Panel discusses outlook for the remaining water year for the State Water Project and Hetch Hetchy water systems, plus a look at Forecast Informed Reservoir Operations
At the May meeting of the Delta Stewardship Council, an agenda item examined the outlook on the water storage and water supply for the remaining water year, as well as how challenges were addressed this past winter. John Leahigh, State Water Project Operations Chief for the Department of Water Resources, discussed how the Department of Water Resources met challenges at Oroville Dam; Steve Ritchie, Assistant General Manager of the Public Utilities Commission, spoke of how the SFPUC dealt with the incident at Moccasin Dam, and Dr. Martin Ralph with the Center for Western Water and Weather Extremes talked about a pilot program, the Forecast-Informed Reservoir Operations Program, which seeks to take advantage of the latest forecasting abilities with the goal of increasing water storage.
JOHN LEAHIGH: Outlook for the State Water Project supplies
John Leahigh, State Water Project Operations Chief for the Department of Water Resources, began by noting that this year was another example of the whipsaw nature of both the inter-annual and intra-annual aspect of California’s hydrology. The state endured one of the driest four year stretches in the historical record, only to be followed by the wettest year on record, 2017, for the Northern Sierra 8 station. This year, there was very little precipitation for the first few months of the winter, and then a quasi-Miracle March that bailed the state out somewhat; the state is at about 80% of average to date on the Northern Sierra 8-station, he said.
Even as late as February, the snowpack was a concern as the water content in the snowpack had been tracking even lower than 2015, which was the lowest snowpack on record (lower, left). The quasi-Miracle March brought the snowpack on April 1st at 50%, so while still one of the lowest on record, the state isn’t in complete dire straits in terms of the outlook for this coming summer, he said.
The slide on the upper right shows the two-year cumulative runoff total for the Sacramento Valley. The blue line shows the precipitation events, the biggest one being February 10th, which was the largest event that had occurred in that basin in 20 years. This water year, there was very little activity until late February; there was a rather warm wet atmospheric river system that came in late March; early April was the second one. “We were about twice the normal runoff up through last year; this year, we’re coming back down to earth a bit in terms of getting closer to average,” Mr. Leahigh noted.
In terms of the US Drought Monitor, prior to 2017, the entire state was in some sort of drought condition; the extremely wet 2017 brought all but about 8% of the state out of drought condition. As a result of the past year being somewhat subpar, about 1/3 of the state is back into some sort of drought as measured by the Drought Monitor, and 2/3rds of the state is abnormally dry.
Since 2017 was such a wet year, surface storage across the state is in good shape with most reservoirs sitting above average for this time of year, including most notably Shasta, Folsom, and a lot of the San Joaquin reservoirs, which did very well this spring when the late spring storms coincided with easing of flood control requirements on the reservoirs.
“A lot of those reservoirs are fairly full, respective to where they typically are this time of year; the big exception is Lake Oroville,” he said. “We’re actually below average to date, and that of course is a direct result of the incident we had back in February of 2017 in terms of the failure of the main spillway and emergency spillway.”
Mr. Leahigh presented a photo sequence showing the progression of construction on the spillway at Oroville, noting that Kiewit Construction worked close to around the clock to complete what would normally be years of work in just over 5 months to get a somewhat functional spillway back in place.
“Although we had impaired capacity in that spillway, it was functional,” he said. “With a combination of that interim design and operating to a lower flood pool, we were able to provide the same level of flood protection we had been providing prior to the incident.”
There is still a lot of work to be done in the coming year. Mr. Leahigh presented a graphic of the spillway, noting that the portions in pink denote the areas to be constructed this year. Construction began on May 8. “There is more structural concrete to be placed this year than last year, so there’s quite a bit of work to be done,” he said. “Our milestone again is going to be November 1st for getting a fully functional spillway with the same capacities as prior to the event in place prior to this coming winter.”
As a result of only having partial capacity, they had to operate Lake Oroville more conservatively, he said, presenting a slide showing the operations plan and with the dark blue line being the actual storage as they went through the year.
“The drawdown last year was in sync with all of our needs for the Delta and otherwise,” he said. “There was plenty of other flows in the system last year, so Oroville water wasn’t as necessary in order to keep pumping to our customers south of the Delta satisfied, but this coming year, we’re still running at a deficit that started as a result of that incident last year.”
