CA WATER COMMISSION: Climate change effects on the State Water Project and Central Valley Project

The latest climate change assessments show reduced Delta exports and carryover storage due to climate change likely by mid-century

In the latter half of 2018, both the federal and state governments released new climate change assessments that outline the projected course of climate change and its potential effects on water resources. Both federal and state assessments include chapters on water resources and California’s Fourth Climate Change Assessment includes two reports about the impacts of climate change on the State Water Project. At the December meeting of the California Water Commission, staff from the Department of Water Resources and the Delta Stewardship Council were on hand to present an overview of the newly released assessments.

John Andrew, Assistant Deputy Director for Climate Change Program, began the presentation by noting that the Department of Water Resources (DWR) was quite involved in the preparation of the state’s fourth climate change assessment, contributing to 9 out of 50 of the technical papers or about 20%. “By my count, only UC Berkeley exceeded the number of papers contributed by an institution and so that means that we’re up there with other recognized science organizations like UC Davis and the USGS,” he said. “I think it’s a real tribute just in the sheer numbers of papers contributed by DWR show DWR’s commitment to climate science.”

Fourth National Climate Assessment (NCA4)

Kevin He, an engineer with the Department of Water Resources, then gave a brief overview of the major findings contained within the Fourth National Climate Assessment (or NCA4), which was a joint effort of over 300 people in different fields across the nation, including three people from three California state agencies. Mr. He served as a review editor for the water chapter with the support of DWR’s climate change program and the Bay Delta Office.

The US Global Change Research Program (USGCRP) was established by Presidential Initiative and mandated by Congress in the Global Change Research Act (GCRA) of 1990 to develop and coordinate “a comprehensive and integrated United States research program which will assist the Nation and the world to understand, assess, predict, and respond to human-induced and natural processes of global change.” The USGCRP works across 13 federal agencies to advance understanding of the changing Earth system and maximize efficiencies in global change research.

The USGCRP is required to produce a synthesis report of climate impacts and trends across the nation every four years. The intention of the NCA is to inform resource managers, officials, and stakeholders in considering climate-related risks in their decision making by distilling a large body of research into a report framed around risks to people and resources. It also serves as a more general educational resource about what’s at stake for society as a result of climate change. The report, known as the National Climate Assessment (NCA), was first produced in 2000, with subsequent iterations released in 2009 and 2014.

The Fourth National Climate Assessment has two volumes. The first volume, released in November, 2017, focuses on the physical science of climate change; the second volume, released in November of 2018, focuses on societal impacts with 29 chapters and has chapters that cover topics such as water, energy, transportation, ecosystem, coast, forest, and human health, as well as ten regional chapters, one adaptation chapter, and one mitigation chapter.

Mr. He gave the major findings of the NCA4. Our climate is changing faster than at any point in modern civilization and those changes are mostly the result of human activities. The corresponding impacts are being felt across the nation. The climate is projected to change even faster in the future, with temperature possibly increasing by 5 to 8.7 degrees Fahrenheit by the end of this century.

Secondly, climate change presents growing challenges to our economy, infrastructure, natural environment, human health, and quality of life. For example, the GDP could potentially lose up to 10% by 2100 if no major action is taken to fight climate change, he said. However, Americans are taking actions to reduce risks and build resilience.

The map on the bottom of the slide shows the number of mitigation-related activities by state with the bluer color meaning more activities; the orange dots are the cities supporting greenhouse gas emission reductions. “So we can say it’s quite clear that California is a champion with no doubt,” said Mr. He. “That being said, nationwide what we’re doing is still not enough to avoid substantial damage to our economy, our environment, and human health. We need to do more.”

The water chapter in volume 2 points out that costs are rising from water-related disaster events. The plot on the left is the number of water-related billion dollar disaster events like the flood, drought, and hurricanes from 1980 to 2017; the plot on the right is the estimate of cost of these events in the same period. “It’s quite clear that in the past couple of decades, we are having more of such events and we are paying average than higher prices,” said Mr. He. “So this number is telling us our water is changing unfortunately in an undesirable direction.”

