Dr. Udall discusses the Colorado River’s hydrology, climate change impacts, shortage risk, and the Drought Contingency Plan
Dr. Brad Udall serves as senior water and climate research scientist at the Colorado Water Institute at Colorado State University. He has extensive experience in water and climate policy issues and has authored numerous peer-reviewed publications on water management and climate change which have been published by the federal government and major journals. He has researched water problems on all major Southwestern US rivers including the Rio Grande, Colorado, Sacramento-San Joaquin and Klamath.
All eyes have been on the Colorado River recently with headlines across the west announcing the progress – or lack thereof – of the efforts of the seven basin states to reach agreement on the Drought Contingency Plan. So is the Colorado River in crisis? At the 2019 California Irrigation Institute conference, Dr. Brad Udall’s keynote presentation focused on answering that question.
He began with a picture of Hoover Dam and Lake Mead, pointing out the white bathtub ring that is almost 150 feet tall and represents 15 MAF of water, enough for an entire year. In the year 2000, the reservoir was absolutely full.
Mr. Udall also noted that the water problems in California are inherently joined to the Colorado River. “If you are from Northern California, it might be easy to think that this river had nothing to do with you, and I would argue that’s absolutely not true,” he said. “Part of it is because of Metropolitan Water District. They have the largest reach of any water system in the world which is to their credit, actually. If you’re going to get water to 20+ million people, you want that reach. As I am told, the Colorado River got them through the recent drought, which is a good thing, because they would have gone looking in California for water if this river hadn’t had it for them.”
The definition of crisis is ‘a time of intense difficulty, trouble, or danger, or a time when a difficult or important decision must be made.’ And the impacts of climate change are being felt; the earth is almost a degree Celsius warmer than it was pre-industrial, he said. “It’s everywhere; it’s us. There’s no credible alternative explanation for what we’re seeing. Experts agree. This is 200 years of science at work and there’s not a credible person out there that says we don’t know what’s going on; it’s bad and we can’t fix it.”
The Colorado River is not a big river; it’s about the size of the Hudson River. Annual flow is about 14.75 MAF at Lee’s Ferry, but because of the drought, it’s down almost 20% at 12.3 MAF per year. The basin is experiencing the worst drought in the gauge record.
There are 40 million people that depend on the river, and that includes every major city in the Southwest – Salt Lake City, Denver, Colorado Springs, Santa Fe, Albuquerque, Las Vegas, Los Angeles, San Diego, Phoenix and Tucson. The river irrigates 4.5 million acres of farmland.
Although the river was fully allocated through the Colorado River Compact in 1922, the supplies equaled demand for the first time in 2000. The river no longer reaches the ocean and hasn’t since roughly about 2000. Even so, there are two big projects being considered in the upper Basin to draw more water out.
In 2007, the Colorado River basin states agreed on what to do in a shortage. He explained that this came about because in 2005, the reservoirs had lost nearly half their contents and Secretary Gail Norton urged the basin states to come to an agreement or the feds would intervene. To their credit, the basin states in two or three very short years came up with the 2007 Interim Guidelines.
Dr. Udall next presented a slide showing total storage in Lake Mead and Lake Powell from 1999 to 2018. The dark blue bars represent percent of capacity; unregulated inflow into Lake Powell is shown as the blue line.
In 1999, the reservoirs were at 95% and at the end of 2018, they were at 42%. The unregulated hydrology, or the amount of water that would flow in to Powell absent upper basin diversions, and what you see is the unprecedented hydrology in the gauge record. “The second, third, fourth, fifth lowest years on record, and out of those 19 years, only 4 years were above average; about half of what you would expect in that kind of period.”
Dr. Udall then presented another graph noting that the vertical axis is winter precipitation in inches which predominantly determines how much water is in the system; the horizontal axis is the summer temperature in Fahrenheit, which is an important determinant of how much water flows. Each dot represents a year and the size of the dot is the value of that flow, so 5 MAF is a little tiny dot, and 20 MAF or more is large dot. The solid line shows the average which is about 15 MAF. The chart shows the years from 1950 to 2018 with the years that are post-2000 in red and the years that are pre-1999 and earlier in blue. The chart has four quadrants: the upper left corner is cool and wet, the upper right hot and wet; the lower right is hot and dry and lower left is cool and dry.
