Tag Archives: water

LA Rain: Skull Emoji Edition

With March in the rearview window and May grey on the horizon, let’s take another look at how SoCal fared this winter with rainfall. The short answer is… not good.

WY precip 20180403

March brought a modest storm to Los Angeles, finally bumping us over 4” of rain for the season. With 4.60”, water year (WY) 2017-18 now stands as the third driest year recorded in LA since 1877. A storm forecast for this weekend might, at the high end, get us to 5” and fourth driest. Either way, barring a truly unusual storm this spring or tropical storm remnants this summer, this year will fall around the 2nd percentile of water years, becoming just the 8th year on record to record less than 6” of rain.

WY hist 20180403

Looking at multi-year trends, the last 7 water years just crushed the record low for a 7 year period, with 62.46” to the previous low of 68.75” (1958-65). The record low 6 year period of 1958-64 with 53.25” holds the record by a hair, with the current 6 year period at 53.76”.

MY 2to7 20180403

Despite the severity of recent drought, it’s important not to read too much about long-term trends into this data. Looking at 10, 20, 30, and 50 year periods shows that recent decades have been on the dry side, but not unknown in LA’s past.

MY decades 20180403

One additional metric I think might be interesting is “streakiness” of precipitation in LA – that is, do we tend to get a lot of dry years clustered together and a lot of wet years clustered together? Here’s a plot of the “streak” for each water year, with positive values representing above average and negative below average. So, a value of 2 means that year is year 2 in a streak of above-average precipitation; a value of -3 means that year is year 3 in a streak of below-average precipitation.

streakiness 20180403

There are more below average years than above average years, a fact also represented in the histogram above that shows rainfall distribution is skewed by a small number of very wet years. There was one streak of 7 below average years, and a further three streaks of 5 below average years. The longest above average streak was in the mid-1960s, with 5 above average years. Four other periods have had 3 above average years. Again, LA rainfall is highly variable, and you cannot use this historic data to predict that we are “due” for a wet year or anything like that.

Looking at SoCal a little more broadly, the Central Coast has fared a little better than LA, but other places have done worse. Parts of coastal Orange County have had less than 25% of normal precipitation and it wouldn’t be surprising if some stations there record all-time lows.

SoCal 20180403

Percent of normal water year precipitation to date

The good news, such as it is, is that northern California received some beneficial storms in March that moved the year from “disaster” like we have in SoCal to just “bad”. The northern and central Sierra are at 65% of average for the whole water year and about 75% for year to date. The south Sierra is at about 52% and 62% respectively. An unusually strong April storm is poised to bring more rain and snow to the Sierra as well.

NSierra 20180403SanJoaquin 20180403Tulare 20180403

Finally, thanks to last year, major state reservoirs are still riding high with plenty of water for the summer.

reservoirs 20180403

Unfortunately, there isn’t really any hope left for SoCal this year. Let’s just write this year off, move on, and hope for a better winter next year.

SoCal Rain Update: Almost a Wrap

First of all, I would like to apologize for single-handedly jinxing and ruining a banner water year for SoCal, with this closing paragraph to the last update:

The last 6 years are a reminder that for SoCal the faucet can turn on just as quickly as it turns off – and vice versa. The forecast for the next week or so is dry and in fact once, water year 1996-97, LA had no measurable rain between March 1 and the end of the water year. So now that I’ve sufficiently jinxed things, you’d better hope extra hard for some more drought relief this year!

While we managed to escape without nothing, all we have to show for March, April, and May is 0.49”, bringing the total for the water year 2016-17 to 18.99”. June through September, the end of the water year, has only brought more than 1” of rain 14 times out of 140 years of records, so let’s call this an almost wrap and see where this year stands.

Currently, downtown LA is at 18.99” of rain for the water year. This is about 4” greater than the yearly average, and well past any of the drought years. However, it’s a little short of the last good year, 2010-11. The strong El Niños of 1982-83 and 1997-98 have left us in the dust.


To put this year in context, here’s where it falls on a histogram of LA precipitation. Falling right into the 18”-20” bin, we can see that this year was indeed wetter than typical, but not a once-in-a-lifetime record breaker like northern California had.


The multi-year water trends show we are still in a multi-year precipitation drought condition, with the 5 and 6 year totals just barely above record lows. However, with WY 2011-12 (8.70”) and WY 2012-2013 (5.93”) falling out of the 6 and 5 year totals, respectively, for next year, hopefully those totals will continue to improve.