The first key message is that water quality and water supply are changing due to multiple factors: Intensifying droughts, floods, and hurricanes; the snowpack is becoming smaller, surface water quality is declining, and groundwater storage is being depleted, he said.

The two figures on the slide indicate the groundwater depletion rate in regional major aquifers across the nation in two different periods: from 1900 to 2000 on the left and 2001 to 2008 on the right with warmer colors indicating a higher depletion rate, with red being the highest depletion rate.

“So looking at the Central Valley in California, our groundwater storage has been decreasing in the past century and this decrease has accelerated recently,” said Mr. He. “If we consider the most 2012 to 2015 drought, the depletion rate is going to be even higher.”

The second key message is that the nation’s water infrastructure is aging and deteriorating and at a higher than normal risk in a changing climate.

“Intensifying extreme events increase the possibility of infrastructure failure,” he said. “For us, 2017 was the most recent example when we had a number of big storm events, and levee breaks. … In spite of changes in the frequency, intensity, and duration of extreme events, they are not always isolated in space and time, so our current risk management needs to consider the impact of compound extreme events like flood after fire, and also the risks of cascading infrastructure failure like dam failure followed by levee break.”

The third key message as that in light of the changing climate, changing water, and changing water infrastructure, our current water management strategies and planning principles do not consider the risks of change with time, so we need to change that and we need to be flexible, he said.

“As an example, the plot on the left hand side shows the Colorado River Basin historical water supply in blue and the water use in red. The plot on the right hand side is the projected future water supply and the future water demand,” he said. “The shaded area is the 10^th and 90^th percentile range, so these two plots highlight a challenge faced by many US managers which is a potential imbalance between future water supply and future water demand, but with considerable long-term variabilities, which is not well understood yet. So we do need to have adaptive water management strategies to address this challenge and to plan for plausible future conditions which we have not experienced in the past.”

“Simply put, how much water we have tomorrow and how good our water will be tomorrow depends on how proactive and how adaptive we could be today,” concluded Mr. He.

CITED REPORTS IN THIS PRESENTATION:

Mean and Extreme Climate Change Impact on State Water Project

Jianzhong (Jay) Wang works for the Department of Water Resources; he spoke next about California’s Fourth Climate Change Assessment Report that was released in August and a report that was produced for the effort, Mean and Extreme Climate Change Impact on the State Water Project.

The main goal of the report was to assess climate change impacts on the State Water Project and the Central Valley Project at the middle of this century (from 2045 to 2074, centered at year 2060) due to rising temperatures, shifting precipitation patterns, and sea level rise. Rising temperatures, earlier and faster snow melting, and a higher ratio of precipitation due to the warming are causing monthly flow pattern shifting. Future water demand for agriculture is expected to rise because of the future warming increasing potential evapotranspiration rate. In developing the report, the newest release of Cal SIM III was used to assess the impacts.

To perform the analysis, they first assessed climate change impacts on model inputs such as rim inflow, mean streamflow in the upper watershed of the Sierra Nevada mountains, sea level rise in the San Francisco Bay, agricultural water demand in the Valley, and river indexes such as the Sacramento River Index and the San Joaquin River index, and others. Then they did model runs and assessed climate change impacts on model outputs such as Delta outflow, Delta exports, carryover storage in north-of-Delta reservoirs, system reliability, and X2.

The approach used for the assessment originates from the first climate change assessment report in 2006 and the second assessment report in 2009. The first step is to select the global climate models projections to use; DWR’s Climate Change Technical Advisory Group selected 20 Coupled Model Intercomparison Project Phase 5 (CMIP5) global climate model projections, including 10 global climate models. Two greenhouse gas emissions scenarios were selected, model rate emission scenario Representative Concentration Pathways (RCP) 4.5 and the highest greenhouse gas emissions scenario, RCP 8.5.

The second step was to downscale the projections as the grid size for global climate models at 100-200 kilometers is too big. They downscaled the temperature and precipitation data to grids of 10 kilometers using a method developed by Scripps Institute of Oceanography called LOCA, or Localized Construction Analog.

