: Recurrence intervals and 100-year floods, http://water.usgs.gov/edu/100yearflood.html (this web page was last visited on 09.14.2014)
    2. Channel 12 News Local Forecast, http://www.azcentral.com/weather/ (last visited on 09.15.2014)
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About Vi Brown

Vi is principal and CEO of Prophecy Consulting Group, LLC, an Arizona firm that provides business and engineering services to private and public clients. Prior to establishing her consulting practice in 2001, Vi worked with Motorola, Maricopa County Government, Pacific Gas & Electric, CH2M Hill, and Procter & Gamble. As an adjunct faculty member, Vi teaches undergraduate calculus classes and graduate level environmental courses. She is also a professional speaker.

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