“In a wet year like that, we would typically be able to fill the lake all the way to its capacity at 3.5 MAF, but we had to manage the lake down to about 2.5 MAF as a result of the incident,” he continued. “That did not have an impact last year, but that lower carryover storage is impacting our ability to meet deliveries to our State Water Project customers this year. We have plenty water to meet all of our other obligations in terms of our share of the Delta standards and deliveries to our senior water rights contractors; it’s essentially our SWP contractors that are on the margins and so they are seeing the impact associated with the lower storages.”
Reservoir levels at San Luis are doing fairly well; it’s much closer to average for this time of year, he said. He pointed out the dip in February. “That’s rather remarkable; it indicates how dry the winter was in February,” he said. “You don’t typically see that even in those driest years where we’re actually having to draft storage out of San Luis in order to meet the deliveries in the middle of the winter, but that’s how dry it was this winter until we did get the March precipitation.”
Mr. Leahigh then presented a slide showing the State Water Project allocations since the 2000s, noting that the allocation for this year was recently adjusted up to 35%. “This is likely to be near the final allocation,” he said. “We are going to continue to assess next month to see if there’s any opportunity for a little bit more supply there, but 35% may be it for this year.”
He noted that the graph is color coded, with the blue and green being the wetter years and the yellow, orange, and red being the drier years. “If you look at the longer term frame here, 10 to 15 years, the representation of dry and below normal years is much greater than it would typically be,” he said. “It’s typically about 50/50 in terms of the cooler colors and warmer colors, but you can see its definitely been skewed drier the last few years. The yellow, the 35%, typically below normal year would typically be about 50% allocation, so the lower storages in Oroville is having somewhat of an impact on us this year.”
STEVEN RITCHIE: Despite dry winter, Hetch Hetchy system will fill; Incident at Moccasin portends a different future
Steven Ricthie began by discussing the Hetch Hetchy regional water system, noting that it spans the width of California. At the top of the system, there are three Sierra reservoirs, there are two reservoirs in Alameda County, and three reservoirs in San Mateo County; he said it is those 8 reservoirs that really drive the water supply for the San Francisco system.
The Hetch Hetchy system serves 2.7 million people; about 1/3 of the water is delivered to San Francisco, and 2/3 of the water is delivered to the 26 customers that are in San Mateo County and Northern Santa Clara County.
He presented a schematic of the water system, noting that the maroon square boxes on the right are the three hydroelectric powerhouses and the red circles are the two regulating reservoirs, Priest Reservoir and downstream of that, Moccasin Reservoir.
There is a tunnel and pipelines that take the water under Don Pedro Reservoir; Mr. Ritchie noted that they are not connected to Don Pedro Reservoir by plumbing, but they are through the Tuolumne River.
“That’s a very important element of our system where we are partners with the Turlock and Modesto Irrigation Districts on how the Tuolumne River is managed,” he said. “They have senior water rights on the river to San Francisco, which is an important part of the aspect, but we paid for 50% of the cost of constructing New Don Pedro Dam, which gives us an operational chunk of storage that is for the benefit of Turlock and Modesto and it allows us to operate our system in a way that we can keep more water up country, despite their senior water rights.”
The Hetch Hetchy system then crosses the Central Valley through a set of pipelines to the Alameda County reservoirs; it then enters the Bay Area, going around and under the bay and coming up the peninsula. The three bright red lines are the earthquake faults the aqueducts cross. He noted they were close to the end of a $4.8 billion capital improvement program that was aimed largely at seismic reliability.
“That system is what I am responsible for at the SFPUC,” he said. “It is a legacy system that has a lot of benefits to it. Our youngest dam in the system was constructed in 1964, four years before Oroville, and our oldest dam was constructed in 1866, so it’s a very old system.”
At the end of May, the Hetch Hetchy reservoir is about 87% full; the water bank in Don Pedro where they store ware for the benefit of the irrigation districts is full at 570,000 acre-feet. The only reservoir that’s low is the Calaveras Dam in Alameda County as it’s under restrictions because it’s seismically unsafe. “We’re almost complete on building a new dam immediately downstream of Calaveras Dam as part of the water system improvement program,” he said. “Overall, our system will fill this year.”
Mr. Ritchie presented a diagram showing the cumulative precipitation over the year. He said although it wasn’t a ‘Miracle March’, it was a ‘Magnificent March’ with the highest precipitation level at Hetch Hetchy for March in their 100 year hydrologic history, which brought the precipitation up to just about median level.
In terms of snowpack, it was tracking the 2015 snowpack until March; during March, it caught up substantially. “It was not the best year ever, but close to median is good enough to fill the system, and that’s what we like.”
