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Western drought: It ain't over 'til...well, it ain't over

Just a few days ago, on January 26th, 2017, we saw something in the U.S. climate that we hadn’t seen since March 2011. Well, technically, we didn’t see something, I guess.

For the first time since March 2011, there was no D4, “exceptional drought,” anywhere in the United States, as analyzed by the U.S. Drought Monitor. The last vestige of D4—the most severe category in the monitoring system—disappeared from its southern California holdout, part of a larger pattern of substantial mid-January drought improvements in California.

Low water in Don Pedro Reservoir, located in the foothills of the Sierra Nevada about 10 miles west of Yosemite National Park. This photo was taken on October 10, 2014, when nearly the entire state of California was still classified as being drought status D4—exceptional drought. Climate.gov photo by Andrew Williams.

(note: it is always difficult to describe drought improvements as “improvements” knowing they came, as they often do, with the price tag of major flooding and personal tragedy).

With all that said, the bottom line is that the nation is in better shape drought-wise than it has been for most of this decade.

The recap

During late 2015, the West was in pretty dire straits. Drought enveloped most of the region, from border to border, Pacific to Rockies. Late 2015 wetness helped the Pacific Northwest and Northern Rockies, and by spring 2016, drought was almost eradicated there.

However, drought held through spring south of the San Francisco Bay, where summer presents almost zero chance of drought recovery. But things did improve in late fall, and the last month brought waves of rain and high-altitude snow that improved things even more.

That’s the update. But going Beyond the Data, let’s stop for a few sidebars.

Sidebar #1: It Ain’t Over / Drought is Complicated

While things are definitely better than they were three months ago, lots of drought remains in the West. The water situation, especially the groundwater situation, is still pretty tough.

We talk quite a bit about scales in climate and meteorology. No, not the kind that give you bad news at the doctor, nor the kind that cover fish, but the kind that describe the bigness and lastingness of things. Orders of magnitude.

Drought sits on the slow end of the time scale, relative to weather systems represented by symbols on weather maps. It’s described over weeks, months, seasons (probably the sweet spot), years and decades. That’s some range.

Various impacts fall out of that range. On the shorter end (weeks to months), we can see immediate impacts. Wildfire danger associated with drought responds (worsens *and* improves) on these scales. Agricultural impacts hang around here too, although maybe not as quick as wildfire. On the long-and-slow end of the scale, we see changes in water supply and ecosystems (not “ecosystem health” but changes in ecosystems, full stop).

These impacts are regimented such that we’ve come up with many lenses to observe drought. Meteorological drought refers pretty straightforwardly to observed precipitation versus expected precipitation. Its tools are pretty useful on the shorter end of the drought time scale. Agricultural drought, as you might expect, refers to plant health and specifically crop health. Its monitoring tools pay a lot of attention to soil moisture. The monitoring tools for hydrological drought are tuned for the long game: measuring change on the year-ish and longer scales.

Drought map of united states

United States Drought Monitor (USDM) assessment for January 24, 2017, released on January 26, 2017. "L" and "S" indicate whether long-term or short-term drought impacts dominated. Areas designated "SL" are experiencing both scales of impact. Map by Climate.gov, based on original by USDM project.

That brings us back to California. The good news is that there is a very healthy snowpack on the western mountains right now, especially compared to recent years. However, there are still groundwater wells that are moving in the wrong direction in parts of California, particularly southern California. The latest rains literally have not had time to filter down to replenish aquifers. And even when they do, they will be but a blip against the big picture. It’s a point worth dwelling on: weeks of rain will relieve wildfire and agricultural impacts, but we need seasons to years of rain to restore groundwater.

Sidebar #2: Drought in the West is especially complicated

These different scales of drought mean that “drought recovery” means different things for different folks. If you rely on groundwater in the West, you’re still feeling drought, significantly.

Moreover, California and the West have very complex water management systems. That’s a nerdy way of saying that there is lots of plumbing in the West that moves water around and between river basins--sometimes from several states away--to meet people’s needs. Simply put, the law of gravity ain’t the only law determining where water goes.

And the drought in the West doesn’t even date to 2012/13. In the longer term—put on those “hydrologic scale” glasses, please—the drought actually dates back to the late 1990s. In hydrologic terms, dryness dominates the last 20 years.

Bar graph of drought index

Time series of the Palmer Hydrological Drought Index (PHDI) for the Western United States (California and Nevada). This PHDI index is tuned for changes on the time scale of 24 months. Increasingly negative values (larger bars) indicate increasingly severe drought. The time series shows that, on this multi-year time scale, the region has been in significant drought for the better part of the last two decades.

Add these complicating factors together and you can see that we aren’t out of the woods in the West, even if many westerners have muddy boots this winter.

Sidebar #3: I work with amazing drought pros

If you’ll allow me a couple paragraphs of personal reflection. One of the many rewarding things about serving at the National Centers for Environmental Information is that I work about 20 feet from one of the Legends of Drought Monitoring, Richard Heim. I’m an old drought guy, and considered myself a good one. But Richard is Big League. If the drought monitoring community made action figures, Richard would be in the first set. (sidebar to the sidebar: I’m convinced that drought monitoring action figures is a slam-dunk winner of an idea—who’s with me?).

So, just to acknowledge out loud: thanks, Richard, for your advice on some of the details of this particular article.

Sidebar #4: The climate is changing

Finally, we’ve covered the interaction between drought and our changing climate recently, and in more detail. But it’s worth mentioning again that, as the atmosphere gets warmer, it gets thirstier, and so it levies a bigger tax on soil and surface water.

The fact that the recent drought episode spanned the three warmest years on record in California is important. We need to learn from episodes like this to plan for the next drought episode, because …

Sidebar #5: Drought ain’t ever really over

I can make two confident predictions about the drought episodes going on in the US right now:

  1. These drought episodes will end

  2. There will be more drought episodes in coming years

In the drought world, we often divide up history into “green times” (non-drought) and “brown times” (drought). What we learn during brown times—and, especially, how we act on that during green times—prepares us for the next episode.

 

Comments

I appreciate the humor & the readability for a non-scientist. Thanks!

Thanks, Johna, I really appreciate it!

Deke

 

In reply to by Johna

Thank you for this. I live north of Scottsdale, and my son is worried about the water issue, esp. since the Colorado river was "alloted" at a time when it was flooded....not at a normal flow, and the people in CA got the most, by far. NOT FAIR

Tamara, The people in California got the most because there were more of them relatively speaking than in any of the other Colorado River Pact states. A situation that holds today, I might add. Cali gets 29%, Arizona gets 19%, Nevada gets a paltry 2%. The northern states split the other 50% of the water, and Mexico gets a good chunk as well.

In reply to by Tamara

Awesome article. Answered my question regarding groundwater recharge. And appreciate the explaining between Meteorological drought vs. Agricultural drought vs. hydrological drought.

Thanks for a great article. The discussion of the types of drought and their time scales is really helpful. Do you think that role of mountain glaciers in western water supply merits a drought type and time scale of their own?

Hi there, this is a great question, but I think it may be a little hypothetical. First of all, I'm assuming you're talking about North American glaciers.

Seasonal snowmelt certainly is a big part of the western water equation. Seasonal changes and long-term changes to snowpack and the timing of snowmelt are major concerns in the water future of the US Pacific Northwest. With that said, I don't think glacial melt (the melting of much, much older snow that has become ice over decades/centuries) is a significant part of the year-to-year water scene. 

So, while North American glaciers are indeed undergoing change and retreat, and there are significant ecological and other ramifications, drought metrics consider that, as they are not really a big component of the water budget on the scales that we apply to operational drought assessment (weeks to years).

(confession: I'm speaking off the cuff here, and my background is mainly in agricultural drought and mostly east of the Rockies. I haven't done any formal homework to answer this question. If I get a note from someone more glacier-minded or Northwestern than me, I'll make sure to follow my comments up here)

But, hypothetically, yes I could see your point that the retreat (or hypothetical advance) occupies a drought timescale that we didn't consider in the article.

Next drought meeting I go to, we could argue about this for days!

Deke

 

In reply to by Dave

Count me as that glacier-guy with some insight on Dave's query and Deke's response on the role of glaciers in droughts. Glaciers can be viewed as water reservoirs that diminish drought severity. In drier or warmer than normal years, glaciers release some of their ice mass in addition to the seasonal snow accumulated that year. In colder or snowier years, not all the seasonal snow melts and the remaining seasonal snow adds to the glaciers' mass. Clearly this decade's drought has exceeded the ability of glaciers in the western US to avoid large areas of that region plunging into severe drought, but glaciers have helped the situation from being even worse. This winter's snowpack in the Pacific NW is well above normal, so I expect glaciers there will experience a year of net growth. I'm not aware if the same applies to the Rockies and southern Sierra Nevada ranges. Variations in glacier size (volume) are usually averaged over the period late fall to late fall, growing in winter and shrinking in summer. Interannual variations occur primarily driven by variations in winter snowfall and summer warmth. Nearly all glaciers, including those in the US, are receding and shrinking, losing more mass each year by melting than they gain in winter snowfall. Thus, their ability to diminish the severity of future droughts is declining.

Great article! Is there somewhere one should go to read more about practical implications of the groundwater situation? You say we need years of wet winters to improve it, but what does this mean? Thanks!

the title is the best title ever

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