DWR prepares for another dry year
At the September 2021 meeting, John Yarbrough, Assistant Deputy Director of the SWP, briefed the Commission on the Department of Water Resources and the State Water Project is addressing the ongoing drought conditions and preparing for the possibility of another dry year.
He began by noting the low storage levels in the state’s reservoirs, particularly those in Northern California. The key reservoirs for the State Water Project and the Central Valley Project are up in the northern part of the state, so the precipitation and runoff in the north part of the state drive how much water supply there is for the system.
The runoff captured by these reservoirs is used in several ways:
- to meet demands from the settlement contractors up in the northern part of the valley;
- to meet instream temperature requirements for fish;
- to push saltwater out to sea and maintain water quality in the Delta, which is critical for both municipal and irrigation use; and
- to move the water down south through the rest of the system when conditions allow providing water to the Bay Area, Central Valley, and Southern California.
The other key reservoir part of the State Water Project system is the San Luis reservoir. So in wetter years, water is moved from the Delta to San Luis Reservoir, where it can be carried over into additional years.
“In a dry year like this, we have to focus on conserving as much water as we can in the store the reservoirs, so as we’re really operating them, we have to start prioritizing our operations,” said Mr. Yarbrough. “We’re focusing on the northern settlement contractors, the instream requirements, and the salinity requirements in the Delta.”
Mr. Yarbrough presented a graph of the 8-station index, noting that 2019-2020 was one of the top 10 driest years in the 100 years of record, and 2021 was even drier. (Note: chart is the latest for the 8-station index, as of the publish date of this post.)
Another key metric is looking at two-year periods. Mr. Yarbrough said 2020-21 was the second driest two-year period; only 1976-77 was drier.
Precipitation is the first step, either snow or rain, which usually becomes runoff captured in the reservoirs. In the spring of 2021, the snowpack was 60-70% of average – less than average but still sizeable snowpack. But what was unanticipated and unprecedented was that only 20% of that snowpack materialized into runoff.
“It’s a large change from what we’ve observed in the past,” said Mr. Yarbrough. “That’s noteworthy for a couple of reasons. For one, it really changed how we were viewing this dry year. We were anticipating having this runoff in March and April. In some ways, we were planning for 2022, thinking of what we would need to do if we saw a continuation of dry conditions. However, as that runoff did not materialize very quickly, we went from thinking about 22 to really needing to think about this year because the conditions changed for the worst very quickly. And so it required a different approach on our part.”
The other noteworthy thing is that as climate change progresses, we would expect to see long-standing relationships start to break down and change, which was observed this year with the long-standing relationship between snowpack and runoff.
“We saw a very different behavior this year,” he said. “So you’re really seeing the impacts of a changing climate as we’re going through the water year.”
All the temperatures for November through April for the 100+ years of record were ranked, and the resulting percentiles are shown on the slide. Last year, the areas shown in dark orange were in the top 10% of temperatures observed, and the remaining regions, shown in the lighter orange, were in the top quarter percentile for temperature.
“Last year, we saw much warmer temperatures than what we’ve experienced in the state on average,” said Mr. Yarbrough. “We think that increase that above normal temperature had an impact on drying soils, so the drier soils were soaking up more of this water that would have otherwise flowed into our reservoirs. We also think that had an effect on the snowpack itself, causing increased evaporation. And so that combination of those effects is what contributed to not seeing the snowpack turn into runoff.”
The figure on the slide is a plot of annual average temperature on the horizontal axis and a measure of wetness on the vertical axis. The yellow triangle in the middle is the average. The average temperature for 1895 to 2000 are the blue diamonds; the average temperatures for the 21st century are the black squares. This figure shows the difference between the hydrology for the 21st century versus the hydrology in the last century.