He presented a chart showing total system deliveries over the course of a year, noting that the demands are lower in the early part of the year, peak during the summer, and drop off later in the year. The purple line is demands fro 2013, the last pre-drought year; the blue year is last year, 2017 demand; and the green is 2018. He noted that in recent years, they are starting to see demand rebound in the service area, noting that in 2015, there was no summertime peak as there was no outdoor irrigation at the height of the drought. “We’re starting to rebound back up but we’re still substantially below 2013 demand levels,” he said.
On March 22, there was 5” of precipitation in one day measured at Priest Reservoir, the regulating reservoir above Moccasin reservoir; 5” in a day is not unusual, but what was unusual is was that 3” of rain came down in four hours, he said. There is a diversion dam above Moccasin Reservoir that diverts the local runoff around the aqueduct to keep the Hetch Hetchy water clean; the streamflow in Moccasin Creek was 16,000 cfs, which is unheard of, he said.
He presented a graph, noting that the red line is the precipitation measured at Priest Reservoir; it started off slow around midnight and picked up in the morning, which was enough to get the ground basically saturated. Then the 3” in four hours started, and the blue line, representing the streamflow in Moccasin Creek, shot from probably about 100 cfs to 16,000 cfs in a matter of about two hours. “It was a pretty monumental flash flood that we were experiencing,” he said.
He presented a slide showing two pictures of Moccasin Reservoir. The picture on the left shows the normal spillway, which is running pretty full, and off to the left, the creek has jumped the banks and the Moccasin Creek fish hatchery was washed out. The fish were either killed or washed out down to Don Pedro; the remaining fish were salvaged and taken down to Don Pedro because the fish hatchery was basically out of operation.
The photo on the right shows the auxiliary spillway which operated well as far as the spillway went, but downstream areas had problems. At one point, there was basically a creek running down the face of the dam. “We thought we were right on the verge of an emergency and evacuated the 12 residents downstream,” he said. “We had a lot of news media show up to say, ‘It’s another Oroville!’, not realizing that this dam is 62 feet tall, not 770 feet tall; at the same time, it’s my dam, so I care a lot about it. And the water definitely looked like chocolate milk, and it was that way for throughout the day. We now have it completely empty as we look at what we have to do to repair the dam. The biggest thing we’re going to do is make more spillway capacity and we have to be able to convey that water downstream.”
So for the Hetch Hetchy system, 2018 was a good water year; there system will fill. Every July 1st it starts over again.
“I tell people, we’re the eternal pessimists; it’s going to be a dry year next year, we know that. The future may hold bigger floods and deeper droughts, I think that’s very clear, and the March 22nd event was a current example. It was a big event for us. We’re looking at probably an investment that’s going to approach $70 million to restore and actually enhance our flood carrying capacity because we know events like this can happen.”
MARTY RALPH: Forecast Informed Reservoir Operations: Bringing Science and Decision-Makers Together to Explore Use of Forecasts to Support Future Reservoir Operations
Dr. Marty Ralph began by noting that the project name is Forecast Informed Reservoir Operations (or FIRO) and it was inspired by a project that DWR had a lot to do with that investigated forecasting coordinated operations for Oroville and New Bullards Bar; it was a project that really broke some new ground in bringing in forecast information into decision making and reservoir operations.
During the recent drought, Dr. Ralph attended a meeting with the folks up in Sonoma County about their reservoir. Secretary John Laird had been to the Coyote Valley Dam and had remarked how low the reservoir level was; there was a storm that had hit the year below where a lot of water had been released mid-winter. 
The question was why did that water get released and is there anything different that could be done? That triggered a grass roots effort to do a study, now that they are getting better at forecasting storms, to look at the possibility of incorporating forecasts of atmospheric rivers into reservoir operations.
The Sonoma County Water Agency provides water to about 600,000 people as well as a grapevine/wine industry. There are two major reservoirs, the Coyote Valley Dam that forms Lake Mendocino, and the Warm Springs Dam, which forms Lake Sonoma. Another challenge for this watershed faces are the endangered salmon which have a biological opinion in place to try to restore their numbers.
“Lake Mendocino, like much of California, went from the worst drought on record in some ways to the wettest year on record within a year or two, which seems to be the nature of things here,” said Dr. Ralph. He presented a photo of that reservoir in 2014, noting that some of the reasons for the low water supply reliability in the area are that storage capacity is relatively small compared to demand; the watershed itself from a hydrology standpoint is a bit inland and gets a little bit rainshadowed; there’s reduced inflow from the Potter Valley Project as there was biological decision to keep more water in the Eel River and that reduced the inflows into Lake Mendocino by about 70,000 acre-feet or so; and variable precipitation patterns, some of the most variable in all of California.