The third step is to use a hydrological model called Variable Infiltration Capacity Model to generate runoff and streamflow for the Sacramento River Basin and the San Joaquin River Basin with the downscaled global model projections.

The fourth step was to assess climate change impacts on model inputs. Rather than putting the above generated streamflow directly into CalSim model, Mr. Wang explained they used climate change information embedded in streamflow from the year 1950 to end of this century to calculate the perturbation ratio and the historical flow from 1992 to 2015 to generate a climate change effect on streamflow. They also determined the estimated sea level rise in San Francisco Bay and the estimated agricultural water demand change for each global climate model projection.

The fifth and last step was to use the latest iteration of DWR’s water planning model, CalSim 3, for each global climate model projection and then analyze mean and extreme climate change impact on the State Water Project and Central Valley Project, including Delta export and the Delta outflow.

The left panel shows the average change in precipitation of 20 climate change scenarios for the middle century. Green color stands for precipitation increase and the yellow color stands for precipitation decrease. “Overall, they project a wetter climate in Northern California and dry climate in Southern California in mid-century,” said Mr. Wang.

The right panel is average change of temperature over 20 climate change scenarios in middle century. Overall, California is projected to become 1.5 to 3.0 Celsius degrees in the middle of the century than current climate with the greatest warming occurring inland.

The models project a precipitation increase in the middle of the century on average with rim flow in the Sacramento River increasing by 4.4% or about 900 TAF. Most of the streamflow increase would occur during the winter high flows.

The left panel is an exceedance probability curve for annual rim flow to Sacramento River Basin for the middle of the century, showing the range of high flows projected (the blue line) as compared to the current climate base line (shown in purple); the dashed line is the 95% confidence curve. The right panel shows the average projected monthly rim inflow to Sacramento River Basin for base and middle of century scenario. Blue line is for the middle century climate change scenario; purple line is for base scenario without climate change.

“You can see peak flow months occur in February for middle of century, one month earlier than base scenario, which is the current climate,” said Mr. Wang. “This is due to early snow melting and higher ratio of rain in precipitation. More warm rain in the future.”

For sea level rise, each model projection was assigned either .5, 1 foot, and 1.5 foot sea level rise based on the middle century surface air temperature at San Francisco Bay. The first column in the table are the names for 20 climate change scenarios; the second column is temperature change in San Francisco Bay in the middle of century compared to the current climate; and the third column is the sea level rise in San Francisco Bay assigned to each climate model projection. There are four climate change scenarios with a half a foot of sea level rise, eleven climate change scenarios with 1 foot sea level rise, and 5 climate change scenarios with 1.5 foot sea level rise. Mean sea level rise is about 1 foot on average for the middle of century; Mr. Wang acknowledged this is a conservative estimate.

Rising temperatures will increase the crop evapotranspiration rate, thereby increasing agricultural water demand. The figure shows exceedance probability curve of annual applied water demand in Sacramento River Valley for the mean of the 20 middle century climate change scenarios; the blue line is the climate change scenario for the middle century and the purple line is the base scenario.

“The Sacramento Valley agricultural demand will increase 527 TAF on average, about half a million acre-feet increase by 6.5% if other things do not change, such as land use remains unchanged, crop types remain unchanged,” Mr. Wang said, noting that this calculation doesn’t consider a number of other factors, such as carbon dioxide increases or the growing period change.

The figure on the slide shows the exceedance probability curve for south of Delta exports for the middle of century scenario, which is the blue line; the base scenario is the purple line.

“South of Delta exports are reduced by 10% due to climate change, which is 521 TAF acre-feet on average for the middle of century,” he said. “A 10% Delta export reduction in middle century is significant. We have to take this seriously. The reduction of Delta exports ranges from a reduction of 44% to a 21% increase. Among the 20 middle century climate change scenarios, 16 scenarios project an export reduction.”

Next, for the mean impact on north of Delta carryover storage, he presented a figure showing the exceedance probability curve of north of Delta carryover storage for middle of century scenario with the blue line showing the projected carryover storage and the base scenario shown in purple. “North of Delta carryover storage will reduce by 24% due to climate change by about 1.5 MAF on average for middle of century,” said Mr. Wang. “North of Delta carryover is decreased by half during drought episodes for middle of century. Carryover storage changes from 62% reduction to 7% increase. Among 20 climate change scenarios, 18 scenarios project carryover storage reduction in the middle of the century.”

