It's not often Tucson is hit with severe flooding, but when we are, it may be difficult to contact first responders for information. Pima County’s Regional Flood Control District relies on a system called ALERT (Automated Local Evaluation in Real Time), a countywide network of weather and stream sensors to watch for flash flooding. The system offers real time notifications on street closings, flooded roads and other local hazards.
The ALERT system now includes 134 sensors positioned across the county to capture when — and how much — rain is falling via the Alert map. The County says the map records the amount of rain fall between the last ten minutes or the last 30 days. The low‑profile, earth‑colored instruments are equipped with solar panels, GPS and a tipping‑bucket rain gauge; some also have lines running into nearby washes to measure rising water levels and stream flow.
“Whenever there’s a change, whether it’s rainfall or a change of the flow in the wash, these sensors are activated and we get the data,” said hydrologist Ali Arabzadeh of Flood Control. Because the data is delivered in real time, the department can monitor potential flooding and respond more quickly. “We’ve done studies for most of our sensors, so we know exactly how long it takes for water to get from point A to point B,” he said. Arabzadeh pointed to a gauge at Marshall Gulch atop Mount Lemmon — the headwaters of Sabino Creek — noting that heavy flow there can signal downstream flooding, giving crews time to alert partners such as the U.S. Forest Service.
ALERT evolved from the county’s post‑1983 flood mitigation work and now feeds information to Pima County Transportation, the Office of Emergency Management, the Sheriff’s Department and the National Weather Service. Researchers at the University of Arizona have also used ALERT data for scientific studies.
Eight ALERT locations are fitted with real‑time cameras that capture fresh images every 15 minutes. The small Flood Control maintenance team — Arabzadeh, Brick Cummins, Jeffrey Mangold and Lynn Orchard — inspects each station at least once a year and more often for gauges in major washes like Tanque Verde and the Rillito. Routine work ranges from cleaning the tipping bucket to brushing off solar panels and replacing batteries. The district installs an average of five new sensors a year and is expanding coverage in areas with sparse monitoring, including the west side of the Tucson Mountains. The system was also bolstered in response to the 2020 Bighorn Fire and subsequent flooding along Finger Rock Wash.
ALERT’s measurements are available to the public: residents can view the Alert map for continuously updated rainfall and flow readings — from totals over the last 30 days down to the last 10 minutes — and can sign up for MyAlerts, the county’s emergency notification system, to receive flood and other hazard alerts for their area.