Looking at the distribution of LA rainfall, this year falls right around the 75th percentile. Again we can see that while this was a wet year, it was by no means into the rarefied territory up above about the 85th or 90th percentile. This was the 35th wettest year in LA, out of 140 on record. By comparison, the 4-year drought period 2012-2016 had three years in the driest 11 on record (2015-16 #11, 2013-14 #8, and 2012-13 #7).


Finally, we should note that while it is rare for southern California to get much rain between now and the end of the water year in September, it has happened 6 times. Most often this precipitation comes in September from tropical storm remnants, such as the 2.39” received in September 2015 from the remnants of Hurricane Linda. This improbable event alone bailed out water year 2014-15, which otherwise would have been only slightly better the rest of the 2011-16 drought years. Meanwhile, the only tropical storm to make landfall in California in the 20th century brought over 5” of rain in September 1939, causing severe flooding. So while this post is probably it for the year, there’s always a chance otherwise!

SoCal Rain Update: Keep it Coming

After 5 long years of drought, a series of powerful storms in January and February 2017 finally brought heavy rain and snow to California. Let’s take another look at where we stand in Los Angeles, and at water supplies around the state. As always, remember that in California we measure precipitation from October through the following September; this period is called the water year.

Currently, downtown LA is at 18.50” of rain for the water year. This is about 3.5” greater than the yearly average, and well past any of the drought years.


February 2017 finally brought a storm that put the Central Coast in the bullseye, and the effect on Lake Cachuma, the largest reservoir for Santa Barbara County, was incredible. So far this winter, Lake Cachuma is up from 7% full to 42% full, and on one day in February gained nearly 30,000 acre-feet of storage. (One acre-foot is enough water to cover an acre of land with one foot of water, about what two average households in CA use in a year).


Precipitation indexes for the Sierra Nevada show it’s been a very wet year throughout the range. The north Sierra, corresponding to the Sacramento River drainage, has had 76.3”, already well above the water year average of 50.0”, and with all-time records within reach.


The central Sierra, corresponding to the San Joaquin River drainage, is also already well above the water year average, with 60.4” to 40.8”. It too is on pace to chase some of the wettest years on record.


The south Sierra, corresponding to the Tulare Basin (Kings, Kaweah, Tule, & Kern Rivers), is now well above the water year average, with 40.9” to 29.3”.


Let’s look over to the other side of California, the east Sierra, corresponding to the Owens Valley. Snow water content has not only already doubled the April 1 average (50.4” to about 24”), it’s already tied the wettest year on record. This is where the water in the LA Aqueduct comes from, so it’s good news for city water supplies, as we’ll have to buy less water from the State Water Project and Colorado River Aqueduct.


The juxtaposition of such a wet year following the worst drought in the state’s history has highlighted that California, especially southern California, is the land of extremes. Annual precipitation in SoCal is almost comically variable, with the wettest year having over 10 times as much rain as the driest year.


Variability is expressed using coefficient of variation (standard deviation divided by mean). LA’s coefficient of variation is 0.48.

To demystify the variability of SoCal rainfall, I thought it might be interesting to do a comparison between Los Angeles and Portland, widely considered to be a pretty rainy place. Here’s the average rainfall for each city by month.


Portland gets about 36” of rain every year to LA’s 15”, though surprisingly enough LA is, on average, wetter than Portland in the month of February. However, when we look at daily rainfall records, a striking pattern emerges.


The all-time daily record rainfall in Portland is 2.69”; in LA it’s over twice that much at 5.88”. It’s never rained 3” or more in one day in Portland; there are 31 daily rainfall records greater than 3” in LA. The 4” mark has been hit ten times and 5” three times. LA’s daily rainfall record is greater than Portland’s for 165 days out of the year, despite Portland getting nearly 2.5 times the annual rainfall and being wetter in nearly every month, and LA being so reliably dry in summer that 19 days have never seen measurable rainfall and the last 140 Julys having delivered a grand total of 1.55” of rain.

The last 6 years are a reminder that for SoCal the faucet can turn on just as quickly as it turns off – and vice versa. The forecast for the next week or so is dry and in fact once, water year 1996-97, LA had no measurable rain between March 1 and the end of the water year. So now that I’ve sufficiently jinxed things, you’d better hope extra hard for some more drought relief this year!

Oroville, Again

A lot has happened at Lake Oroville in the three days since I posted an introduction to the State Water Project (SWP), to put it mildly.