He then presented a slide showing the mean impact on Delta outflow. The upper panel is net monthly Delta outflow averaged over 20 climate change scenarios shown by the blue line and the Delta outflow base scenario as the purple line. He noted that net Delta outflow increases significantly in the winter and early spring, and it decreases in late spring and summer because of climate change.

The lower panel is monthly rim inflow to Sacramento River Basin averaged over 20 climate change scenarios shown in blue; the rim inflow base scenario the purple line. “Increased rim flow in the winter and the early spring due to early snow melting and higher rain ratio of precipitation matches with the Delta outflow pattern shifts pretty well,” he said. “That’s the mean increase in rim flow in the winter and the early spring due to the warming most likely becomes Delta outflow.”

To assess extreme impact on State Water Project and Central Valley Project, the driest climate model project for the middle century made by the Australia climate model ACCESS 1.0 on the highest emission scenario, RCP 8.5, was selected. The left panel shows the precipitation change in the middle century compared to the current climate; yellow means precipitation is reduced in the middle century statewide by 5% to 25%. The right panel shows the temperature change in middle century compared to the current climate; an increase in 2 to 3 degrees Celsius is projected.

He then presented a slide showing the impact of the extreme scenario on South of Delta exports. The figure show the south of Delta exports for the middle century as the blue bar and Delta exports for the base scenario show in purple for two historical drought periods: the 1987-1992 drought and the 1929-1932 drought. During the 1987-1992 drought, Delta exports were 2969 TAF, but in the middle of century, this kind of drought becomes more severe under the driest climate change scenario, with Delta exports reduced to 1581 TAF in the middle of century, or reduced to half. For the 1929 to 1932 drought, Delta exports has 3155 TAF but in the middle of century, Delta exports were reduced to 1684 TAF.

“For the driest climate model projection, Delta exports were reduced to half of exports in historical severe drought episodes,” said Mr. Wang.

Digging deeper into the impacts to south of Delta exports, there are four climate change factors that affect the State Water Project and the Central Valley Project: Seasonal flow pattern shift due to early snow melting and the higher rain ratio in the precipitation, sea level rise due to global warming, agricultural water demand change due to the increased crop evapotranspiration rate, and the annual rim inflow change due to the future precipitation change.

This figure shows a series a sensitivity experiments on the impact of the four factors on State Water Project and Central Valley Project. “The seasonal pattern shift of rim flow had the most impact, causing a 42% reduction,” he said. “Annual inflow change makes positive contribution to exports. The sea level rise causes 35% reduction.”

Mr. Wang then gave his conclusions. “At the middle of the century, south of Delta export will decrease by 10% or half a million acre-feet because of climate change,” he said. “Carryover storage will decrease 24%, which is 1.5 MAF. Mid-century under current operating conditions, increases in winter rim inflows to the Sacramento River basin because of early snow melt and higher rain ratio in precipitation become net Delta outflow to the Pacific Ocean, not increased Delta exports or carryover storage. This is a main message.”

CITED REPORTS IN THIS PRESENTATION:

DISCUSSION PERIOD

Commissioner Andrew Ball notes that the study considered 20 different scenarios, with some earlier slides showing that Northern California was actually going to be wetter, and then the later slides showed that in the driest scenario, it was going to be considerably drier. The mean impact on south of Delta export ranges a 44% decrease to a 21% increase. “That is a wide range; it’s difficult to really predict what’s actually going to occur and then you come down to your final conclusions and you conclude that we’re actually going to have significant reductions due to a variety of different things. It’s a little bit confusing there. Can you provide clarity as to why within just 20 scenarios, you have ranges that are so extreme as to cast some doubt upon the reliability of the predictions?”