“The make or break phenomenon is atmospheric rivers in this part of the world,” he said. “Future growth and climate change will likely impact reliability as well.”
“At the same time as this reservoir was low, there was a big atmospheric river that hit which put some water into that reservoir, but it created near flood conditions downstream,” he said. “Simultaneously this water agency is dealing with a flood warning and a drought emergency. It’s hard for people back east to even fathom that, but that’s the way it is here.”
Mr. Ralph then stepped through the situation a few years ago when the reservoir was so low. He presented a graph of the storage on Lake Mendocino, noting that the blue line is the reservoir level, the green line is the precipitation, and the gold line is the amount of water the reservoir is supposed to have in it. He pointed out how the green line takes big jumps up and then is sort of flat for awhile; those big jumps are the atmospheric river storms. It’s partly empty of course as in the winter there’s a need for flood control, he said.
“Notice how that blue curve in the middle there jumped up and rose right as the gold curve rose,” he said. “Basically the atmospheric river storms hit just perfectly and helped refill the reservoir. If they had happened a month earlier, that water would needed to have been released.”
The next fall, there was an atmospheric river in November which encroached into the flood pool slightly and then another one right behind it that encroached pretty seriously into the flood pool. “If one more atmospheric river hit suddenly, they’d be in trouble, so just as the system is designed to do, the Corps released that water and got back to the rule curve,” he said. “Little did anyone know that began a drought. There were no atmospheric rivers coming to refill later that year and that continued on for the rest of the year.”
“So it’s a real logical question, is there anything we can do about this? It really hinges on, is it possible to predict these atmospheric rivers well enough, a few days ahead, to maybe hedge bets and keep some of that water temporarily? That was the calling for our committee.”
The project was an ad hoc effort between the Center for Western Weather and Water Extremes, DWR, the Army Corps, USGS, and the Bureau of Reclamation. They had terms of reference, but it wasn’t a legal document; it was more of a shaking hands and committing to integrity and good work together, he said. They set goals, one of them being to determine if it was feasible or viable to temporarily keep 10,000 acre-feet of water in the case of that 2012 event and safely be able to release it if a storm was predicted. Is the forecast good enough, are the facilities capable of handling that, and what are the risks involved with that> They developed a 5-year plan and a major technical effort to pursue the study.
Dr. Ralph explained the basic concept of the study. “Our idea, hypothetically as a committee, was could we keep 10,000 acre-feet pending another storm; would it be viable to have 10,000 acre-feet of extra storage in this case or future cases where it was like this?” said Dr. Ralph. “The idea was, a hypothetical study that would determine based on current forecast skill, would it be plausible that we could have kept that water safely? In other words, what’s the lead time for example to release that water to get it out of harms way. Turns out it’s 3 to 5 days, so that sets that forecasting target. Can we predict with atmospheric rivers with 3 to 5 days of lead time accurately enough to get that water out of the way if a storm did come, and if it didn’t prove out to be viable based on current forecasts, what could we do to improve the forecast skill to potentially reach that goal.”
They developed a strategy, did a preliminary viability assessment with the ad hoc team over two years; he presented a graph of the results (below). “It’s a water supply reliability diagram; the higher the line is, the better it is; the lower it is, the worse it is,” he said. “Each of these lines represents a different scenario we tested. The bottom line is what’s current, the top line is imagined perfect forecasts, and the red and green lines in the middle were some intermediate versions of that.”
It was a highly technical study with the Hydrologic Engineering Center at the Army Corps running their scenarios, Sonoma County running their scenarios, and scientists and hydrologists at Scripps running their scenarios. “We came up with 20,000 acre-feet water supply reliability enhancement in about 60% of the years, so well above our conservative goal of 10,000 acre-feet,” said Dr. Ralph. “Recall this is a paper study. Now the question is, would that have increased flood risk at all? This is where HEC and UC Davis came in and did their assessment, and the fact that all these curves lie on top of each other says essentially there’s no change to flood risk. So this current forecast skill is adequate on Lake Mendocino to potentially implement FIRO; that’s the conclusion of our preliminary viability assessment.”
The study is now looking at two steps: First, what would be the potential gains if forecasts could be improved as we have some very serious opportunities to improve forecasts to the point that greater benefits would emerge, and secondly, what would happen if we ended up in a flood year?
