Metro Phoenix's water supply got a much-needed boost after a major storm swept through Arizona Wednesday through Friday, adding to rain and snow accumulation from an increasingly wet winter.

Salt River Project estimates that the Salt and Verde river reservoirs will fill to 75 percent capacity by the end of the current water runoff season, which runs from about January to May.

That's a significant rise from what the reservoirs gained in 2018. On May 31 last year, the reservoirs had reached only 56 percent capacity.

"There is no doubt that the Phoenix area is in much better condition than last year," said Charlie Ester, manager of surface water resources at SRP.

The recent storm brought vital snowfall to the White Mountains in northeastern Arizona and other areas where melting snow contributes a significant portion of Phoenix's water supply. In addition to the recent snowstorm, a wet winter marked by weeks of rainfall on the Salt and Verde river watersheds is also bringing much-needed relief.

"That one storm in itself does not change our situation," Ester said. "It started off in October with a very wet October that primed our watersheds for runoff." A series of storms in December and January also contributed.

To put the recent storms into perspective: SRP's reservoir system, one of Phoenix's main water sources, received 100,000 acre feet of runoff last year between Jan.1 and May 31. Earlier this month, the entire system received 108,000 acre feet of rain runoff in just two days, Ester said.

That said, don't expect reservoirs to return to full capacity unless more productive storms come this way, Ester said. The last time SRP's reservoir system was at full capacity was in 2010.

Snowpack is four times last year's

Based on the current snowpack, Arizona's thirsty reservoirs can look forward to plenty of spring snowmelt.

The Natural Resources Conservation Service calculates snowpack density by measuring depth and weight. From there, the federal agency can calculate how much water is in the snow.

"This last storm was a game changer for sure," said Travis Kolling, water supply specialist at the agency's Arizona office.

As of Feb. 25, Arizona's snowpack is 418 percent over what it was last year on the same date. The current snowpack is also 38 percent higher than the 30-year average.

"This will help fill up the reservoirs," Kolling said. "Good snowpack, good precipitation and soil condition is in good shape. All things are pointing to good (when it comes to) filling up reservoirs to more reasonable levels."

If temperatures don't warm up too soon, a "nice, slow melt out" could also improve wildfire season, Kolling said.

READ MORE: Wildfires increase with shrinking snowpack, changes in snowmelt timing

Snow melt typically begins in March and lasts through April, sometimes into May. A gradual release of runoff is vital for hydrating soil and vegetation. The affected areas are then less susceptible to wildfires that can spread quickly into the megafires that have become more common in recent decades.

Last year the snow melted out by early April and total precipitation level was low, resulting in the soil and plants drying out earlier, Kolling said. This year's precipitation and snowpack could shorten the fire season window, he said.

Rising temperatures have been the main reason for Arizona's shrinking snowpack in recent years, Kolling said. Although January storms brought precipitation to Arizona, it was too warm for snowfall, he explained. Instead it rained on top of the snowpack, causing some quick and early snowmelt to already occur.

Kolling stopped short of pointing to human activities as the cause of these rising temperatures, but scientists have come to global consensus that human activities are responsible for climate change over the past century.

"All I can say is that in the last five years, we have seen a later start to the snow season and earlier end," Kolling said. "Typically this has affected the snowpack."

Reach the reporter at Priscilla.Totiya@azcentral.com or 602-444-8092. Follow her on Twitter: @PriscillaTotiya.

Environmental journalism in The Arizona Republic and azcentral is supported by a grant from the Nina Mason Pulliam Charitable Trust. For more stories visit environment.azcentral.com or follow OurGrandAZ on Facebook, Twitter and Instagram.