Depleting fossil water

The NYT has an interesting article on the decline of the High Plains aquifer, which includes the famous Ogallala aquifer. Water tables are dramatically down (red) in many areas, making irrigation impractical.

Vast stretches of Texas farmland lying over the aquifer no longer support irrigation. In west-central Kansas, up to a fifth of the irrigated farmland along a 100-mile swath of the aquifer has already gone dry. In many other places, there no longer is enough water to supply farmers’ peak needs during Kansas’ scorching summers.

And when the groundwater runs out, it is gone for good. Refilling the aquifer would require hundreds, if not thousands, of years of rains.

This is a widespread, generic problem, and instance of the tragedy of the commons archetype:

Alternately, as an economist might put it, depletion of groundwater is typically an externality, with zero rent paid from users to owners (us).

There are three facets to management of the problem: the commons problem, detail complexity from the complex geology of aquifers, and dynamic complexity. Allocation of property rights solves the commons problem, but not the others (see Erling Moxnes’ interesting work on this).

Sniffing around for material for this post, I found it easy to get lots of complicated information about aquifers, but hard to find any simple stock-flow pictures that revealed their state or dynamics, like this:

Source: USGS

This suggests that there’s some low-hanging fruit to be harvested through provision of simple feedback, as in the Climate Scoreboard.

Dry Lake Mead

The systems story on Lake Mead deepens (unlike the lake itself). I heard about some more interesting dynamics in a side conversation at the Balaton Group meeting in Iceland.

First, it’s not just Mead that’s impacted; upstream Lake Powell is also low. One consequence of this is that hydro generation is down, because the head is lower. Since both lakes are half full, it might make sense to drain Powell into Mead. That would raise the head at Mead, making up for the loss of generation at Powell. Water losses would also decrease. One possible obstacle to this strategy is that stakeholders in Powell fear that it could never be refilled, because endangered species would reinhabit the empty canyons.

Second, as the lakes get lower, bad things happen. Evidently the deep waters are stratified, and there are plumes of nasty saline gunk near the bottom. If lake levels continue to drop, there’s a possibility of serious water quality problems to go with the quantity issues.

One thing that’s striking about the media coverage of data and projections by agencies is that there’s little discussion of the nature or magnitude of variability. The implicit assumption behind current behavior is that droughts are cyclical or just noise. The hope seems to be that, since we’re in a low period for basin rainfall, the magic of reversion to the mean will soon bring forth the waters again. I don’t think there’s any good reason to act as if that will really happen, especially if climate makes the distribution nonstationary. Modelers seem to think that the Southwest will move to a drought regime as the earth warms, but what if they’re wrong, and the hydrologic cycle accelerates? Glen Canyon Dam was nearly lost in 1983, so a healthy increase in rainfall wouldn’t necessarily be a blessing either.

LakeMeadProjection2010Current Bureau of Reclamation projections for Lake Mead elevation. Documentation is pretty opaque, but it looks like the projections are based on quantiles of historic inflows, i.e. they neglect autocorrelation or changes in the distribution of supply.

Edward Abbey must be smiling at least a little at this mess.

Waiting for a miracle at Lake Mead

Lake Mead has dropped another ten feet since I wrote about its open-loop management,

My hypothesis is that the de facto policy for managing water levels is to wait for good years to restore the excess withdrawals of bad years, and that demand management measures in the interim are toothless. That worked back when river flows were not fully subscribed. The trouble is, supply isn’t stationary, and there’s no reason to assume that it will return to levels that prevailed in the early years of river compacts. At the same time, demand isn’t stationary either, as population growth in the west drives it up. To avoid Lake Mead drying up, the system is going to have to get a spine, i.e. there’s going to have to be some feedback between water availability and demand.

An article in the Arizona Republic confirms my thinking,

To slow the lake’s years-long decline, river users have built a reservoir west of Yuma to catch unused runoff, paid farmers to leave fields unplanted and are negotiating with Mexico to leave some of its allocation in Lake Mead while its farmers recover from an earthquake.

None of the steps will yield significant amounts of water, but together, they could keep Lake Mead from sinking below the drought triggers, buying time until a wet winter can replenish some of the water lost to drought.

“It’s time that we need,” said David Modeer, general manager of the Central Arizona Project, which moves water from the Colorado River to Phoenix and Tucson. “The reservoirs have shown they’re resilient. After a 12-year drought, they’re still half-full. What we do now will be worth it to stay out of a shortage.”

Managers are assuming that a return to historic rainfall patterns will save their bacon. But if climate models are right, and the Southwest will be on the losing end of trends in precipitation, that won’t happen. Even if they’re wrong, increasing demand can easily overwhelm restored rainfall. At some point, the loop will have to close – the question is how. Will property rights get reallocated and price signals aligned so that people live within the limits of supply? Or will the lake wind up permanently depleted? There are some signs of improved cooperation among states, but Nevada appears to be betting on failure:

if the reservoir fell below elevation 1,050 feet, one of the tunnels Nevada uses to draw water from the lake would sit above the waterline and would be useless. Nevada is working on a new, deeper tunnel

(Dry) Lake Mead

I’m just back from two weeks camping in the desert. Ironically, we had a lot of rain. Apart from the annoyance of cooking in the rain, water in the desert is a wonderful sight.

We spent one night in transit at Las Vegas Bay campground on Lake Mead. We were surprised to discover that it’s not a bay anymore – it’s a wash. The lake has been declining for a decade and is now 100 feet below its maximum.

Lake Mead water level

It turned out that this is not unprecedented – it happened in 1965, for example. After that relatively brief drought, it took a decade to claw back to “normal” levels.

The recent decline looks different to me, though – it’s not a surprising, abrupt decline, it’s a long, slow ramp, suggesting a persistent supply-demand imbalance. Bizarrely, it’s easy to get lake level data, but hard to find a coherent set of basin flow measurements. Would you invest in a company with a dwindling balance sheet, if they couldn’t provide you with an income statement?

It appears to me that the Colorado River system is simply overallocated, and their hasn’t been any feedback between reality (actual water availability) and policy (water use, governed by the Law of the River). It also appears that the problem is not with the inflow to Lake Mead. Here’s discharge past the Lees Ferry guage, which accounts for the bulk of the lake’s supply:

Lees Ferry flow

Notice that the post-2000 flows are low (probably reflecting mainly the statutory required discharge from Glenn Canyon dam upstream), but hardly unprecedented. My hypothesis is that the de facto policy for managing water levels is to wait for good years to restore the excess withdrawals of bad years, and that demand management measures in the interim are toothless. That worked back when river flows were not fully subscribed. The trouble is, supply isn’t stationary, and there’s no reason to assume that it will return to levels that prevailed in the early years of river compacts. At the same time, demand isn’t stationary either, as population growth in the west drives it up. To avoid Lake Mead drying up, the system is going to have to get a spine, i.e. there’s going to have to be some feedback between water availability and demand.

I’m sure there’s a much deeper understanding of water dynamics among various managers of the Colorado basin than I’ve presented here. But if there is, they’re certainly not sharing it very effectively, because it’s hard for an informed tinkerer like me to get the big picture. Colorado basin managers should heed Krys Stave’s advice:

Water managers increasingly are faced with the challenge of building public or stakeholder support for resource management strategies. Building support requires raising stakeholder awareness of resource problems and understanding about the consequences of different policy options.