“That’s where we’re at now in pursuing the full viability assessment,” said Dr. Ralph. “It’s a major scientific effort; this is all built on solid scientific work, peer reviewed, published, communicated with others.”
Dr. Ralph said they are exploring the transferability of the process and evaluating the viability to another reservoir jointly with Orange County Water District for Prado Dam in the Los Angeles Basin. “Orange County has been very strong at working with this, the Army Corps of Engineers is involved again, and we started another steering committee for that reservoir,” he said.
“Atmospheric rivers are really the problem here in terms of flood, but they’re also the source of much of our water,” said Dr. Ralph, presenting a diagram from Lake Oroville during the spillway incident and acknowledging it’s a complicated diagram. “The forecast of a moderate strength atmospheric river was made two days before the Oroville event. The next day the forecast was upped to a strong atmospheric river, and the next day when it hit, it came in as extreme.”
He likened it to the equivalent of a category 2 hurricane being predicted but comes in two days later as a category 4. “We’re inventing a scale for this,” said he said. “It’s going to come out this winter as a way to scale atmospheric rivers.”
There are reasons for this error, one being that the storms move from over the ocean to onshore, and the weather prediction system doesn’t have as much data in it to make the forecasts as good as they should be over the ocean, he said.
“We have a lot of satellite data, and over the continent we have a lot of other data, balloons launched from airports, aircraft flying, the commercial jets, all sorts of surface data, radars – over the ocean, we have none of that,” he said. “So we have an approach here we’re inventing called atmospheric river reconnaissance, it’s an airborne thing. The Air Force has ten C130s dedicated to hurricane reconnaissance in the summer and fall; we asked to borrow them for this winter, and we did it once before to try out whether they could fly atmospheric rivers off shore, collect data by dropping sensors into the storms, radioing that back, inserting it into the models that produce the weather forecasts, and try to improve it.”
They tried it out for this first time last year with two aircraft from Hawaii and Travis AFB along with a NOAA G4 jet, also a hurricane hunter. “We proved first of all that it’s feasible to do this, the facilities are available, the staff, the mechanisms, and the science behind it. Now we’re going through the very tough and difficult process of evaluating quantitatively the impact of these data.”
It’s going to mean inventing some new modeling approaches. “It’s a very exciting ongoing thing in meteorology that we’ve got a potential now, we know to target atmospheric rivers, we have methods to do it, we understand the importance of forecasting for water management and flood control, and we’ve got a team formed to work on this.”
DISCUSSION HIGHLIGHTS
Vice Chair Susan Tatayon asks about developing a Moccasin Dam scenario.
Dr. Ralph acknowledged he hadn’t heard of Moccasin Dam before today, but the potential is there for this method of assessing viability in a careful and deep way to be applied to other reservoirs. “It’s not a simple thing to do this well. Every reservoir is like a person; they all have their own personality, their strengths, their weaknesses, the challenges in their context, and I’m amazed at how fundamentally different each one is that I have had chance to get know better, if only a handful.”
Chair Randy Fiorini suggests a better candidate for this might be New Don Pedro. “On that system, the channel capacity below Don Pedro is 12,000 cfs. Last year, they began full releases in January anticipating what might happen and they still had to spill, so the kinds of information that could be provided in a system that has limitations like that could be very critical for flood protection.”
Councilmember Ken Weinberg asks how forecast informed reservoir operations relate to critically overdrafted groundwater basins. Is there a way to make conjunctive use work?
John Leahigh said there are a lot of aspects to that question. “The program that coordinated operations between DWR and Yuba County Water Agency was one of the other programs that was looked at as part of the Lake Mendocino program. It was because New Bullards Bar and Feather have a common downstream control point and coordination is critical under these large events, and so our activity with them was about improving the decision support system and the tools that we had in terms of the Res-SIM (?) model and producing a lot of hypotheticals. There’s been huge advances in terms of the forecasting capabilities, so we now have a new tool in terms of these ensemble forecasts – rather than just one deterministic forecast to work with, we have a whole range of probabilities that we can put into these tools to play the what ifs. What if it comes in on the high end, the wet end of the forecast, what happens if it’s on the dry end, so you can assess your risk, because it’s a two sided coin. You’re constantly balancing the flood protection with the water supply, and to the extent that you can do exactly what Marty did in terms of seeing what your benefits could be in one area without increasing the risk in the other, that’s what it’s all about in terms of producing some favorable outcomes.”
