We’re diving into a semester studying (and modeling) Colorado River management in the University of New Mexico Water Resources Program. We’ve got a smart group of next-generation water managers, and we’ll be using the Goldsim modeling platform to build some system models. The students will be helping me think through the set of questions folks in basin management are grappling with as we think about what the management rules, due by the end of 2025, should look like.
Getting ready for class this week, I realized I hadn’t updated my datasets, which we’ll be using in class. I’ve put a few of them on Github, data I’ve assembled that isn’t easily accessible in a single place and that I find useful. One of the important things I’m trying to help students with is the endless and important task of data hustling in the service of policy analysis. Here’s an updated version of the graph of storage in Lake Mead and Lake Powell, with water-year end final numbers.
One of the things I do with the students in my University of New Mexico Water Resources classes is try to develop the habit of paying attention, through repetition, to the available data on the systems we’re talking about.
We use USGS river gauges to do this – checking the gauges is a classroom routine.
A member of the Colorado River brain trust argues that when you use reservoir elevation to define an action level of some sort, the reservoir remarkably ends up hovering around that level. The updated annual USBR Lake Mead elevation chart, just published with the 2019 data, nicely illustrates their point.
The 2007 Interim Guidelines set elevation 1,075 as the action level for the first tier of Lower Basin water use reductions. When the reservoir drops to that level (insert complicated rules about how and when the determination is made), cutbacks. You can see that in the years that followed, Mead dropped toward 1,075. In fact it actually dropped past it in 2015 and 2016 but bounced back sufficiently that we never actually triggered the cutbacks.
This year, the Basin community adopted new rules under the “Drought Contingency Plan” that created a horribly named “Tier Zero”, with cutbacks now triggered at elevation 1,090 (insert an even more complicated layer of rules about how and when the determination is made).
Mead’s lowest 2019 elevation was 1,081.47 on Jan. 1. Its highest elevation was at midnight Dec. 31, at 1,090.49.
The impact of drought on water resources in arid and semiarid regions can be buffered by water supplies from different source regions. Simultaneous drought in all major source regions — or perfect drought — poses the most serious challenge to water management. We examine perfect droughts relevant to Southern California (SoCal) water resources with instrumental records and tree?ring reconstructions for the Sacramento and Colorado Rivers, and SoCal.
Woodhouse and colleagues found five “perfect droughts” in the 20th century, which they concluded was not unusual when they used tree rings to extend the record back in time. But….
Although the causes of perfect droughts are not clear, given the long?term natural variability along with projected changes in climate, it is reasonable to expect more frequent and longer perfect droughts in the future.
soil moisture heading into the 2020 runoff, courtesy CBRFC
Despite an above-average snowpack in significant parts of the Colorado River Basin, the initial 2020 forecast is for below-average runoff thanks to a dry summer and fall.
According to the Colorado River Basin Forecast Center’s Cody Moser, speaking in today’s first-of-2020 forecast briefings, the monsoon over the Colorado River Basin was the 9th driest and 3rd hottest in a record that goes back to 1895. That means very dry soil moisture heading into the snow season. And that dry soil must then soak up the first pulse of melt before water can get to the rivers.
With Lake Mead ending 2019 at elevation 1090.49 feet above sea level – up 9 feet for the year – it’s worth visiting the Bureau of Reclamation’s classic “structural deficit” slide and seeing how it compares to 2019’s real world data. First, a reminder of where the oft-quoted “1.2 million acre foot structural deficit” comes from:
the structural deficit
Now, let’s compare that to 2019 data, and to a “what if” scenario:
Structural deficit slide
2019 with an 8.23 release
Look, no structural deficit this year!
Well, sorta. In order for Lake Mead to rise that much (the biggest one-year rise since the monster runoff of 2011), we needed
We ended up with 1.2 million acre feet of water flowing down the Rio Grande past Albuquerque this year, according to my quick and dirty calculations based on the USGS Central Avenue gauge. That would be the biggest flow through town since 1995.
Rio Grande total flow
That’s 42 percent above the long term mean (this gauge’s data goes back to 1966, the first full year at the site) and nearly double the 21st century mean. Here’s the hydrograph of a good year on the Rio Grande.
Elephant Butte reservoir, the biggest storage on the Rio Grande, ended 2019 with ~557,000 acre feet, the most at years’ end since 2008, but still hovering around “drought of the ’50s” levels (which as you can see really stretched from the 1940s into the 1970s).
Elephant Butte storage, data via USBR
Not sure where we ended up in terms of meeting our Rio Grande Compact delivery obligation to folks downstream, but I’m speaking in a week at the annual New Mexico Water Dialogue, I’ll track down the answer and report back here.
And finally one of my favorite water measures, the aquifer beneath my house was up more than 3 feet in 2019. This is one of the metrics that, as I watched it over time, finally began to persuade me that not all was doom and gloom: