El Nino boosts 2016 runoff; more expected to come

(Courtesy photo of Verde River)

(Courtesy photo of Verde River)

After five consecutive runoff seasons of below-median inflow into the reservoirs on the Salt and Verde rivers, Salt River Project is projecting that the January-to-May 2016 runoff season will be finishing up right around the 30-year median.

And median is a good thing, considering the last five runoff seasons have finished below the median runoff of 534,336 acre-feet (AF) for the January-to-May period - many among the driest in years.

SRP's current streamflow forecast is projecting the 2016 runoff to come in at about 585,000 AF - assuming above-normal precipitation with a below-normal snow water equivalent through May. The last wet winter came in 2010, when 1,430,000 AF of precipitation filled the Salt and Verde reservoirs and prompted releases in the normally dry Salt River through the Valley.

Over the last five years, the final runoff season numbers were 328,360 AF in 2015; 148,000 AF in 2014, the eighth-driest since SRP has been keeping records for the last 118 years; 444,788 AF in 2013; 196,064 in 2012; and 222,907 in 2011.

An SRP snow-measuring team recently visited locations in the White Mountains to get an early indication of where this year's runoff numbers are headed. The good news is that the El Nino weather pattern, while sporadic this winter, delivered an early amount of snow over SRP's 13,000-square-foot watershed -- much of which has already started to melt into the reservoirs that are designed to capture runoff from wet years such as 2016. The better news is that El Nino may not be finished for the season.

While near four weeks have passed since the last measureable precipitation showed up in SRP's daily watershed average precipitation report, the current forecast guidance still offers hope for an El Niño "bump" in precipitation after the February hiatus -- before the spring temperatures start climbing again. The latest National Weather Service outlook for March favors "above-normal" precipitation (about a 43 percent chance) over "below normal" (about a 24 percent chance).

"We're keeping our fingers crossed that the pattern of strong El Ninos holds up, and that this one still may have some work to do in March," said Charlie Ester, SRP's manager of Water Resource Operations. "If that's the case this year, we'll take it."

Ester said the initial SRP winter runoff forecast in early 2016 was for the El Nino to produce 1 million AF, but that forecast was downgraded in early February to 830,000 AF after a less-productive January.

He said a "median" January-to-May runoff season would help refill the six SRP reservoirs, which today have risen to 57 percent compared to 53 percent one year ago, but would likely not completely fill the reservoirs.

Current storage on the Salt River system is also at 57 percent; the two reservoirs on the Verde River are a combined 52 percent of capacity. Theodore Roosevelt Lake, which holds about two-thirds of the combined water stored on the Salt and Verde rivers, today stands at 49 percent full and will continue to rise as the snowpack melts at the higher elevations.

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