“I do think we have an opportunity as it relates to Lake Oroville,” continued Mr. Leahigh. “We’re going to be looking at a formal re-do of the current water control manual that dates back to 1970, so certainly there’s been significant advances since then. In terms of the forecasting, we’re going to be stepping through a period of interim plans that maybe give us some opportunities to test out some of these forecast-informed operations in terms of perhaps eventually getting something more formal in when we eventually do update that manual. It’s incorporated into the American River-Folsom manual, and I think you have some people over at the Corps who are actually pretty excited about perhaps entertaining some of these new aspects.”
“As far as the groundwater recharge, for the customers of the State Water Project that have the recharge capabilities, typically the source for that water is just the unregulated flows that are coming into the Delta and it’s really about our ability to capture those when they are well in excess of the other needs, so that’s our biggest opportunity to get to those groundwater recharge basins,” said Mr. Leahigh. “It’s not so much Oroville itself.”
“The hydrology is easy; the weather predictions are getting easier and better, and the plumbing isn’t really that hard,” said Steven Ritchie. “It’s the institutional issues that are the ones that need resolution. In 2017, the Tuolumne River, our share of the Tuolumne River that we could theoretically had diverted was 3 MAF. The average flow of the Tuolumne River was 1.8 MAF, so there was a huge amount of water there that was theoretically something we could take, if we had a place to put it. We don’t have a place to put it. We are tied together with the irrigation districts on the Tuolumne through Don Pedro, that’s where our operations link very closely. If we were to develop some kind of relationship with the same irrigation districts around the groundwater basin there, we might find some way to have mutual benefit out of that, but the will isn’t there yet. Certainly we have several environmental groups suggesting we do that. On the record, San Francisco would not be opposed to such an idea. We think that really would merit some exploration, but it’s really the institutional issues more than anything else. The answer is obvious. If there’s a lot of water, and that’s what happened in 2017. People weren’t prepared with the plumbing and the institutional to make it happen that year when we all had so much water.”
Chair Randy Fiorini then asked what the lessons learned from the recent 5-year drought has impacted the current decisions of the amount of water to allocate for this year.
John Leahigh said that Oroville operations have been highly driven by the dam safety aspects associated with the spillway. “We wanted to draw the lake down as a safeguard in terms of where we were, in terms of the timing of the reconstruction of the spillway, versus we didn’t want to put ourselves in a position where if we were hit with a drought, we wouldn’t have supply to work with. … Moving forward, once we get the spillway rebuilt, that’s a constant assessment we continue to do, in terms of evaluating what is that right balance between flood protection and water supply.”
Steven Ritchie said that they developed a drought plan after the 1987-1992 drought when San Francisco faced 45% rationing. “People ask me, if you knew this last drought was going to happen, what would you have done differently, and my answer was nothing, because our system worked exactly as we intended it to do,” he said. “What was stored in Don Pedro, we have 570,000 AF that’s available to the district, so we get to keep the water on the river while they take that, that dropped down to a low of 60,000 AF so if we had one more year of drought, it would have started to get much more challenging for us. We would have gone to higher levels of rationing, but we actually never dictated rationing to our customers based on our storage levels because we were in relatively good shape throughout this. It was the State Water Board regulations that drove that. The Governor standing at Phillips station saying there’s no snow here really did a lot for everybody with conservation.”
“I would say that drought taught us a little bit more about what we might expect but the Moccasin flood event may have taught us more, or at least opened our eyes to the other things we have to deal with,” continued Mr. Ritchie. “We don’t have any flood control responsibility on the Tuolumne River, but that those kinds of flows can happen is going to make us reevaluate where we are just in terms of prudent management of our system.”
Dr. Marty Ralph said that he can’t speak to management decisions, but he can speak to the field of meteorology and atmospheric science. “There’s an emerging emphasis on something called sub-seasonal to seasonal prediction – S2S is our nickname,” he said. “The idea that in the atmosphere, there are sometimes these periods when it appears there some skill potentially there to predict wet versus dry periods. Very research-y, very limited, I wouldn’t recommend anybody make a decision on it yet, but I can say it’s a promising a direction. We are taking an approach at Scripps in my group of pushing weather forecasts out in time to try and make them better at further lead times, whereas the climate folks are bringing their climate projections down. Instead of saying what’s going to happen in ten or a hundred years, trying to some of those methods to say what might happen in the next six months or few months … I won’t go deep but QBO + MJO = AR predictability at week 4 or 5, under some circumstances.”
FOR MORE INFORMATION …
- For the full agenda and meeting materials for the April meeting of the Delta Stewardship Council, click here.
- To watch this meeting on webcast, click here.
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