Dr. Udall then gave his interpretations. “Since 2000, there are only two red dots in that upper left quadrant, 2011 and 2008,” he said. “Only 6 years had greater than average winter precipitation, so looking at the red horizontal line, there are only six red dots. There are 13 years sitting in that lower hot and dry quadrant – two-thirds. Only four of those are greater than average.”
What about the risk of shortage in the Colorado River Basin? So far, the basin has never had a shortage declared. He presented a chart that was released by the Bureau of Reclamation in August of 2018. The red circles show the risks for the next five years for shortage, which is Lake Mead at an elevation less than 1075. There is a 70% chance of any kind of shortage and a 14% chance that Mead during that 5 year period sits below 1025.
“Lake Mead at 1025 is a little more than 6 MAF of water,” he said. “The water is circling the drain at that point, and as a water manager, you do not want to see the reservoir at that level, yet here, Reclamation is using hydrology that actually goes back to 1906 and arguably should not be used because it contains very large years, the likes of which we will probably not see or at least not a long sequence of them going forward.”
2018 was the fourth warmest year on record (lower, left), which dates back to 1850. Dr. Udall noted that in December of last year, three very well-known scientists hypothesized that warming may in fact speed up due to three factors: Global emissions of greenhouse gases have not leveled off and in fact went up last year; dirty air actually masks warming and may be masking up to half of what we’re seeing and as we clean up the air, we may see increased warming; and two big oceanic circulation patterns, one in the Atlantic and one in the Pacific, appear to be shifting into patterns where heat in the ocean will remain on the surface rather than going to the bottom of the ocean which will affect air temperatures.
He presented a slide showing precipitation and temperature for the Southwest for 2018 (upper, right). He pointed out the darkest red are record driest conditions and it is centered over the Four Corners; much below normal is that darker yellow which extends into large parts of California. “It was the lowest precipitation on record in the Four Corners area and the warmest temperatures on record in five states – Colorado, New Mexico, Arizona, and portions of California and Nevada, and even small portions of Wyoming,” he said.
In October of 2018, the IPCC Government Panel issued a special report on the impacts of 1.5 degree warming at the request of governments around the world. “You might think that it’s only a half a degree Celsius, no big deal, but this report came out and said it’s been about .8 C already; 1.5 C is damaging and 2 C could approach intolerable in some places,” he said. “The current promises in place out of the Paris Agreement in 2015 would get us to 3.5 C so that’s not even on the map of where we need to be. To avoid 1.5 C, we need unprecedented actions and by 2030. We don’t have until 2030 to start; they actually need to start now if we want to avoid 1.5 C.”
But despite the gloomy prognosis, Dr. Udall emphasized that it’s not too late. “Every .1 Celsius is important and there’s not cliff beyond which it’s too late to act,” he said. “The important thing is to get greenhouse gas emissions to zero as soon as we can so we really need to focus on greenhouse gas emissions and less on temperatures. To the extent that we can’t do that, we’re going to have to do negative emissions. At some point in time, we’re going to wake up and realize we need to do negative emissions, and agriculture will have a good big role there, once we decide to do that.”
The Fourth National Climate Assessment was released in November of 2018. The 29-chapter document was written by 400 scientists over three years; Dr. Udall was one of the authors. Some of the major findings:
- Impacts already being felt: Fires, Floods, Droughts, Hurricanes: “Hurricane Harvey – 60 inches of rain in 4 days. Single highest precipitation total in lower 48 ever and scientists tell us that was juiced by about 40% by climate change,” Dr. Udall said. “Paradise Fire, worse fire in US history, $16 billion in damage, 20,000 structures destroyed, and 86 lives lost. Every one of those statistics is off the charts.”
- Future impacts will disrupt many areas of life
- Without substantial and sustained mitigation and adaptation, will cause growing losses to infrastructure, property and impede economic growth
- Quality and quantity of water changing
The paper, Increasing Influence of Air Temperature on Upper Colorado River Streamflow, was published in 2016 by tree ring scientist Connie Woodhouse, et al. Using data back to 1900, she mapped water year flow in October to April precipitation and then normalized so they could be put on the same axis.
