Maps of the difference from average December-February temperature (top row) and precipitation (bottom) during the 22 El Niño and 19 La Niña episodes in the past 60 years. (Maps by NOAA climate.gov team, based on data provided by Michelle L’Heureux, NOAA Climate Prediction Center.)

For a water manager like Adams, the connection between Florida’s climate and El Niño and La Niña is both a curse and a blessing. On the one hand, having a La Niña occur every 2-5 years means she has to deal with drought and water shortages that generally accompany it. On the other hand, El Niño and La Niña are fairly predictable a few months ahead of time. That means Adams can plan ahead for capturing the excess water in the wetter years and being more mindful of storing it in the drier ones.

Of course it’s not as easy as flipping a switch in a given year. Climate forecasts come with a degree of confidence (ENSO increases the likelihood of certain conditions) not a guarantee. For example, there was a La Niña in winter 2010. While the region did, in fact, see decreased rainfall, temperatures were unexpectedly cooler than normal due to other climate factors.

Underscoring everything is the matter of cost. Processing water through the desalination plant can cost around $5 per 1,000 gallons. Those same 1,000 gallons only cost about $2 to treat and deliver when they are drawn from rivers and processed at the surface water treatment plant. When you start talking about processing tens of millions of gallons of water each day, the price differences can add up pretty quickly.

(Click to enlarge.) This drawing shows all the steps involved in making seawater from Tampa Bay into drinkable tap water. (Drawing provided by www.tampabaywater.org.)

Making up for dry years with more groundwater pumping also carries a risk. The state regulatory authority has set a limit for Tampa Bay Water allowing them to pump 90 million gallons per day over a 12-month running average from 11 of its regional well fields.

Tampa Bay Water can request an emergency order to pump beyond the permits, but only if all other supplies are exhausted. And their requests aren’t always granted.

A case in point was the spring of 2009. Tampa Bay Water went over its groundwater pumping limit during a drought. The state regulatory authority denied their emergency request, however, and instead fined them roughly $46,000. Ultimately, good rainfall in the latter half of the year put Tampa Bay Water back in compliance.

Adams uses a seasonal forecast to try to balance these economic considerations along with the natural and societal ones. The NOAA Climate Prediction Center issued an El Niño Watch in June, which Adams is already using to think about for the coming winter.

“If I’m expecting, say a moderate or mild El Niño in the winter, I can expect that the river flows will maintain themselves right on through December,” Adams said. “Then I can plan on turning the desal [desalination] plant on at minimal quantity and not be in danger of exceeding the groundwater permits.

“[During a strong El Niño], I might delay turning on the desalination plant by a month or so, which means our operational cost will go down. Then in the spring, if it’s also wet and cool, river flows will stay higher so I’ll be able to keep the surface water treatment going through the spring.” That means in addition to lower costs, Adams can use less groundwater as the region enters its dry season, giving the aquifer and the wetlands that rely on it more of a buffer.

Adams even accounts for human demand based on seasonal forecasts. “If it’s a strong El Niño, it means I could have wet and cold weather. Then my demand is going to plummet. In that case, I’m going to let some river flow go by,” Adams explained. This again provides the benefits to the aquifers and wetlands and also gives estuaries in Tampa Bay itself more freshwater to stay at equilibrium.