The “official” monsoon period for 2021 has faded with the end of September and by all available accounts, it was record-breaking year for rainfall. The National Weather Service has established the summer monsoon for Arizona as beginning on June 15 and continuing until Sept. 30.
This summer, rainfall totals for that period reached or exceeded 10 inches in Fountain Hills nearly across the board. The Maricopa County Flood Control District maintains nine ALERT weather monitoring sites within town limits, and there are three additional outside of town that are watched with interest.
With the exception of the rain gauge at the ALERT site at Fountain Hills Fire Station #1 at Palisades Boulevard and Avenue of the Fountains, all the county sites recorded more than 10 inches of rain, with as much as 12.48 inches collected at the location near Adero Canyon Trailhead (identified by the county as Cloudburst Wash). The fire station received 9.73 inches. The Town of Fountain Hills reported 9.88 inches at Fountain Park over the monsoon period. The only other location aside from the fire station to received less than 10 inches.
Hesperus Dam, near Teepee Drive off Richwood Avenue, received 12.44 inches of rain this summer.
At McDowell Mountain Park the ALERT site is at the park operations facility near the campground, and it received 10.59 inches. The Verde Communities received more rain than Fountain Hills this summer. The monitoring site at Asher Hills, west of Tonto Verde south of Rio Verde Drive, collected 12.56 inches.
As is typical of the desert monsoon, the storms can be sporadic and many home weather stations likely collected varying rainfall amounts, surpassing the county gauges in some cases.
Two multi-day monsoon systems accounted for well over half of the seasonal rainfall. July 21-25 brought 2.61 inches as recorded at Fountain Park. From Aug. 11-18, there were 5.25 inches received, again at Fountain Park. Both of those left significant flood damage to streets and washes including a storm that washed cars off the road into washes. One vehicle ended up a quarter mile downstream from the road it was travelling. The driver did escape injury. There were also a number of homes reporting flood damage from the bloated washes.
The Flood Control District maintains the history of its rain gauges since they were installed. Most of the monitoring sites were installed as development picked up in this area in the early 1990s. The closest comparison to this year’s monsoon rainfall was in 2014 and this year surpassed all of those readings by at least two inches. Fire Station #1, installed in 1994, received 7.60 inches in 2014; Hesperus Wash, which received 10 inches this year, was at 8.14 in 2014. Cloudburst Wash received 9.25 in 2014. At Rio Verde in 2014 the monitoring site received 5.19 inches.
The County ALERT sites monitor rainfall year around and what we were looking at here is just for the monsoon period. The calendar for a “water year” runs from October through the end of September. For example, 2005 appears to be the record year for annual rainfall (per water year) and that was clearly influenced by winter rains. Fire Station #1 recorded 17.05 inches for the year in 2005, but only 3.54 inches during the monsoon. Similarly, Hesperus Wash received nearly 20 inches for the year in 2005 (19.25), but only 4.41 inches fell during the monsoon period.
Salt River Project, which manages water from the Salt and Verde River watersheds, also reports substantial runoff from the summer monsoon. This summer the utility released water into the normally dry Salt River bed through the East Valley, something nearly unheard of during the monsoon months.
SRP also reports that at the end of the monsoon its four Salt River reservoirs are an overall 73% full, while the two reservoirs on the Verde River are 52% percent full making the overall SPR system 70% full going into the winter.