“You would think these two lines would sit on top of each other normally, but there are places where the water year flow is higher than the precipitation, meaning the efficiency that year was really good; you had good runoff despite precipitation that said you wouldn’t get that much,” said Dr. Udall. “The inverse also happens, where you get less flow than you would expect given the precipitation. So she has marked areas where the efficiency is high in those green and blue bars, and where the efficiency is low in the red and pink bars, and if you look, the right side of that graph is overwhelming pink and rose colored. It’s from 2000 or even 1988 roughly onward telling you that something is going on there.”
“What Connie said in this paper is normally we think precipitation is a flow driver and it’s what causes droughts, but temperature can also be important,” he continued. “Since 1988, flows have been less than expected given winter precipitation, and that warm temperatures exacerbated modest precipitation deficits in what many of us now call the millennium drought that started in 2000.”
In 2017, Dr. Udall and Johnathon Overpeck published the paper, 21st Century Colorado River Hot Drought and Implications for the Future. The graphic from the paper shows the declining Colorado River flows since 1906 on the top; the Colorado River basin temperatures that have been increasing since 1895 in the middle, and Colorado River basin precipitation basically flat since 1895 on the bottom.
He pointed out the dry drought in the 1950s that was precipitation dominated and the hot drought in the 2000s. “We said that precipitation declines can only partially explain this flow loss,” he said. “About 2/3rds of the loss was due to the decline in precipitation; the total loss is about 20% in this 2000 drought. Temperature increases explain the remainder, hence the hot drought, and that’s about 1/3 of the loss. And why? More evaporation. Any given day is hotter. The growing season is longer. We had more opportunity to snow to sublimate in the winter time because of higher temperatures, and finally you have this notion of the atmosphere which wants to hold more moisture and hence is thirstier.”
“We said that temperature-induced losses right now are about 6%,” he said. “If the loss in the river flow is about 20%, 6% is about 1/3 of that, but if you flash forward to 2050 with the temperature predictions, you lose about 20% due to temperature, and by 2100, about 35%.”
In 2018, another research paper was published on the causes of declining Colorado River stream flows. The data starts in 1915, and since then, there’s been a 17% decline. “We ran a model and calibrated it,” Dr. Udall said. “We then ran the model twice, one with the temperatures we’ve had and then one with flat temperatures which is called a de-trend experiment. Then we looked at the 1950s and the 2000s drought analysis. Here’s what we found. About 50% of that decline is due to higher temperatures and 50% of the decline was due to changing precipitation patterns.”
About 55% of the runoff is generated in the areas shown in green and blue on the map. “What happened is precipitation moved from those green and blue areas over into the deserts of Utah, which are much less efficient at generating runoff,” he said.
A study in 2016 looked at the potential for megadrought. The left hand side of the graph shows the risk using three different metrics from 1950 to 2000 which was about maximum 10% chance of megadrought, which is defined as a drought of multi-decadal length, typically 10, 20 or more years. For this paper, it was 35 or more years. “Look at the end of century 2050-2099 metrics there,” he said. “Almost 90% chance of a multi-decadal megadrought in the American Southwest because of the warming.”
The paper, Relative impacts of mitigation, temperature, and precipitation on 21st century megadrought risk in the American Southwest, carried that further. Dr. Udall presented a graph with temperature on the horizontal axis and risk of megadrought on the vertical axis. The line for RCP 2.6 is the lowest greenhouse gas emission scenario that is thought possible in the 21st century; the warming associated with that is about 2 Celsius and there is a .6 or 60% chance of a multi-decadal drought. The line for RCP 8.5 is the path we’re currently on which is over 90% chance of megadrought.
The colors on the chart show what happens if precipitation changes. “The results I just gave you were for no change in precipitation,” he said. “So what happens if precipitation goes up by 10% or 20%? By conventional 20th century thinking, you would think how could you have a drought when precipitation is going up. Yet if you do the math, you have a 70% chance of megadrought with a 10% increase in precipitation. There’s a 35% chance of megadrought if precipitation goes up by 20%. So the lesson here is that precipitation is not everything in this century because of these extreme temperatures.”