At the time of that writing, Saturday afternoon, the lake level was at 902.02’, with water flowing over the emergency spillway sill at 901’, and releases from the damaged controlled spillway at 55,000 cubic feet per second (cfs). The lake level peaked at 902.59’ at 3am Sunday morning and then began to slowly decline. At 11am Sunday, the California Department of Water Resources (DWR) reported that flow over the emergency spillway had peaked at 12,600 cfs and since declined to 8,000 cfs, with the situation stabilized. At 4:40pm Sunday, an emergency evacuation was ordered, with the emergency spillway predicted to fail in as soon as an hour.

This photo from February 11 shows the emergency spillway not long after water began to flow over it. Note the roadway in front of the spillway. Very little erosion has occurred in this photo, though some channelization is visible bottom center.

This photo from February 12 shows the emergency spillway with erosion having progressed further uphill. Note the road has been washed out, and the channel has deepened and worked its way uphill.

Faced with this situation, DWR increased the releases from the controlled spillway, to try to save the emergency spillway. Releases were increased to 100,000 cfs, and after a few very tense hours, the lake level dropped below 901’ at about 8pm Sunday. Water stopped flowing over the emergency spillway, and the erosion stopped.

This photo from February 13 shows the damage to the emergency spillway. Note the people for scale. I do not know which channel was of the most concern but the large channel near the washed out road and white truck was not the closest to the emergency spillway sill. Top right, just left of the far end of the concrete spillway, are two workers in yellow vests standing by the channel that got closest. This photo shows a closer view, with that channel just behind the workers.

It’s obviously a huge relief that the lake level is below the emergency spillway and that the structure survived. It’s also a huge relief that the damaged controlled spillway has been able to maintain 100,000 cfs releases, which as of this writing (9pm February 14, 2017) have lowered the lake level to 883.60’, over 17’ below the surface of the emergency spillway sill.


This has allowed DWR to being making emergency repairs to the emergency spillway, in case it must be used again. This photo shows placement of rock in the channel that got closest to the emergency spillway sill. DWR also posted two videos, one from yesterday and one from today, showing the repair work. Emergency evacuation orders have been lifted, but residents are to remain vigilant under an evacuation warning, in case the situation changes.

It is very good news indeed that the emergency spillway survived. However, it is only mid-February and we still have a lot of winter to go, followed by spring runoff when an above-average snowpack melts. In another stroke of good fortune, the National Weather Service (NWS) Sacrament office is predicting the next storm, for Wednesday night and Thursday, to have lower snow levels (5000’-6000’) than originally expected (7000’-8000’). This will keep the precipitation as snow, rather than rain and melted snow that will immediately run down into Lake Oroville. This will allow DWR to keep lowering the lake level to create flood storage for the spring, and keep making repairs on the emergency spillway. Another series of storms is expected for Monday and Tuesday next week, but with snow levels between 3500’-5500’.

After the snow is gone, there are going to be a lot of questions to be answered. I’m not going to litigate the decisions made by DWR here; I’m sure there will be plenty of people to do that soon enough. I also want to say that I have great respect for the many DWR engineers and workers, the Butte County Sheriff, and many other public employees and safety officials that have worked hard to ensure public safety, and have had to make many extremely difficult decisions about how to proceed in a dangerous and dynamic situation.

As a civil engineer, things like this really hurt. Like many civil engineers, I went into this business because I believe it is a profession where I can put my natural skills to work in a way that improves people’s lives. I never want to see our works fail or put people at risk.

This is going to be a case study for future civil engineers, for that is what we must always do when something doesn’t work the way it should: ask ourselves why, figure out what went wrong, learn from it, and improve our designs and processes so that we increase public safety and public benefits in the future. I think there will be four main questions to be researched here:

  • What was the proximate cause of the damage to the controlled spillway?
  • Why was the emergency spillway damaged so critically by relatively modest flows (12,600 cfs) relative to its capacity (several hundred thousand cfs)?
  • What was the decision making process after the initial damage to the controlled spillway? Was all relevant information available to decision makers?
  • Was information available before the crisis that should have led to corrective actions, and if so, what stopped corrective actions from being taken?

In short there are several distinct things here: pre-crisis actions, controlled spillway damage, emergency spillway damage, and crisis management.

Again, none of this is to question the hard-working people who are doing everything they can to mitigate the crisis and have faced very difficult decisions. As engineers, we must seek to improve our understanding of our designs, how the natural world interacts with our designs, and how our decisions and processes affect those systems. My heart goes out to anyone affected by this situation, and I sincerely hope that we, as Californians, can pull through this and use the lessons to help make our state a better place.

