For now, a Lake Mead “shortage” is off the table

The booming Rocky Mountain snowpack has eliminated the risk of a formal Lake Mead “shortage” declaration in 2020, and has substantially reduced the risk in 2021, according to the latest Bureau of Reclamation 24-month study. More importantly, in my view, is the reduction of a longer term risk of a legal battle over the Upper Basin’s Mexican Treaty delivery obligation.

The current forecast calls for Mead ending 2019 at elevation 1,080, five feet above the threshold at which a set of rules previously developed by state and federal governments would have reduced allocations to Arizona, Nevada, and Mexico. That is more than eight feet higher than the projected elevation just a month ago.

More importantly, the new projections suggest now that there will be another 9 million acre foot release from Lake Powell in 2020, rather than the 7.48maf 2020 release projected just a month ago. The result is a preliminary end-of-2021 Mead forecast 20 feet higher than was expected just a month ago:

Comparison between Lake Mead elevation forecast in February vs. March 2019


It’s that shift from a 7.48maf release next year to a projected 9maf release, the result of operating rules in the 2007 Interim Guidelines governing balancing the contents of Mead and Powell, that’s the huge deal here. It means the water users in the Lower Colorado River Basin will continue to get extra water, above and beyond their legally expected 8.23maf releases each year. If this forecast holds, it would mean that since 2011, the Upper Basin would have delivered an excess of at least 9.4 million acre feet, above and beyond the legal requirements of the Colorado River Compact.

A series of 7.48maf releases from Powell – possible under the current operating rules if we were to have really bad Upper Basin hydrology – would have put us into dangerous legal territory, in terms of how the rules governing water delivery obligations under the Mexican treaty are interpreted. One of the basin’s unresolved legal questions is the extent of the Upper Basin’s obligations to deliver half of the water needed to meet the U.S. obligation to deliver 1.5maf per year to Mexico. A series of 7.48maf release years could have forced a legal test of that question, which is one of my “how the legal system could crash” fears.

This year’s snowpack seems to have significantly reduced that risk for the foreseeable future.


  1. Snowpacks only last one year at a time, except at the very top of the Rockies. So, IMO, you should have said “one year” or at best “two years” rather than foreseeable future. And, it’s still only mid-March. There could be major new snow — or the pipeline could cut off.

    NWS says Western Slope and further west have a slight chance of above normal temps in March and April, albeit with chance of above-normal precip, and definitely likely to be above normal May and beyond on temps. Possibly WAY above normal.

  2. “…reduced that risk for the foreseeable future.” Nope. I can see farther than that John, as can Brad Udall. This is a a pause from Nature, a reprieve that might allow us us to get our act together and ready ourselves for really hard times ahead. I pray that we don’t lose the ancient fish in the meantime.

  3. Ha! Yes, you’re both right, “foreseeable future” is a terrible phrase!

    By “that risk”, Brian, I was referring to the Mexican Treaty obligation fight, which happens if the 10-year rolling Powell delivery drops below 82.3maf, and by “foreseeable future” I meant 2026, which is as far as the current rules take us, and therefore is as far as I’ve modeled. One expects the legal disagreement over the Mexican Treaty obligation will be one of the Law of the River ambiguities sorted out as part of the renegotiations.

  4. It’s best to take a cautiously optimistic approach as the uncertainty in the forecast is still too large, and hard to quantify. I don’t believe the CBRFC is taking warmer temperatures into account regarding the unregulated inflow into Powell. Warmer temps are linked to a decrease in streamflow efficiency in both the Colorado and Rio Grande watersheds. It’s also hard to quantify just how much will be lost through soil moisture absorption, or the complexities on the demand side…

  5. All of these uncertainties and caveats are valid, yet one set of statistics still bears some examination.

    From Dec. 1999 to Dec. 2009, Lake Mead dropped about 117 feet, from 1,213 to 1,096 feet.
    From Dec. 2009 to Dec. 2019–as the 24-month study now projects, the lake will have dropped another 16 feet, to about 1,080 feet.

  6. Tony – That was a bit cryptic. I’m curious what questions you think should be asked about those numbers, or what hypotheses/conclusions you draw?

    A few more numbers to add to the mix – average Colorado River use by the 3 lower basin states:
    99-09 – 7.67maf
    09-19 – 7.3 maf

    Average Powell releases:
    99-09 – 8.67maf
    09-19 – 9.02maf

  7. John, I don’t know what conclusions to draw other than if the lake’s decline had continued as it had been going in the 2000s, we’d be staring dead pool in the face right now. We’ve now had four years of heavy, Upper Basin winter snows or spring rains to bail us out since 2010. Since 2014, the bailouts have come at a rate of one every two years.

    The questions these conflicting decadal stats raise are: First, how much longer will our luck hold out? Second, or is this decade’s weather going to be the new normal, or will we return to the dry times of the 2000s?