Aridification is a concept that some scientists have begun to use for the American Southwest because when it lasts for 20 years, it’s hard to call it a drought, he said. “Drought implies a return to normal, yet this doesn’t look like we’re going back. We have a declining snowpack, we have higher temperatures, we have drying soil, a thirsty atmosphere, and the whole idea that storm tracks actually move north is something scientists have found in previous warm and dry periods. Shorter winters and longer falls. It’s even possible, shockingly, to have areas green up in this because of carbon fertilization, and actually taking yet more water out of the system.”
The image is showing an index of aridity mid-century from a paper that showed that the 100th meridian which is the line that separated the wet east from the dry west has now migrated about 100 miles to the east and will continue moving east, he said.
He noted that there are a number of other studies that have been done within the basin. The upper images on the slide show snow water equivalent trends with model-based results on the right and station-based results on the left; the circles indicate declines in April 1 snow water equivalent which is almost uniformly throughout the West. The lower image is the vapor pressure deficit, which is the measurement of the thirsty atmosphere or the amount of moisture that the atmosphere wants to hold; the red points there are where it has increased the most.
Dr. Udall then turned to the Drought Contingency Plan. In 2007, the basin states came to an agreement to solve the structural deficit that existed because the lower basin was using 1.2 MAF more water than to which it’s entitled. However, it only dealt with about 600,000 acre-feet or 50% of that deficit, but since 2000, it’s really been shown that the 600,000 acre-feet was not going to help avoid potentially catastrophic outcomes, he said. Also, the plan was to reconsult if Lake Mead reached 1020’ elevation, which they later realized was way too low.
The graph shows the difference between 2007 and now of the risk of Mead less than 1025, shown by the gray-shaded area on the bottom of the graph. “We thought in 2007 that the risk of Lake Mead less than 1025’ was about 5,6,8%,” he said. “Now it’s over 40%.”
The Central Arizona Project averages 1.5 MAF per year in deliveries; the canal is 336 miles and rises 3000 vertical feet as it takes water into Tucson and Phoenix. The CAP is especially important to Tucson as the city has no surface water, only groundwater.
Dr. Udall explained why the Colorado River situation is so important for Arizona. “In 1968 when my father, Morris Udall and my uncle Stuart and a whole bunch of other people got that CAP decision passed, they set up CAP knowing full well that the structural deficit at some point would come back to haunt them,” he said. “If you don’t believe me, there is a report in 1965 that the Upper Basin did that has the structural deficit laid out in one graph for you to look at, and we forgot about it for almost 50 years. So they knew in 1968 that the Central Arizona Project was living on borrowed time, and guess what, we’re now getting to deal with it.”
There are five pools of water in CAP. Ag has the lowest priority and is shown at the top; the tribes and the cities have the highest priority and are shown towards the bottom.
The 2007 agreement cutback the Central Arizona Project by 480,000 acre-feet, which effectively takes the ag pool out (lower, left). “If you’re a Pinal County irrigator in Arizona, you would have no water under that,” said Dr. Udall. “What did Arizona decide to do? They added another 240,000 acre-feet of reductions, and it now gets all the way down through what they call the NIA priority, all the way down into Indian and M&I, and those cuts really hurt. That’s almost half of the Central Arizona Project’s water supply.”
The chart (above, right) shows the lake levels and the various shortages that occur at those levels. “Arizona’s total there is circled and you can see at the very bottom, below 1025 feet in Mead, you get the 720,000 acre-feet of cuts,” he said. “California is going to join the party here. They join at about 1044-1040 at 200,000 and go up to 350,000. On the far right, you can see almost 1.5 MAF in cuts total when you include Mexico and the feds contribution.”
Arizona Governor Ducey signed the legislation on January 31; there are still interstate agreements that need to be put in place. At the last minute, the Imperial Irrigation District decided they wanted $200 million to fix the Salton Sea, so they apparently want the last say on this, he said. Reclamation issued a notice in the federal register on February 1, saying the deadline was now moved from January 31 to March 19.
“Who knows exactly where that is headed right now,” he said. “There’s supposed to be federal legislation but anyone who thinks the Congress is fully functional right now, I want to have a discussion with you. If we get all of this done, we’re going to have a short break before we then get to renegotiate the 2007 guidelines, and that renegotiation is supposed to start by the end of 2020.”