The State Water Project: An Introduction

If you follow this blog’s twitter account, you know that engineering & water twitter has been closely watching the situation at the Oroville Dam in northern California. Many people know, conceptually, that much of the water we use in SoCal comes from northern California, but are not familiar with Oroville or the State Water Project. So, here’s a brief introduction to what the State Water Project (SWP) is, what it does, and what’s happening at Oroville now.

The SWP is an important source of water for SoCal, and Lake Oroville is the main reservoir. While popular conception hold that LA’s water comes from the east Sierra and Owens Valley via the LA Aqueduct, over the last 5 years, that facility has only delivered 29% of LA’s water. The SWP is the largest supplier of water to the city of LA, with 48% of LA’s water over the last 5 years coming from the SWP. So what happens at Lake Oroville is of interest to, well, anyone south of Lake Oroville.

The State Water Project: California Dreaming… Big

Everyone knows the split nature of California’s climate: the north is wetter, the south is drier. However, many people and much of the best farmland are in southern California. Over half of the state’s population lives in relatively dry climates south of the Transverse Ranges, which separate the southern quarter of the state from the rest. In addition, California experiences wide swings in annual rainfall, with droughts and floods often following on each other’s heels. In fact, 2014-15 was the driest water year in state history, but 2016-17 may prove to be the wettest.

This situation naturally led to the desire for civil engineering improvements to both prevent devastation from flooding in wet years and store water for human use during drought years. The SWP was conceived to help meet these goals. The map below shows the main components of the SWP.


The major components of the SWP are:

  • Oroville Dam: this dam is located on the Feather River, which drains a portion of the northern Sierra Nevada, and is the source of water for the SWP. Lake Oroville can store up to 3.5 million acre-feet of water, making it the second largest reservoir in the state after Lake Shasta. One acre-foot of water is enough water to cover an acre of land one foot deep – about 325,000 gallons.
  • California Aqueduct: this aqueduct conveys water from the delta to users in central and southern California. Water released from Lake Oroville flows down the Feather River and Sacramento River to the delta. From there it is pumped south out of the Clifton Court Forebay.
  • San Luis Reservoir: this is a large off-line reservoir in the southern Central Valley that can store 2 million acre-feet of water. “Off-line reservoir” means that it is not located on a major river – it was created by damming an existing valley and filled with water from the California Aqueduct. The creek that formed the valley, San Luis Creek, would never carry enough water to fill the reservoir on its own.
  • Distributary aqueducts: these aqueducts carry water from the main California Aqueduct to water uses. These are:
    • North Bay Aqueduct and South Bay Aqueduct, which serve the East Bay area.
    • Coastal Branch, which serves San Luis Obispo and Santa Barbara Counties, including a connection to Lake Cachuma, Santa Barbara’s main water supply.
    • West Branch, which serves the Los Angeles area and includes Castaic Lake and Pyramid Lake, the lakes you see from the 5 when you drive through the Grapevine.
    • East Branch, which serves the Inland Empire and includes Silverwood Lake and Lake Perris.
    • Second San Diego Aqueduct, which connects Lake Perris to San Diego County.

Because of the complicated geography and politics of water in California, the SWP includes some water agencies that don’t even have a physical connection to the project. For example, the Desert Water Agency (DWA) and Coachella Water Valley District (CVWD) serve Palm Springs and the Coachella Valley, which have no connection to the SWP. The DWA and CVWD buy SWP water and then swap it with the Metropolitan Water District of Southern California (MWD SoCal) for water from the Colorado River. So DWA and CVWD pay for SWP water, which is delivered to MWD SoCal, and in exchange, MWD SoCal gives DWA and CVWD water from the Colorado River Aqueduct.

Construction on the SWP started in the early 1960s and the major components were done by the late 1970s, though construction on various pieces such as the East Branch Extension continues up to the present day. The SWP is just one legacy of the leadership of Governor Pat Brown, who for his investments in water infrastructure, freeways, and education ought to be known as the father of modern California.

Ok, So What’s Going on at Oroville?

Lake Oroville is a dual-use reservoir – it is used both to store water for human use and to capture water from torrential rainstorms and snowmelt to prevent devastating flooding downstream. Every such reservoir has its storage divided into conservation storage and flood control storage. Under normal conditions during the rainy season, the reservoir is not allowed to fill up beyond the conservation storage level, so that if a big rainstorm or snowmelt event happens, there will be enough capacity to prevent flooding. Reaching the top of conservation storage is like the gas light coming on in your car: it means you need to start looking for a gas station, because you don’t want to run out of gas before you start looking.