Mr. Wang acknowledges the uncertainty in the model projections, and pointed out that some elements are more uncertain than others. “Annual rimflow change is very uncertain. We don’t know. The certain part is the seasonal pattern shift because of the warming. All the common model projections project a warming and sea level rise. 1 foot sea level rise in mid-century is conservative estimate. Also, if evapotranspiration increases due to warming, we need more water for watering crops, this is pretty certain. … Because climate models project an increase or decrease in precipitation, then rimflow increase or decrease, this is uncertain a lot.”

Commissioner Ball then notes that there is higher rim inflow on the Sacramento River, and an impact relative to temperature change on the snow, so wouldn’t we be able to capture in storage that increased amount of water?

“Because of earlier snow melting and also because more precipitation falls as rain than current climate, so most of the rim inflow is shifted to March and February,” said Mr. Wong. “The current system cannot capture this shift of water. They release it as a flood flow, so it cannot be captured. These kinds of flood flow, they just go to the Delta outflow, so we need to figure out a way to capture this shifted water.”

Commissioner Ball said, “It seems to me we need increased water storage in order to be able to capture the earlier flows.”

Climate change risk faced by the California Central Valley water resource system

Andrew Schwartz is one of the authors of the report, Climate Change Risks Faced by the California Central Valley Water Resource System, which was also prepared as part of California’s Fourth Climate Change Assessment Report. Mr. Schwartz is working with the Delta Stewardship Council now, but when he worked on this report, he was working at the Department of Water Resources under John Andrew’s supervision. This project was a collaboration between the Department of Water Resources and a research group at the University of Massachusetts Amherst.

“The key message that I’d like you to get out of this presentation is that by using our tools differently, we can handle climate change uncertainty in a way that uses the most reliable information from the data that we have and provides decision-relevant information consistent with a risk management approach that’s more familiar to resource managers,” Mr. Schwartz said. “What I mean by that is I’m going to discuss an approach that’s a bit different than the previous presentation but gets at many of the same metrics and uses almost all of the same tools, but uses them in a different way to get different information.”

Mr. Schwartz said he would contrast the two studies, but he doesn’t want it to be interpreted that the previous study isn’t relevant; it provides useful information; this type of study provides a different type of information, and there are ways to use them both.

The study area was the State Water Project and Central Valley Project watersheds that flow into Oroville, Shasta, and Folsom and provide water for those projects.

Mr. Schwartz noted that the previous presentation described a top-down scenario analysis approach starting with the climate change models, selecting ten scenarios from climate change models and representation concentration pathways that the state has chosen, downscaling them, running them through a hydrologic model and CalSim 3, and then getting system performance predictions. What comes out of that are some projections such as the impact of Delta exports could be anywhere from -44% to +27%, so how are decision makers to go forward and make investments with that level of uncertainty?

For this project, they took a risk management approach to make the information more decision-relevant. They started with the system model, CalLite, which is a simplified version of the CalSim model, and they fed the model many different scenarios to understand how the system reacts when things are warmer, wetter, and drier and how that in turn affects things like reservoir storage, Delta exports, and Delta outflows. That gives a range of how the system responds; they then looked at how likely it is that a situation would occur where there would be a bad response out of the system.

“We use the climate models in a different way,” he said. “We use the same information but in a little different way to try and understand how likely it is that we’ll get one of these responses. And we can put all that information together to get more of a probabilistic system response prediction.”

There are a number of sources of uncertainty in climate modeling, such as whether humans will work to reduce emissions, or in the models in terms of how sensitive the atmosphere really is to CO2, or how ice dynamics are going to result in sea level rise. “Instead of using that as the foundation piece, it’s the last piece, and the benefit of that is we can change those climate projections if we disagree on what they are or if we want to look at more climate change projections or less or IPCC comes out with a new assessment,” Mr. Schwartz said. “We can add those in very quickly and very easily.”

He presented a plot showing the projected range of climate changes by 2050, based on the same 20 climate models used in the previous presentation plus a few more; there are 32 climate model projections used in this analysis. “Each of the scenarios are compressed down to a change in average temperature and average precipitation by 2050,” he said. “There are projections going up to almost 4 degrees Celsius or 8 degrees Fahrenheit, and projections down to a half or maybe 1 degree Fahrenheit 2050; then ranging from almost -20% precipitation to a positive of almost 30%, so a huge range. How do you deal with that?”

