Precipitation in Northern Nevada may be headed for extremes, water summit told
The amount of precipitation Northern Nevada receives in the coming decades could remain the same, but more will fall as rain and snowpack will runoff earlier in the season.
And while the average amount may not change significantly, precipitation will come and go in more extreme weather events.
“Think of the last eight years, very dry and very wet. That’s more what our future looks like in terms of precipitation,” Mike Dettinger, research hydrologist, U.S. Geological Survey (USGS), told attendees at the 2018 Water Summit hosted by Carson Water Subconservancy District on Tuesday.
The biggest storms will likely be 20 percent larger or as much as 40 to 50 percent bigger in the worst case scenario, he said.
That is concerning for cities and counties.
“The projection that the storms would be less frequent, but bigger when they came was cause for some alarm. After the two storms we had back to back last year and knowing the damage that was caused, I would have to say that we would need to start planning differently when it comes to storm water,” said Darren Schulz, Carson City Public Works director, who attended the event.
By the end of the century, temperatures are predicted to rise by 6 degrees, if greenhouse gas emissions level off, or 9 degrees if emissions continue to rise, Dittenger said.
“This isn’t rocket science. If there are warmer winters there will be more rain than snow and earlier snowmelt,” he said.
The total outflow of water will not change much, said Dittenger, because earlier runoff means less evaporation.
But those users higher in the Carson River watershed will get the water earlier than they might want.
The growing season will start earlier and end later, extending it two months to 40 days, he said.
“I don’t know if that’s good news or bad news. That’s for you to say,” said Dittenger.
Snow levels — elevation, not amount — already are rising while snowfall is dropping.
Benjamin Hatchett, postdoctoral fellow, Desert Research Institute, talked about 10 years of data, from 2008 to 2017, collected in the northern Sierra Nevada mountains.
“We estimate a decrease of 3 percent a year or nearly a 30 percent decrease in the fraction of precipitation that falls as snow,” said Hatchett.
Looking at data collected since 1951, the last 10 years show the steepest decline in snow fractions, he said.
At the same time, measurements of snow levels, the elevation where snow changes to rain, rose 1,200 feet.
Wes Kitlasten, hydrologist, USGS, talked about a way to store some the early runoff.
“Carson Valley lacks storage, which prompted us to look at managed aquifer recharge,” he said.
The process is essentially winter irrigation to recharge groundwater in areas with a deep enough water table, which include the Gardnerville Ranchos.
“But it’s not long-term. It will flow through by the end of the year,” he said.
Carson City is considering more storage, too.
“The city is starting to look into possible options of surface water storage such that the water could be held temporarily, and then used later when the summer really gets hot and the demand is higher,” said Schulz.
“This will take a lot of effort to analyze and will likely take a couple years to know if it’s even feasible, but we are most definitely looking into it.”
Another idea is indirect potable reuse by further treating reclaimed water and discharging it into reservoir or groundwater as a drinking water source.
Right now, 80 percent of Nevada’s water is reused on 50 golf courses and 13 agricultural sites, said Bruce Holmgren, chief, water pollution control, Nevada Department of Environmental Protection.
There are categories of reusable water, from A to E, with A being the most treated for use in snowmaking, food crop irrigation, commercial window washing, and other applications.
Holmgren said water can be treated to meet drinking water standards, what he called an A+ category for reuse.
“The treatment is easy. The toughest part is public acceptance,” King said.
“Most people don’t respond positively to the idea. “
Jason King, state engineer, talked about the state’s 256 water basins, 20 percent of which are considered severely over-appropriated.
Only one so far, in central Nevada’s Diamond Valley, has been designated a critical management area.
The state engineer’s office is working with water rights holders there now on a groundwater management plan.
“They’re submitting a plan within the month. Plans are to reduce pumping by 30 percent in the first 10 years,” said King.