Early this week, a large winter storm hit northern California. The storm was warm, meaning that it had high snow levels (the elevation in the mountains where the storm changes from rain to snow), so much of the precipitation went into the rivers right away instead of adding to the snowpack in the mountains. The warm temperatures and rain also caused some of the existing snowpack at low elevations to melt and flow into the rivers.

On Tuesday, Lake Oroville was near the top of conservation storage, and with a large amount of water on its way to enter the lake, state water managers increased water flow through the controlled spillway on the Oroville Dam. A controlled spillway is a structure on a dam that has gates that can be opened and closed by motors, allowing the agency in charge to control how much water leaves the reservoir. The Oroville controlled spillway had a theoretical maximum capacity of 250,000 cubic feet per second.

However, as flows ramped up, a sinkhole appeared in the lower portion of the spillway, and water releases had to be stopped to allow inspection. After assessing options, it was determined that because of the large volume of water entering the lake, it was necessary to continue to allow water to flow through the damaged spillway to keep the lake from rising too quickly. Water flowing through the spillway has caused additional erosion, although yesterday and today the discharge appears less muddy. Hopefully, this is an indication that the channel has cut down to bedrock, and erosion has slowed down.

As water flows downhill, erosion will tend to cut back uphill. This is why Niagara Falls is at the head end of a long gorge; the falls have cut the gorge back upstream from the Niagara Escarpment since the end of the last ice age. It is critical that erosion on the controlled spillway at Oroville not be allowed to proceed uphill and damage the spillway gates, which would negatively impact the ability to control releases down the spillway. That is why the damaged spillway is only being allowed to operate at a reduced capacity.

Because inflow is currently greater than outflow, the lake level is rising. However, this is NOT a threat to the Oroville Dam itself, because there is an emergency spillway that the water will flow over first. The dam crest elevation is at 922’, while the emergency spillway sill is at 901’. The emergency spillway is an uncontrolled weir, so once the lake reaches elevation 901’ water starts to flow down the emergency spillway. This happened at about 8am this morning and as of 3pm February 11, 2017, the lake elevation is at 902.02’, so water continues to flow over the emergency spillway. In a noon press conference, the state announced that it expects this flow to continue for 36-56 hours.

The emergency spillway is an unlined, unimproved channel, which means water that flows over down it is just flowing over dirt, vegetation, and rocks. This means some erosion will occur and enter the Feather River downstream.

What’s Next?

Because it’s only mid-February, winter is only part way over, and more rain and snow storms may be on the way. The state will face challenges with water coming into the lake over the next few months as additional storms hit, and then as spring and summer temperatures melt the snowpack. At the moment, it does not appear there will be enough time to much in the way of repairs before more rain and snow arrive. Resource managers will face difficult decisions between increasing flow on the damaged spillway and allowing additional flows over the emergency spillway.

It’s important to emphasize that as of this writing (3pm February 11, 2017), there is no threat to the Oroville Dam itself, no flooding occurring downstream, and no imminent public danger. Everyone should pay attention to information from the California Department of Water Resources, the Butte County Sheriff, and the California Office of Emergency Services for updates on changing conditions.

After the rainy season and spring snowmelt is over, the state will face a busy summer construction season at Oroville, including repairs to erosion and/or improvements to the emergency spillway, and repairs to the existing damaged controlled spillway or replacement with a new controlled spillway.

Is the SWP the Same Thing as the Central Valley Project?

No, though they are related. The SWP is operated by the state of California, while the Central Valley Project (CVP) is operated by the federal Bureau of Reclamation. The main CVP components are:

  • Shasta, Trinity, and Whiskeytown Lakes in northern California, which store water for use in the Central Valley.
  • Tehama-Colusa Canal, which distributes water for use in the northern Central Valley.
  • Friant Dam and Millerton Lake on the San Joaquin River, and the Friant-Kern Canal, which distribute water from the San Joaquin River for use in the southeastern Central Valley.
  • Delta-Mendota Canal, which distributes water from the delta for use the San Joaquin River drainage basin below Friant Dam.
  • San Luis Canal, which is shared with the SWP, and distributes water for use in the southwestern Central Valley.


In addition, there are interconnections between the SWP and the CVP such that if the south Sierra has a very wet year, water from the Tulare Basin rivers (Kings, Kaweah, Tulare, and Kern Rivers) can be sent to the SWP.

What Are All Those Grey Squares on the SWP Map?

Curious readers may have noticed several reservoirs and other facilities on the SWP map shown in grey. These are facilities that were proposed as part of the SWP but never constructed.