Dr. Udall then shared his thoughts on the Drought Contingency Plan. “It’s incredibly difficult,” he said. “Almost half of CAPs water supply they are planning to disappear. As messy as this is, there’s no alternative to it. You just get to sit down and talk about it. I think everyone in this room understands you cannot litigate these things. Courts do not have the capability to understand this.”
He noted that it’s been harder to accomplish than many thought and the 2020 renegotiations are going to be a whole lot harder. “If you’ve been following this, those Pinal County irrigators are actually going to go back to pumping groundwater. Well, there’s no easy source of groundwater to replace additional reductions that we may need in the basin. There’s desal, but that’s really expensive. So I just see the 2020 renegotiation much more difficult.”
The graph shows a future full of loss as a function of temperature, he said. There are two columns for midcentury and two columns for end century. There are three different temperature sensitivities shown in blue, green, and red. The chart shows a 20% midcentury flow loss due to temperatures, and there are the two places where that occur on that graph, and there is a 35% loss at end of century under high emissions, he said.
With respect to the renegotiations, we need to understand the worst could happen here, and hope that it doesn’t, he said. The Upper Basin has the obligation to deliver that 75 MAF every 10 running years under the Colorado Compact, and Upper Basin consumptive use right now is 4.5 MAF, or almost half of that number.
“For a long time, people thought that the lower basin’s savior was that the upper basin is going to guarantee this, but if you read the Compact, very clearly it says the upper basin shall not cause the flows to decline below 75 MAF. For years, the Upper Basin has said, if something else causes it and not our depletion, then we’re off the hook. For a long time, I didn’t believe that. I was in the camp of many legal scholars who thought that 75 MAF was a hard and fast number but I don’t think so anymore. I think the Upper Basin has a very strong case to make if they are only using 4.5 MAF and if the river is flowing 10 – 11 MAF, they are not obligated to cut themselves.”
The current Drought Contingency Plan allows agencies to bank those so-called contributions or reductions and get them back later. “I sometimes worry if that might stress the system,” he said. “You might have a wet year or wet couple of years and Lake Mead goes up and everybody wants to get their water out, we may ultimately regret that.”
Dr. Udall said he thinks there needs to be strict rules on new demands as new demands should not add to the risk of existing demands, particularly for the upper basin. He also noted that the Upper Basin wants an insurance account in Lake Powell, much like Intentionally Created Surplus.
The 1968 Act says that the CAP canal will go to zero before CA faces one drop of shortage, but Dr. Udall said he’s does not believe it is politically feasible to cut CAP to zero. “There are five million people in Phoenix; that’s half of their water supply. Tucson has about 1 million with no surface water supply. All CAP dependent. I do not believe that 1968 law can be implemented as it says. In fact, I would argue I am not sure how much more you can go into cutting CAP. I know that’s not a particularly fun thing to say in California or lovely to hear, but I’m not certain that you can cut CAP to zero.”
Climate change is already impacting the Colorado River Basin and the impacts are only going to get worse, he said. “The ‘new normal’ is the wrong word; maybe ‘new abnormal’ is a better one,” he said. “We have aridification underway, it’s going to get hotter, we’re seeing shifting runoff patterns, there is more year to year variability in the weather, and the flow reduction risk is really high.”
However even so, Dr. Udall still remains somewhat optimistic. “I like to say there’s an opportunity for change here,” he said. “I’ve worked on this issue now for 16 years. I’m been an author of two national climate assessments and one international assessment, and with each passing year, the threat grows. Water has been and is going to continue to be a challenge because you warm the earth, you change the water cycle. It’s as clear as that. Climate scientists have known this even before we had models. The water cycle moves heat around the planet. If you add heat, the water cycle is going to change.”
“We have the tools,” he added. “We know what we need to do; we’re just not using them.”
So is the Colorado in crisis? “I don’t really like the word ‘crisis’ because it partially implies out-of-control and something that we’re not responsible for, but that’s not really part of the definition. If you truly acknowledge the facts: that the reservoirs are low – only 42%, and 40 million people depend on this system. It’s the worst hydrology in gauge record and climate change is already impacting these flows. To lose the ag in Imperial and Yuma and Central Arizona – that’s really important ag in the concept of winter vegetables and produce in this country, and it would be really hard on those economic areas.”
“So my answer is yes, of course it’s in crisis.”
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