    Third, is there a scenario for this year in which another bout of dry April-May weather could kick us back into a 2020 shortage?

    Fourth, I presume the BOR’s forecast for end of 2020 assumes “normal” weather conditions next year. Correct? If so, how much worse than normal will the weather have to be next year to create shortage conditions once again?

    It is really amazing to see one month’s heavy snowpack turn a forecast so much so quickly. Could it be too good to be true?

    Those will do for a start.

  8. I guess the other question is: Will this sudden turn of events in the 2020 shortage risk have any impact on the ongoing DCP proceedings and potential or real disputes?

  9. Regarding the Third– although who am I to question authority–two factors could reduce the unregulated inflow into Powell, namely 1) extremely dry conditions that will absorb moisture and therefore runoff to Powell, and 2) increased temps that could cause sublimation of the snowpack, or otherwise increased evapotranspiration. Reclamation takes the unregulated inflow forecast directly from the Colorado Basin River Forecast Center (CBRFC) and inputs it into the 24-month study; hence, the importance of Miller’s comments from the CBRFC. But this forecast and the resulting 24 month study needs to be put in the context of climate change such as increased temperatures, and what science actually knows regarding the soil moisture deficit caused by aridification. It’s unclear to me if either Reclamation or CBRFC are taking increased temperatures into account, or fully understand how much loss will be caused from dry soils. The agencies are using the 1980 to 2010 thirty year time period for the basis of their hydrology; given the increased energy in the atmosphere and hence increased variability, its not uncommon to see large swings in the forecast.

  10. On another note, flooding will likely be a concern this year. Water and emergency managers along the river upstream of Powell should be prepared for a rain-on-snow type of event. While its impossible to predict when of if an extreme event will occur, its also imprudent not to be prepared. Given higher temps and changes to precipitation patterns, a rapid melt off of the snowpack is certainly a possibility. Analogs already exist, such as the Missouri River flooding in 2011, originating from a rain on snow event to the large snowpack that year. This occurred just north over the continental divide from the Colorado Basin. I’m not sure if flooding this year on the Platte/Elkhorn/Missouri is a good analog but is certainly a sobering reminder of the potential for extreme events.

  11. Tony –

    First: “We’ve now had four years of heavy, Upper Basin winter snows or spring rains to bail us out since 2010. Since 2014, the bailouts have come at a rate of one every two years.”

    This is wrong. Since 2010, just two years – 2011 and 2017 – have been above the long term average. Also two years since 2010 – 2010 and 2018 – are among the five driest years on record. USBR estimated natural flow from 2010-2018 was 13 percent below the period-of-record average (1906-2018). So the premise that we’ve been bailed out in recent years by unusually wet hydrology is wrong.

    But your question really is – if we had really bad hydrology, starting from lower reservoir elevations than we had in 1999, would Lake Mead crash?

    The answer depends on the rules.

    From 2000-2010, the Lower Basin states took an average of 7.6 million acre feet per year out of the Lake, even as the hydrology was crashing. They didn’t use less water. There were no rules in place to reduce use, and no one did. This led to the 100-plus foot drop.

    Going forward, the new DCP rules (assuming we finally get them) mean Lower Basin states will take 6.3maf per year if/when the hydrology turns really bad. A 100-plus foot drop with 7.6maf annual withdrawals would not be repeated with 6.3maf withdrawals. So no, your hypothetical repeat of the 117 feet of loss would not happen.

    If the Upper Basin continues to meet its minimum 8.23 maf annual “objective release”, Lake Mead will not crash, stabilizing instead, by my calculation, at around 1,040-ish.

    If the hydrology is bad enough that the Upper Basin can’t deliver 8.23maf per year on average, we’ll need new rules. It’s interesting to think about how bad that would have to be.

  12. I’m loving learning so much from all of you! My interest in the Colorado River Basin states Upper & Lower, the DCP all started as a curiousity/novel interest as my now ex-significant other is a water resource specialist for CRWCD and I was interested in her work. Now that I work quarterly in an area affected by the dust storms caused by the Salton Sea & since I started grad school for a MPH I’ve gone from curiosity/novelty to a genuine interest in this area!
    Thank you all! I look forward to learning more

  13. Friends,
    We are in a long term epic drought of 100 to 200 year duration.

    EVEN if we are not, long over due, is a serious planning matrix which takes this
    into consideration..

    Hope for best and plan for worst…prudent and reasonable policy.

  14. Friends,
    We are in a long term epic drought of 100 to 200 year duration.
    Very long term records this has happened before.

    EVEN if we are not, long over due, is a serious planning matrix which takes this
    into consideration..
    There will be periods of normal or above, do not get careless.

    Hope for best and plan for worst…prudent and reasonable policy.

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