They made an assumption that these projections from the best climate models represent the likely range of impacts, and where more climate models project that same output, that is more likely. “So we apply a bivariant normal distribution to these data, which basically means we make these little clouds based on this data, and the darker areas represent higher probability based on more models projecting that outcome, and lighter is still possible, but less likely; and the outer black ring is the 99.7% confidence interval, so pretty much everything we think we might see.”

He showed an animation showing the projection over time from now to 2100, acknowledging that the uncertainty grows as the projection goes farther out, but there is still information that can be derived from this. “Temperature is undeniably going up by 2030 or by 2040, we’ve left the area where a 99.7% confidence interval, you would see no temperature rise. We’re going to see temperature rise,” said Mr. Schwartz. “But in terms the average precipitation change, it’s all over the place. From negative -30 to +30 possibilities, a huge range – so how are we going to use that information?”

Mr. Schwartz then explained how they got to these projections. He presented a grid showing change in temperature plotted against change in precipitation, and said that each of these black dots represents a simulation they performed using the CalLite model. At every one of these combinations of temperature change and precipitation change, they ran an 1100 year simulation using data from paleo records of tree ring reconstructions which included longer droughts.

“We used historical data to inform what the precipitation would look like during those historical droughts, so we can simulate this whole period and then what we get is what is called a ‘response surface,” he said. “This is the response of the State Water Project system to be able to deliver project water over varying conditions of temperature and precipitation.”

He noted that at the ‘00’ mark, there’s no change in temperature and no change in precipitation from current conditions; that’s what can be delivered right now. The black line represents combinations of climate conditions where the project could continue to deliver about the same amount of water; so actually if it gets warmer, deliveries can probably be maintained as long as there is about 10% more precipitation every year.

The colors represent the percentage change in the ability to deliver water. The red or orange colors are conditions are worse than historical conditions; the blue and green colors are better than historical conditions. The circle is the same plot of climate change shown a few slides earlier now imprinted over the response surface. He noted that the response surface is not time dependent; it is agnostic with respect to time. It just shows the response of how our system responds to warming, whether that warming occurs tomorrow, or in 28 years or in 50 years, he said.

“So we can imprint the probability of getting a certain amount of warming and precipitation over the top and what you see is the vast majority of our probability space is over worse areas,” said Mr. Schwartz. “There are areas in blue on the right side … something like your 20% better. But it’s the outer range; it’s very, very unlikely. It is there, it is a possibility, and so is the outer range on the really hot dry side. So this gives us a little bit better picture of how likely these outcomes are, where we we’re comfortable with our residual risk is now a policy decision that can be informed by this. How much of this space are we willing to leave to chance?”

Mr. Schwartz said that figures he just presented were for State Water Project deliveries, but they performed the analysis for a whole range of other impact metrics that are important. He presented a summation of those other impact metrics, and pointed out that there are very high probabilities of inferior condition situations across a whole range of different metrics.

“Specifically, carryover storage gets hammered because of the seasonal pattern shift and the warming with the water coming off earlier,” Mr. Schwartz said.

In water management, the concern is what is happening from one year to the next. He presented a chart for Delta exports, explaining that the bell curves are based on all of the data underlying the response surface and the climate model data to calculate an expected value for the 11 years of simulation across all the different uncertainties in climate. He explained that the blue line is the historical climate; there has always had a range of deliveries from very dry years to very wet years and the current system was designed to handle that to a certain extent; the red line shows how it moves across the uncertainty range.

“By 2040, on average, we’d lose about 500,000 acre-feet of deliveries,” he said. “One of the things I would point out is the fatness of that red tail off to the left: those are drought years, those are the years that are really dry. There will get to be a lot more of them, and they will get drier. Those are where our system is really going to struggle, and we have fewer and fewer wet years to refill the system. The shift to the left is really the loss of performance; the slumping down is really a loss of certainty.”