“As we look at the wetness, the up and down, maybe there isn’t really a trend there,” said Mr. Yarbrough. “We get a lot of variability on how wet things are in California; we’ve seen that in the last century, and we continue to see that moving forward. But temperature really is where we see a trend. All of the black squares in all recent years tend to be above average temperatures. So it’s where we see this trend having this impact on our runoff on our water supply. So this is another sign of these changing conditions that we need to be thinking of, as we think about our water supply picture and as we think about how are we planning for next year’s conditions.”
The figure shows the levels in Lake Oroville showing the reservoir elevations for three of the most severe droughts: the 1976-77-78, 2013-14-15, and 2020-21-? He noted that Oroville reservoir is at the lowest level since the reservoir was filled (Note: this presentation was in September.)
“Of course, we don’t know what the conditions will bring next year, but what we do know is that as we’re going into next year, we’re starting with the smallest water supply buffer that we’ve ever had by not having that storage in Lake Oroville,” said Mr. Yarbrough. “So that really informs now how we need to think about 2022 and the increased uncertainty as last year, we saw things that we hadn’t seen before. And then also with this lowest starting conditions.”
The slide lists come of the actions taken by the State Water Project and Central Valley Project as the rapidly drying conditions occurred.
One of the main objectives was to retain as much storage, particularly cold water, in Oroville and the Central Valley Project reservoirs. One of the actions was to file a petition asking to relax some of the salinity requirements in the Delta; the Water Resources Control Board issued an order that did relax some of those standards.
“What that means is, is instead of having to release the same volume of water to push saltwater out to sea, that allowed us to retain some of that storage up in our reservoirs,” said Mr. Yarbrough.
In conjunction with that, the Department installed a salinity barrier (or a rock dam) in the Delta, which reduces the amount of water needed to be released from upstream reservoirs to repel salinity intrusion.
“What the barrier is doing is keeping higher salinity to the left side of the figure, which is helping lower salinity on the right side in the interior part of the Delta,” said Mr. Yarbrough. “There are a lot of users that pull water out of the Delta, so the water quality is really important.”
The Department also worked with member agencies on the timing of water diversions and the different exchange relationships, which allowed the agencies to continue to keep cold water in the reservoirs. The cold water is particularly important for salmon runs during the spawning seasons.
Other actions included reducing the State Water Project allocation to 5%; the Central Valley Project reduced their allocations to M&I based primarily on public health and safety. The state also called for 15% voluntary conservation. There was a lot more coordination between the state and federal projects and the member agencies on managing this year as well as planning for next year.
Looking forward to 2022
The Department is planning for ongoing drought conditions. The state is into this water year with the lowest storage levels ever, so it’s a small buffer. Warming trends continue to be observed, and concerns about snowpack and the amount of runoff definitely persist.
“It’s warm and dry right now, and with those conditions, it leads us to believe that there’s a higher risk that we’re going to have a low water supply picture next year,” said Mr. Yarbrough. “So that’s changing how we’re doing our planning for next year. While our usual approach is to look more at a range of conditions, we’re focusing on some of the more worst-case scenarios and planning around those, and looking for off-ramps, so we’re looking for hydrology to provide some extra water to the system to move us out of those worst-case scenarios.”
As part of that planning, the Department acknowledges that there is a lot of uncertainty to be considered in what conditions will be next year. That uncertainty exists not just for the State Water Project but also the Central Valley Project, the State Water Resources Control Board, and other partners.
“So as we’re thinking about our hydrologic data, and that our past might not be as representative of what’s happening moving forward, because we noticed these trends of warmer conditions, the role of warmer temperatures, and the dryness of the soils, So we have some uncertainty that we need to be more mindful of,” said Mr. Yarbrough. “When we have lower exports, that also minimizes our operational buffers and our ability to react to the issues that crop up throughout the year there, so we have less room to operate with.”
The Department is starting much earlier, regularly, and robustly with their multi-agency coordination with the Bureau of Reclamation, the Water Resources Control Board, and their member agencies to understand what allocations create specific issues for those member agencies and to have a better sense of where our member agencies will start to have issues within their systems.