The undeveloped facilities in northwestern California are of the greatest consequence. The project as originally proposed included dams on the Klamath River and Eel River, which would have created the Ah Pah Reservoir and the Dos Rios Reservoir. At 15 million acre-feet and 7.5 million acre-feet, respectively, each of these reservoirs on their own would have dwarfed Lake Shasta and Lake Oroville. These facilities would have been located in the wettest part of California. An additional reservoir, the Glenn Reservoir, would have been located east of the coastal mountains, with water directed there via tunnel from Dos Rios.


Since the Klamath and Eel Rivers are not currently connected to the SWP, these dams would have greatly increased the water available to the SWP. However, they would have destroyed some of California’s last free-flowing river segments, and would have had enormously negative consequences for fish and other wildlife. The large environmental impacts resulted in these projects being canceled, and they are unlikely to ever be revived.

The other two unbuilt large reservoirs are the Sites Reservoir and Los Banos Grandes Reservoir. The Sites Reservoir would be able to store between 1.2 million and 1.8 million acre-feet, with Los Banos Grandes adding another 1.7 million acre-feet. Together, they would equal another Lake Oroville of off-line reservoir storage, increasing SWP storage by over 50%. Since they would be off-line reservoirs, not located on main rivers, the impact of these facilities might be less.

The last major unbuilt piece of the SWP is the Delta Peripheral Canal, or as we know it today, the Delta Peripheral Tunnel. The purpose of this facility would be to channel water from the Sacramento River (released from Lake Oroville, Lake Shasta, or the Sites Reservoir) around the delta to the pumping facilities that send the water south via the California Aqueduct. This would reduce the environmental impact on the delta and increase the reliability of SWP water deliveries.

With climate change possibly making droughts and floods more likely, and causing precipitation to fall as rain instead of snow, there may be renewed interest in the Sites Reservoir, Delta Peripheral Tunnel, and maybe even Los Banos Grande Reservoir.

El Niño Update: Joke’s on SoCal Edition

Somehow, it’s already April, and despite intense media hype and warning, SoCal residents have watched storm after storm deliver rain to northern California but die on the way past Point Conception. The storms that have made it to LA have been mediocre, with limited moisture; the remnants of a tropical storm in September brought more rain than any system since. Through the end of March, this year has been no better for LA than the last four drought years.


If El Niño is going to bring any rain to SoCal, this is the eleventh hour. The April through June period has brought over 5” of rain only 5 times since 1877 (including the 1982-1983 El Niño), and even this amount would leave LA well below normal for the year.

Major water supply reservoirs in northern California have continued to fill up. The biggest reservoirs in the state, Lake Shasta and Lake Oroville, will almost certainly fill to capacity this spring, after starting out the water year about 30% full. Folsom Lake and Bullards Bar will likely fill, and other large reservoirs like Trinity Lake, Don Pedro Lake, and Millerton Lake have risen significantly.


The snowpack in the northern and central part of the state is running close to average, and about 75% of average in the south Sierra, which will keep water flowing into reservoirs through the spring.


The situation in SoCal, though, is dire. While urban areas in LA and San Diego draw water from all across the southwest, the Central Coast is much more dependent on local supplies, with only small State Water Project allocations of NorCal water. Lake Cachuma, in Santa Barbara County, has fallen every year since 2011 and this year was no different. Nearly at capacity in 2011, it currently sits at only 14% full.


Urban water supplies are one thing; we humans will figure out a way to get by. The impact of this fifth dry year on SoCal’s environment is going to be depressing. Wildlife will have tough times finding water. There are going to be a lot of dead trees in the hills and mountains, increasing the fire danger. At this point, all we can do is hope for monsoon moisture and tropical storm remnants to somehow find their way to LA this summer. At least it would do something to help stop forests from drying out.

To see how dry it has been in SoCal the last 5 years, let’s look back to 1877, when weather records started being kept in downtown LA. SoCal is a land of extremes: the wettest water year (2004-2005, 38.25”) had over ten times the rain of the driest water year (2006-2007, 3.73”).


While dry years are common in SoCal, the last 5 years have been severe, and it is unusual to have so many in a row. Water years 2012-2014 were the driest 2-year period in LA’s history, with just 11.97”, 0.69” less than the previous record of 1897-1899. 2011-2014, 2012-2015, and 2013-2016 are the third, fourth, and fifth driest 3-year periods in LA’s history. Water year 2015-2016 doesn’t end until September 31, but we very close to LA’s dry season and 2012-2016 is currently the driest 4-year period by over 2”, with 29.80” – and the current record holder is 2011-2015 with 31.91”, beating the previous record by 1.50”.