“When we start to think about adaptation strategies and building infrastructure and responding to this, we are not going to be able to deal with this loss of certainty,” he said. “That is, we just don’t know about the future, so we can’t look for solutions that are going to be the best, because we don’t know what the situation we’re going to have to deal with is. So we should look at strategies that increase performance in the places that we most care about, so maybe this left fat tail and shift the distribution over.”

He then presented a graph of what he called an adaptation strategy caricature, noting that the shaded area in the background is where we are today, the red line is where we would be in 2050 if we do nothing, and the purple line is an adaptation strategy at 2050. “What this is showing is that it looks pretty good on the average,” he said. “You’re getting much more water out of the system, but on the far left hand side, you still have a lot of dry years that are much more problematic than what you’ve had historically. So this looks like a real good adaptation strategy and it does some things, but it would probably need to be paired with some other strategies to really be effective at dealing with drought. For SWP deliveries, this is going to get you more water out for SWP deliveries but it’s not going to help you in the dry years.”

Mr. Schwartz said that this type of information does a better job of exploring climate change uncertainty, being really explicit about the uncertainty that we face, and understanding that uncertainty, and then putting it in a probabilistic way that fits within a risk informed decision making framework which we are very comfortable with as water resource managers.

“Flood projects are all considered in a risk management framework,” he said. “We understand that there is residual risk. We don’t build our levees for a 10,000 year flood. We’ve accepted a certain amount of residual risk in the interest of public finance and what we can possibly do.”

“So I think that it’s a useful framework for thinking about adaptation to climate change. We often want to think about the worst case scenario. How does this do under the worst case scenario? Well, it may not do well, but that may not mean that we shouldn’t build some of those things. We just have to, as a society and as decision makers, come to an understanding about what kind of residual risk we’re willing to take in these adaptations and how much money we have to deal with this.”

DISCUSSION PERIOD

Chair Armando Quintero noted that as a result of the recent drought, most water agencies are really looking at diversifying their water portfolios. It’s promising to see that Los Angeles just passed a local measure to fund $30 million a year for stormwater capture and treatment and putting that into their water supplies. “I think part of what you’re doing here is really making the case that water agencies throughout the state really need to look at local solutions, but at the same time be focused on things that you raised,” he said.

Commissioner Andrew Ball noted that it’d be interesting to take this information and now start to apply it to solutions. “There were a lot questions we all had as we went through this process, as we look forward, how can we possibly have the same amount of water or more water going forward than we do now, when it’s obvious that we’re having more periods of drought that we have to deal with, and that was always a conundrum certainly for me and other commissioners. This type of approach would be one that as you start to use this information to come up with possible structural solutions, it could be very informative and very interesting.”

Mr. Schwartz said that this report forms one of the key elements of the DWR vulnerability assessment, and the second phase of that is to look at what physical mechanisms or reoperations or things that we could do in the system to really ‘turn the dial’. “It’s challenging because some of the solutions like groundwater storage aren’t necessarily really well captured in the model that we used. There are other strategies, upper watershed effects that we think we can model better, and then having to consider how operation of the system itself would change if you add a big reservoir near Colusa County or somewhere else.”

“It would be great to see how we can really use this extra water and put it into groundwater storage,” said Commissioner Ball.

“I think that’s the plan with lots of work going on at DWR with Flood MAR which is definitely looking at these types of impacts and how they can be moved through the system and put into the ground,” said Mr. Schwartz. He noted that the Army Corps of Engineers is looking flood impacts and a pilot study on the Tuolumne that is bringing this information in figure out how to run flood models and water supply operations at the same time. “When we do flood risk analysis, it’s mostly event based, and we run a big flood through it and show that, and those aren’t really connected to these monthly time step water supply models and so there’s still this gap. And I think those studies are trying to get at how to put these together and really be able to work with solutions.”

REPORTS CITED IN THIS PRESENTATION:

Climate Change Risks Faced by the California Central Valley Water Resource System

FOR MORE INFORMATION …

FOURTH NATIONAL CLIMATE ASSESSMENT

CALIFORNIA’S FOURTH CLIMATE CHANGE ASSESSMENT

OTHER

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