The Department is also evaluating their modeling since the modeling didn’t predict the lack of runoff materializing last year. So they are adjusting current practices to reflect some of last year’s observations to capture some of the drier conditions. As a mid-term action, they are working with other agencies to get additional data, including flights over the watersheds to better capture the characteristics and effects of burned watersheds. A longer-term action is considering different modeling approaches.
If conditions remain dry, the Department is considering additional barriers in the North Delta and communicating the expectation that another temporary urgency change order will be needed, similar to last year and probably sooner, to modify or adjust some of the salinity requirements in the Delta.
The Department is prioritizing what they would do with a limited water supply. Part of it is considering the human right to water. So they are talking with their member agencies on what their minimum needs for sanitary use, domestic use, and fire suppression as a minimum, and ensuring that as water quality standards are modified in the Delta, that the Department will be able to meet those. Cold water for fish remains a priority, as well as having some level of conservation of storage for next year because 2023 could also be a dry year.
The last priority is making sure member agencies can access the water that they have through their system. Mr. Yarbrough noted that a lot of water agencies have stored water in groundwater banks, so they have been looking at how to pump water backward up the California Aqueduct if need be so that they can ensure the ability to access water stored by agencies that they need to help meet those critical agricultural needs.
Mr. Yarbrough concluded by saying that conservation is an integral part of the picture. “The level of conservation depends on what the water supply picture looks like as we move to next year. We’re already at 15% for the voluntary contribution, but it definitely will be important for all of us to continue to push that conservation message and do what we can also conserve water.”
DISCUSSION PERIOD
Commissioner Fern Steiner asked about reversing the direction of the Aqueduct. How does that work? And, noting that Southern California storage looks better at this point than Northern California, how do you figure out how to balance the water when there’s storage in one place and not the other? And who facilitates that conversation?
“With the reservoirs in Southern California, a lot of that water is water that we had made available to our southern contractors, and they have it set aside there,” said Mr. Yarbrough. “In some cases, it’s how those contractors are using that water that they’ve carried over. And so we facilitate how that happens, according to the law that spelled out within our contract. There are a lot of different exchanges of water, and I’d say we serve in a facilitating role there as well. A lot of that is led by our customer agencies, as they figure out how to use the water they have in different places for what makes the most sense for their areas. The use of those southern reservoirs that is part of the conversation that as one of the tools that we were reluctant to look at, that storage in Southern California, because that is one of the last storage sources that there is, and so that we don’t want to casually go and start doing that. It would need to be coupled with conversations about additional conservation; it would need to be part of a suite of actions. It’s not one that I would see us just going to on its own.”
Daniel Whisman, program manager of the State Water Project’s California Aqueduct Subsidence Program, pointed out that the Aqueduct is not level; it has a gradient of about two feet drop in 10 miles, with each pool approximately 10 miles long, for the most part. “So even though it’s not as efficient as utilizing gravity to help that flow downstream, we still have the ability to move water upstream with that flat gradient,” he said.
Commissioner Fern Steiner said that when you talk about severe extreme weather events, she assumes it includes fire as one of the results of the extreme weather conditions, as well as issues with our water quality that have to be addressed. It may require more power to try and purify the water further. Your thoughts?
Mr. Yarbrough said it’s definitely part of what they are seeing. “The watershed up above Orville, in just over the last three years, a substantial percentage of the watershed has burned over the last three years, and that poses a handful of different things that we need to be mindful of, such as future debris. So when we do get a wet year, we would expect there to be a lot more debris in the lake, so we’re ready to scale up our debris management efforts if that occurs. Also, the runoff characteristics … last year, we didn’t have a lot of runoff in general, so we weren’t able to see how the watershed performed. The prior year, we hadn’t noticed as much of a change in runoff characteristics, but that was a much smaller percentage of the watershed. So that’s one of the reasons why as a part of our enhanced forecasting, we’d like to get flights over that watershed to look at the extent of those burn areas, so we can have that data so we can better understand what the effects of that change in the watershed will be from the water supply standpoint. So that’s definitely part of the picture that we have to be mindful of.”
