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Rainfall and Weather

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The Flood Control District of Maricopa County operates a 24-hour rain, stream and weather gage network which provides "real-time" information to the County and many other agencies about rainfall, floods and weather conditions in Maricopa County.

This network operates in the National Weather Service ALERT (Automated Local Evaluation in Real Time) format and is commonly referred to as an ALERT system. The ALERT system uses "automatic" telemetry gages for data collection. A collection of gages or sensors at a single location is considered an ALERT Station. The gages transmit their information to the District base computers via VHF radio. The computers quickly compile the information and display it on video screens. The automatic gages are powered by 12-volt batteries, which are recharged using small solar panels attached to the top or sides of the gage.

ALERT Station of the Month

The information provided by the ALERT system is important to the District because occasional heavy rainfall can generate stream flows which significantly impact flood control facilities such as dams and channels. Each gage is programmed with an alarm setting. The alarm sounds when measurements reach a certain threshold. An on-call hydrologist then evaluates and monitors the situation. Flood warnings are provided to District observation teams, other County departments, city emergency management departments and the National Weather Service. Public flood warnings and other weather advisories are issued by the National Weather Service. Emergencies are declared by the Maricopa County Department of Emergency Management.

The ALERT system data is also valuable after a storm. The stored data is used to reconstruct storm events in order to show the origin of flooding problems and to provide data for use in floodplain studies, computer modeling of watersheds and design of future flood control structures.

The Flood Control District started the ALERT system in 1980 after the late-1970s floods. Gages were first placed to monitor the major rivers, then later installed on District dams and flood control structures. After the 1993 floods, the District started placing more gages in smaller washes and upstream of unbridged road crossings. In addition to operating the ALERT system, the District also provides information for several local Flood Warning Plans, and provides information to the Maricopa County Department of Transportation Flooded Roadway Response Program.

Currently, the District has 313 automatic rain gages, 175 automatic stream gages and 36 automatic weather stations at 354 ALERT Stations located throughout Maricopa and neighboring counties.

In addition to the automated gages, the District partners with a Web-based collaborative network of volunteer weather observers - Rainlog.org. Flood hazards are a statewide concern, and Rainlog.org is a place where citizens from all over Arizona can help record rainfall. These observations provide useful data to many types of users, including K-12 educators, water resource managers and scientists. If you would like to join this statewide volunteer observer network, please visit the Rainlog.org Web site.

Another web site available for viewing/posting of rainfall information reported by volunteers is called CoCoRaHS, the Community Collaborative Rain, Hail and Snow Network. CoCoRaHS is sponsored locally by the State Climatologist and reports are often cited by the National Weather Service.