As it stands today, the five year period 2011-2016 has had 38.50” of rain, which would shatter the previous record of 45.63” set in 1985-1990. Simply put, since 1877, LA has never had a five-year period where every year was below average by so much.


Even in that context, though, you can see just how variable precipitation is in SoCal. If we look to the driest 6-year periods, 1945-1951 (57.78”) and 1958-1964 (53.25”) are both drier than 2010-2016 (58.70”). Next year would only have to be a normal year to avoid 2011-2017 stealing the crown.

The 1958-1964 period is particularly illuminating. Monthly totals are presented below.


In that 6-year period, LA had 5 years that were every bit as bad as the last 5 years have been – worse, actually – split up by one year of above average precipitation in 1961-1962, with 18.71”. That year would have been below average if not for one monster month, February 1962, which recorded 11.57”, more than any other year in the period and more than the driest 2 years combined.


Furthermore, almost all of the rain that February fell in a 2 week period, with 10.88” between February 7th and 19th. Almost 4” of rain fell on February 8, 1962 alone, and 7.56” fell between February 7th and 11th. That 5-day period saw more rain than the entire water year for 1958-1959, 1960-1961, and 1963-1964.In other words, if not for that one 5-day period in February 1962, the 6-year period 1958-1964 would have been drier than the 5-year period 2011-2016. The last wet year in LA, 2010-2011, was above average thanks to 10.23” of rain in December 2010, of which 7.90” fell in just 5 days.

Precipitation in SoCal is of the ultimate capriciousness, even without humanity running an uncontrolled experiment in geoengineering. Storms struggle to bring rain until conditions are just right, and then the skies open like a breached dam. Hating on California’s water supply system is a popular pastime in much of the country, but it’s exactly the logical thing for a civilization to build in a place like SoCal. LA’s water comes from local supplies, the East Sierra via the LA Aqueduct, northern California via the State Water Project, and Wyoming-Colorado-Utah-New Mexico via the Colorado River Aqueduct. Properly managed, it’s a robust system that ensures reliable supply, and makes much more sense than trying to depend on wildly erratic local precipitation.

(Note: data at left is for LAX, so it doesn’t match monthly totals above. All other data in this post is for downtown LA.)

Looking even longer-term, at decade-long totals, we can see that the last 10 years have been unusually dry, averaging just over 10” of rain a year, the lowest since 1877. However, the 20-year, 30-year, and 50-year trends are unremarkable.


Fortunately, people who know much more about California’s climate have been doing much more detailed research on long-term trends than the armchair analysis above.

Recent research published by Daniel Swain, who writes the excellent California Weather Blog, finds that weather patterns that cause dry years in California are becoming more frequent. However, this does not appear to be at the expense of patterns that cause wet years, which may also be increasing in frequency. The result is that long-term precipitation averages may stay the same, even as global warming causes temperatures to increase, but California’s wet and dry extremes may become even more pronounced.


Source: California Weather Blog.

If long-term trends are leading toward even move variability in California’s water supplies, it heightens the importance of improving water storage and management. If there’s a silver lining to the persistence of SoCal’s drought this year, maybe it will be a continued focus on tackling these challenges.

El Niño Fever: Volume 2

January is behind us, so here’s another update on rainfall and this year’s El Niño. Yesterday’s storm proved to be underwhelming across much of metropolitan LA, though the mountains did get a good dose of rain and snow. Downtown LA recorded 0.43”, for a January total of 3.17” – just above the average of 3.12”. The bad news is that thanks to dry weather in November and December, LA is still about 3” of rain below normal for the water year.


In fact, we are actually behind where we were at this point in water year (WY) 2012-2013, which turned out to be the worst year of the drought. Not exactly inspiring. The good news, of course, is that being in an El Niño year gives us much better odds of having a wet February-May than we had over the last four years.


I added the median to the graph in green for this update. Because of a few monster years, the rainfall distribution skews high; the median of just under 13” may be considered more typical than the average of just under 15”.

The other good news is that the season has not been so cruel to the rest of the state. Most of California is having an average to above average year, including much of San Diego County and the San Joaquin Valley. Much of the Sierra Nevada and the northern third of the state are at or above average – and being 25% above average there make a much bigger difference.


This has helped replenish reservoirs, especially in northern California. Lake Shasta and Lake Oroville, the two biggest reservoirs in the state, will soon have more storage than they had at the end of spring last year. Folsom Lake and Bullards Bar have actually crept above the historical average.

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We’re including San Luis Reservoir (a large off-line reservoir in the southern Central Valley) in NorCal, because that’s where the water comes from. It’s below where it was last year but that’s likely due to restrictions on when water can be pumped.

Reservoirs in the central Sierra haven’t done as well, partly because they were all very low, and probably partly because the terrain is higher and more of the precipitation has fallen as snow.

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This year, the state’s snowpack is in much better shape than it was last year, so there will be a good bit of water headed to the reservoirs this spring.

In the meantime, if El Niño is going to make a dent in LA’s drought, it might want to start soon.

Baja California State Water Project

As California grinds through year 4 of a terrible drought, it’s become clear that the state needs to overhaul its water management practices. However, the need to reform how manage the demand side shouldn’t turn us off to augmenting things on the supply side. Climate change and a growing economy have reduced the margin for error, and supplies are nearly maxed out. So here’s an exploration of an off-beat idea to increase water supplies for California and the Southwest in general.

Desalinization has long been a sort of Holy Grail of water supply in California; every day, the sapphire Pacific taunts us with its endless supply of unusable water. Desalinization technology has been improving, and costs decreasing, but the process unavoidably produces large quantities of concentrated brine as a waste byproduct. This highly saline water can have a negative impact on ocean ecosystems without careful management.

Enter Baja California. Just south across the border from the sweltering farms of the Imperial Valley, west across a low mountain range, lies an enormous salt flat know as Laguna Salada. This large, closed drainage basin, created by the same tectonic forces that created Death Valley and Nevada’s endless basin and range, is located about 60 miles northwest of the Gulf of California. Like Death Valley and the Salton Sea, this basin has been dropped below sea level, which means the energy needed to get sea water there is pretty low. It’s also a blazing hot desert, with enormous evaporative potential: over 4 feet per year from a free water surface.

The centerpiece of this plan would put huge desalinization facilities at the north end of the Gulf of California, powered by solar energy farms. Rather than cause environmental issues by being discharged into the ocean, the concentrated brine would flow north to Laguna Salada, where it would simply evaporate. The sea salt precipitating out of the brine would be harvested for sale. With the intense Baja California sun, and assuming a 50% recovery ratio, each square mile of the Laguna Salada would yield 2,560 acre-feet of drinkable water per year. Inundating the 300 square miles of the Laguna Salada would yield over 750,000 acre-feet of water per year.

As the title of the post suggests, this project would be built by the state of Baja California. The admittedly complex scheme would work as follows. Baja California would produce fresh water, which it would sell to water users in the southwest with the most junior water rights: the states of Nevada and Arizona, and the CA State Water Project (SWP).

Since there is no way to convey water from Laguna Salada to Arizona and Nevada, project water would be swapped with Colorado River water via the Imperial Irrigation District (IID) and users in Mexico. Nevada and Arizona would get additional water from the Colorado in exchange for IID and Mexican users getting water from the project. This swap actually has a side benefit in that it would mix demineralized water from the project with the excessively mineral waters from the Colorado River, alleviating salt build up in IID and Mexican fields. In wet years, NV and AZ transfers would be represented by additional storage in Lakes Mead and Powell.

Meanwhile, water from the project could also serve the Coachella Valley, which extends from Palm Springs to Indio. Coachella users would swap project water for water from the Southern California Metropolitan Water District, which would in turn swap water with SWP users. In wet years, SWP transfers would be represented by additional storage, in this case recharging groundwater supplies in the San Joaquin Valley.

Some notes on the scale of facilities. The largest desalinization plant in the world is Sorek, in Israel, produces 150 million cubic meters of water per year, equal to about 120,000 acre-feet. Thus, the project would require 6-7 facilities the size of Sorek, which seems reasonable. Salt content in the Pacific Ocean is about 35 g/L, so completely evaporating 1.5 million acre-feet of sea water per year would yield over 50 million tons of salt. If that sounds like a crapload of salt, it is – it’s equivalent to at least 15% of global production.

If harvesting the sale doesn’t work, or if you wanted to expand the scale of the project, you’d have to return the brine to the ocean. However, that might impact the Gulf of California’s unusual thermohaline circulation (salty water out on top), which contributes to biodiversity in the gulf. Even with large desalinization facilities, it’s a very small amount of brine relative to the volume of the gulf – I just have no idea what the impacts would be.

This scheme is obviously pretty half-baked, and not without impacts, such as impacts from running such an enormous salt farm. Consider it a jumping off point for creative ideas to augmenting California’s water supply. The drought is pushing us, but human ingenuity can overcome it, both with ways to provide more water as well as ways to conserve and wisely use what we have.